In the desert, rainfall may be scarce but the tap water supply is reliable and sunlight is plentiful. Phoenix (Ariz.) Water Services is harnessing sunshine to create electricity for its Lake Pleasant drinking water treatment plant. By using solar power to offset 50 percent of the facility’s needs, the utility is helping stabilize rates for 20 years and saving more than $4 million in energy costs.

To serve a population of 1.5 million, Phoenix Water has 160 employees who operate five drinking water treatment plants and 16 wells with a total capacity of 680 mgd (average flow 330 mgd). The extra capacity allows the utility to shut down plants for maintenance and prepare for population growth. A staff of 400 maintains nearly 7,000 miles of distribution pipeline and 109 booster pump stations across 65 pressure zones.

Phoenix purchases raw water from the Salt River Project and the Central Arizona Project (sourced from the Colorado River). The three conventional plants fed by the Salt River water use pre-sedimentation, flocculation, final sedimentation, granular activated carbon (GAC) filtration, pH adjustment and disinfection. Phoenix reactivates and reuses its old GAC filters instead of buying virgin carbon, saving money and reducing landfill fees.

Water from the Colorado River is less turbid, requiring only direct GAC filtration and disinfection. The wells require disinfection, and water from some wells is treated for arsenic removal. The annual budget for water production and distribution is $139 million.

Going solar

In 2008, local utility Arizona Public Service began a Renewable Energy Incentive Program, providing financial incentives for solar installations. SunPower Corp. approached Phoenix Water about installing a solar array. “As a water utility, we have a great appetite for using power at a steady rate,” says Troy Hayes, deputy director of water production. “We use it all day, every day, so we were very attractive to a company that makes solar panels.”

In December 2012, SunPower installed nearly 23,000 solar panels at the Lake Pleasant plant with 7.5 MW capture capacity, meeting half the facility’s needs (15 million kWh annually). A 1.5 MW array of SunPower T10 fixed solar tiles was installed on the roof of a reservoir. The remaining ground-mounted panels cover 22.5 acres and track the sun’s movement to optimize sun capture up to 25 percent better than fixed systems.

The city solidified a 20-year contract in which SunPower would install and maintain the solar array at no cost to the utility. In exchange, Phoenix Water buys the power at a lower price than grid power for two decades. “We locked in a guaranteed rate for our customers,” Hayes says. “It’s different than grid power, which is adjusted annually. Solar rates are predictive and stable, so we know how much we will be paying for electricity. It’s a good thing for everybody.”

Improving efficiency

To reduce energy costs further, Phoenix Water began an energy management program in April 2012 that includes power-monitoring systems in all its treatment plants. The systems, which cost $230,000 to install, monitor energy use on processes such as centrifugal filtering, raw water pumping, and finished water pumping.

“We are isolating each of the main processes to see how much electricity they use and how that plays into the combined use of the plant,” says Paul Zelenka, water services superintendent for production. “The information goes into a database, and an online dashboard shows operators how the power is being used.”

The utility also plans to implement energy management software that will give staff more information to make choices that optimize energy use, such as taking advantage of lower electric rates by shifting power usage to off-peak hours.

Shared responsibility

“Our water system is very complex, so it’s difficult for operators to make decisions taking a holistic approach of what’s happening in the entire system,” says Andy Terrey, project coordinator in water engineering and construction. “Our main goal is to produce water and get it out to our customers safely and reliably. With the addition of energy management, we have to take our primary goal and figure out how to do that most economically. We are now evaluating energy optimization software, which can help us make decisions that are otherwise too complex to make on our own.”

Implementing system-wide power monitoring and energy management software will take several years to complete.  Empowering operators to make more energy-minded decisions will require training. “Once we get the data and see how the equipment affects the electric bill, we can educate the operators on the impact their decisions have on our operating costs,” says Terrey. “They will have more information at their fingertips to make more educated choices. Everyone is budget-minded, so it’s a way the operators can do their part.”