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Transcript of Energy Engineering
Without The Hot Air
David JC MacKay
University of Cambridge
What's this book about?
Clear numbers to calculate energy used
and energy made available for use.
Understand cost of energy resources
We live at a time when emotions and feelings count more than truth, and there is a vast ignorance of science.
Out of Gas, Caltech physicist David Goodstein
energy crisis soon brought on by The End of the Age of Oil.
oil extraction can’t meet demand – perhaps as soon as 2015 or 2025.
if switched all our energy- guzzling to nuclear power right away, Goodstein says, the oil crisis would simply be replaced by a nuclear crisis in just twenty years or so.
The Skeptical Environmentalist, Bjørn Lomborg
“Everything is fine.”
“everything is getting better.”
“we are not headed for a major energy crisis,”
“there is plenty of energy.”
Michael Meacher, former environment minister,
“if we’re going to cut greenhouse gases by 60% ... by 2050 there is no other possible way of doing that except through renewables;”
Sir Bernard Ingham, former civil servant
, speaking in favor of nuclear expansion,
“anybody who is relying upon renewables to ﬁll the [energy] gap is living in an utter dream world and is, in my view, an enemy of the people.”
This debate is fundamentally about numbers.
How much energy can we get from each energy source?
What are the economic and social costs?
What are the risks?
“turn off your cell phone charger when it’s not in use;”
“every little bit helps”
1. Is it possible for a country like Britain live on its own renewable energy sources?
Third, using fossil fuels (probably) changes the climate.
several human activities --> climate change
Biggest reason: increase in greenhouse effect
carbon dioxide (CO2): greenhouse gas
fossil-fuel burning --> carbon dioxide emissions
Why do we burn fossil fuels?
We need for energy
The climate problem is mostly an energy problem.
Climate change will affect
hundreds of years
Climate Change Theory
1. human fossil fuel burning causes carbon dioxide concentrations to rise
2. carbon dioxide is a greenhouse gas
3. increasing the greenhouse effect increases average global temperatures
These are natural flows in and out of the atmosphere.
They have been almost exactly in balance for 1000s of years.
They are huge amounts but they natural flows balance
Human emissions are not in balance with nature.
What will CO2 do to the climate?
CO2 - greenhouse gas -
absorbs infrared radiation (heat) leaving the earth re-emits it in a random direction.
The best climate models say:
increase in the CO2 concentration would
1. increase the intensity of the sun by
2. increase global average temperature by about
Who is responsible?
world’s greenhouse gas emissions - 34 billion tons of CO2-equivalent per year.
the number of people on the planet, 6 billion,
about 5½ tons CO2e per year per person.
our energy consumption vs. possible sustainable energy production (not fossil fuels)
tons of oil equivalent
a barrel of oil
a million BTUs
10 pence in UK in 2008
1kWh/d = 1 human servant
Have you seen kWh before?
power - rate at which something uses energy
volume - measured in liters
flow - measured in liters per minute
volume = flow × time
energy - measured in kWh
power - measured in kWh per day
energy= power × time
joule is the standard international unit of energy
kilowatt-hour = 3.6 million joules
one joule per second = one watt
toaster consumes power --> one kilowatt.
the toaster consumes one kilowatt-hour (kWh) of energy per hour
it consumes 24 kilowatt-hours per day.
kWh/d per person
UK waste incineration produces a power of 7 TWh per year and Denmark’s waste incineration produces 10 TWh per year
Can we say Denmark incinerates “more” waste than the UK? While the total power produced from waste in each country may be interesting, I think that what we usually want to know is the waste incineration per person.
Denmark, 5 kWh/d per person; UK, 0.3 kWh/d per person. So Danes incinerate about 13 times as much waste as Brits.
Is energy really consumed?
Energy can neither be created nor be destroyed. It can only be transformed from one state to another.
When we “use up” one kilojoule of energy, what we’re really doing is changing one kilojoule of low entropy energy (for example, electricity) into an exactly equal amount of energy in another form with much higher entropy (for example, hot air or hot water).
concentrated energy = low entropy
What is entropy?
Entropy is a measure of how evenly energy is distributed in a system. In a physical system, entropy provides a measure of the amount of energy that cannot be used to do work.
The second law of thermodynamics can be stated as saying that the entropy of an isolated system always increases, and processes which increase entropy can occur spontaneously. Since entropy increases as uniformity increases, the second law says qualitatively that uniformity increases.
When we’ve “used” the energy, it’s still there; but we normally can’t “use” the energy over and over again, because only low entropy energy is “useful” to us. Sometimes these different grades of energy are distinguished by adding a label to the units: one kWh(e) is one kilowatt-hour of electrical energy the highest grade of energy. One kWh(th) is one kilowatt-hour of thermal energy for example the energy in ten litres of boiling-hot water. Energy in higher-temperature things is more useful (lower entropy) than energy in things at room temperature. A third grade of energy is chemical energy. Chemical energy is high-grade energy like electricity.
Is all energy equal?
All forms of energy are not equal and interchangeable
2.5 kWh of chemical energy ---> 1 kWh electrical energy
(when changing oil into electricity)
3 kWh electrical energy -----> 1 kWh chemical energy.
(when changing electricity into gasoline)
In this book:
1 kWh of chemical energy = 1 kWh of electricity.
distance traveled per day ~ 50 km (30 miles).
distance per unit of fuel ~ 33 miles per UK gallon
33 miles per imperial gallon ~ 12 km per liter
energy per unit of fuel ~ 10 kWh per liter
Why does the car get 33 miles per gallon?
Where’s that energy going?
Could we make cars that do 3300 miles per gallon?
What about the energy-cost of producing the car’s fuel? (It’s been estimated that making each unit of petrol requires an input of 1.4 units of oil and other primary fuels (Treloar et al., 2004).)
What about the energy-cost of manufacturing the car?
How is the energy used?
The energy in a typical fossil-fuel car is used in four main areas.
1.speeding up then slowing down using the brakes;
4.heat: – 75% of the energy is thrown away as heat, because changing fuel to mechanical energy is inefficient.
A car accelerates rapidly up to a speed v, and maintains that speed for a distance d, which is the distance between traffic lights, stop signs, or traffic. At this point, he presses the brakes and changes all his kinetic energy into _______ in the brakes. Acceleration gives the car kinetic energy; braking throws that kinetic energy away.
We are interested in the rate of energy used so the equation is:
energy used / time spent
•The car speeds up and slows down once in each duration d/v. The rate at which energy pours into the brakes is:
Kinetic energy / time between braking
KE = .5mvv, time = d/v
•The tube of air created in a time t has a volume Avt,
where A is the cross-sectional area of the tube, which is similar to the area of the front view of the car.
(For a streamlined car, A is usually a little smaller than the frontal area Acar, and the ratio of the tube’s effective cross-sectional area to the car area is called the drag coefficient cd. Throughout the following equations, A means the effective area of the car, cd x Acar.)
The tube has mass m = (rho)Avt (where rho is the density of air) and moves at speed v, so its kinetic energy is:
and the rate of generation of kinetic energy in swirling air is:
If v = 70 mph, drag coefficient =.33, A=3 m*m, rho=1.3 kg/m*m*m
How much power(kW) will it use in 1 hour?
If v = 35 mph
How much power will it use in 2 hours?
What about rolling resistance?
rolling resistance -
1. energy consumed in the
of the car,
2. energy that goes into the
of wheels against asphalt,
3. energy that goes into
rubber off the tires,
4. energy that vehicles put into
force of rolling resistance is proportional to the weight of the vehicle
coefficient is different due to:
1. the quality of the road,
2. the material the wheel is made from,
coefficient of rolling resistance for a car = 0.01
The effect of rolling resistance is just like perpetually driving up a hill with a slope of one in a hundred.
So at a speed of 31 m/s (70 mph), the power required to overcome rolling resistance, for a one-ton vehicle, is
force × velocity = (100 newtons) × (31 m/s) = 3100 W;
which, allowing for an engine efficiency of 25%, requires 12 kW of power to go into the engine;
the power required to overcome drag was estimated on p256 to be 80 kW. So, at high speed, about 15% of the power is required for rolling resistance.
1. typical speed of 50 km/h (30 mph);
2. drag-area of 0.8 m2;
3. rolling resistance of 0.01;
4. distance between stops of 500 m;
5. engine efficiency of 85%;
6. during stops and starts, regenerative braking recovers half of the kinetic energy of the car.
7. Charging up the car is assumed to be 85% efficient.
old-style lead-acid batteries:
energy density is 40 Wh/kg,
range of 400 km,
2000 kg of batteries are required
= above 25 kWh per 100 km.
lighter lithium-ion batteries:
energy density of 120 Wh/kg,
range of 500 km
electric cars with 500 kg of batteries
= 13 kWh per 100 km.
How much wind power could we possibly generate?
Estimate of the potential of on-shore (land-based) wind in the United Kingdom
average power per unit land-area of a wind farm
the area per person in the UK:
power per person = wind power per unit area × area per person.
If the typical wind speed is 6 m/s (13 miles per hour, or 22 km/h), the power per unit area of wind farm is about 2 W/m2.
British population density: 250 people per square kilometer, or 4000 square meters per person
Wind turbines are getting bigger all the time. Do bigger wind turbines change this chapter’s answer?
Chapter B explains. Bigger wind turbines deliver financial economies of scale, but they don’t greatly increase the total power per unit land area, because bigger windmills have to be spaced further apart. A wind farm that’s twice as tall will deliver roughly 30% more power.
Wind power fluctuates all the time. Surely that makes wind less useful?
Maybe. We’ll come back to this issue in Chapter 26, where we’ll look at wind’s intermittency and discuss several possible solutions to this problem, including energy storage and demand management.
Imagine that you make one intercontinental trip per year by plane. How much energy does that cost?
A Boeing 747-400 with 240 000 liters of fuel carries 416 passengers about 8 800 miles (14 200 km). And fuel’s calorific (energy density) value is 10 kWh per liter (just like gasoline). So how many kWh per passenger is that?
And how many kWh/person/day is that if you make one trip a year?
