By Steve Lund

When officials in the Nebraska city of Atkinson decided to install solar power at the wastewater treatment plant, they didn’t aim to reduce the electric bill. They aimed to eliminate it.

The solar array, installed by GenPro Energy Solutions, consists of 668 panels with a total capacity rating of 200 kW. It is expected to produce 377 MWh per year, which should be enough. Built in 2014 by Fluidyne, the plant has a design capacity of 149,000 gpd and an average flow of 130,000 gpd.

Mayor Paul Corkle, concerned about keeping rates down, came up with the idea of using solar power. “We use a lot of electricity,” Corkle says. “A long time ago, I was one of the founders of an ethanol plant in the same town, and we were looking at wind turbines, but they weren’t very efficient. When solar came out, I saw that it possibly would work for us.”

Following the sun

Atkinson’s solar array is a tracking system. The panels are mounted and powered so that they follow the path of the sun. That boosts energy production by about 30% compared to fixed systems, according to Molly Brown, vice president of energy production at GenPro. The tracks were made by Array Technologies. The site next to the treatment plant where city officials placed the solar array presented some unusual construction problems.

Gary Thurlow, city maintenance supervisor, says the site had limited potential uses because of its history: “It was an old gravel pit, and it had been filled up with old trees and busted-up concrete. It was just basically bad ground. We couldn’t build anything on it. It was the perfect site to give this thing a try.”

Digging out some of the debris and filling in the pit would have been extremely expensive. So Corkle suggested setting posts in the ground and putting them on a stringer. GenPro did something similar but with a twist: Instead of posts, the company used large aluminum screws. The depth of embedment was 30 feet, three times what is normal for a solar array foundation. “They look like gigantic screws like you would use at your house,” Corkle says. “By the time it was all done, it was cheaper to do it this way to make it level.”

The ribbon-cutting for the solar array was held last January, so it’s still too early to tell if Atkinson’s venture into solar power will perform as well as expected, but Corkle is confident. The array is connected to the power grid with net metering, so if the panels produce more power than the plant needs, the excess goes to the grid.

Seven-year payback

The solar array cost $484,000. The city got a grant from a state energy program to buy down the interest rate and borrowed the money from a local bank. “The payback for this system, because of the grant and some other money we got, is seven years,” Corkle says.

If that works out it will be good for ratepayers and the city, which made significant investments in wastewater treatment in recent years. The city (population 1,200) spent about $4 million on the new treatment plant. The old plant was obsolete and was not meeting permit requirements. “We looked at a lagoon system, but because of our high water table, we weren’t able to do that, so we had to put in a mechanical plant,” Corkle says.

The new sequencing batch reactor plant is built with two identical trains so one can be taken offline for maintenance or inspection without shutting down operations. Biosolids are applied to farm fields. The effluent is UV disinfected from May 1 through September and is discharged to the Elkhorn River. Operator Scott Fix says the plant processes three or four batches per shift.

Surviving a flood

The treatment plant survived the major flooding in Nebraska last March. “We had the world’s worst storm,” Corkle says. “The frost wasn’t out of the ground yet, we had 15 inches of snow on the ground, and we got 3 inches of rain. The warm rain melted the snow and broke up the ice on the rivers. Ice started jamming up on the rivers, and we just had a domino effect.”

The streets were underwater in Atkinson, and the treatment plant was overwhelmed with stormwater, among other problems. “The river rose so much that the discharge pipe was underwater,” Corkle says. “I’ve never seen anything like it.”

When the flood receded, the plant and the new solar field were still intact. The city passed a half-percent sales tax to provide some relief from sewer rates after the plant was built. He hopes the solar system will reduce operating costs significantly: “Nobody will live in this town if the rates are through the roof.”