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Unbridled Energy: Predicting Volatile Wind, Sun

Utilities Ramp Up Focus on Forecasting When Renewable Fuel Is at a Peak to Avoid Squandering Power That Still Can't Be Stored

By JEFFREY BALL

For more than a century, producing power has been a matter of flipping a switch. Need more electricity? Fire up some fuel. Need less? Dial the flame back down.

Things won't be that easy in a world that gets much of its energy from renewable sources, which come and go at nature's whim. Wind tends to blow hardest at night -- a problem, since people use electricity mostly during the day. Sunshine can lose its intensity in seconds if eclipsed by a cloud -- inconvenient for people who like their air conditioners to run steadily on summer days.

To harness renewable energy more reliably, some companies are experimenting with ways to story energy when the output is high and then distribute it when output is low. WSJ's Jeff Ball reports on the efforts to build a better battery.

Many states and countries are pledging to produce 20% or more of their electricity from renewable sources within about a decade. That will be a major stretch. The recession has severely crimped renewable-energy investment. Proposals to turn over large swaths of desert and coastline to renewable-energy generation are encountering angry opposition. And the drop in fossil-fuel prices has removed much of the public appetite for a big renewable-energy bid. Yet those very pressures are pushing renewable-energy proponents to pursue their goal as efficiently as possible. And so the search for ways to accommodate the vicissitudes of wind and sun continues to shape up as one of today's great technological quests.

A convenient solution would be to overcome wind and sun's intermittence by storing the energy and then dispensing it later, on windless or overcast days. But storage technology is still embryonic.

So the power industry is having to change the way it operates. To adapt its fossil-fuel-dependent infrastructure to renewable energy's ebbs and flows, it is trying to forecast them better. Knowing how nature is likely to behave will help the industry better balance different sources of renewable energy, scientists and utility executives say. The goal: maximizing wind, sun and other natural sources when each is at its peak.

Currently, every wind farm and solar installation has to be backed up by a nearly equivalent amount of conventional fuel to keep the power grid running. That raises costs.

"We're putting renewables into a system that wasn't designed for renewables," says Paul Denholm, an analyst for the federal government's National Renewable Energy Laboratory, in Golden, Colo.

Wind power is the fastest-growing renewable source of electricity. Buoyed by government mandates and subsidies, wind farms accounted for more than half of all net electricity-generating capacity added in the U.S. in 2008, according to the Department of Energy.

But capacity to produce is not actual production. Largely due to wind's unpredictability, the thousands of wind turbines installed across the country collectively produced only 1.3% of actual U.S. electricity in 2008, the department's figures show.

The Bonneville Power Administration, a government-owned utility based in Portland, Ore., taps one of the biggest collections of wind farms in the country. Between January and August, average wind-power production accounted for 12% of average electricity consumption in Bonneville's service area.

From hour to hour, though, wind power swings wildly depending on how things blow at the Columbia River Gorge, where most of the wind turbines in Bonneville's service area are located.

This Tuesday was typically erratic. At 1 a.m., wind farms in the Bonneville service area were cranking out about 1,550 megawatts of power. By 7 a.m., that fell to about 800 megawatts, just as people were waking up and turning on their lights and toasters. That night, once most people were asleep, the wind picked up again. By 11:45 p.m., wind power topped 2,000 megawatts.

Most of the electricity in Bonneville's service area comes from hydroelectric power. To compensate for the volatility of wind, Bonneville tweaks the amount of water it lets through the dams. But that doesn't work for the most extreme shifts in wind. Sometimes, when the wind is blowing hard, Bonneville releases extra water over the tops of dams without using it to generate electricity. Otherwise, electrical wires might get overloaded. And when the wind is so strong that Bonneville can't ditch enough water, the utility orders wind turbines shut off.

"Everything changes with wind," says Bart McManus, a wind expert at Bonneville.

Sudden doldrums can be as troublesome as sudden gusts. That was the problem on Feb. 26, 2008, in Texas, which produces more wind power than any other state.

At 3 p.m. that afternoon, Texas's wind farms, concentrated in the western part of the state, were throwing off about 2,000 megawatts of electricity, enough to serve about one million households. Then a cold front blew in. By 6:30 p.m. -- when electricity demand typically peaks -- wind production in Texas had cratered to about 360 megawatts.

Exacerbating matters, Texans began turning up their heat -- much of which, in rural parts of the state, comes from electricity.

The operator of Texas's electrical grid, the Electric Reliability Council of Texas, known as Ercot, scrambled. It cut off power to various industrial customers that, in exchange for payment, had agreed to let Ercot pull their plugs in emergencies.

To avert situations like these, Ercot has hired a company to provide, every hour, a forecast of how the wind will blow at every wind project on the Ercot grid. It requires wind-power producers to install gauges that feed into those forecasts.

The forecasts look not just at temperature, but also at wind speed and direction at the height of wind turbines, an altitude that until now hasn't attracted much interest.

If there were a viable way to store large amounts of renewable energy, Ercot might have been able to tap it on that February afternoon. Investors and the government are backing storage development. One hope is a better battery. Other ideas include systems that would store water in uphill sites or compressing air underground, for later release when electricity is needed.

So far, these are largely experimental. Making renewable energy big, many studies suggest, would require a combination of approaches: investment in high-voltage transmission wires to carry renewable electricity from remote areas to cities; policies to encourage energy efficiency; and coordinated construction of renewable facilities so that one form of energy can fill in when others are dormant. In many places, wind is calmest at midday, when solar power is most available.

For now, better renewable-energy forecasting is important. Today's forecasts remain frustratingly inexact. Just after midnight on Christmas morning, 2007, an unexpected wind surge hit in Colorado, a state with a lot of wind turbines. It sent power production soaring on the system operated by Xcel Energy, a utility that is trying to improve its wind forecasts.

"We were walloped," says Tom Imbler, vice president of commercial operations for Minneapolis-based Xcel. To compensate, Xcel scrambled to dial down some of its fossil-fuel power plants. Those plants "were never designed to ramp up and ramp down at the level we're asking them to" in the age of renewable energy, he says. "We're learning as we go."