Floating PV System Provides Smart Energy and Savings for Wastewater Plant

Installing floating photovoltaic solar panels on a water reservoir provides Kelseyville Wastewater Treatment Plant with low-cost, clean energy, reduces algae growth, minimizes bank erosion, and lessens evaporation.

The Environmental Protection Agency reports that drinking water and wastewater systems account for approximately 2% of total energy use in the U.S. due to the electricity required to pump large volumes of water. It’s estimated that this adds more than 45 million tons of greenhouse gases to the atmosphere annually. For many local governments, drinking and wastewater plants account for up to 40% of their total energy consumed.

The Challenge: Rising Electricity Rates and Limited Space for Solar

Many California electric utilities have been forced to raise electricity rates in recent years for a variety of reasons. Meanwhile, the increased frequency of wildfires in Northern California could exacerbate the situation, as expensive countermeasures and grid enhancements add to costs that must be passed on to end-users.

Lake County Special Districts is the water and wastewater agency of the County of Lake, California, which is about 130 miles north of San Francisco. Leadership for Lake County Special Districts knew the solution to controlling wastewater treatment plant costs was turning to cheaper renewable sources of electricity. However, they were concerned that the property they had available did not have adequate land or rooftop space to install a photovoltaic (PV) solar system large enough to offset consumption.

1. Lake County Special Districts opted to install a floating solar power system to reduce its energy costs. Courtesy: SolarEdge

After issuing a request for proposals (RFP) and reviewing the bids, Lake County Special Districts selected North Coast Solar, a pioneering energy consulting and contracting firm based in Santa Rosa, to implement its proposal to install a solution from Ciel Et Terre—well-known developers of the Hydrelio floating solar power system (Figure 1).

Turning to Water for Solar

“A lack of roof and ground space put our creative minds to work, ultimately driving the floating solar concept,” said Brian Hines, president of North Coast Solar.

2. The Kelseyville Wastewater Treatment Plant floating solar system includes SolarEdge inverters and Power Optimizers. Courtesy: SolarEdge

The 252-kW solution includes 720 Canadian Solar modules rated at 350 W each. It also utilizes one SE100K and two SE66K SolarEdge three-phase inverters with Synergy technology, and 360 SolarEdge P800s Power Optimizers (Figure 2).

The system was engineered to cover much of the plant’s annual energy usage, and projected annual electricity savings of $90,000, which is expected to grow over time as Pacific Gas and Electric (PG&E) rates increase while monthly lease payments remain constant. And, with the innovative municipal lease financing arranged by North Coast Solar, only minimal upfront investment was required, allowing Lake County Special Districts to generate positive cash flow in the first year of operation.

Floating solar power plants improve energy production by keeping the solar system cooler, which prolongs the lifetime of the PV system and improves performance. This cooling factor is an even bigger benefit in Lake County where summer temperatures can reach 106F.

3. Floating solar panels reduce the amount of sunlight available to algae, limiting its growth. Courtesy: SolarEdge

Utilizing the pond surface for a solar plant also reduces algae growth (Figure 3), bank erosion (through reduced water movement), and evaporation, while generating virtually free energy. Benefits also include reduced greenhouse gas emissions, offsetting 131 tons of CO ₂ per year—enabling the county to meet specific carbon reduction goals (see sidebar).

“Our SolarEdge DC [direct current]–optimized solution for Lake County Special Districts’ Kelseyville Wastewater Treatment Plant has generated about 16% more energy than predicted from the computer simulation, and it produced 389,580 kilowatt-hours of clean, free electricity in its first year,” reported Hines. “By reducing operating costs, they can now redirect funds to capital improvement projects.”

Maximum Power with a Focus on Safety

With modules on water, on-site monitoring, maintenance, and the safety of personnel are potentially more challenging. Through module-level monitoring, SolarEdge Power Optimizers help reduce maintenance visits and costs through remote problem-solving and upgrades. SolarEdge meets safety regulations by complying with National Electrical Code (NEC) requirements for arc-fault circuit-interrupter (AFCI) protection and photovoltaic rapid shutdown system (PVRSS) technology. SolarEdge Power Optimizers are also designed to meet the International Electromechanical Commission (IEC) Ingress Protection (IP) 68 rating and National Electrical Manufacturers Association (NEMA) 6P rating for water and humidity resistance.

Module mismatch is almost always unavoidable, especially with floating (moving) installs. SolarEdge’s maximum power point tracking ensures each module produces at its maximum power. SolarEdge technology also allows up to 40% less DC cabling compared to string inverter solutions, cutting down on the amount of material needed in a typical floating PV installation with long rows of solar modules in landscape orientation. In addition, long Power Optimizer input cables support the landscape orientation that is standard for floating PV installations.

“After experiencing module-level monitoring, you don’t go back,” said Hines. “The SolarEdge three-phase commercial inverters with Synergy technology are pretty brilliant. They’re modular, lightweight, and allow for very long string lengths. Plus, the advanced safety capabilities are huge, especially on water. Each Power Optimizer includes the built-in SafeDC feature, which automatically reduces voltage to a safe level, providing protection to our installation and maintenance personnel.”

—This article was contributed to POWER by SolarEdge Technologies.