By Mike Kline
Recently P&D installed a 100 kW DC solar photovoltaic (PV) plant on top of our roof at our Norcross, Georgia headquarters. The array consist of 334 ReneSola America 300 watt solar panels, installed facing south at a pitch of 10 degrees to produce the optimum amount of power for their fixed position. Each panel produces a maximum power output of 300 watts, has an open circuit voltage (Voc) of 44.8 volts DC and a maximum power voltage (Vmp) of 36.6 volts DC.
The panels are connected in series to form strings, with each string consisting of twelve panels operating at a combined string voltage ranging between 400 and 500 volts DC. The outputs from seven of these strings are then connected together in two combiner boxes to provide a DC input source to a wall mounted SMA 24 kVA inverter. We have a total of four of these SMA 24 kVA inverters on our system. The wall mounted inverters each convert their DC inputs to an AC output (@ 277 / 480 volts AC) where it connects via a 30 ampere circuit breaker to the incoming Georgia Power electric service (inside the padmount transformer).
Georgia Power has installed separate metering for credit billing purposes. Through our 20-year agreement with the Georgia Power Company, they have committed to purchase all of our kWH solar production at a fixed rate of $0.13 per kWH. Although we considered an option to install a net metering system that allowed us to offset our building use with energy that we produced, then sell unused energy back to Georgia Power for a fee of $0.056 per kWH, our economic analysis indicated that it would be the more advantageous to sell all of our power back to Georgia Power.
Peak AC production from this plant will be approximately 75 kW and the inverters will be operating at unity power factor, 60 hertz, and 480 volt three phase AC output. We will receive a tax credit subsidy of 30% from Uncle Sam, and are allowed to depreciate our installation costs over an accelerated timeframe (5 years). With these incentives, we should break even in about five years, and make money after that
On sunny days, we have been producing about 400 kWH. According to SunPower (a major provider of solar installations around the world), each 100 kWH of solar production conserves 1.841 trees, is equivalent to 165 miles driven by a car, and conserves 0.1936 barrels of crude oil. As for air quality, the same 100 kWH circumvents 158 pounds of carbon dioxide, 0.2555 pounds of nitrogen dioxide, and 0.59 pounds of sulfur dioxide emissions.
P&D held an internal contest to name of our solar project. Jimmy Grinzaid in the testing department came up with the winner: L.E.A.F. Initative (Lead. Educate. Aspire. Facilitate.). Congratulations Jimmy! P&D will use this installation for “show and tell” seminars, internal continuing education, and to offer Professional Development Hours and Continuing Education Units.