London to Cape Town (10 000 km), London to Los Angeles (9000km) overestimated?
but planes are not 100% full... maybe 80%
Let’s make clear what this means. Flying once per year has an energy cost slightly bigger than leaving a 1 kW electric fire on, non-stop, 24 hours a day, all year.
energy per distance
(kWh per 100 p-km)
Car (4 occupants) 20
Ryanair’s planes, year 2007 37
Bombardier Q400, full 38
747, full 42
747, 80% full 53
Ryanair's planes, year 2000 73
Car (1 occupant) 80
Table 5.3. Passenger transport efficiencies, expressed as energy required per 100 passenger-km.
Planes move through air, so, just like cars and trains, they experience a drag force, and much of the energy consuming by a plane goes into pushing the plane along against this force. Additionally, unlike cars and trains, planes have to expend energy in order to stay up.
The total power required by the plane is (=) the sum (+) of the power required to create lift and the power required to overcome ordinary drag.
force = rate of change of momentum
force exerted on A by B = − force exerted on B by A
we’re going to find that the power required to create lift turns out to be equal to the power required to overcome drag. So the requirement to “stay up” doubles the power required.
Let's calculate the lift force on a plane
moving at speed v
plane moves a distance vt (in time t)
leaves behind it a sausage of downward-moving air at speed u (figure C.2).
cross-sectional area of this sausage A.
sausage’s diameter is equal to the wingspan w of the plane.
m = density × volume = (rho)vtA
momentum = mass × velocity = m x u
downward momentum must equal upward momentum
vtAu = mgt
fuel-efficiency of the plane, expressed as the energy per distance traveled (force)
Real jet engines have an efficiency of about 1/3, so the energy-per- distance of a plane traveling at speed v is
What is the real energy per distance flown if the area of the plane is 180 meters squared, mass is 363,000 kg, wing span is 64 m, drag coefficient is 0.03, density is 0.4 kg/(meters cubed), and speed is 580 mph?
Power from the Sun
The power of raw sunshine at midday on a cloudless day is 1000W per square meter. That’s 1000 W per m2 of area oriented towards the sun, not per m2 of land area.
What reduces the suns intensity?
We can turn this raw power into
in four ways:
Let’s imagine we cover all south-facing roofs with solar thermal panels.
10 meters squared of panels per person
50%-efficient at turning the sunlight’s 110 W/(m*m) into hot water.
That equals 13 kWh per day per person
Solar Photovoltaic (PV)
Typical solar panels have an efficiency of about 10%; expensive ones perform at 20%. (Fundamental physical laws limit the efficiency of photovoltaic systems to at best 60% with perfect concentrating mirrors or lenses, and 45% without concentration. A mass-produced device with efficiency greater than 30% would be quite remarkable.)
20% × 110 W/(m*m) = 22 W/(m*m)
every person gets 10 (m*m)
= 5 kWh per day per person
if we covered 5% of the UK with 10%-efficient panels
10% × 100 W/(m*m) × 200 (m*m) per person
= 50 kWh/day/person
Could this flood of solar panels co-exist with the army of windmills we imagined in Chapter 4?
Yes, no problem: windmills cast little shadow, and ground-level solar panels have negligible effect on the wind.
How possible is this plan?
The solar power capacity required to deliver this 50 kWh per day per person in the UK is more than 100 times all the photovoltaics in the whole world.
4 main ways to get energy from solar-powered biological systems:
let’s simply estimate the power at the first staging post. The average harvestable power of sunlight in Britain is 100 W/mm.
The best performance of any energy crops in Europe is 0.5 W/mm.
Let’s cover 75% of the country with these energy plants.
That’s 3000 (m*m) per person for bio-energy.
The maximum power available:
(ignoring all the additional costs of growing, harvesting, and processing the plants)
0.5 W/m2 × 3000 m2 / person = 36 kWh/d per person
Even burning dried wood in a good wood boiler loses 20% of the heat up the chimney.
So true power from biomass and biofuels cannot be any bigger than 24 kWh/d per person.
We need some plants to make food for us and for our animals too.
Energy crops as a coal substitute
willow, miscanthus, or poplar 0.2 W/m2
Oilseed rape 0.13 W/m2
Sugar beet 0.4 W/m2
Sugar cane 1.2 W/m2
Corn 0.02 W/m2
Switchgrass 0.2 W/m2
Algae to biodiesel (but CO2 required) 4 W/m2
Algae to hydrogen 3.6 W/m2
Incineration of agricultural by-products
agricultural by-products 0.002 W/m2
Bavarian solar photovoltaic farm 5 W/m2
Heating and Cooling
Where do we use heating and cooling?
1. controlling the temperature of our surroundings at home and at work
2. warming or cooling our food, drink,
3. warming water for laundry and dirty dishes
Domestic water heating
biggest use of hot water in a house: depends on your lifestyle
(maybe baths, showers, dish-washing, or clothes-washing)
Boiling water 20 minutes per day: power consumption = 1 kWh per day.
3 other examples: (2 people per household)
Adding up the estimates relating to hot water, I think it’s easy to use
12 kWh per day per person
A small electric fan heater is 1 kW (24 kWh per day).
In winter, you might need one of these per person to keep toasty. In summer, none.
One person needs to use
12 kWh per day
on hot air.
Most people use more than they need, keeping several rooms warm simultaneously (kitchen, living room, corridor, and bathroom, say). So a plausible consumption figure for hot air is about double that:
24 kWh per day per person
An electric blanket for a double bed uses 140W;
for one hour it uses 0.14 kWh.
My fridge-freezer consumes 18 W on average - that’s roughly
To estimate how much energy someone might use in the UK, I assumed they might switch such an air-conditioning unit on for about 12 hours per day for 30 days of the year.
On the days when it’s on, the air-conditioner uses
The average consumption over the whole year is
The total energy that one person might spend on heating and cooling, including home, workplace, and cooking, is:
37 kWh/d per person
(12 for hot water, 24 for hot air, and 1 for cooling).
1.Conduction - heat flowing directly through walls, windows and doors;
2.Ventilation (convection) - hot air coming out through cracks, gaps, or deliberate ventilation ducts.
The rate of conduction of heat through a wall, ceiling, floor, or window is the product of three things:
1. the area of the wall,
2. a measure of conductivity of the wall known in the trade as the “U-value” or thermal transmittance, and
3. the temperature difference –
power loss = area × U × temperature difference.
The U-value is usually measured in W/m2/K. (One kelvin (1 K) is the same as one degree Celsius (1 °C).)
Bigger U-values mean bigger losses of power. The thicker a wall is, the smaller its U-value. Double-glazing is about as good as a solid brick wall. (See table E.2.)
The U-values of objects that are “in series,” such as a wall and its inner lining, can be combined in the same way that electrical conductances combine:
To work out the heat required to warm up incoming cold air, we need the heat capacity of air: 1.2 kJ/m3/K.
In the building trade, it’s conventional to describe the power-losses caused by ventilation of a space as the product of:
the number of changes N of the air per hour,
the volume V of the space in cubic meters,
the heat capacity C,
the temperature difference T between the inside and outside of the building
Energy loss and temperature demand (degree-days)
Since energy is power × time, you can write the energy lost by conduction through an area in a short duration as
energy loss = area × U × (T × duration),
and the energy lost by ventilation as
1⁄3 NV × (T × duration).
Both these energy losses have the form
Something × (T × duration),
where the “Something” is measured in watts per °C. As day turns to night, and seasons pass, the temperature difference T changes; we can think of a long period as being chopped into lots of small durations, during each of which the temperature difference is roughly constant. From duration to duration, the temperature difference changes, but the Somethings don’t change.
When predicting a space’s total energy loss due to conduction and ventilation over a long period we thus need to multiply two things:
1.the sum of all the Somethings (adding area × U for all walls, roofs, floors, doors, and windows, and 1⁄3 NV for the volume); and
2.the sum of all the Temperature difference × duration factors (for all the durations).
The first factor is a property of the building measured in watts per °C.
I’ll call this the leakiness of the building. (This leakiness is sometimes called the building’s heat-loss coefficient.) The second factor is a property of the weather; it’s often expressed as a number of “degree-days,” since temperature difference is measured in degrees, and days are a convenient unit for thinking about durations. For example, if your house interior is at 18 °C, and the outside temperature is 8 °C for a week, then we say that that week contributed 10 × 7 = 70 degree-days to the (T ×duration) sum. I’ll call the sum of all the (T × duration) factors the temperature demand of a period.
energy lost = leakiness × temperature demand.
We can reduce our energy loss by reducing the leakiness of the building, or by reducing our temperature demand, or both. The next two sections look more closely at these two factors, using a house in Cambridge as a case-study.
There is a third factor we must also discuss. The lost energy is replen- ished by the building’s heating system, and by other sources of energy
such as the occupants, their gadgets, their cookers, and the sun. Focusing on the heating system, the energy delivered by the heating is not the same as the energy consumed by the heating. They are related by the coefficient of performance of the heating system.
energy consumed = energy delivered/coefficient of performance.
For a condensing boiler burning natural gas, for example, the coefficient of performance is 90%, because 10% of the energy is lost up the chimney.
To summarize, we can reduce the energy consumption of a building in
1.by reducing temperature demand;
2.by reducing leakiness; or
3.by increasing the coefficient of performance.
To make hydroelectric power, you need altitude (height), and you need rainfall. Let’s estimate the total energy of all the rain as it runs down to sea-level.
Let’s do the lowlands first.
To estimate the gravitational power of low-land rain, we multiply the rainfall in Bedford (584 mm per year) by the density of water (1000 kg/m^3), the strength of gravity (10 m/s^2) and the typical lowland altitude above the sea (say 100 m).
Let’s turn to the highlands. Kinlochewe is a rainier spot: it gets
per year, four times more than Bedford. The height drops there are bigger too large areas of land are above
. So overall a
in power per square meter is plausible for mountainous regions. The raw power per unit area is roughly
If the highlands generously share their hydro-power (at
1300 m^2 area per person
), we find an upper limit of about
7 kWh per day per person
. As in the lowlands, this is the upper limit on raw power if there is no evaporation and every drop were perfectly exploited (100% efficiency).
What should we estimate is the plausible practical limit? Let’s guess
of this 1.4 kWh per day, and round it up a little to allow for production in the lowlands:
1.5 kWh per day.
The actual power from hydroelectricity in the UK today is 0.2 kWh/d
per person, so this 1.5 kWh/d per person would require a seven-fold increase in hydroelectric power.
The power per unit area works out to 0.02 W/m2. That’s the power per unit area of land on which rain falls.
