1. a)  For every 100 J of solar energy shining on a photocell, only 5 J is transferred to useful

          energy (as electricity). The other 95 J is wasted.

     b)  The efficiency of the photocell is:

          Efficiency = (useful energy transferred ÷ total energy input) x 100%

          Efficiency = (5 ÷ 100) x 100%

          Efficiency = 5 %

     2.  a) The amount of energy that is converted to electricity is: 100 - (10 + 30 + 8) = 52 J

          b) The efficiency of the power station is: 52 ÷ 100 = 52 %