FIGURE 39.4 Photovoltaic solar energy. (a) In this domestic photovoltaic system, photovoltaic solar panels convert sunlight into direct current (DC). An inverter converts DC into alternating current (AC), which supplies electricity to the house. Any electricity not used in the house is exported to the electrical grid. (b) Photovoltaic panels on the roof of this house in California provide 4,200 kWh of electricity per year—nearly all of the electricity this family uses.

(Inga Spence/Alamy)