When we multiply this by the area per person (2700 m2, if the lowlands are equally shared between all 60 million Brits), we find an average raw power of about 1 kWh per day per person. This is the absolute upper limit for lowland hydroelectric power, if every river were dammed and every drop perfectly exploited.
1. We will only dam rivers with huge drops in height.
2. The rain that flows into those big rivers with huge drops are much smaller than the whole country.
3. Much of the water evaporates before it gets to the turbine
4. No hydroelectric system can use the full potential energy of the water. (efficiency)
We thus arrive at a firm conclusion about lowland water power.
The brightest domestic lightbulbs use 250 W, and bedside lamps use 40 W. In an old-fashioned incandescent bulb, most of this power gets turned into heat, rather than light. A fluorescent tube can produce an equal amount of light using one quarter of the power of an incandescent bulb.
How much power does a moderately affluent person use for lighting? My rough estimate, based on table 9.2, is that a typical two-person home with a mix of low-energy and high-energy bulbs uses about 5.5 kWh per
day, or 2.7 kWh per day per person. I assume that each person also has a workplace where they share similar illumination with their colleagues; guessing that the workplace uses 1.3 kWh/d per person, we get a round figure of 4 kWh/d per person.
Do we need to include public lighting too, to get an accurate estimate, or
do home and work dominate the lighting budget? Street-lights in fact use
about 0.1 kWh per day per person, and traffic lights only 0.005 kWh/d per
person both negligible, compared with our home and workplace lighting.
The economics of low-energy bulbs
Generally I avoid discussing economics, but I’d like to make an exception for lightbulbs. Osram’s 20 W low-energy bulb claims the same light output as a 100 W incandescent bulb. Moreover, its lifetime is said to be 15 000 hours (or “12 years,” at 3 hours per day). In contrast a typical incandescent bulb might last 1000 hours. So during a 12-year period, you have this choice (figure 9.3): buy 15 incandescent bulbs and 1500 kWh of electricity (which costs roughly £150); or buy one low-energy bulb and 300 kWh of electricity (which costs roughly £30).
Bulb type efficiency
white LED 35
compact fluorescent 55
large fluorescent 94
sodium street light 150
Researchers say that LED (light-emitting diode) bulbs will soon be even more energy-efficient than compact fluorescent lights. The efficiency of a light is measured in lumens per watt.
Benefit at sea (offshore): winds are stronger and steadier than on land.
Offshore wind farms deliver a higher power per unit area than onshore wind farms.
The Kentish Flats wind farm in the Thames Estuary was predicted to have an average power per unit area of 3.2 W/m2. In 2006, its average power per unit area was 2.6 W/m2.
Assume: power per unit area of 3 W/m2 (50% larger than our onshore estimate of 2 W/m2)
How much area of sea could plausibly be covered with wind turbines?
There is shallow offshore wind and deep offshore wind, as illustrated in figure 10.2.
Shallow offshore wind (depth less than 25–~30 m), while roughly twice as costly as land-based wind, is economically feasible, given modest subsidy.
Deep offshore wind is at present not economically feasible. As of 2008, there’s just one deep offshore wind farm in UK waters, an experimental prototype sending all its electricity to a nearby oil rig called Beatrice.
Within British territorial waters, the shallow area is about 40 000 km2, most of it off the coast of England and Wales. This area is about two Waleses.
The average power available from shallow offshore wind farms occupying the whole of this area would be 120 GW, or 48 kWh/d per person.
But it’s hard to imagine this arrangement being satisfactory for shipping. Substantial chunks of this shallow water would, I’m sure, remain off-limits for wind farms.
The requirement for shipping corridors and fishing areas must reduce the plausibly-available area; I propose that we assume the available fraction is one third (but please see this chapter’s end-notes for a more pessimistic view!). So we estimate the maximum plausible power from shallow offshore wind to be 16 kWh/d per person.
I want to emphasize the large area two thirds of a Wales that would be required to deliver this 16 kWh/d per person.
Offshore wind is tough to pull off because of the corrosive effects of
Danish wind farm, Horns Reef: all 80 turbines had to be dismantled and repaired after only 18 months’ exposure to the sea air.
Kentish Flats: turbines seem to be having similar problems with their gearboxes, one third needing replacement during the first 18 months.
Deep Offshore Wind
The area with depths between 25 m and 50 m is about 80 000 km2 the size of Scotland.
Assuming again a power per unit area of 3 W/m2, “deep” off-shore wind farms could deliver another 240 GW, or 96 kWh/d per person, if turbines completely filled this area.
Again, we must make corridors for shipping. I suggest as before that we assume we can use one third of the area for wind farms; this area would then be about 30% bigger than Wales, and much of it would be further than 50 km offshore.
The outcome: if an area equal to a 9 km-wide strip all round the coast were filled with turbines, deep offshore wind could deliver a power of 32 kWh/d per person. A huge amount of power, yes; but still no match for our huge consumption. And we haven’t spoken about the issue of wind’s intermittency.
“The nuclear power stations will all be switched off in a few years. How can we keep Britain’s lights on? ... unplug your mobile-phone charger when it’s not in use.”
Modern phone chargers, when left plugged in with no phone attached, use about half a watt. In our preferred units, this is a power consumption of about 0.01 kWh per day. For anyone whose consumption stack is over 100 kWh per day could potentially reduce their energy consumption by one hundredth of one percent.
Admittedly, some older chargers use more than half a watt if it’s warm to the touch, it’s probably using one watt or even three. A three-watt-guzzling charger uses 0.07 kWh per day.
A vacuum cleaner, if you use it for a couple of hours per week, is equivalent to about 0.2 kWh/d.
Mowing the lawn uses about 0.6 kWh.
Maybe computers and entertainment systems are the big suckers on most people’s electrical balance-sheet.
This chapter’s summary figure: it’ll depend how many gadgets you have at home and work, but a healthy houseful or officeful of gadgets left on all the time could easily use 5 kWh/d.
If wave power offers hope to any country, then it must offer hope to the United Kingdom and Ireland with the Atlantic Ocean on one side, and on the other side the North Sea.
First, let’s clarify where waves come from: sun makes wind and wind makes waves.
1. Most of the sunlight that hits our planet warms the oceans.
2. The warmed water warms the air above it, and produces water vapor.
3. The warmed air rises; as it rises it cools, and the water eventually re-condenses, forming clouds and rain.
4. At its highest point, the air is cooled down further by the freezing blackness of space.
5. The cold air sinks again.
This great solar-powered pump drives air round and round in great convection rolls. From our point of view on the surface, these convection rolls produce the winds. Wind is second-hand solar energy. As wind rushes across open water, it generates waves. Waves are thus third-hand solar energy.
If waves traveling in a particular direction encounter objects that absorb energy from the waves for example, a row of islands with sandy beaches then the seas beyond the object are calmer. The objects cast a shadow, and there’s less energy in the waves that get by. So, whereas sunlight delivers a power per unit area, waves deliver a power per unit length of coastline.
We can find an upper bound on the maximum conceivable power that could be obtained from wave power by estimating the incoming power per unit length of exposed coastline, and multiplying by the length of coastline.
The power of Atlantic waves has been measured: it’s about 40 kW per meter of exposed coastline. That sounds like a lot of power! If everyone owned a metre of coastline and could harness their whole 40 kW, that would be plenty of power to cover modern consumption. However, our population is too big. There is not enough Atlantic-facing coastline for everyone to have their own meter.
Britain has about 1000 km of Atlantic coastline (one million meters), which is 1⁄60 m per person. So the total
raw incoming power is 16 kWh per day per person. Practical
systems won’t manage to extract all the power, and some of the power will be lost during conversion from mechanical energy to electricity. Let’s assume that wave-machines are 50%-efficient at turning the incoming wave power into electricity, and that we are able to pack wave-machines along 500 km of Atlantic-facing coastline. That would mean we could deliver 25% of this theoretical bound. That’s 4 kWh per day per person.
Food and Farming
A moderately active person
weight of 65 kg
consumes about 2600 “Calories”/day.
(A “Calorie,” in food circles, is actually 1000 chemist’s calories (1 kcal).)
2600 “Calories” per day is about 3 kWh per day.
Where does that energy go?
Most of this energy eventually escapes from the body as
a typical person = 100 W space heater (a medium-power lightbulb)
Put 10 people in a small cold room, and you can switch off the 1 kW convection heater.
If I drink a pint of milk a day, what energy does that require?
A typical dairy cow produces 16 liters of milk per day.
So my one pint per day (half a liter per day) requires that I employ 1⁄32 of a cow.
I love cheese too. And to make 1 kg of Irish Cheddar takes about 9 kg of milk. So consuming 50 g of cheese per day requires the production of an extra 450 g of milk.
milk and cheese habit requires that I employ 1⁄16 of a cow. A cow of weight 450 kg needs 85 MJ/d, which is 24 kWh/d.
1⁄16 of a cow has an energy consumption of about 1.5 kWh per day.
Eating two eggs a day requires a
power of 1 kWh per day.
The energy cost of eating meat
Maybe a person eats about half a pound a day (227 g). (This is the average meat consumption of Americans.)
To work out the power required to maintain the meat-eater’s animals as they mature and wait for the chop, we need to know for how long the animals are alive, consuming energy. Chicken, pork, or beef?
Chickens are alive for roughly 50 days.
So the steady consumption of half a pound a day of chicken requires about 25 pounds of chicken to be alive, preparing to be eaten. And those 25 pounds of chicken consume energy.
Pigs are around for longer maybe 400 days from birth to bacon so the steady consumption of half a pound a day of pork requires about 200 pounds of pork to be alive, preparing to be eaten.
Beef production involves the longest times.
Cows are alive for 1000 days.
So the steady consumption of half a pound a day of beef requires about 500 pounds of beef to be alive, preparing to be eaten.
Tidal power: an artificial pool next to the sea, with a water-wheel that is turned as the pool fills or empties.
Assume range = 4 m (typical)
The maximum power of an artificial tide-pool = ~3 W/m2
(a) filled rapidly at high tide and emptied rapidly at low tide
(b) generating power from both flow directions)
tidal range power density
2 m 1 W/m2
4 m 3 W/m2
6 m 7 W/m2
8 m 13 W/m2
The power we can extract from tides can never be more than the total power of these tidal waves from the Atlantic. The total power crossing the lines in figure 14.6 has been measured.
On average it amounts to 100 kWh per day per person.
