A Demand Response Program helps a Los Angeles treatment plant save money while reducing environmental impact and stress on the power grid
When the weather heats up, electric utilities face pressure to meet the demand on their systems. Utilities can only make or buy so much energy, so most have programs that reward customers who agree to reduce their use during times of high demand.
The Sanitation Districts of Los Angeles County have taken advantage of such rewards for more than two years at one of the 11 wastewater plants serving 78 cities. The program has proven to be a low-risk way to save energy and benefit financially.
The Districts provide solid waste and wastewater services for 5.7 million people, handling an average of 460 million gallons per day (mgd) in Los Angeles county. The 100 mgd San Jose Creek Water Reclamation Plant provides primary, secondary, and tertiary treatment and reclaims about 35 mgd for groundwater recharge and irrigation.
Constellation Energy, a national energy company and electricity wholesaler in California, started its Demand Response Program in 2001. The San Jose Creek plant enrolled in 2009. “We wanted to gain the financial benefits, obviously,” says Andre Schmidt, senior engineer with the Districts. “And we’re a public agency, so we wanted to be a good citizen and provide a public service.”
Upping the ante
The plant used to take voluntary measures during hot weather, like turning off lights in office buildings, and was looking for a more significant way to contribute to energy reliability and environmental protection.
“Our weather can get extremely hot, so there is high risk of brownouts and blackouts,” explains Aimee Riley, account manager for commercial and industrial customers for Constellation Energy. “We contract with a lot of businesses we can call on to balance the electrical grid.”
Supply emergencies don’t happen often, but utilities and wholesale providers still see such programs as valuable insurance to maintain an adequate power supply. Riley says the Demand Response Program is typically used once or twice in a normal summer. San Jose Creek was called upon to reduce its use only once in 2010. “There are other demand response programs that have been used more often,” Riley says.
The rarity of such events makes enrollment attractive for businesses that can reduce load without too much impact on operations. The programs offer a monthly incentive, either through discounted rates or direct payments, and may include further discounts or payments when customers reduce their use. Load curtailments usually last about two hours, according to Riley, and Constellation’s program restricts them to four hours per event.
If the Demand Response Program is activated, the plant is notified by an automated dialing and email system at Constellation Energy. Plant personnel then take manual steps to reduce the load. Riley says other customers may curtail their loads automatically.
Load control may not be an option for some wastewater treatment plants. San Jose Creek has more flexibility than most because it can bypass part of its flow through the sewer system to another treatment plant about 25 miles away in Carson. It takes at least eight hours for the wastewater to get to Carson, so that plant has ample time to prepare for the added flow.
“Since we’re able to bypass some of our flow, we can turn down our influent pumps during curtailments,” says Bob Shimokochi, operations superintendent. “That allows us to turn off one of our large 900 hp air compressors, which is one of the largest types of equipment in the plant. That alone saves more than 600 kilowatts. Other pumps and motors in the plant might automatically shut off due to the lower flow — the same thing that happens as flows fluctuate during the day — but that’s not guaranteed.”
It doesn’t take long for operators to take the actions. The influent pump is controlled from the control room. An operator does have to go to the air compressor to shut it off. Once the load curtailment ends, the operator turns the compressor back on, and the influent pump is returned to normal. If wastewater flows happen to be low at the time, operators may elect to leave those devices off until flows increase.
Peaks don’t coincide
Wastewater plants are potential candidates for load control because their peak demand times don’t usually coincide with peak demand on the electrical grid. That is the case at the San Jose Creek plant. “Our peak load is during the morning after people shower and get ready for work, about 9 a.m. to 11 a.m.,” says Schmidt. “It would be difficult to shut down the compressor during our peak.”
Typically, electrical demand peaks from mid-afternoon to early evening. In Constellation’s case, its load curtailment program requires curtailments to begin no earlier than 11 a.m. San Jose Creek’s agreement restricts load reduction to after 2 p.m. “Typically,” says Riley, “it’s going to happen after 2 o’clock anyway.”
Constellation’s program requires that curtailments end by 7 p.m. and that’s before the plant’s evening peak, which runs from about 8 to 11 p.m. Other wastewater plants may have different peak times, depending on how far they are from their customer base.
How it works
Under the Demand Response Program, Constellation makes a monthly payment to San Jose Creek, plus an additional amount based on how much the plant reduces its load if the program is activated. Usually, a customer designates monthly how much power it will save when called upon. San Jose Creek has agreed to reduce its load by 500 kW in most months. That amount doesn’t create much risk for the plant, which has a peak electrical load of 7 MW.
Constellation pays about $35,000 a year to San Jose Creek. While only about 1 percent of the plant’s annual electricity bill, it is still a revenue stream that also helps ensure an adequate supply of electricity for the entire community.
Schmidt says the plant could enroll in other programs, but Constellation’s Demand Response Program provides the flexibility the plant needs to make sure it can adequately treat its wastewater. “Our contract is set up so that if we’re not able to respond, we don’t receive any penalties,” he says. “We may not be able to respond if there is some unforeseen event going on in the plant or our flows are high.”
Riley says the lack of penalty is unusual, but Constellation recognizes the special circumstance at San Jose Creek. Other customers may have their own special situations, so Constellation negotiates individual contracts with each customer. “Compliance has been good,” says Riley.
Such programs at California utilities and wholesalers have prevented brownouts or blackouts in California over the last several years.