Experiment To Store Surplus Wind Power In Home Water Heaters

An oft-cited criticism of clean, low-water using energy technologies such as wind and photovoltaic solar is that they generate energy intermittently and can overload power grids with electricity at times when nobody needs it. The Bonneville Power Administration is exploring one potential solution to this problem: storing surplus power in water heaters.

Using water heaters to store renewable energy is an interesting twist to the water-energy nexus, turning the approximately 9% of residential electricity used for water heating from a burden into an asset. While more people heat their water with natural gas than electricity (50% vs. 40%), there are still plenty of electric water heaters in most regions to suck up surplus power and help balance the variability inherent with renewables.

Which is why the Bonneville Power Administration is asking 100 homeowners to participate in a study that will allow the utility to use their water heater like a sort-of battery, by turning it on and off based on the amount of electricity entering the grid so that excess power gets absorbed by the water heater instead of being wasted. It is unclear if or how power would be drawn back from the water heater. Even if the stored power cannot be brought back into the grid, managing water heaters based on the availability of electricity can help balance the grid and in effect reduce the electricity demand of water heating by shifting it off of peak usage periods.

The year-long study by BPA and a local utility based in Washington will look at, among other things, whether or not customers have enough hot water when they want it. Here’s a description of the program from the BPA, which i first learned about through Oregon Public Broadcasting:

The Bonneville Power Administration and Mason County Public Utility District Number 3 announced today that they are partnering on a smart grid pilot project to help manage the electricity grid and use wind power more effectively.

The project address two fundamental bottlenecks in the power grid; congestion during times of high power use and the imbalance created when more wind-powered energy is being generated than is being used.

"Homeowners who choose to participate in this pilot project can help the region ease strain on the region's electrical system," said Bonneville Power's Smart Grid Program Manager Lee Hall. "They will also make help the region make the best use of wind; a clean and renewable, yet variable power source."

Mason County PUD 3 will install special devices on water heaters that will communicate with the electrical grid and tell the appliances to turn on or off, based on conditions of the regional electrical system and the amount of renewable energy available.

Homeowners can override the water heater device at any time, and with modern insulated water heaters, it is unlikely they will even notice a change in water temperature.

To thoroughly understand the benefits of the project, you have to understand a basic principle of an electrical system. That is, at any given moment, the amount of electricity consumed must match the amount that is generated. Otherwise, the grid can destabilize causing a blackout.

Shifting water heater energy use to a time when consumption is lower helps level out the peaks and valleys of energy use, which makes the balancing act of supply and demand a little easier. This is especially valuable when managing variable power sources like wind power.

"Reducing electricity use during peak hours can be a money saver for Mason County PUD 3 and our customers," says Jay Himlie, Power Supply Manager for PUD 3. "It reduces the fees a utility has to pay for their peak power demand. It's really exciting to help pioneer this technology in the Pacific Northwest."

Another goal of the project is to see if the device can find out when wind power is readily available and fire up the water heaters to take advantage of it.

Wind power can only be produced when the wind blows, so using water heaters as energy storage devices gives the power system another tool to help balance out the variable nature of wind generation. When there is excess wind, the project can also help keep it from going to waste by turning on the water heaters that had been previously turned off by the device. The wind energy is put to use in heating up the water, which is stored for the family's use. With enough of these "storage units" in place, the region can reduce the need to rely on the hydro system to maintain the power system balance of supply and demand. With increasing demands on the Northwest hydro system, this project provides a valuable additional source for system flexibility.

To goal is for the device to find the balance between making sure the homeowner has enough hot water, while making wise use of wind power in the system.

Installation of the devices in the 100 participating homes should begin in October 2010.

While water heaters probably won’t be a silver bullet for the intermittency issues associated with renewable energy, hopefully this study will show that they are yet another viable option for utilities seeking to expand their wind and solar capacity. As more solutions like this are explored and proven reliable and cost-effective, it will become easier for utilities to embrace the types of clean, water protecting sources of power we need to mitigate climate change and protect our watersheds.

Update (8/18/10): NW Energy Coalition has a great post describing in much more detail how utilities can use simple smart water heaters to integrate intermittent renewables. Here's an excerpt:

The Northwest power system serves about 4.3 million electric water heaters. If all were running at once, their loads would total more than 19,000 MW. Of course, they don’t all run at the same time. Actual demand might be just a few hundred megawatts in the middle of the night, surging to more than 5,000 MW around 8 a.m. when people take their showers. Use drops during the day, and then peaks again at about 3,500 MW around 8 p.m. as people come home and wash dishes, clothes, etc.

Now imagine that as part of the smart grid, each water heater contains a chip that can receive signals from grid operators to raise or lower the water temperature by a few degrees. As wind generation picks up, the grid operator slightly raises the temperature set points on millions of water heater thermostats, thus “storing” the wind power for later use. Should the wind suddenly drop, the operator lowers the temperature points, causing many water heater elements to click off for a time.

Most people won’t even notice the small temperature changes. But spread over millions of water heaters, those few degrees of difference are enough to avoid ramping fossil-fuel and hydro generation up and down, thus improving system-wide fuel efficiency and leaving more water in the river for migrating salmon.

Once the infrastructure — smart meters that can communicate with both the utility and home appliances — is in place, manufacturers could start installing computer chips, adding perhaps $5-10 to the cost of a water heater, Given the system savings the water heater controls would generate, utilities could afford to cover the additional cost, and/or offer customers a rate discount or other incentive in exchange for limited control of their water heaters.

Currently, for example, Idaho Power pays residential customers $7 per month to participate in its A/C Cool Credit Program, which slightly backs down air conditioning power during peak demand periods.
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Aside from facilitating the integration of thousands of megawatts of wind power, controllable water heaters (and other appliances and equipment that draw electricity 24/7) provide two other benefits:

1. Reliability. Major power lines and generating plants occasionally suffer sudden outages due to fires, ice, wind or equipment failure. Turning down a few million water heaters could quickly shave demand enough to cover the power loss and avoid a major blackout. In fact, the chips discussed above can be made to automatically and instantaneously detect frequency changes in the electricity they use without any operator intervention. The chip reacts to a sudden change from the standard 60 cycles per second by instantly turning the heater on or off to keep the grid stable.

2. Money. Utilities spend a lot of money following the daily peaks and valleys of human activity. Thirty to 40% of their generation capacity sits idle for much of each 24-hour day. Another 5-10% come on only during very extreme weather — the hottest or coldest days. But utilities must cover the capital and maintenance costs of all these resources, no matter how little used.

Controllable water heaters would rarely go on during system peaks and could help utilities respond to system emergencies … at huge cost savings. Utilities would be able to spread demand more evenly throughout the day, increasing power line and substation efficiency and avoiding the costs of some mostly idle generation resources. These actions could lower bills substantially and/or provide savings to fund additional smart grid investment.