If we extract 10% of this energy and
if the conversion and transmission processes are 50% efficient the average power would be 5 kWh per day per person.
Tidal stream farms
One way to extract tidal energy would be to build tide farms, just like wind
The first such underwater windmill, or “tidal-stream” generator, to be connected to the grid was a “300 kW” turbine, installed in 2003 near Hammerfest, Norway. Detailed power production results have not been published, and no-one has yet built a tide farm with more than one turbine, so we’re going to have to rely on physics and guesswork to predict how much power tide farms could produce.
1. the rules for laying out a sensible tide farm are similar to those for wind farms, and
2. that the efficiency of the tide turbines will be like that of the best wind turbines.
Table 14.7 shows the power of a tide farm for a few tidal currents.
Given that tidal currents of 2 to 3 knots are common, there are many
places around the British Isles where the power per unit area of tide farm
would be 6 W/m2 or more. This power per unit area can be compared to
our estimates for wind farms (2-3 W/m2) and for photovoltaic solar farms
Tide power is not small!
9 kWh/d per person could be extracted if the best places around the UK were used
speed power density
(m/s) (knots) (W/m2)
0.5 1 1
1 2 8
2 4 60
3 6 200
4 8 500
5 10 1000
Tidal barrages are a proven technology.
Famous barrage at La Rance in France.
Tidal range = 8 meters on average
Produced an average power of 60 MW since 1966.
Tidal range: 11.3 m - 5.8 m.
A 500 km2 tide-pool can be made. (figure 14.8) (bigger than the estuary at La Rance.)
What power could this tide-pool deliver, if we let the water in and out at the ideal times, generating on both the flood and the ebb?
When the range = 11.3 m, the average power (at 30 W/m2) = 14.5 GW, or 5.8 kWh/d per person.
When the range = 5.8 m, the average power (at 8 W/m2) = 3.9 GW, or 1.6 kWh/d per person.
(We assume that the water is let in in a single pulse at the peak of high tide, and let out in a single pulse at low tide. NOT REALITY) In reality, the in-flow and out-flow would be spread over a few hours, which would reduce the power delivered a little.
The current proposals for the barrage will generate power in one direction only. This reduces the power delivered by another
The engineers’ reports on the proposed Severn barrage say that, generating on the ebb alone, it would contribute
0.8 kWh/d per person
The barrage would also provide protection from flooding valued at about £120M per year.
Tidal lagoons are created by building walls in the sea; they can then be used like artificial estuaries. The required conditions for building lagoons are that the water must be shallow and the tidal range must be large.
Economies of scale apply: big tidal lagoons make cheaper electricity than small ones.
If two lagoons are built in one location, we can boost the power delivered and to enable the lagoons to deliver power on demand at any time, independent of the state of the tide.
One lagoon can be designated the “high” lagoon, and the other the “low” lagoon.
At low tide, some power generated by the emptying high lagoon can be used to pump water out of the low lagoon, making its level even lower than low water. The energy required to pump down the level of the low lagoon is then repaid with interest at high tide, when power is generated by letting water into the low lagoon.
Similarly, extra water can be pumped into the high lagoon at high tide, using energy generated by the low lagoon. Whatever state the tide is in, one lagoon or the other would be able to generate power. Such a pair of tidal lagoons could also work as a pumped storage facility, storing excess energy from the electricity grid.
The average power per unit area of tidal lagoons in British waters could be
, so if tidal lagoons with a total area of 800 km2 were created (as indicated in figure 14.9), the power generated would be
1.5 kWh/d per person
Adding everything up, the barrage, the lagoons, and the tidal stream farms could deliver something like
11 kWh/d per person
Tide power has never been used on an industrial scale in Britain,
Economic and technical challenges: corrosion, silt accumulation, entanglement with flotsam
But here are seven reasons for being excited about tidal power in the British Isles.
1. Tidal power is completely predictable. (unlike wind and sun) it works day and night all year round. Energy can be stored so that power can be delivered on demand.
2. Successive high and low tides take about 12 hours to progress around the British Isles. A collection of tide farms could produce a more constant contribution to the electrical grid than one tide farm.
3. Tidal power will last for millions of years.
4. It doesn’t require high-cost hardware, in contrast to solar photovoltaic power.
5. Moreover, because the power density of a typical tidal flow is greater than the power density of a typical wind, a 1 MW tide turbine is smaller in size than a 1 MW wind turbine (smaller = cheaper)
6. Life below the waves is peaceful. (wind turbines require costly engineering to withstand rare windstorms).
7. Humans live on the land, and they can’t see under the sea. (Wind turbines are ugly and noisy.)
Largest Tidal Power Plant
One of the main uses of energy in the “developed” world is the creation of stuff. In its natural life cycle, stuff passes through three stages.
1. New stuff is displayed in shiny packaging on a shelf in a shop. At this stage, stuff is called “goods.”
2. As soon as the stuff is taken home and sheds its packaging, it undergoes a transformation from “goods” to its second form, “stuff.”
3. We get tired of stuff and throw it away. It is "trash."
What is the full energy-cost of stuff?
This is called life-cycle analysis. There are 4 parts.
aw materials. This phase involves digging minerals out of the ground,
them into manufacturers’ lego: plastics, glasses, metals, and ceramics, for example. The
of this phase include the
costs of the raw materials to their next destination.
roduction. In this phase, the raw materials are processed into a manufactured product. Manufacturing uses
. The energy costs of this phase include
se. Many products we have consume energy when we use them.
isposal. This phase includes the energy cost of
putting the stuff back in a hole in the ground
(landfill), or of
turning the stuff back into raw materials
(recycling); and of
cleaning up all the pollution
associated with the stuff.
Assume you drink five cans of coke per day, and throw the aluminum cans away.
The raw material phase dominates. The production of metals is energy intensive, especially for aluminum. Making one aluminum drinks-can needs
. So a five-a-day habit wastes energy at a rate of
As for a
500 ml water bottle
made of PET (which weighs 25 g), the embodied energy is
just as bad as an aluminum can!
The average Brit throws away 400 g of packaging per day mainly food packaging. The embodied energy content of packaging ranges from
7 to 20 kWh per kg
(glass, paper, plastics, steel). Taking the average energy content to be
, the energy footprint of packaging is
(A little of this embodied energy is recoverable by waste incineration, as we’ll discuss in Chapter 27.)
Making a personal computer costs
of energy. So if you buy a new computer every
, that corresponds to a power consumption of
2.5 kWh per day
The energy cost of making a rechargeable nickel-cadmium AA battery, storing
of electrical energy and having a mass of 25 g, is
1.4 kWh (phases R and P)
. If the energy cost of disposable batteries is similar, throwing away two AA batteries per month uses about
The energy cost of batteries is thus likely to be a minor item in your stack of energy consumption.
Transport of stuff by road
In 2006, the total amount of road transport in Britain by heavy goods vehicles was 156 billion t-km. Shared between 60 million, that comes to 7 t-km per day per person, which costs
7 kWh per day per person
(assuming an energy intensity of 1 kWh per ton-km). One quarter of this transport, by the way, was of food, drink, and tobacco.
To summarize all these forms of stuff and stuff-transport:
48 kWh per day per person
for the making of stuff
40 for imports
2 for a daily newspaper
2 for road-making
1 for house-making
3 for packaging
12 kWh per day per person
for the transport of the stuff by sea, by road, and by pipe, and the storing of food in supermarkets.
The largest stuff most people buy is a house. I estimate the energy cost of making a new house.
Assume we replace each house
every 100 years.
The estimated energy cost is
This is the energy cost of creating the shell of the house only the foundation, bricks, tiles, and roof beams.
If the average house
occupancy is 2.3
, the average energy expenditure on house building is thus estimated to be
1 kWh per day per person
Geothermal energy comes from
1. from radioactive decay in the crust of the earth
2. from heat trickling through the mantle from the earth’s core.
The heat in the core is there because the earth used to be red-hot, and it’s still cooling down and solidifying; the heat in the core is also being added to by tidal friction.
Geothermal is an attractive renewable because it is “always on,” independent of the weather; if we make geothermal power stations, we can switch them on and off so as to follow demand.
15-km down in the earth it is easily hot enough to boil water.
Put two "straws" down, and pump cold water down one straw and suck from the other. You’ll be sucking up steam, and you can run a power station.
Limit-less power? No.
After a while, your sucking of heat out of the rock will have reduced the temperature of the rock. You weren’t sucking sustainably. You now have a long wait before the rock at the tip of your straws warms up again.
Geothermal heat can be treated the same way we currently treat fossil fuels: as
a resource to be mined rather than collected sustainably.
Living off geothermal heat in this way might be better for the planet than living unsustainably off fossil fuels; but perhaps it would only be another stop-gap giving us another 100 years of unsustainable living?
First imagine using geothermal energy sustainably by sticking down straws to an appropriate depth, and sucking gently. Sucking at such a rate that the rocks at the end of the our straws don’t get colder and colder. This means
sucking at the natural rate at which heat is already flowing out of the earth.
The maximum power we can get per unit area is
. But that power is not high-grade power, it’s low-grade heat that’s trickling through at the ambient temperature up here.
We want to make electricity, and that’s why we must drill down. Heat is useful only if it comes from a source at a higher temperature than the ambient temperature. The temperature increases with depth as shown in figure 16.4, reaching a temperature of about
500 °C at a depth of 40 km
Every gun that is made, every warship launched, every rocket fired signifies a theft from those who hunger and are not fed, those who are cold and are not clothed.
This world in arms is not spending money alone. It is spending the sweat of its laborers, the genius of its scientists, the hopes of its children.
President Dwight D. Eisenhower April, 1953
Let’s try to estimate how much energy we spend on our military.
In 2007, the fraction of British central government expenditure that went to defense was £33 billion/£587 billion =
. If we include the UK’s spending on counter-terrorism and intelligence (£2.5 billion per year and rising), the total for defensive activities comes to £36 billion.
As a crude estimate we might guess that 6% of this £36 billion is spent on energy at a cost of 2.7p per kWh. (6% is the fraction of GDP that is spent on energy, and 2.7p is the average price of energy.) That works out to about 80 TWh per year of energy going into defense: making bullets, bombs, nuclear weapons; making devices for delivering bullets, bombs, and nuclear weapons. In our favorite units, this corresponds to
4 kWh per day per person
UK universities use 5.2 billion kWh per year. Shared out among the whole population, that’s a power of
0.24 kWh per day per person
Can we live on renewables?
