The city of Fayetteville, Arkansas, jumped on the solar energy bandwagon in a big way in 2019.

In September, the city in northwestern Arkansas connected its two wastewater treatment plants to 10 MW of solar energy with 24 MWh of battery storage. The three solar farms on city-owned land next to the plants represent a big step toward the goal to have 100% of city government operations running on clean energy by 2030.

Wastewater treatment is the city’s biggest energy consumer. The Paul R. Noland Wastewater Treatment Plant (30 mgd design, 12.6 mgd average) and the West Side Wastewater Treatment Plant (32 mgd design, 10 mgd average) account for about two-thirds of the electric load.

The solar farms were developed by Today’s Power, a subsidiary of Arkansas Electric Cooperatives, which includes the power distribution co-op Ozarks Electric. Fayetteville has a power purchase agreement with Today’s Power that is expected to save the city about $180,000 a year. The rate for the solar-produced electricity is set for 20 years.

Tim Nyander, utilities director, says the city had contemplated small solar projects but had not installed any until last year. “We had thought about solar panels on some of the buildings, possibly for lighting, but nothing on the scale that was proposed by Ozarks Electric,” Nyander says. “We thought it was a great idea.”

Good for everyone

Peter Nierengarten, P.E., environmental director, recalls the electric utility approaching the city with a win-win-win: good for the wastewater treatment plants, the developer and the utility. “We had the land, but Today’s Power brought the money for the investment in the solar generation components,” Nierengarten says.

“We had to put in a little bit of money to upgrade to connect to the solar array. Today’s Power borrowed $23 million or so to buy the solar components. They were able to take advantage of tax credits. Their revenue stream to pay off that loan is the payments we make.” Nyander and Nierengarten estimate the city’s make-ready expenses at $760,000, which should be recovered by the cost savings in a little over four years.

The lithium-ion batteries are made by Northern Reliability. The Fayetteville project is the largest energy storage facility in the Southeast. The batteries are owned by Today’s Power but operated by Ozarks Electric to shave demand during periods of peak demand when buying additional power from the grid is expensive.

The solar panels are on a tracking system that follows the path of the sun to maximize the energy they produce. The batteries can be charged either from the solar panels or the grid.

The project was sized to offset 100% of the electricity consumed by the wastewater treatment plants. The city uses net metering with the grid to bank extra power produced on sunny days and draw electricity from the grid at night and on cloudy days. “We’re using everything the panels produce,” Nyander says.

Reduced demand

Before the solar project, Fayetteville had taken numerous steps to reduce power consumption at the plants. Those steps include:

• Installing 66 variable-frequency drives — Altivar (Schneider Electric), Allen-Bradley (Rockwell Automation) and ABB — on motors
• Installing high-efficiency motors when old motors wear out
• Installing capacitors to prevent power factor penalties
• Using solar dryers to dewater biosolids
• Conducting an energy management assessment to identify future energy reductions
• Switching to LED lighting and putting all light switches on motion detectors
• Making adjustments to mechanical mixers

“At one of the facilities, we went to bare-minimum lighting at night because it can be operated by SCADA from the other facility,” Nyander says. “That does cut down on electrical usage.”

Fayetteville also generates power with three 2 MW diesel generators from Caterpillar Inc., Electric Power Division. “The on-site generation is for load shedding, so we are not on the grid when it is stressed due to demand versus capacity,” Nyander says. “We would pay exorbitant prices for electricity at that time.”

The solar power will not eliminate the need to operate the generators to cut peak summer demand. “We still need to load-shed between June and September each year,” Nyander says. “The solar is tied to the grid, and we must be off the grid during peak demand.”

Ozone disinfectant

The city has increased demand by switching from UV to ozone disinfection at the Noland plant starting in June 2017. The plant uses the HyDOZ (hyperconcentrated dissolved ozone) disinfection system from BlueInGreen, a company in Fayetteville.

“We’re preparing for emerging contaminants,” Nyander says. “Someday we’re going to be regulated on pharmaceuticals and those types of things, so we are using ozone for disinfection.”

Fayetteville already faces strict effluent limits because both treatment plants discharge to high-quality waters. The West Side plant empties into Goose Creek, which flows into the Illinois River, classified as a scenic river in neighboring Oklahoma. The Noland plant discharges to the White River, which flows into Beaver Lake, the drinking water source for 600,000 people, including Fayetteville residents.

The city takes prides in pioneering new environmental technologies. In 2016 it was designated as a Utility of the Future by the Water Environment Federation and partnering associations. In 2018, the city adopted an energy action plan that looks to have the entire city — not just government operations — running on clean energy by 2050.

Before the solar panels were installed, Fayetteville was about 16% of the way toward the 2030 goal of running government operations on clean energy. Now, Nierengarten says, it’s about 72% of the way there.