GCSE Questions: Energy Sources

Q14. The photo shows a solar thermal power station that has been built in a hot desert.

The power station uses energy from the Sun to heat water to generate electricity.

Energy from the Sun is reflected towards a solar receiver using many mirrors.

(a)

(i) Which part of the electromagnetic spectrum provides most of the energy to heat the water in a solar thermal power station?

Infrared (radiation)

[1 mark]

(ii) Describe how heated water is used to generate electricity by this solar thermal power station. The process is the same as in a fossil fuel power station.

Water is heated by the water absorbing the infrared radiation and turns to steam.

Steam pressure is used to turn a turbine.

The turbine turns an electric generator.

[3 marks]

(b) A new type of solar power station, called a solar storage power station, is able to store energy from the Sun by heating molten chemical salts. The stored energy can be used to generate electricity at night.

(i) It is important that the molten chemical salts have a high specific heat capacity. Suggest one reason why.

So a small mass of the molten salts can store a large amount of energy.

[1 mark]

(ii) The solar storage power station can store a maximum of 2 200 000 kWh of energy. The solar storage power station can supply a town with a maximum electrical power of 140 000 kW.

Calculate for how many hours the energy stored by the solar storage power station can supply the town with electrical power.

Give your answer to 2 significant figures.

Power from station/power needed by the town = 2 200 000/140 000

= 2200/140 = 110/7

= 15.7

= 16 hours (to 2 sf)

[3 marks]

(iii) The table below gives information about the place where the solar storage power station has been built.

 

The solar storage power station does not operate at the maximum possible electrical output every day of the year.

Suggest why.

The number of hours of daylight varies according to the time of year. Daylight is least during the winter and greatest in the summer.

When the sun is low in the sky the intensity of the sun's rays is less. Therefore in winter, the intensity of the sunlight is lower - less energy falls on each square metre of the earth, than in the summertime when it is high in the sky.

[2 marks]

(c) Power stations do not work at maximum possible electrical output all the time.

The 'capacity factor' of a power station is calculated using the equation:

Capacity factor = (actual electrical output per year)/ (maximum possible electrical output per year)

The table below shows capacity factors for different types of power station.

(i) Compare the capacity factors of the renewable power stations with those of the non-renewable power stations in the table.

Explain the reason for the difference between the capacity factors.

The capacity factor of the non-renewable sources is higher than that of the renewable ones.

Non-renewable powerstations can operate 24/7 as they have a constant supply of fuel, renewable ones rely on natural conditions to operate and these are not conditions are not constant.

Just saying non-renewable power stations can 'operate all the time' or 'are reliable' was insufficient to get you the mark - you had to say they could operate 24/7 because they had a constant fuel supply.

[3 marks]

(ii) The capacity factor of a solar storage power station is higher than for all other renewable power stations. Suggest one reason why.

The (proportion of) time that solar storage power stations can generate electricity is greater than for the other renewable energy sources.

[1 mark]

(Total 14 marks)