Consumption: 195 kWh per day per person.
Production: 180 kWh per day per person.
But please remember:
1. economic issues
2. social issues
3. environmental issues
Also, some energy production is
with each other:
1. PV panels and hot-water panels need to be on roofs.
2. Solar PV farms using 5% of the country and energy crops which cover 75% of the country.
If we were to lose just one of our bigger green contributors then the production stack would no longer match the consumption stack.
For example, if we decided that deep offshore wind is not an option, or that paneling 5% of the country with photovoltaics at a cost of
£200 000 per person
is not possible.
1. reflect on our estimates of consumption and production,
2. compare them with official averages and with other people’s estimates
3. discuss how much power renewables could possibly deliver in a country like Britain.
Our estimate of a typical affluent person’s consumption (figure 18.1) has reached
195 kWh per day
Another difference between our red stack and the national total is that in most of the consumption chapters
we ignored the energy lost in converting energy from one form to another,and in transporting energy around
For example, the “car” estimate in Part I covered only the energy in the petrol,
1. not the energy used at the oil refinery that makes the petrol,
2. not the energy used in moving the oil and petrol from A to B.
The national total accounts for all the energy, before any conversion losses. Conversion losses in fact account for about
of total national energy consumption. Most of these conversion losses happen at power stations. Losses in the electricity transmission network chuck away
of total national energy consumption.
When building our red stack, we tried to imagine how much energy a typical affluent person uses. Has this approach biased our perception of the importance of different activities?
Let’s look at some official numbers. Figure 18.2 shows energy consumption by end use.
The top two categories are
heating (hot air and hot water)
. Those two categories also dominated the red stack in Part I. Good.
Let’s look more closely at transport. In our red stack, we found that the energy footprints of driving a car 50 km per day and of flying to Cape Town once per year are roughly equal.
Table 18.3 shows the relative importance of the different transport modes in the national balance-sheet. In the national averages, aviation is smaller than road transport.
How do Britain’s official consumption figures compare with those of other countries?
Figure 18.4 shows the power consumptions of lots of countries or regions, versus their gross domestic products (GDPs). There’s an evident correlation between power consumption and GDP:
the higher a country’s GDP (per capita), the more power it consumes per capita
. The UK is a fairly typical high-GDP country, surrounded by Germany, France, Japan, Austria, Ireland, Switzerland, and Denmark.
The only notable exception to the rule “big GDP implies big power consumption” is Hong Kong. Hong Kong’s GDP per capita is about the same as Britain’s, but Hong Kong’s power consumption is about 80 kWh/d/p.
The message I take from these country comparisons is that the UK is a fairly typical European country, and therefore provides a good case study for asking the question “How can a country with a high quality of life get its energy sustainably?”
People often say that Britain has plenty of renewables. Have I been mean to green? Have I underestimated sustainable production?
Let’s compare my green numbers with several estimates. Remarkably, all the estimates in the Sustainable Development Commission’s document are smaller than mine! (To be precise,
all the estimates of the renewables total are smaller than my total.
The Sustainable Development Commission’s publication gives estimates from four sources detailed below (IEE, Tyndall, IAG, and PIU). Figure 18.6 shows my estimates alongside numbers from these four sources and numbers from the Centre for Alternative Technology (CAT). Here’s a description of each source.
The Institute of Electrical Engineers published a report on renewable energy in 2002 – a summary of possible contributions from renewables in the UK. The second column of figure 18.6 shows the “technical potential” of a variety of renewable technologies for UK electricity generation – “an upper limit that is unlikely ever to be exceeded even with quite dramatic changes in the structure of our society and economy.” According to the IEE, the total of all renewables’ technical potential is about
27 kWh/d per person
The Tyndall Centre’s estimate of the total practicable renewable-energy resource is
15 kWh per day per person
The Interdepartmental Analysts Group’s estimates of renewables, take into account economic constraints. Their total practical and economical resource (at a retail price of 7p/kWh) is
12 kWh per day per person
The “PIU” column shows the “indicative resource potential for renewable electricity generation options” from the DTI’s contribution to the PIU review in 2001. For each technology I show their “practical maximum,” or, if no practical maximum was given, their “theoretical maximum.”
The final column shows the numbers from the Centre for Alternative Technology’s “Island Britain” plan Helweg-Larsen and Bull (2007).
Sometimes people ask me “surely we used to live on renewables just fine, before the Industrial Revolution?”
What is different now?
Green ambitions meet social reality
Technically, Britain has “huge” renewables. But realistically, I don’t think Britain can live on its own renewables - at least not the way we currently live.
There is always
to any major renewable energy proposal. People love renewable energy, unless it is big. If the British are good at one thing, it’s saying “no.”
Figure 18.8 offers guidance to anyone trying to erect wind farms in Britain.
On a map of the British mainland I’ve shown in white a
2-km radius exclusion zone surrounding every hamlet, village, and town
. These white areas would presumably be excluded from wind-farm development because they are too close to the humans.
I’ve colored in black all regions that are
more than 2 km from any human settlement
. These areas are largely excluded from wind-farm development because they are peaceful, and it’s essential to protect peaceful places from industrialization.
If you want to avoid objections to your wind farm, pick any piece of land that is not colored black or white.
Some of these environmentalists who have good hearts but confused minds are almost a barrier to tackling climate change.
Malcolm Wicks, Minister of State for Energy
We want to stop using fossil fuels, for one or more of the reasons listed in Chapter 1 –
climate change or security of supply
. Figure 18.9 shows how much power we
get from renewables and nuclear. They amount to just
of our total power consumption.
The two conclusions from Part I are:
To make a difference, renewable facilities have to be country-sized.
For any renewable facility to make a contribution comparable to our current consumption, it has to be country-sized.
To get a big contribution from wind, we used wind farms with the
area of Wales
To get a big contribution from solar photovoltaics, we required
half the area of Wales
. To get a big contribution from waves, we imagined wave farms covering
500 km of coastline
To make energy crops with a big contribution, we took
75% of the whole country
Renewable facilities have to be country-sized because all
renewables are so diffuse
. Table 18.10 shows most of the powers-per-unit-area in Part I.
To sustain Britain’s lifestyle on its renewables alone would be very difficult. A renewable-based energy solution will necessarily be large and intrusive.
2.It’s not going to be easy to make a plan that adds up using renewables alone. If we are serious about stop using fossil fuels, Brits are going to have to learn to start saying “yes” to something. Indeed to many things.
Every BIG Helps
Balancing the Energy Budget
We’ve established that the UK’s present lifestyle can’t be sustained on the UK’s own renewables (except with the industrialization of country-sized areas of land and sea). So, what are our options, if we wish to get off fossil fuels and live sustainably? We can balance the energy budget either
1. by reducing demand, or
2. by increasing supply, or, of course,
3. by doing both.
1.by reducing our population;
2.by changing our lifestyle;
3.by keeping our lifestyle, but reducing its energy intensity through “efficiency” and “technology.”
Simplify British energy consumption
Suppose Britain consumes energy in just three forms:
Having adopted this simple idea of Britain, our discussions of demand reduction will have just three bits.
, how can we reduce
’s energy-demand and eliminate all fossil fuel use for transport? This is the topic of Chapter 20.
, how can we reduce
’s energy-demand and eliminate all fossil fuel use for heating? This is the topic of Chapter 21.
, what about
? Chapter 22 discusses efficiency in electricity consumption.
For the impatient reader
Are you eager to know the end of the story right away? Here is a quick summary, a sneak preview of Part II.
About 1/3 of our energy goes into transportation.
Can technology deliver a reduction in consumption?
In this chapter we explore options for achieving two goals:
1. to reduce transport’s energy use
2. to eliminate fossil fuel use in transport
Transport featured in three of our consumption chapters: Chapter 3
(cars), Chapter 5 (planes), and Chapter 15 (road freight and sea freight). So there are two sorts of transport to address:
1. passenger transport
Our unit of passenger transport is the passenger-kilometer (p-km).
If a car carries one person a distance of 100 km, it delivers 100 p-km of transportation.
1p x 100km = 100 p-km
If it carries four people the same distance, it has delivered 400 p-km.
4p x 100km = 400 p-km
We’ll measure the energy consumption of passenger transport in “
kWh per 100 passenger-kilometers
Similarly our unit of freight transport is the ton-km (t-km).
If a truck carries 5 t of cargo a distance of 100 km then it has delivered 500 t-km of freight-transport.
5t x 100km = 500 t-km
We'll measure the energy consumption of freight in "
kWh per ton-km
Notice that these measures are the other way up compared to “kms per liter”: whereas we like vehicles to deliver many kms per liter, we want energy-consumption to be few kWh per 100 p-km.
How to reduce the energy consumption of transportation.
1. understand where the energy is going
2. understand how to reduce energy consumption
Let's review what we learned about transportation.
short-distance (city) travel
with lots of starting and stopping, the energy mainly goes into speeding up the vehicle and its contents.
Key strategies for consuming less in this sort of transportation are therefore
a) to weigh less, and
b) to go further between stops.
c) Regenerative braking, which captures energy when slowing down, may help too.
d) In addition, it helps to move slower, and to move less.
These observations lead us to six principles of vehicle design and vehicle use for more-efficient surface transport:
a) reduce the frontal area per person;
b) reduce the vehicle’s weight per person;
c) when traveling, go at a steady speed and avoid using brakes;
d) travel more slowly;
e) travel less; and
f) make the energy chain more efficient.
We’ll now discuss a variety of ways to apply these principles.
Someone said, “
Only 1 percent of the energy used by a car goes into moving the driver.
Is this true?
A train is a possible replacement for the petrol car: a train, with an energy-cost, if full, of
1.6 kWh per 100 passenger-km
Trains manage to achieve outstanding efficiency
a) without traveling slowly, and
b) without having a low weight per person.
Trains make up for their high speed and heavy frame by using the principle of small frontal area per person.
A regular car has an effective frontal area of about
, a full commuter train from Cambridge to London has a
frontal area per passenger of 0.02 m2
How much could consumption be reduced by a switch from personal gas-guzzlers to excellent integrated public transport?
At its best, shared public transport is far more energy-efficient than individual car-driving.
, carrying 49 passengers and doing 10 miles per gallon at 65 miles per hour, uses
6 kWh per 100 p-km
13 times better than the single-person car!
