When electrical demand peaks, South Plant quietly fires up its own power supply

From left, Sean Franklin, Brandon Shaver and Jhanvi Rana look at equipment in the cogeneration facility at South Treatment Plant.

It was the mid-2000s and Western states were reeling from blackouts and skyrocketing electricity prices as the energy company Enron manipulated the spot market for profit. South Treatment Plant, which was purchasing electricity on the spot market, endured a 10-fold price spike from 1999 to 2000 and was looking for stable power pricing that was not tied to the craziness of Wall Street.  

So, in 2004, in exchange for fixed rates with Puget Sound Energy (PSE), South Plant installed a cogeneration (otherwise known as “cogen”) system that could convert natural gas or biomethane to electricity and heat to run the plant in a pinch. South Plant, which serves the southern and eastern communities of King County, is one of the largest energy users in the region, drawing electrical power to drive the massive pumps that move wastewater through the treatment process.  

The cogen system consists of two 3.5 megawatt turbines that can draw from the nearby PSE natural gas pipeline or the plant’s on-site biomethane supply fed by the giant digesters. With the Enron scandal eventually receding to history and electricity prices restored to normal levels, the cogen system has since been put to good use as a backup power supply. 

Twenty years later, a new kind of energy crisis is brewing in the Pacific Northwest as the demands on the electrical grid grows due to population increases, climate impacts, and of course a greater reliance on electricity to power data centers, electric vehicles, and many other home appliances. This is where South Plant’s Cogen system comes to the rescue, once again. 

Inside the cogeneration facility at South Treatment Plant, specialized piping and instrumentation precisely monitor and control the flow of natural gas.

King County is working with PSE to find practical ways to support the region’s changing energy needs. South Plant’s operators have been piloting a PSE demand response program that eases pressure from the grid during peak demand times. This year the facility was ready for prime time, activating the cogen system five times from November to April after receiving the call from PSE to help out.  

Each occurrence took 6.0 megawatts of demand off the grid by supplying South Plant with on-site electrical power during a two- to-three-hour interval, equivalent to the electrical usage of about 4,200 homes for that duration. Besides helping to stabilize the power grid, South Plant’s participation in this incentive program netted $340,000 in cost savings in the first 6-month season, with more expected for the rest of the year.  

“This program not only delivered financial savings and revenue for the utility but allowed us to fulfill a greater purpose — supporting our regional power grid during times of vulnerability,” said Mike Wohlfert, the plant manager for South Plant. 

The cogen system doesn’t replace all of the plant’s power needs — though it sometimes gets close for a few hours at a time. But it’s there when it’s needed, doing its part to help power a more resilient future for the Puget Sound region.

Jhanvi Rana, right, energy engineer at South Treatment Plant, shares a laugh with Eric Hart, operator, in main control at the plant.