Through the first ten months of 2009, Chapman’s 47 kW photovoltaic array has generated 53,112 kWh of electricity, while we’ve used just 52,387 kWh–a net overproduction of 750 kWh that spins our electric meter backward and earns us a credit with NSTAR.

As you can see from the above chart, using data from our online metering system, our power production well outpaced our usage in March, April, May, and September, and remained close in every month except for January, thanks to near-record snowfall.

What does this translate to financially?

In the last full year, we’ve purchased just 4,164 kilowatt-hours of electricity, worth about $832. In the twelve months before that, we purchased 101,500 kWh for roughly $20,300. That’s an astonishing 96% savings of $19,500.
To put some perspective on those figures, we bought an average of 350 kWh of electricity per month to power our 11,400-square-foot facility over the last year, whereas the average American, living in an average American home buys nearly 600 kWh more than that each month, according to official statistics from the U.S. government.
How did we do it? We did it by:

• generating most of our own electricity with our 47 kW (DC) photovoltaic array;
• installing a white roof, reducing summer cooling loads;
• reducing our lighting power density by more than 30 percent;
• increasing daylighting;
• and relamping fixtures.

Not only did those energy-saving strategies help us reduce costs they also contributed to the Platinum LEED certification that our office renovation recently achieved.

published 11.05.2009