, which violate two of our energy-saving principles by going twice as fast as the car and weighing a lot, are much more energy efficient: if the electric high-speed train is full, its energy cost is
3 kWh per 100 p-km
27 times smaller than the car’s
Energy consumption (kWh per 100 p-km)
Table 20.8. Overall transport efficiencies of transport modes in Japan (1999).
There are four ways to save energy as a vehicle slows down.
Electrical energy storage:
An electric generator coupled to the wheels can charge up an electric battery or supercapacitor.
Compressed air energy storage:
Hydraulic motors driven by the wheels can make compressed air, stored in a small canister.
Mechanical energy storage:
Energy can be stored in a flywheel.
Gravitational energy storage:
Braking energy can be stored as gravitational energy by driving the vehicle up a ramp whenever you want to slow down. This gravitational energy storage option is rather inflexible, since there must be a ramp in the right place.
A flywheel system weighing just 24 kg (figure 20.18), designed for energy storage in a racing car, can store 400 kJ (0.1 kWh) of energy enough energy to accelerate an ordinary car up to 60 miles per hour (97 km/h); and it can accept or deliver 60 kW of power.
Electric batteries capable of delivering that much power would weigh about 200 kg. So, unless you’re already carrying that much battery on board, an electrical regenerative-braking system should probably use capacitors to store braking energy. Super-capacitors have similar energy-storage and power-delivery parameters to the flywheel’s.
Hybrid cars such as the Toyota Prius (figure 20.19) have more-efficient engines and electric regenerative braking, but to be honest, today’s hybrid vehicles don’t really stand out from the crowd.
seem to give
fuel savings of 20 or 30%
. So neither these petrol/electric hybrids, nor the petrol/hydraulic hybrid featured in figure 20.17 seems to me to have really cracked the transport challenge.
A 30% reduction in fossil-fuel consumption is impressive, but it’s not enough by this book’s standards.
We want to
:get off fossil fuels, or at least to reduce fossil fuel use by 90%.
Can this goal be achieved without reverting to bicycles?
The Tesla Roadster 2008
220 miles (354 km)
lithium-ion battery pack stores
450 kg (120 Wh/kg)
motor’s maximum power is
What is the energy-consumption of this muscle car?
15 kWh per 100 km
Evidence that a range of
should be enough for most people most of the time:
only 8.3% of commuters travel more than 30 km to their workplace.
Some questions about electric vehicles
electric cars are more energy-efficient than fossil cars.
But do they reduce CO2 emissions if the electricity is still generated by fossil power-stations?
electric vehicle’s energy cost is 20 kWh(e) per 100 km. (I think 15 kWh(e) per 100 km is perfectly possible)
If electricity has a carbon footprint of
500 g per kWh(e)
then the effective emissions of this vehicle are
100 g CO2 per km
, which is
as good as the best fossil cars
switching to electric cars is already a good idea, even before we green our electricity supply.
I live in a cold place. How could I drive an electric car? I demand power-hungry heating!
The motor of an electric vehicle, when it’s running, will on average use something like 10 kW, with an efficiency of 90-95%.
Some of the lost power, the other 5-10%, will be dissipated as heat in the motor.
Perhaps electric cars that are going to be used in cold places can be carefully designed so that this motor-generated heat, which might amount to 250 or 500 W, can be piped from the motor into the car. That much power would provide some significant windscreen demisting or body-warming.
What about freight?
International shipping is a surprisingly efficient user of fossil fuels; so getting road transport off fossil fuels is a higher priority than getting ships off fossil fuels. But fossil fuels are a finite resource, and eventually ships must be powered by something else. Biofuels may work.
Another option will be nuclear power.
The first nuclear-powered ship for carrying cargo and passengers
launched in 1962
one 74-MW nuclear reactor driving a 15-MW motor
service speed of 21 knots (39 km/h)
carry 60 passengers and 14000 t of cargo. (cost of 0.14 kWh per ton-km)
She could travel 500 000 km without refueling.
There are already many nuclear-powered ships, both military and civilian.
What sort of energy-savings can technology or lifestyle-change offer?
The power used to heat a building is given by multiplying together three quantities:
power used = (
average temperature difference
leakiness of building
) / (
efficiency of heating system
OK, how can we reduce the power used by heating? Well, obviously, there are three areas.
1. Cool technology: the thermostat
You turn down the thermostat, and your building uses less energy.
For every degree that you turn the thermostat down, the heat loss decreases by
Turning the thermostat down from 20 °C to 15 °C would nearly halve the heat loss.
Thanks to incidental heat gains by the building, the savings in heating power will be even bigger than these reductions in heat loss.
Unfortunately, however, this remarkable energy-saving technology has
. This is a lifestyle change, and people are not happy with it.
The war on leakiness
What can be done with leaky old houses? Figure 21.3 shows estimates of the space heating required in old detached, semi-detached, and terraced houses as progressively more effort is put into patching them up. Adding loft insulation and cavity-wall insulation reduces heat loss in a typical old house by about 25%.
Thanks to incidental heat gains, this 25% reduction in heat loss translates into roughly a 40% reduction in heating consumption
. Let’s put these ideas to the test.
In 2004 4 house upgrades that saved on heating
1. I had a
condensing boiler installed
, replacing the old gas boiler. (Condensing boilers use a heat-exchanger to transfer heat from the exhaust gases to incoming air.)
2. I changed
the hot-water heater
(so hot water is now made only on demand).
put thermostats on all the bedroom heaters
4. Along with the new condensing boiler came a
new heating controller
that allows me to set different target temperatures for different times of day.
With these changes, my consumption decreased from an average of 50 kWh/d to about 32 kWh/d.
Isn't it crazy to set the thermostat of the air-conditioning to 18 °C in the summer?
If you set the thermostat to 18 °C in the winter people would be too cold!
In Japan, the government’s “Cool-Biz” guidelines recommend that air-conditioning be set to 28 °C (82 F).
Ways to ensure smaller heating consumption in
a new building
The three key ideas for the best results are:
really thick insulation
in floors, walls, and roofs;
(2) ensure the building is completely sealed and use active
ventilation to introduce fresh air
and remove stale and humid air,
with heat exchangers
passively recovering much of the heat from the removed air.
(3) design the building to exploit
as much as possible.
Today, building-heating is primarily delivered by burning a fossil fuel, natural gas, in boilers with efficiencies of 78%–-90%.
Can we get off fossil fuels at the same time as making building-heating more efficient?
Like district heating and combined heat and power, heat pumps are already widely used in continental Europe, but strangely rare in Britain.
Heat pumps are back-to-front refrigerators. Feel the back of your refrigerator: it’s warm.
A refrigerator moves heat from one place (its inside) to another (its back panel).
So one way to heat a building is to turn a refrigerator inside-out put the inside of the refrigerator outside; and put the back panel of the refrigerator in your home. This is a really efficient way to warm your house.
of power drawn from the electricity grid, the back-to-front refrigerator can pump
of heat from the outside, so that a total of
of heat gets into your house.
So heat pumps are roughly four times as efficient as a standard electrical bar-fire. Whereas the bar-fire’s efficiency is 100%, the heat pump’s is 400%.
The efficiency of a heat pump is usually called its
coefficient of performance or CoP
. If the efficiency is 400%, the coefficient of performance is 4.
Some heat pumps can pump heat in either direction.
When an air source heat pump runs in reverse, it uses electricity to warm up the outside air and cool down the air inside your building. This is called air-conditioning.
Many air-conditioners are indeed heat-pumps working in precisely this way. Ground-source heat pumps can also work as air-conditioners. So a single piece of hardware can be used to provide winter heating and summer cooling.
Heat pumps, compared with combined heat and power
I used to think that combined heat and power was the answer.
“Obviously,we should use the wasted heat from power stations to heat buildings instead of just losing it up a cooling tower!”
However, looking carefully at the numbers describing the performance of real CHP systems, I’ve come to the conclusion that there are better ways of providing electricity and building-heating.
I’m going to build up a diagram in three steps.
The diagram shows
how much electrical energy or heat energy can be delivered from chemical energy
The horizontal axis shows the electrical efficiency.
The vertical axis shows the heat efficiency.
The standard solution with no CHP
In the first step, we show simple power stations and heating systems that
deliver pure electricity or pure heat.
Combined heat and power
Next we add combined heat and power systems to the diagram. These
simultaneously deliver, from chemical energy, both electricity and heat.
Finally we add in heat pumps, which use electricity from the grid to
pump ambient heat into buildings.
The steep green lines show the combinations of electricity and heat
using heat pumps (coefficient of performance of 3 or 4, allowing for 8% loss in the national electricity network between the power station and the building where the heat pumps pump heat.)
The top-of-the-line gas power station’s efficiency is 53%, assuming it’s running optimally.
(In Japan, thanks to strong legislation favoring efficiency improvements, heat pumps are now available with a coefficient of performance of 4.9.)
Each of the filled dots shows actual average performances of CHP systems
in the UK, grouped by type.
hollow dots marked “CT”
- ideal CHP systems quoted by the Carbon Trust;
hollow dots marked “Nimbus”
- manufacturer’s product specifications.
dots marked “ct”
- performances quoted by the Carbon Trust for two real systems (at Freeman Hospital and Elizabeth House).
The electrical efficiencies of the CHP systems are significantly smaller than the 49% efficiency delivered by single-minded electricity-only gas power stations.
So the heat is not a “free by-product.” Increasing the heat production hurts the electricity production.
Condensing boilers (the top-left dot, A) are 90% efficient because 10% of the heat goes up the chimney.
Britain’s gas power stations (the bottom-right dot, B) are currently 49% efficient at turning the chemical energy of gas into electricity.
If you want any mix of electricity and heat from natural gas, you can obtain it by burning appropriate quantities of gas in the electricity power station and in the boiler. Thus the new standard solution can deliver any electrical efficiency and heat efficiency on the line AB by making the electricity and heat using two separate pieces of hardware.
combined heat and power < air-source or ground-source
The heat-pump advantages:
1. heat pumps
can be located in any buildings
where there is an electricity supply;
can use any electricity source
, so they keep on working when the oil runs out or the oil price goes through the roof
3. heat pumps are flexible: they
can be turned on and off to suit the demand
of the building occupants.
Limits to growth (of heat pumps)
Because the temperature of the ground, a few meters down, stays close to 11 °C, whether it’s summer or winter, the ground is theoretically a better place for a heat pump to grab its heat than the air, which in midwinter may be 10 or 15 °C colder than the ground.
