Staff members at the Boulder (Colo.) Wastewater Treatment Plant know exactly how much they will pay for about 15 percent of the facility’s electricity 20 years from now. That’s because of a 1 MW solar photovoltaic (PV) system that began supplying power to the plant last July.

The city’s Environmental Action Division developed the idea a few years ago when solar developer EyeOn Energy Ltd. approached officials about leasing five acres of city property at the treatment plant in exchange for a purchased power agreement (PPA) at rates lower than those from the local utility, Xcel Energy.

The resulting contract locks in electrical rates for 20 years at levels below what the plant now pays for the utility power it still uses, according to project manager Douglas Sullivan. “This was a great deal for the city,” he says. “We pay an average of about 6.5 cents per kWh for utility power now, and the solar facility production is about half the cost.”

The price from the PV system started at 3.25 cents per kWh and escalates at 2.75 percent per year for the first ten years, after which it will be 4.17 cents. That’s where the price will stay for the last 10 years of the contract.

“We had very few up-front costs,” adds Andrew Barth, public works communications specialist. “Normally the city would be funding large capital projects, but the brunt of this was funded by the developer and construction contractor.” Xcel was also able to count the facility toward its Portfolio Standards requirement to have 10 percent of its generation from renewables by 2020.

The system will reduce annual emission by about 3.2 million pounds of carbon dioxide, 18,000 pounds of sulfur dioxide, and 8,500 pounds of nitrous oxide. According to the U.S. EPA, that is equivalent to taking 296 cars off the road and planting 360 trees.

Exceeding expectations

As is often the case, Boulder’s treatment plant is the largest power user of all of the city’s facilities. Its on-site PV system is one of the largest in the state and one of the largest municipal systems in the country. It is designed to provide 15 percent of the plant’s annual electrical needs and would save about $43,000, according to original design estimates.

“When the facility went online, it immediately dropped one of the two utility feeds to zero, so it was providing 65 percent of the plant’s power for six hours,” says Sullivan. That happened to be a sunny day and the array went online during the peak time for sunshine (10 a.m. to 4 p.m.).

The system includes 4,452 solar panels on 900 aluminum posts in a fixed array facing due south at a 43-degree angle to the ground. The developers, who had the final decision on the design, considered a tracking system.

“They looked at a couple of different options,” says Sullivan. “There are pros and cons from a price perspective, and there is a maintenance cost associated with a tracking system. The feeling was that the fixed system made the most sense.”

The fixed system had the best cost/benefit ratio because of Boulder’s location relative to the equator and because of the climate in the Colorado mountains. “We average 300-plus sunny days a year in Boulder, so it is a beneficial spot for solar,” says Barth. Other locations may be better served by a single-axis tracking system that follows the sun, or dual-axis tracking that also adjusts to the angle of the sun in the sky.

The PV system feeds power into a high-voltage switchyard in the plant. The only time plant operators may become involved is if the PV system does not automatically disconnect in case of a utility power outage. They would need to disconnect the system to prevent backfeeding of voltage onto the grid and endangering utility crews, and to prevent phasing problems with the plant’s two cogeneration engines and its emergency diesel generators.

Complicated arrangement

While the city doesn’t operate the PV system, it was still a complex deal to complete. EyeOn Energy ran into significant difficulty getting long-term financing during the economic downturn in 2008 and 2009.

To help fund the project, the company sold the $6 million plant to SOLON Corporation. SOLON is a manufacturer of PV panels, and its North American unit focuses on building PV facilities, not owning them long term. So as construction ended, the plant was sold again, to SunEdison.

Still, it took significant effort from the city. “We learned a lot, and we now have expertise on staff that positions us well in the event we have the interest to pursue this kind of a contract at another facility,” says Barth. It took substantial staff time and due diligence on both the contract and the technology to make sure the solar system would meet the plant’s requirements and would not interfere with plant operations.

Sullivan suggests that treatment plants considering solar look for outside help if they don’t have the expertise in-house. “We were reactionary at first to the proposal, but we hired some consultants to look at what made sense for the city,” he says.

What happens at the end of the 20-year contract will be decided near the end of the agreement. “We might see a proposal from SunEdison to replace the panels with new technology that could be significantly more efficient,” says Sullivan. “We could renegotiate the contract, or the city could purchase the facility.”

More renewables?

The Boulder plant has been using cogeneration since 1987. Two digester-gas-powered cogeneration engines provide 2.1 million kWh per year, 10 to 15 percent of the plant’s electrical demand. The PV system doubled the plant’s self-generation portfolio.

Energy consultant McKinstry Company is exploring possibilities for more renewable energy at every city facility, including two water treatment plants, three recreation centers, and several other municipal buildings.

Boulder also has eight hydroturbines to take advantage of its elevation in the foothills of the Rocky Mountains. The city owns several reservoirs 3,000 to 6,000 feet above the city and uses hydro-turbines in those water pipelines to generate 42.5 million kWh per year. The city was among the first in the country to use that technology. One hydroturbine due to be replaced soon is 73 years old; another turned 100 in August.

“The city is constantly looking at new renewable energy resources,” says Barth. “We’re putting solar panels on buildings right now, and we’re looking at wind energy. We have a goal of achieving the targets established by the Kyoto Protocol, which would reduce greenhouse gas emissions to 7 percent below 1990 levels by 2012 for the whole city.”