On a recent gray December morning, nearly 8,500 solar panels covering 13 acres in Germantown tilted toward the sky, straining to harness any glimmer of sunlight.

Their host: a sewage-treatment plant in Montgomery County, one of the first in the Washington region to try solar power. The panels, also installed at a Washington Suburban Sanitary Commission facility in Upper Marlboro, began operating in October.

Solar panels are expected to provide up to one-fifth of the two plants’ electrical needs at rates 25 percent cheaper than traditional electricity, WSSC officials said. (And, yes, if it’s a cloudy day or the middle of the night, your toilet will still flush.)

“For a utility, it’s a huge milestone, because very few have solar power,” said Rob Taylor, the WSSC’s energy manager. “If we can show we can buy alternative energy cheaper than conventional energy, it’s a win-win situation.”

The idea is catching on with water and sewer utilities across the country, in part because they guzzle electricity. Operating round-the-clock, the facilities run enormous pumps to deliver drinking water and then use huge blowers, centrifuges and other equipment to treat sewage and return the disinfected water to local rivers. Those energy costs can fluctuate dramatically, putting pressure on operating budgets, utility officials say.

“We’re a massive energy user, and we pay a pretty penny for it,” said George S. Hawkins, DC Water’s general manager.

Sewage-treatment plants, in particular, are being looked at for solar power because vast parcels of land bought decades ago as buffers for nearby communities can accommodate acres of the panels. Meanwhile, the panels’ prices have dropped significantly in recent years, helping utilities achieve bigger savings.

Utility officials say they also are exploring ways to reduce their dependence on the electrical grid during and after severe storms, when power outages can wreak havoc on sewer systems and cause overflows into streams.

It’s also about saving money. DC Water, the largest consumer of electricity in the District, is installing equipment similar to a giant pressure cooker at its Blue Plains Advanced Wastewater Treatment Plant in Southwest Washington. The equipment will “cook” and sterilize the brown, goopy sludge collected from treated sewage and turn it into food for methane-generating bacteria. The methane gas will then be burned to power steam turbines that produce electricity, officials said.

DC Water officials said they expect the system to save the utility $10 million in electricity costs — and another $10 million in trucking costs because half as much sludge will need to be hauled away. The utility also is exploring selling the sterilized sludge as fertilizer, Hawkins said.

The annual savings are expected to more than cover the debt service on the $470 million borrowed for the project, Hawkins said. That will free up money needed to repair and replace aging infrastructure, such as underground pipes that burst after too much decay, he said.

Hawkins, the former head of the District’s Department of the Environment, said the new process also is expected to cut the treatment plant’s greenhouse gas emissions by one-third. “We’re very aware of the fact that a lot of the energy we’re using is coming from big Midwestern coal plants with quite a big environmental footprint,” Hawkins said.

Blue Plains has less open land available for solar panels than some other treatment plants, he said. Still, DC Water is considering putting panels on underground settling tanks and other structures on the 150-acre campus.

Howard County officials began looking at alternative energy sources last year, after Hurricane Sandy knocked out power to the Little Patuxent Water Reclamation Plant in Savage. The outage caused 19 million gallons of diluted but untreated sewage to flow into Little Patuxent River, officials said.

The county is installing three diesel-powered generators to provide backup power, along with a solar panel system to offset the diesel emissions and provide alternative power.

The solar panels are projected to save about $22,800 in annual electricity costs and offset the generators’ carbon dioxide emissions by 150 percent, Howard officials said.

“If we’re going to be able to expand our solar capacity, we have to creatively look at publicly owned infrastructure that has capacity” for solar equipment, Howard County Executive Ken Ulman (D) said. “Especially in urban areas, treatment plants are a big part of the solution.”

In Northern Virginia, Fairfax Water officials recently determined that it would take too long — 36 years — for the annual electricity savings to cover the costs of installing solar panels at a large drinking-water filtration plant, said Shawn O’Neill, the utility’s manager of energy programs.

However, he said Fairfax Water is considering solar-powered security cameras, outdoor lights and office building heating. O’Neill said solar power would be especially useful to automate remote valves that now must be operated manually in areas with no electricity.

The WSSC solar program is a public-private partnership. Washington Gas Energy Systems paid the $12 million to install the solar panels and will operate them for 20 years. The WSSC pays only for the solar power it uses. WSSC officials say they expect to save $3.5 million total in electricity costs over the 20 years and cut the two plants’ annual carbon dioxide emissions by 3,200 metric tons — described as the equivalent of taking 665 cars off the road.

Scott Wiater, president of Rockville-based Standard Solar, which installed the WSSC solar panels and will maintain them, said utilities are focused on those savings.

“They’re doing it for the bottom line. That’s the primary driver,” Wiater said. “The feel-good environmental aspects are just gravy for them.”

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