(Heat pumps work less efficiently when there’s a big temperature difference between the inside and outside.)
However, the ground is not a limitless source of heat
My conclusion: can we reduce the energy we consume for heating? Yes.
Can we get off fossil fuels at the same time? Yes.
the low-hanging fruit
we should replace all our fossil-fuel heaters with
electric-powered heat pumps.
We can reduce the energy required to
25% of today’s levels
. Of course this plan for electrification would require
. But even if the extra electricity came from gas-fired power stations, that would still be a much better way to get heating than what we do today, simply setting fire to the gas.
Heat pumps allow us to heat buildings efficiently with electricity from any source.
Efficient electricity use
We already examined gadgets in Chapter 11. Some gadgets are unimportant, but some are astonishing guzzlers.
The laser-printer in my office, sitting there doing nothing, is using 17 W nearly 0.5 kWh per day!
friend bought a lamp from IKEA. Its awful adapter guzzles 10 W (0.25 kWh per day)
whether or not the lamp is on!
If you add up a few stereos, DVD players, cable modems, and wireless devices, you may even find that half of your home electricity consumption can be saved.
A vampire-killing experiment
Figure 22.2 shows an experiment I did at home. First, for two days, I measured the power consumption when I was out or asleep. Then, switching
off all the gadgets that I normally left on, I measured again for three more
I found that the power saved was 45 W –which is worth £45 per year
if electricity costs 11p per unit.
Since I started paying attention to my meter readings, my total electricity consumption has halved (figure 22.3). I’ve made a habit of reading my meters every week, so as to check that the electricity-sucking vampires have been banished.
The Plan and the Cost
There are some plans that are technically feasible for the UK by 2050.
The current situation in the UK is as follows.
(of both humans and stuff) uses
40 kWh/d per person
. Most of that energy is currently consumed as
petrol, diesel, or kerosene
of air and water uses
40 kWh/d per person
. Much of that energy is currently provided by
and uses fuel (mainly
coal, gas, and nuclear
) with an energy content of
a)goes up cooling towers
b)is lost in the wires of the distribution network
The total energy input to the UK is 125 kWh/d per person.
In my future idea of the UK, the energy consumption is reduced by using more
for transport and heating.
In the five plans for the future, transport is largely electrified.
Electric engines are more efficient than petrol engines
, so the energy required for transport is reduced.
Public transport (also largely electrified) is better integrated, better personalized, and better patronized.
Electrification makes transport about four times more efficient
1. Economic growth cancels out some of these savings
2. the net effect is a halving of energy consumption for transport.
In all five plans, the energy consumption of
is reduced by improving the
of all buildings, and improving the
control of temperature
through thermostats and education.
New buildings (all those built from 2010 onwards) are really well insulated and require almost no space heating.
In these plans, I assume the current demand for electricity for gadgets, light, and so forth
. So we still require
18 kWh(e)/d/p of electricity.
Yes, lighting efficiency is improved by a switch to light-emitting diodes (LED) for most lighting, and many other gadgets will get more efficient; but thanks to the blessings of
, we’ll have increased the number of gadgets in our lives for example video-conferencing systems to help us travel less.
The total consumption of electricity under this plan goes up
(because of the 18 kWh/d/p for electric transport and the 12 kWh/d/p for heat pumps)
to 48 kWh/d/p (or 120 GW nationally)
This is nearly a tripling of UK electricity consumption. Where’s that energy to come from?
Let me try to make clear the scale of the previous chapter’s plans by showing you a map of Britain bearing a sixth plan.
This sixth plan lies roughly in the middle of the first five, so I call it plan M (figure 28.1).
The areas and estimated costs of these facilities are shown in table 28.3. For simplicity, the financial costs are estimated using today’s prices for comparable facilities, many of which are early prototypes.
We can expect many of the prices to drop significantly.
The rough costs given here are the building costs, and don’t include running costs or decommissioning costs.
The “per person” costs are found by dividing the total cost by 60 million.
Every wind farm costs a few million pounds to build and delivers a few megawatts.
As a very rough ballpark figure in 2008, installing
one watt of capacity costs one pound;
one kilowatt costs 1000 pounds;
a megawatt of wind costs a million;
a gigawatt of nuclear costs a billion or perhaps two
Other renewables are more expensive. We (the UK) currently consume a total power of roughly 300 GW, most of which is fossil fuel.
The estimated costs in table 28.3 add up to £870 bn, with the solar power facilities dominating the total.
The photovoltaics cost £190 bn and
The concentrating solar stations cost £340 bn.
Both these costs might well come down dramatically as we learn by doing.
A good comparison to make is with our annual expenditure on insurance: some of the investments we need to make offer an uncertain return just like insurance.
UK individuals and businesses spend £90 bn per year on insurance.
£56 billion over 25 years
: the cost of decommissioning the UK’s nuclear power stations E. That’s the 2004 figure; in 2008 it was up to
(£1200 per person in the UK). [6eoyhg]
£4.3 billion: the cost of London Heathrow Airport’s Terminal 5.
(£72 per person in the UK.)
Cost of the London 2012 Olympics:
Business as usual
£2.5 billion/y: Tesco’s profits (announced 2007). (£42 per year per person
in the UK.)
: spent by British people on food that they buy but do not
eat. (£170 per year per person in the UK.)
£11 billion/y: BP’s profits (2006).
£13 billion/y: Royal Dutch Shell’s profits (2006).
$40 billion/y. Exxon’s profits (2006).
$33 billion/y. World expenditure on perfumes and make-up.
$700 billion per year
: USA’s expenditure on foreign oil (2008). ($2300 per
year per person in the USA.)
Government business as usual
£1.5 billion: the cost of refurbishment of Ministry of Defense offices. (£25 per person in the UK.)
£15 billion: the cost of introducing UK identity card scheme [7vlxp]. (£250
per person in the UK.)
: in October 2008, the US government committed $700 billion to
bailing out Wall Street, and ...
: the UK government committed £500 billion to bailing out
£5 billion per year: UK’s arms exports (£83 per year per person in the
UK), of which £2.5 billion go to the Middle East, and £1 billion go to Saudi
Arabia. Source: Observer, 3 December 2006.
£8.5 billion: cost of redevelopment of army barracks in Aldershot and Salis-
bury Plain. (£140 per person in the UK.)
£3.8 billion: the cost of two new aircraft carriers (£63 per person in the
$4.5 billion per year: the cost of not making nuclear weapons – the US
Department of Energy’s budget allocates at least $4.5 billion per year to
“stockpile stewardship” activities to maintain the nuclear stockpile without
nuclear testing and without large-scale production of new weapons. ($15
per year per person in America.)
which is more?
can we live sustainably?
What is the average energy used per day per person in Korea?
What is the average distance traveled per day?
What is the average car used in Korea?
What is the average fuel economy in Korea?
How many cars are used per day?
What is the population of South Korea?
Let’s assume you eat half a pound (227 g) per day of meat, made up of equal quantities of chicken, pork, and beef.
This meat habit requires 8 pounds of chicken meat, 70 pounds of pork meat, and 170 pounds of cow meat. That’s a total of 110 kg of meat, or 170 kg of animal (since about two thirds of the animal gets turned into meat). And if the 170 kg of animal has similar power requirements to a human (whose 65 kg burns 3 kWh/d) then the power required to fuel the meat habit is
170kg × 3 kWh/d =
I’ve again taken the physiological liberty of assuming “animals are like humans.”
The power required to make the food for a typical consumer of vegetables, dairy, eggs, and meat is 1.5 + 1.5 + 1 + 8 = 12 kWh per day.
For the temperature profile shown in figure 16.4, I calculated that the optimal depth is about 15 km. Under these conditions, an ideal heat engine would deliver 17 mW/m2.
At the world population density of 43 people per square km, that’s 10 kWh per person per day
, if all land area were used. In the UK, the population density is 5 times greater, so wide-scale geothermal power of this sustainable-forever variety could offer at most
2 kWh per person per day
Between depths of 0 km where the heat flow is biggest but the rock temperature is too low, and 40 km, where the rocks are hottest but the heat flow is 5 times smaller (because we’re missing out on all the heat generated from radioactive decay) there is an optimal depth at which we should suck. The exact optimal depth depends on what sort of sucking and power-station machinery we use. We can bound the maximum sustainable power by finding the optimal depth
assuming that we have an ideal engine for turning heat into electricity, and that drilling to any depth is free.
To achieve our goal of getting off fossil fuels, these reductions in demand and increases in supply must be
. We must do a lot. What’s required are
changes in demand and in supply.
3.We could buy, beg, or steal renewable energy from other countries.
a. most countries will be in the same situation as Britain
b. using renewable energy from another country doesn’t reduce the renewable power facilities required.
i. If we import renewable energy from other countries facilities will need to be about the size of Wales in those other countries.
The next seven chapters discuss:
1. how to reduce demand substantially
2. how to increase supply to meet that reduced, but still “huge,” demand.
In these chapters, I won’t mention all the good ideas. I’ll discuss just the big ideas.
2.We could invest in nuclear fission.
Is current nuclear technology “sustainable”?
Is it at least a temporary fix that might last for 100 years?
1.We could get off fossil fuels by investing in “clean coal” technology. Oops! Coal is a fossil fuel.
If we used coal “sustainably” (a notion we’ll define in a moment), how much power could it offer?
If we don’t care about sustainability and just want “security of supply,” could coal offer that?
Supply could be increased in three ways:
So, what’s required are big changes in demand and in supply. Demand for power could be reduced in three ways:
consumption of Britain is
40 kWh per day per person
(currently all supplied by fossil fuels);
consumption is also
40 kWh per day per person
(currently all supplied by fossil fuels);
18 kWh(e) per day per person.
a. the electricity is currently almost all generated from fossil fuels;
of fossil-fuel energy to electricity is
c. supplying 18 kWh(e) of electricity in today’s Britain requires a fossil-fuel input of
45 kWh per day per person
This simplification ignores some important details, such as
, and the
embodied energy of imported goods
But I want to talk about the main things we need to do to get off fossil fuels.
Heating, transport, and electricity account for
more than half of our energy consumption
so if we can come up with a plan for heating, transport, and electricity sustainably,
then we have made a big step
Three supply options
other people’s renewables
are then discussed in Chapters 23, 24, and 25. Finally, Chapter 26 discusses how to cope with fluctuations in demand and fluctuations in renewable power production.
