A photovoltaic (PV) plant's output varies widely between days, and even hours, depending on such factors as cloud cover and the sun's angle to the solar panels. These fluctuations present a problem: the source of the PV plant's energy is variable, yet the need to meet electricity demand and keep the grid stable is constant.
"On cloudy days, customers aren't changing their usage based on when the sun comes out," says Jon Hawkins of the Public Service Company of New Mexico (PNM). "As a utility, we are still required to give customers quality power.
" PNM is New Mexico's largest electricity provider, serving more than 500,000 customers. In 2009, PNM received a grant for $2.3 million from the U.S. Department of Energy's Smart Grid Demonstration Program to modernize electric distribution systems."