Your recent article on nuclear plant upgrades confuses "capacity factor" with time spent generating power - an error that misrepresents and understates the potential of wind and solar technologies to produce electricity ("Squeezing the atom," Nov. 29).

Capacity factor is a measure of the actual production of electricity compared with the theoretical production if the generator operated at full power all of the time. Solar panels generate maximum power when the grid needs it most (hot, sunny days when air conditioners are operating full-blast), but they produce power even when it is cloudy or raining. Using the measure of capacity factor, solar panels operate at an average 21 percent capacity; in other words, they generate 21 percent of the power they theoretically could generate if the sun shone brightly 24 hours a day. That is not to say, as you did, that solar panels generate power only 21 percent of the time.

Similarly, wind turbines generate electricity between 80 and 90 percent of the time, producing about 31 percent of the energy they theoretically could produce operating at full capacity around the clock.

As Pennsylvania transitions to an alternative energy-based economy, it's vital that consumers receive clear, accurate information about the potential of these technologies.

John Hanger

Secretary, Pennsylvania Department of Environmental Protection