Tuesday, April 15, 2008

New Ways to Harness the Sun and the Wind

The New York Times
April 15, 2008

Technology Smooths the Way for Home Wind-Power Turbines
by John Casey

Wind turbines, once used primarily for farms and rural houses far from electrical service, are becoming more common in heavily populated residential areas as homeowners are attracted to ease of use, financial incentives and low environmental effects.

No one tracks the number of small-scale residential wind turbines — windmills that run turbines to produce electricity — in the United States. Experts on renewable energy say a convergence of factors, political, technical and ecological, has caused a surge in the use of residential wind turbines, especially in the Northeast and California.

“Back in the early days, off-grid electrical generation was pursued mostly by hippies and rednecks, usually in isolated, rural areas,” said Joe Schwartz, editor of Home Power magazine. “Now, it’s a lot more mainstream.”

“The big shift happened in the last three years,” Mr. Schwartz said, because of technology that makes it possible to feed electricity back to the grid, the commercial power system fed by large utilities. “These new systems use the utility for back up power, removing the need for big, expensive battery backup systems.”

Some of the “plug and play” systems can be plugged directly into a circuit in the home electrical panel. Homeowners can use energy from the wind turbine or the power company without taking action.

Federal wind energy incentives introduced after the oil crisis of the late 1970s helped drive large-scale turbine use. But the federal government does not currently provide a tax credit for residential-scale wind energy, as it does for residential solar applications, according to the American Wind Energy Association, a trade group for wind-power developers and equipment manufacturers.

A number of states, however, have incentive programs. In New York, “we have incentive levels for different installations, but a homeowner could expect to get approximately $4,000 per electric meter for a wind turbine,” said Paul Tonko, president of the New York State Renewable Energy Development Authority, which administers the state’s renewable energy incentives. “That would cover about 30 to 40 percent of the project cost.”

“Certainly, the technology has improved, and the cost per project is coming down,” Mr. Tonko said. “Turbines for farms and residential applications are seeing much more activity.”

States have also enacted so-called net metering laws that require utilities to buy excess power made by a residential turbine at retail rather than wholesale prices. “Many of the barriers to residential turbines have been lowered, but net-metering removes what may be the biggest barrier,” said Jim Green, a senior project leader at the Wind Technology Center, part of the National Renewable Energy Laboratory in Golden, Colo.

“Along with state incentives, net metering entirely changes the economics of residential wind generation,” Mr. Green said.

Ecological concerns, more than cost savings may drive many new residential turbine installations. “People want to reduce their carbon footprints,” Mr. Tonko said. “They’re concerned about climate change and they want to reduce our reliance of foreign sources of fuels.”

Mr. Schwartz, the editor, said that even with the economic benefits, it can take 20 years to pay back the installation cost.

“This isn’t about people putting turbines in to lower their electric bills as much as it is about people voting with their dollars to help the environment in some small way,” he said.

Despite growing interest, some hurdles will not change. Whether a residential turbine saves a money or just eases ecological guilt depends largely on the wind . The wind energy available in any given location is called the “wind resource.”

Even if the wind is strong, zoning and aesthetics can pose problems. “Turbines work in rural areas with strong wind,” Mr. Schwartz said. “But in urban and suburban areas, neighbors are never happy to see a 60- to 120-foot tower going up across the street.”

New Ways to Store Solar Energy for Nighttime and Cloudy Days
by Matthew L. Wald

Solar power, the holy grail of renewable energy, has always faced the problem of how to store the energy captured from the sun’s rays so that demand for electricity can be met at night or whenever the sun is not shining.

The difficulty is that electricity is hard to store. Batteries are not up to efficiently storing energy on a large scale. A different approach being tried by the solar power industry could eliminate the problem.

The idea is to capture the sun’s heat. Heat, unlike electric current, is something that industry knows how to store cost-effectively. For example, a coffee thermos and a laptop computer’s battery store about the same amount of energy, said John S. O’Donnell, executive vice president of a company in the solar thermal business, Ausra. The thermos costs about $5 and the laptop battery $150, he said, and “that’s why solar thermal is going to be the dominant form.”

Solar thermal systems are built to gather heat from the sun, boil water into steam, spin a turbine and make power, as existing solar thermal power plants do — but not immediately. The heat would be stored for hours or even days, like water behind a dam.

A plant that could store its output could pick the time to sell the production based on expected price, as wheat farmers and cattle ranchers do. Ausra, of Palo Alto, Calif., is making components for plants to which thermal storage could be added, if the cost were justified by higher prices after sunset or for production that could be realistically promised even if the weather forecast was iffy. Ausra uses Fresnel lenses, which have a short focal length but focus light intensely, to heat miles of black-painted pipe with a fluid inside.

A competitor a step behind in signing contracts, but with major corporate backing, plans a slightly different technique in which adding storage seems almost trivial. It is a “power tower,” a little bit like a water tank on stilts surrounded by hundreds of mirrors that tilt on two axes, one to follow the sun across the sky in the course of the day and the other in the course of the year. In the tower and in a tank below are tens of thousands of gallons of molten salt that can be heated to very high temperatures and not reach high pressure.

“You take the energy the sun is putting into the earth that day, store it and capture it, put it into the reservoir, and use it on demand,” said Terry Murphy, president and chief executive of SolarReserve, a company backed in part by United Technologies, the Hartford conglomerate.

Power plants are typically designed with a heat production system matched to their electric generators. Mr. Murphy sees no reason why his should. His design is for a power tower that can supply 540 megawatts of heat. At the high temperatures it could achieve, that would produce 250 megawatts of electricity, enough to run a fair-size city.

It might make more sense to produce a smaller quantity and run well into the evening or around the clock or for several days when it is cloudy, he said.

At Black & Veatch, a builder of power plants, Larry Stoddard, the manager of renewable energy consulting, said that with a molten salt design, “your turbine is totally buffered from the vagaries of the sun.” By contrast, “if I’ve got a 50 megawatt photovoltaic plant, covering 300 acres or so, and a large cloud comes over, I lose 50 megawatts in something like 100 to 120 seconds,” he said, adding, “That strikes fear into the hearts of utility dispatchers.”

Thermal storage using molten salt can work in a system like Ausra’s, with miles of piping, but if the salt is spread out through a serpentine pipe, rather than held in a heavily insulated tank, it has to be kept warm at night so it does not solidify, among other complications.

A tower design could also allow for operation at higher latitudes or places with less sun. Designers could simply put in bigger fields of mirrors, proponents say. A small start-up, eSolar, is pursuing that design, backed by Google, which has announced a program to try to make renewable electricity for less than the price of coal-fired power.

Mr. Murphy helped build a power tower at a plant in Barstow, Calif., sponsored by the Energy Department in the late ’90s. It ran well, he said, but natural gas, a competing fuel, collapsed in price, and the state had few requirements for renewable power.

“There were not renewable portfolio standards,” Mr. Murphy said. “Nobody cared about global warming, and we weren’t killing people in Iraq.”

Copyright 2008 The New York Times Company


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