GCSE Questions: Energy Sources
Q27.
(a) During one year, 1.25 × 1018 J of energy was transferred from the National Grid.
Given that the number of seconds in 1 year = 3.16 × 107 calculate the mean power transfer from the National Grid.
Give your answer to 3 significant figures.
Power = energy/time ![](../../../../graphics/symbols/nuclides/ticksmall.png)
1.25 × 1018 J/3.16 × 107 ![](../../../../graphics/symbols/nuclides/ticksmall.png)
Power = 3.96 x 1010 J/s
P = 3.96 x 1010
W ![](../../../../graphics/symbols/nuclides/ticksmall.png)
P = 39.6 GW
[4 marks]
(b) The diagram shows a house with a solar power system.
The solar cells generate electricity.
When the electricity generated by the solar cells is not needed, the energy is stored in a large battery.
![](solarhouse.png)
(i) The charge flow through the cable between the solar cells and the battery in 24 hours box was 27 000 coulombs. Calculate the mean current in the cable.
t = 24 h = 24 x 602 s ![](../../../../graphics/symbols/nuclides/ticksmall.png)
I = Q/t ![](../../../../graphics/symbols/nuclides/ticksmall.png)
I = 27,000/(24 x 602) ![](../../../../graphics/symbols/nuclides/ticksmall.png)
I = 3.125 x 10-4 A ![](../../../../graphics/symbols/nuclides/ticksmall.png)
I = 3.1 x 10-4 A
[4 marks]
(ii) At one time, the total power input to the solar cells was 7.8 kW.
The efficiency of the solar cells was 15%
Calculate the useful power output of the solar cells.
Useful power output = 15% of total power input
Useful power output = 0.15 x total power input ![](../../../../graphics/symbols/nuclides/ticksmall.png)
Useful power output = 0.15 x 7.8 kW ![](../../../../graphics/symbols/nuclides/ticksmall.png)
Useful power output = 1.17 kW ![](../../../../graphics/symbols/nuclides/ticksmall.png)
[3 marks]
(c) It is unlikely that all of the electricity that the UK needs can be generated by solar power systems. Explain why.
A really large area of land would need to be covered with solar cells ![](../../../../graphics/symbols/nuclides/ticksmall.png)
due to (any one of the following reasons): ![](../../../../graphics/symbols/nuclides/ticksmall.png)
the low useful power output/efficiency of the solar cells
number of hours of daylight in UK is too low
low solar intensity (in UK)
material for construction of solar cells and/or lithium batteries is in limited supply
[2 marks]
(Total 13 marks)