Solar Proves its Power

A small wastewater treatment plant in Massachusetts cuts its annual electricity bill in half with a fixed-array photovoltaic system

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Dawn Peters laughed when writing a $108 check for the monthly utility bill for the Charlemont (Mass.) Wastewater Treatment Plant.

Granted, Charlemont is a small, rural town of 1,300 people, and the 20,000-gpd plant serves only part of the town, about 190 households. Still, its annual electric bill is about half of what it used to be, thanks to a photovoltaic solar system installed in 2005.

The town’s sewerage district was created in the early 1990s and the plant went online in January 1992 to help protect the Deerfield River, a popular resource for fly fishing, kayaking, canoeing, tubing, swimming, and camping. “A lot of the septic systems near the river weren’t working, and a lot of people didn’t have septics and were dumping right into the river,” Peters says.

Thirteen years later, the treatment plant became the first in the state to use solar energy when it tapped into funds from the Massachusetts Renewable Energy Trust. The program covered half the $150,000 installation cost through a cash grant and with production credits over three years. The district paid the balance out of cash reserves.

Small but effective

The 14.5-kW system includes 96 solar panels from Isofoton of Málaga, Spain. A local worker-owned company, PV Squared (Pioneer Valley PhotoVoltaics Cooperative), installed them in arrays of 12 panels on eight 16-foot metal posts near the plant’s filtration beds and ran all the wiring, completing the project in less than a month.

From installation to operation, the project has had no impact on operations or operators, other than a significant savings. “It just sits there and it works,” says Peters. “That’s what I love about solar. PV Squared does a maintenance check every two years to make sure everything is operating correctly, and that’s it.”

The plant’s annual electric bill was more than $5,000 before the photovoltaic addition and is now around $2,500. “The week we turned it on, the electric rates went up,” Peters says. “We were grinning. Every time the rates go up, we win.” The district planned for a 17-year payback, but Peters believes it will be shorter than that.

Fixed system

The system went online in May 2005 and was designed to provide about half of the plant’s annual electricity. It is actually providing about 54 percent of the power for the plant’s pumps, motors, lights and other equipment. The only items operators have to watch are the single cooling fans on each inverter that coverts DC power to AC.

The panels are permanently aligned to maximize sun exposure but do not track with the sun — that would have cost more. “You would be adding moving parts that require maintenance and use power,” Peters says.

Since the system does not use storage batteries, any excess electricity goes right back into the grid. “When the sun is out and we’re getting good electricity production, the electric meter is running backwards,” says Peters. “That is so nice to see. I used to stand there and just stare at it for a few minutes.”

Contrary to what many people believe about solar, the panels produce some power on overcast days — about 15 to 20 percent of maximum output.

Is bigger better?

Peters says the district would have liked a bigger system to provide all the plant’s power, but that would have been too costly, there wasn’t enough room on the property, and the building roof isn’t aligned properly to take advantage of sunlight. “If we had the space, we would definitely consider doubling the size,” says Peters.

The Charlemont plant is very basic, with settling tanks and recirculating sand filters. “We don’t have aeration, which is a big consumer of electricity,” Peters says. “To the large plants, our electric bill is laughable.” On the other hand, she says, large plants have more complicated systems, and many were designed at a time when energy efficiency was less of a concern. That gives them even more savings opportunities.

Growing program

The state’s solar rebate program issued awards for 23.5 MW of solar power in less than two years with a goal of 250 MW by 2017. More than 1,200 homeowners, businesses, and municipalities took advantage of the program, which is now part of the Massachusetts Clean Energy Center, formed to promote a green economy by supporting research and development, entrepreneurship, and workforce training.

The two programs were merged this year to provide “a one-stop shop for development and deployment of clean energy innovations,” according to Ian Bowles, Energy and Environmental Affairs secretary and chair of the center’s board of directors.

In fiscal 2009, the trust provided $55 million for more than 800 renewable energy projects, including wind, hydroelectric, biogas, and fuel cell projects in nearly 300 cities. That included $28 million for 10 MW of photovoltaics, $4 million for 49 wind projects, $1.7 million to improve output from five hydroelectric plants, and $1.5 million for bioenergy and biofuels.

Massachusetts now requires new plants to be designed for efficiency and to include alternative energy sources. Older plants are also being refurbished with green technology. “I’m so happy to see that,” says Peters, a long-time fan of solar energy. And every month, she can feel happy as she writes out that utility check.


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