California Wastewater Treatment Plant Harnesses Power of the Sun

By Pete Cavagnaro

In the heart of California's most productive farmland, the city of Tulare is taking an integrated approach to water conservation. Fertile soils and plentiful water from the nearby Sierra Nevada mountains have helped make Tulare one of the most bountiful agricultural areas in the nation, and the world's number one producer of dairy products.

To preserve and protect this advantageous environment, the city sought renewable energy technology and water solutions to save residents money and promote efficiency. Additionally, worsening drought conditions prompted California legislature to require that local governments and utilities install water meters on all commercial and residential properties by 2025.

In August 2006, the city partnered with Johnson Controls, an energy services company (ESCO), to get a jump-start on meeting this mandate. City leadership, in partnership with the ESCO, worked to develop a comprehensive water efficiency program that would significantly upgrade its domestic water infrastructure and expand energy savings and capital improvements.

Onsite Power Generation

Wastewater treatment plants can account for 30 to 40 percent of a midsized city's energy bill. Implementing energy efficiency and operational changes can reduce energy consumption at wastewater treatment plants by up to 20 percent. The cornerstone of Tulare's energy and water program was the installation of a solar photovoltaic (PV) system at its wastewater treatment plant in the summer of 2011.

Plentiful sunshine made Tulare an ideal place to generate energy from the sun. With the help of the ESCO, the city installed solar panels on the roof of the municipal wastewater treatment plant's 20-space carport. In the planning phase of this project, engineers from the ESCO confirmed the feasibility of the project by studying the amount of sunlight that struck the roof of the carport and projected the amount of electricity that sunlight would reliably produce.

The energy generated from the solar array provides 30 kilowatts of electricity per hour, which equates to 32 percent of the onsite energy usage. The carport is expected to save the city more than $6.4 million in energy and operational costs over 15 years, offsetting power needs for the plant and municipal buildings.

In addition, the PV system is connected to the local utility grid, enabling the city to sell power generated by the solar panels to the utility. The city then buys the power back from the utility at rates negotiated through a power purchase agreement, allowing it to lock in favorable electricity rates at a time when power usage is rising.

AMR System

In Tulare, the additional benefits from efficiencies gained by installing a solar system were applied towards other energy improvements throughout the city. These include facility upgrades at select municipal buildings, including the city hall, new street lighting across the community, and the installation of an advanced meter reading system (AMR).

To ensure accurate water rates for its citizens, the city installed more than 16,000 new water meters connected to a mobile meter reading system. The new meters helped mitigate apparent water losses due to the aging of existing water meters.

Additionally, many area properties – owned by farmers, businesses and residents – lacked water meters, which made it difficult to manage water use.

According to the U.S. Environmental Protection Agency (EPA), adding water meters can help reduce water usage by more than 15 percent. Under Tulare's new AMR system, human error is virtually eliminated by enabling city workers to read meters remotely from their vehicles. This technology is helping to increase billing accuracy, allowing employees to focus on tasks necessary to provide superior municipal services.

Performance Contracting

Tulare chose to finance its renewable energy installation through performance contracting. This budget strategy enables a municipality to offset the cost of advanced energy solutions from a combination of operational and maintenance savings over the term of the contract. The ESCO financially guarantees that the utility will realize the calculated benefits, and the ESCO will pay the city for savings guaranteed but not realized within the contract timeframe and terms.

Over the course of the 15-year performance contract, the solar installations, combined with other energy improvements, are expected to generate more than $13.9 million in energy cost savings. The program was also funded in part by a $2.3 million California Solar Incentive Program grant and $438,000 in American Recovery and Reinvestment Act funding.

The city's environmental stewardship efforts resulted in achieving the U.S. EPA Clean Air Excellence Award, ranking Tulare as one of the top 15 entities that generate and consume green power onsite.

Tulare is positive proof that municipalities – as well as schools, universities and businesses – can generate their own clean power from the sun, while helping to conserve water resources, ensure their energy security, and save money at the same time.

About the Author: Peter Cavagnaro, P.E., works for the Solutions Group within the Building Efficiency business of Johnson Controls. Cavagnaro has a B.S. in Civil Engineering from Northeastern University and a M.S. in Environmental Engineering from the University of Colorado, Boulder. He is a member of the Water Environment Federation, American Society of Civil Engineers, and the American Water Works Association.

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