Question

1. Solar cells (the figure) can produce about 40 W of electricity per square meter of surface area if directly facing the Sun. How large an area is required to supply the needs of a house that requires 21 kWh/day? Assume there are 9 hours of sunlight per day. Express your answer to two significant figures and include the appropriate units.

2. Energy may be stored by pumping water to a high reservoir when demand is low and then releasing it to drive turbines during peak demand. Suppose water is pumped to a lake 105 mm above the turbines at a rate of 5.00×105kg/s5.00×105kg/s for 10.0 hh at night. How much energy (kWh)(kWh) is needed to do this each night? If all this energy is released during a 14-hh day, at 74 %% efficiency, what is the average power output? Express your answer using two significant figures.

Answer 1