Outline, with reference to energy changes, the operation of a pumped storage hydroelectric system.

The hydroelectric system has four 250 MW generators. The specific energy available from the water is 2.7 kJ kg^–1. Determine the maximum time for which the hydroelectric system can maintain full output when a mass of 1.5 x 10¹⁰ kg of water passes through the turbines.

Not all the stored energy can be retrieved because of energy losses in the system. Explain one such loss.

At the location of the hydroelectric system, an average intensity of 180 W m^–2 arrives at the Earth’s surface from the Sun. Solar photovoltaic (PV) cells convert this solar energy with an efficiency of 22 %. The solar cells are to be arranged in a square array. Determine the length of one side of the array that would be required to replace the
hydroelectric system.

PE of water is converted to KE of moving water/turbine to electrical energy «in generator/turbine/dynamo»

idea of pumped storage, ie: pump water back during night/when energy cheap to buy/when energy not in demand/when there is a surplus of energy

total energy = «2.7 x 10³ x 1.5 x 10¹⁰ =» 4.05 x 10¹³ «J»

time = «\(\frac{{4.0 \times {{10}^{13}}}}{{4 \times 2.5 \times {{10}^8}}}\)» 11.1h or 4.0 x 10⁴ s

For MP2 the unit must be present.

friction/resistive losses in walls of pipe/air resistance/turbulence/turbine and generator bearings

thermal energy losses, in electrical resistance of components

water requires kinetic energy to leave system so not all can be transferred

Must see “seat of friction” to award the mark.
Do not allow “friction” bald.

area required \( = \frac{{1 \times {{10}^9}}}{{0.22 \times 180}}\) «= 2.5 x 10⁷ m²»

length of one side \( = \sqrt {area}  = 5.0\) k«m»