Half-MW Solar Energy System for Water Treatment Plant

Summer time in Northern California used to mean people would plan when to water the lawn according to times set by the water utility. But South Feather Water and Power Agency wanted to give their customers more options for water use, so they commissioned Sun Power & Geothermal Energy to design and install a 566 kW DC electric solar photovoltaic (PV) system that would cut back on the plants reliance on the electric grid. The 2.2-acre solar system is situated on unused land adjacent to the freshwater treatment plant, and it provides all the electrical power for plant operations during the day.

San Rafael, California – July 23, 2004 [SolarAccess.com] The treatment plant runs all day, every day of the year. It will still use grid power at night and on rainy days, but surplus energy produced by the PV system on sunny days is automatically sent to the grid for credit with the California utilities company Pacific Gas and Electric (PG&E) through net metering. The combination of solar energy consumed by the treatment plant and utility credits from PG&E should eliminate the agency’s net annual electric bill completely by 2024 when the system is due to be paid in full. “Going solar allows us to have more control over our rates,” said Michael Glaze, general manager of South Feather Water & Power. “As PG&E’s rates go up, our ratepayers’ water rates have to go up, too. I can’t imagine that a public agency would sit around and continue to pay an ever-increasing electric bill. When they can have the power for less money, doing nothing just does not make sense.” Energy costs are one of the largest expenses in running a water treatment facility. In 2003 South Feather’s electric bill exceeded US$ 160,000, and that was up approximately 17 percent from 2002. The 566 kW PV system should generate the equivalent energy needed to supply 200 homes. Having the on-site power source removes South Feather’s demand on the public utility grid and adds energy to the grid during afternoon peak demand periods when California needs it the most. The state has a shortfall of energy on hot summer afternoons when air conditioning is in high use. This is also when solar produces the most energy. The PV system includes 3,060 Sharp 185 W panels, two Xantrex PV225 inverters and one Xantrex PV45 inverter. The arrays are tilted at a 22.5-degree angle to collect the most sunlight during peak periods on summer afternoons at South Feather’s latitude. Because the silicon panels perform better when they are cool, they are mounted on open steel supports to allow air to flow across the top and bottom of the panels. For those extra hot California afternoons there is a water misting system in the panel supports that turns on when the air temperature reaches 90 degrees Fahrenheit (32 degrees Celsius). A separate water spray system rinses dust off the top surface of the panels during dry periods to keep them clean and productive. South Feather supplies water for the misting system. The total cost of the PV system was US$ 4 million, and the company received a $2 million rebate on the installation from the California Public Utilities Commission.


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