Treatment plant uses an array of savings

Plant may return power to the grid

By Mara Stine

The Gresham Outlook, Dec 8, 2009, Updated Dec 8, 2009

Since early November, workers have braved the wind, mud, rain — and now record-breaking low temperatures — to install the largest ground-mounted solar facility in the state at Gresham’s wastewater treatment center.

“It’s actually the largest in the Northwest,” said Andy Noel, regional sales manger of REC Solar Inc., which is installing the solar panels at no cost to local ratepayers.

The glistening panels, or modules, cover an entire acre on the wastewater treatment plant’s southeast corner facing busy Sandy Boulevard.

“Having this array in such a prominent location shows that we do take this seriously,” said Laura Bridges-Shepard, Gresham’s spokeswoman. After all, Gresham officials are trying to woo solar companies to the area, so why hide such a groundbreaking project in the “back 40”, she said.

It may seem ironic that clean energy should be all the rage at a place where 13 million gallons of solid waste are processed every day of the year, rain or shine.

But the wastewater treatment center is already ahead of the sustainability curve, said Michael Nacrelli, project manager and a city of Gresham civil engineer.

And that appealed to REC Solar Inc. and SunEdison, which will own, operate and monitor the solar facility.

“I would think that this is one of the greenest (wastewater treatment plants) from a renewable perspective,” Noel said.

“It’s a benchmark project,” said Russ Wright, SunEdison regional sales manager. Although other municipal buildings have installed solar array projects, none are as large as Gresham’s, he said.

“It really reflects the city’s focus and commitment to sustainability,” Wright said.

Seventy percent of the power used by Gresham’s wastewater facility is already considered sustainable — 50 percent is produced on site by converting methane gas into energy and another 20 percent is from wind power purchased from Portland General Electric.

The solar panels will be fully installed by the end of the year. They’re expected to generate on average 8 percent of the plant’s annual electricity usage, or about 400,000 kWh (kilowatt hours). Put another way, that’s enough to power about 42 average-sized homes for a year, Wright said.

But the Northwest is cloudy. How is this going to work?

“The system produces more than people think in low-light conditions,” Noel said. In fact, Portland produces more solar energy than stereotypically sunny cities, such as Phoenix, (Ariz.), because solar cells slow down when the mercury hits 100 degrees.

During summer’s peak, the wastewater treatment center’s solar panels could max out their full capacity of nearly 420 kW. That’s enough to power half the wastewater treatment plant.

“On sunny days it is likely we won’t be buying any power, but run the plant on all our renewable energy features,” Nacrelli said.

In such a scenario, excess power the plant doesn’t use will return to the grid, and be sold to other users.

“It’s going to spin our meter backwards actually,” he said. “In theory, we could become a net producer.”

The goal is for the treatment plant to be energy independent in five years, Nacrelli said. “It won’t be free power, but it will be clean and renewable,” he said.

Other energy generating ideas include the erection of wind turbines at the wastewater treatment plant, installation of a hydro turbine to harness power from the plant’s outflow into the Columbia River and conversion of grease waste from fast food establishments into methane gas.

“It looks promising,” Nacrelli said of the cooking-oil concept, adding that it could double the amount of methane gas produced at the plant.

A hydro turbine is estimated to generate 400,000 kWh per year, or the equivalent of 8 percent of the plant’s energy use, to be returned to the grid.

The turbine would be too far from the treatment plant for the energy to be used there, Nacrelli said.

For now, the city has entered into a 20-year power purchasing agreement with solar electricity company SunEdison, which will own, operate and maintain the solar array, valued at approximately $2 million. In return, the city will buy the power it generates.

So what does this mean for ratepayers?

Well, over the purchasing agreement’s 20 years, the cost savings to the city is estimated at $102,500, Wright said.

That’s because instead of paying PGE 9-10 cents per kWh for clean wind energy, or 8 cents per hour for plain old electricity, the plant can buy electricity generated from the solar panels for 6 cents per kWh.

“The cost, with a modest escalation, is fixed for the next 20 years,” Wright said. “There’s no utility rate spikes.”

So what does this mean for ratepayers?

“Any of our cost savings definitely helps us keep the rates down, and we’re one of the cheapest in the region regarding wastewater,” Bridges-Shepard said. “So it definitely matters that we do make over 70 percent of our own energy at the plant.”

For Nacrelli, the solar project’s major advantage is its sustainability.

As Wright puts it, “part of the beauty of solar is it’s very quickly deployable.

“You don’t have to spend five years building a dam. It’s something that can be put up, put up now and it’s a long-term sustainable resource. There isn’t a community in the state that can’t do the same thing.”

Solar pros

• Clean, quiet and visually unobtrusive

• Produces no pollution or unpleasant emissions

• Uses little to no water to produce that zero-emission electricity

• Can be placed in just about every region because the sun is available everywhere.

• No moving parts, so less need for repairs

• Modules that make up the solar panels degrade slowly. After 20 years, a solar panel will still produce at 90 percent of its original capacity.

Source: SunEdison

If you go

What: Switch On Event, a grand opening of sorts for the city’s solar project

When: 11 a.m. Thursday, Jan. 28

Where: Gresham’s Wastewater Treatment Center, 20015 N.E. Sandy Blvd.

By the numbers

• 1,904 – Panels or modules

• 60 – Number of solar cells per module

• 114,240 – Solar cells for entire project

• 32 – Number of subarrays, or groupings of modules

• 45 – Weight in pounds of each module