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Transcript of Solar power
similar to photoelectric effect
solar energy -> electric energy (DC)
solar energy -> thermal energy
collecting surface -> flat, covered by
glass and coated to reduce reflection
used for household purposes or gives a heating effect
disadvantage - bulky, cover too much space
may involve parabolic mirror - temp. 500-2000*C
Solar heating panels
Short quiz time! Yaaaay!
Which of the following correctly shows the energy change in a photovoltaic cell and in a solar heating panel?
Photovoltaic cell Solar heating panel
A. solar ->→ electrical solar →-> thermal
B. electrical ->→ thermal solar →-> electrical
C. solar ->→ electrical electrical ->→ thermal
D. electrical ->→ thermal solar ->→ thermal
(a) State the energy change that takes place in a solar panel.
(b) A village consists of 120 houses. It is proposed that solar panels be used to provide hot water to the houses.
The following data are available.
average power needed per house to heat water = 3.0 kW
average surface solar intensity = 650 W/m^2
efficiency of energy conversion of a solar panel = 18 %
Calculate the minimum surface area of the solar panels required to provide the total power for water heating.
(c) Suggest two disadvantages of using solar power to provide energy for heating water.
The annual variations of solar power incident per unit area at a particular point on the Earth’s surface is mainly due to the change in the
A. distance between the Earth and the Sun.
B. angle at which the solar rays hit the surface of the Earth.
C. average albedo of the Earth.
D. average cloud cover of the Earth.
One disadvantage of using photovoltaic cells to power a domestic water heater is that
A. solar energy is a renewable source of energy.
B. the power radiated by the Sun varies significantly depending on the weather.
C. a large area of photovoltaic cells would be needed.
D. photovoltaic cells contain CFCs, which contribute to the greenhouse effect.
When sunlight is incident on a solar cell an electric current is produced. This is due to
A. a temperature gradient within the cell.
B. very long wavelength infrared radiation.
C. very short ultraviolet radiation.
D. the photoelectric effect.
The amount of power that arrives from the sun is measured by the
. It is properly defined as the amount of solar energy that falls per second on an area of 1m2 above the Earth’s atmosphere that is at right angles to the Sun’s rays. Its average value is about 1400 W/m^2.
Earth’s Energy Budget
This is not the same as the power that arrives on 1 m2 of the Earth’s surface. Scattering and absorption in the atmosphere results in less than half of this arrives at the Earth’s surface. The maximum amount of solar radiation that can be incident on Earth's surface is 1000W/m^2, which assumes direct sunlight during a clear day. Average over 24h - 340W/m^2.
The effect of latitude on incoming solar radiation
Heating is most intense when the sun is directly overhead, so that incoming solar radiation strikes perpendicular to the earth’s surface. The higher latitudes are cooler than the tropics because the same quantity of solar radiation is dispersed over a greater surface area (a as opposed to a’) and passed through a.
The effect of seasons on incoming solar radiation
summer = more intense sunlight
same amount of light dispersed over smaller area
winter - opposite
Works during the day only
Affected by cloudy weather
Low power output
Requires large amount of space