In what is clearly becoming a major trend, the city of Raleigh recently installed solar photovoltaic (PV) panels to the roof of its E.M. Johnson Water Treatment Plant and is selling the power to Progress Energy Carolinas, a regional electric utility.

The solar array is one of the state’s largest, at 250 kilowatts, and the installation comes courtesy of Durham-based Carolina Solar Energy, a design-build solar energy firm offering hosted or owner-operated solar PV systems via professional, in-house financing that captures benefits from both ARRA (the 2009 American Recovery and Reinvestment Act) and, in this case, Progress Energy's SunSense commercial solar PV program, which pays $0.18 cents per kilowatt-hour for 20 years in exchange for renewable energy credits.

The SunSense program is limited to solar systems between 10 kilowatts and 250 kilowatts (nameplate capacity), and is Progress Energy’s way of meeting North Carolina’s renewable portfolio standard (RPS) of 12.5 percent by 2021, a mandate imposed on all investor-owned utilities, with an additional mandate of .02 percent from solar by 2018.

The state also offers, under HB 512, a 35-percent incentive, to a maximum of $2.5 million, for solar (PV, daylighting, water heating and space heating) installations at commercial and industrial facilities.

The E.M. Johnson solar array is reportedly the first in the Southeast to use First Solar's cadmium telluride (CdTe) thin-film PV technology, which means more panel efficiency, since First Solar’s panels capture not only direct solar irradiance, but low and diffuse solar energy as well.

The wastewater system became operable on Dec. 30 of 2009, and is expected to produce about 325,000 kilowatt-hours of electricity in 2010, or enough to supply about 22 average American homes.

This amount of electricity, not produced by Progress Energy (whose generation mix includes more than 35 percent coal and a large portion of nuclear), will reduce carbon emissions by 233 metric tons per year, which is equivalent to taking more than 44 cars off the road every year, or planting almost 6,000 tree seedlings.

The solar system operates under a 20-year lease with Carolina Solar Energy, and the city has the option to buy the system in the future at undisclosed terms. Perhaps most important for Raleigh, which – like most American cities – is cash-strapped by a persistent recession and falling real estate tax revenues, there was no required outlay of capital funds to get the solar system installed.

The E.M. Johnson Water Treatment Plant is not the first solar project that Carolina Solar Energy and Progress Energy have collaborated on. Two other solar systems – a 75-kilowatt solar PV array at the RBC Center in Raleigh, and a 650-kilowatt solar PV array in Person County – are currently operating, producing clean, renewable solar energy for Progress’s grid.