A dual-axis solar photovoltaic system means a future of major savings on electricity for the treatment plant in Madera, Calif.


Solar power makes a lot of sense when you live in a community that gets 90 percent of its possible sunshine most of the year. It makes even more sense when you can harness that power without spending any money.

The 1.16 MW photovoltaic system at the Madera (Calif.) Wastewater Treatment Plant is one of the largest of its kind in the state. The joint turnkey project between REC Solar and SunEdison went online in August 2010 and is meeting all expectations.

“We are very happy with the results so far,” says Matt Bullis, Madera Public Works operations director. “The data is limited at this point, but we’re seeing a savings in the first year of operation.”

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Located just north of Fresno in the middle of the San Joaquin Valley in the Sierra Nevada mountain range, the 10.1 mgd (design) activated sludge treatment plant has about 10,000 residential, commercial and industrial customers. Bullis expects to generate about 62 percent of the plant’s electricity with the solar units.

That will save the city around $150,000 a year in electricity at today’s rates, a 25 percent savings in power costs and 6 percent overall savings to the operating budget that can be used elsewhere to cover rising costs. Over the 20-year contract, the city will save an estimated $3 million on electricity.

 

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No cost to the city

There are 5,200 panels at the plant, grouped in 94 modules of 56 panels each. Together, they generate 2.5 million kWh (2,500 MWh) a year and will offset 47 million pounds of carbon dioxide over the first 20 years of operation.

The 9-acre solar facility is on property provided by the city. SunEdison is the owner and operator and is responsible for maintenance. It also financed the project, designed by REC Solar. The project was selected in a request for proposal process issued by the Madera City Council in an effort to increase its use of sustainable energy.

“Finding ways to reduce costs for taxpayers while reducing our carbon footprint for our children and grandchildren should be a goal of responsible government at all levels,” said Mayor Gary Svanda. “I’m very proud that Madera is leading the way.”

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Besides providing the land, the city signed a 20-year purchased power agreement with SunEdison. The rates are comparable to those of the local utility, Pacific Gas & Electric, in the first few years. “The real savings is in the fixed escalation rate of 3 percent,” Bullis says. “That is significantly less than the anticipated escalation of 5.5 percent in our utility rates. The future is when our big savings come in to play.” When the contract ends, the city has the option of buying the facility.

The treatment plant generally uses all the electricity from the photovoltaic system. During the summer, it could generate more power than the facility needs during peak sunlight hours of 10 a.m. to 2 p.m. That extra energy runs the meter backwards, earning the plant credits for off-hour power use.

 

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Dual-axis system

A fixed photovoltaic system is the simplest and least expensive type of solar installation. The solar panels are set at a fixed angle to capture as much energy as they can, considering the changing movements of the sun throughout the year. It achieves maximum generation for only a few minutes a year.

The Madera photovoltaic project is a dual-axis system. Automated motors change the tilt and angle of the solar panel modules to follow the sun, maximizing generation throughout the day. The panels move with the sun from east to west, as a single-axis system does, while also tracking the sun as its north/south angle from the horizon changes through the year.

By staying focused directly on the sun, dual-axis tracking increases the electrical output of solar panels by 35 percent over a fixed system and about 20 percent over a single-axis system.

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More solar?

Beyond solar, there are no other big renewable projects on the horizon for the Madera plant, according to Bullis. The staff considered biogas for electrical generation, but, “We’re not producing enough gas to make it worthwhile,” he says. “We have to generate more effluent and more gas to make that happen.”

Madera’s police department and youth center are getting solar systems, and Bullis says a few more units may be added to the treatment plant’s system. That would boost electrical production to nearly 80 percent of the plant’s demand, meaning even more savings for the next 20 years with no expense.


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