Chapters 27 and 28 discuss various ways to put these options together, in order to supply Britain’s transport, heating, and electricity.
But what about “stuff”? According to Part I, the embodied energy in imported stuff might be the biggest fish of all! Yes. But let’s focus on the animals over which we have direct control.
So, here we go: let’s talk about
Among other countries’ renewables, solar power in deserts is the most plentiful option. As long as we can build peaceful international collaborations, solar power in other people’s deserts certainly has the technical potential to provide us, them, and everyone with 125 kWh per day per person.
, we get all the green electricity from a mix of four sources: from our own renewables; perhaps from “clean coal;” perhaps from nuclear; and finally, and with great politeness, from other countries’ renewables.
, to supplement solar-thermal heating, we electrify most heating of air and water in buildings using heat pumps, which are four times more efficient than ordinary electrical heaters. This electrification of heating further increases the amount of green electricity required.
, we electrify transport. Electrification both gets transport off fossil fuels, and makes transport more energy-efficient. (Of course, electrification increases our demand for green electricity.)
3.In all forms of travel, there’s an
, which takes energy in some sort of fuel and uses some of it to push the vehicle forwards. This energy chain has inefficiencies.
For example, in a standard fossil fuel car only
is used for pushing, and roughly 75% of the energy is lost in making the engine and radiator hot.
So a final strategy for consuming less energy is to
make the energy-conversion chain more efficient
long-distance (highway) travel
at steady speed, by train or automobile, most of the energy goes into making air swirl around, because you only have to accelerate the vehicle once.
The key strategies for consuming less in this sort of transportation are therefore
a) to move slower, and
b) to move less, and
c) to use long, thin vehicles.
Regenerative systems using flywheels and hydraulics seem to work a little better than battery-based systems,
salvaging at least 70% of the braking energy
. Hydraulics and flywheels are both promising ways to handle regenerative braking because small systems can handle large powers.
Electric regenerative braking (using a battery to store the energy)
salvages roughly 50% of the car’s energy in a braking event
, leading to perhaps a
20% reduction in the energy cost of city driving
It’s an option that’s most useful for trains, and it is illustrated by the London Underground’s Victoria line, which has hump-back stations. Each station is at the top of a hill in the track. Arriving trains are automatically slowed down by the hill, and departing trains are accelerated as they go down the far side of the hill.
The hump-back-station design provides an energy saving of 5% and makes the trains run 9% faster.
Is there enough lithium to make all the batteries for a huge fleet
of electric cars?
World lithium reserves:
~9.5 million tons
in ore deposits (p175).
A lithium-ion battery is
If we assume each vehicle has a
200 kg battery
, then we need
6 kg of lithium per vehicle
. So the estimated reserves in ore deposits are enough to make the batteries for
1.6 billion vehicles
. That’s more than the number of cars in the world today (roughly 1 billion) but not much more.
There’s many thousands times more lithium in sea water, so perhaps the oceans will provide a useful backup. However, lithium specialist R. Keith Evans says “concerns regarding lithium availability for hybrid or electric vehicle batteries or other foreseeable applications are unfounded.”
Other lithium-free battery technologies such as zinc-air rechargeables are being developed [www.revolttechnology.com].
Are lithium-ion batteries safe in an accident?
Some lithium-ion batteries are unsafe when short-circuited or overheated, but the battery industry is now producing safer batteries such as lithium phosphate.
performance figures for lots of electric vehicles summary:
electric vehicles can deliver transport at 15 kWh per 100 km.
five times better than our fossil-car
, and significantly better than any hybrid cars.
Hurray! To achieve economical transport, we don’t have to gather together in public transport. We can still move around, enjoying all the pleasures and freedoms of solo travel,
thanks to electric vehicles
I live in a hot place. How could I drive an electric car? I demand power-hungry air-conditioning!
There’s an elegant fix for this demand:
fit 4 m2 of photovoltaic panels in the upward-facing surfaces of the electric car
. If the air-conditioning is needed, the sun must surely be shining.
20%-efficient panels will generate up to 800 W
, which is enough to power a car’s air-conditioning. The panels might even make a useful contribution to charging the car when it’s parked, too. Solar-powered vehicle cooling was included in a Mazda in 1993; the solar cells were embedded in the glass sunroof.
Electric cars, like fossil cars, have costs of
both manufacture and use
. Electric cars may cost less to use, but if the batteries don’t last very long, shouldn’t you pay more attention to the
The batteries in a Prius are expected to last just 10 years, and a new set would cost £3500.
Will anyone want to own a 10-year old Prius and pay that cost?
It could be predicted that most Priuses will be junked at age 10 years. This is certainly a concern for all electric vehicles that have batteries.
I guess I’m optimistic that, as we switch to electric vehicles, battery technology is going to improve.
Finally, to calculate the power required, we divide this heat loss by the efficiency of the heating system. In my house, the condensing gas boiler has an
efficiency of 90%
, so we find:
power used = (
) / (
) = 77 kWh/d
That’s bigger than the space-heating requirement we estimated in Chapter 7. In chapter 7 it was 24 kWh/d. Why is it more here?
The product average temperature difference × leakiness of building is the rate at which heat flows out of the house by conduction and ventilation. For example, if the average temperature difference is
then the heat loss is
The leakiness of the building describes how
heat gets out through walls, windows, and cracks, in response to a
The leakiness is sometimes called the
of the building. It is measured in kWh per day per degree of temperature difference.
I calculate that the leakiness of my house in 2006 was
My house is a three-bedroom house built about 1940.
The average temperature difference between the inside and outside of the house depends on the setting of the
and on the
. If the thermostat is permanently at 20 °C, the average temperature difference might be
It’s bigger for two reasons:
1. This formula assumes that all the heat is supplied by the boiler.
Other heat gains from people, gadgets, and the sun.
2. In Chapter 7 we assumed that two rooms are kept at 20 °C.
Keeping an entire house at this temperature would require more heat.
Increase the efficiency of the heating system.
You might think that 90% sounds hard to beat, but actually we can do much better.
Reduce the leakiness of the building.
This can be done by
a. improving the building’s insulation in walls, around doors and windows and in attics.
b. by demolishing the building and replacing it with a better insulated building.
c. perhaps by living in a building of smaller size per person. (Leakiness is bigger, the larger a building’s floor area, because the areas of external wall, window, and roof tend to be bigger too.)
Reduce the average temperature difference.
Turning thermostats down (or changing the weather.)
This reduction from 50 to 32 kWh/d is quite satisfying, but it’s not enough.
Goal: reduce one’s fossil fuel footprint below one ton of CO2 per year. (32 kWh/d of gas is to over 2 tons CO2 per year.)
In 2007, I started paying more careful attention to my energy meters.
1. I had
cavity-wall insulation installed
Improved my loft insulation
3. I replaced the single-glazed back door by a
4. I added an
extra double-glazed door
to the front porch .
5. Most important of all, I
paid more attention to my thermostat
This attentiveness has led to a further halving in gas consumption. The latest year’s consumption was 13 kWh/d!
According to the International Energy Agency,
standby power consumption accounts for roughly 8% of residential electricity demand.
the UK and France, the average standby power is about 0.75 kWh/d per
The problem isn’t standby itself it’s the poor way in which
standby is implemented. It’s perfectly possible to make standby systems
that draw less than 0.01 W; but manufacturers, saving themselves a penny
in the manufacturing costs, are making the consumer pay for more electricity every year.
The area required for the biofuel production is about
12% of the UK (500 m2 per person)
a. biofuel production comes from 1%-efficient plants b. conversion of plant to fuel is 33% efficient
Alternatively, the biofuels could be imported.
There are a few essential vehicles that can’t be easily electrified, and for those we make our own liquid fuels (for example
biodiesel or biomethanol or cellulosic bioethanol
The energy for transport is
of liquid fuels
The wood for making heat (or possibly combined heat and power) comes from nearby forests and energy crops (perhaps miscanthus grass, willow, or poplar) covering a land area of 30 000 km^2, or 500 m^2 per person; this is
18% of the UK’s agricultural land
The energy crops are grown mainly on the lower-grade land, leaving the higher-grade land for food-farming.
Each 500 m^2 of energy crops yields
0.5 oven dry tons per year
This has an energy content of about
30% is lost in the process of heat production and delivery.
The final heat delivered is 5 kWh/d per person.
Old buildings (which will still dominate in 2050) are mainly heated by
air-source heat pumps
ground-source heat pumps
. Some water heating is delivered by
(2.5 square meters on every house), some by
, and some by
. Some buildings located near to managed forests and energy-crop plantations are heated by
The power required for heating is thus reduced from 40 kWh/d/p to
12 kWh/d/p of electricity,
2 kWh/d/pE of solar hot water, and
5 kWh/d/p of wood
The Korean government decision in July 2008 to increase investment in renewable energy to reduce reliance on foreign oil imports may provide an incentive for conglomerates' solar plans.
The Ministry of Knowledge and Economy said the country intends to spend 194.4 billion won ($193 million) on technologies and projects, including solar, wind and biofuels, in 2008.
(4,000 won per person)
£0.012 billion per year
: the smallest item displayed in figure 28.5 is the UK government’s annual investment in renewable-energy research and development.
(£0.20 per person in the UK, per year.)
What is energy?
"Energy Is the Ability to Do Work."
What are some different forms of energy?
chemical energy, electrical energy, heat (thermal energy), light (radiant energy), mechanical energy, and nuclear energy
What are the two types of energy?
Stored energy is called potential energy.
Moving energy is called kinetic energy.
How do we measure energy?
1,000 joules (J) = 1 kilojoule = 1 Btu
A piece of buttered toast contains about 315 kilojoules (315,000 joules) of energy. With that energy you could:
Jog for 6 minutes
Bicycle for 10 minutes
Walk briskly for 15 minutes
Sleep for 1-1/2 hours
Run a car for 7 seconds at 80 kilometers per hour (about 50 miles per hour)
Light a 60-watt light bulb for 1-1/2 hours
Energy has the same units as Work and Heat
1. Stored energy in a flashlight's batteries becomes light energy when the flashlight is turned on.
Energy can be transformed into another kind of energy.
But energy cannot be created AND it cannot be destroyed.
Energy has always existed.
First, fossil fuels are a