Parking-lot owners are finding a new use for their vast expanses of pavement: solar power.

From Long Island to the Arizona desert, developers are covering their lots with canopies of solar panels. Lot owners get to double up on their use of underutilized land and to offset their utility bills at the same time. And very little stands between most lots and the sun, so they can produce plenty of power. What's more, the canopies provide shade when it's hot and prevent snow from accumulating in the winter. Some have charging stations for electric vehicles.

The Washington Redskins last year completed the largest parking-lot solar installation in the NFL. (Sports stadiums are famous for their acres of open parking lots.) The team covered 841 parking spaces at FedExField in Landover, Md., with electricity-producing awnings; the two-megawatt system can supply 20% of the stadium's power needs on game days and all its electricity on off days.

NRG Energy Inc., Princeton, N.J., installed and owns the panels, leasing the site and selling power. The company and the team both declined to disclose financial details about the project.

One of the country's largest solar carports is now under construction at Rutgers University's Livingston Campus in Piscataway, N.J. The eight-megawatt installation will cover about 32 acres and will cost about $40.8 million before federal and state incentives. The project is being built by a private company, which will lease the panels to the university. Rutgers expects to save $28 million in electricity costs over 20 years.