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Interviewee: Rob Pratt, Carl Imhoff, Pacific Northwest National Laboratory
Beat the Peak
Engineers at the Pacific Northwest National Laboratory (PNNL) have a favorite demonstration they like to show visitors. Rob Pratt, PNNL staff scientist and manager of their “Gridwise" program, calls it, “An army of small appliances riding to the rescue of a bad situation.”
“What we like to show folks when they come visit our ‘kitchen’ is a set of appliances all running and humming along, making noise.” says Pratt. He says the refrigerator has its “door open, the lights on, the dishwasher’s running and the clothes dryer’s tumbling.” There’s a power meter on the wall that shows the appliances are consuming four or five kilowatts of power.
But when the engineers simulate a stressed electrical power grid, he says a controller “senses that … and shuts them (the appliances) down, but the light’s still on in the fridge, the dryer is still tumbling, the sound is all there, the dishwasher’s still running.” But, the meter on the wall shows an obvious drop in the amount of energy being consumed.
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What happened? The controller “turned off pieces of those appliances, the internal parts that consume most of the energy,” explains Pratt. The controller ordered a cut, not of all the functions, but rather to some of the appliance’s high-energy operations that could be temporarily delayed. In this case the refrigerator turns off its defrost cycle or even the compressor, the dryer momentarily turns off its heating unit, while a similar heating unit in the dish washer and in a nearby hot water heater also turn off.
By momentarily delaying these optional power-hungry functions — Pratt’s “appliances riding to the rescue”– utilities can lessen peak demands for electricity. That’s something that can save energy. It can also reduce the need for expensive generators to stand by in case they’re needed to handle peak demand, reduce electrical costs, and lessen the likelihood of large blackouts similar to the one that hit the Northeast in 2003.
Engineers are currently exploring two types of smart appliances. Some of these smart devices get their cues from the power company, while others power down on their own as they sense minute changes in the electricity’s frequency or voltage. Such changes are an indicator that the supply is having a hard time keeping up with demand.
Matching supply to demand is a challenge for operators of the nation’s electrical grid. Whenever we turn on a light or power up our computer, the electrical energy we need has to be produced the moment we need it. Unlike water, for example, there is no reservoir.
Comparably cheap and reliable sources of electricity such as hydroelectric and nuclear power run fairly constantly, supplying us with a base level of power. As people turn on electrical devices, demand surges. Since supply and demand must match, utilities power up additional plants that have been standing idle. These stand-by plants are usually more costly sources such as coal or oil fired plants. So, without even knowing it, you’re suddenly using more expensive electricity.
By using smart appliances, consumers can influence how often peak demands happen, or shortening their severity or duration, utilities could reduce the use of theexpensive sources.
Initial Test Successful
PNNL engineers have already tested the smart appliance concept in 112 homes. For a year homeowners had a controller in their home that was also connected to the Internet. Appliances such as their dishwasher, refrigerator or thermostat were retrofitted to become “smart appliances” that could receive signals from the controller. As the cost of generating electricity goes up and down during the course of the day, PNNL engineers could send price change notices they call “price signals” to the test home through the Internet.
Carl Imhoff, Grid Infrastructure Market Sector Leader for PNNL, says this controller “would receive the price signal and then communicate out to the appliances that would respond.”
However, how the appliances responded was still up to the consumer, a concept that both Pratt and Imhoff emphasize as important. They also say such a program would not let utility companies see what appliances you are using or when. They would only see overall household electrical usage.
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Also important, noted Imhoff, was the concept of keeping the system simple. He says, “We gave them a simple slider switch.” The switch ran from business as usual to green. They could adjust the slider as often as they wanted, but Imhoff said users on average touched it only six times in the year of the experiment. People also had an override switch so they could opt-out for 24 hours in case they had something special going on.
Imhoff says those who kept the controlling slider on the green side were able to save 10-12 dollars a month. The engineers saw they could reduce the peak electrical loads by an average of 15 percent. If repeated throughout thousands of homes, such a change could have a real impact on both the cost and reliability of electricity.
This research was published in a 2008 Department of Energy Report entitled “Pacific Northwest Gridwise Testbed Demonstration Projects” and was funded by the Department of Energy.