Making Smart Windows that Are Also Cheap
"Tunable" windows would let people adjust light and heat levels, but so far it's been hard to make them affordable.
Windows that absorb or reflect light and heat at the flick of a switch could help cut heating and cooling bills. A company called Soladigm has developed methods for making these "electrochromic" windows cheaply, making them more viable for homes and office buildings.
Existing electrochromic window designs cost around $100 per square foot. Soladigm has not disclosed how much its windows will cost, but some experts say the method could reduce the cost to around $20 per square foot.
The Milpitas, CA-based company uses a thin-film deposition process that creates conducting layers between two panes of glass for controlling the amount of sunlight and heat that can pass through. A homeowner or office dweller could control how much light or heat a window lets in or absorbs and reflects.
The company's windows contain two transparent conducting oxide films sandwiching an ion storage layer, an electrolyte, and an electrochromic layer -- all between two layers of glass. Applying a low voltage to the conductive oxide kicks the ions out of the storage layer and across the electrolyte to meet with the electrochromic layer. The collision prompts the electrochromic material to absorb or reflect light. It also causes the material to darken, giving the window a tinted look. Reversing the voltage sends the ions back to its storage layer, causing the window to lighten in color and let more light in.
"We did a case study in five cities, and the average savings in commercial buildings are about 25 percent of the heating, ventilation, and air-conditioning energy use annually," says Rao Mulpuri, CEO of Soladigm.
The trick to making electrochromic windows cheaply is the right materials and latest manufacturing method, says Mulpuri. Today's thin-film deposition equipment -- the same used to make flat panel display and thin-film solar panels -- is much better than that used a few decades ago, when the electrochromic window concept emerged.
Soladigm will use a tungsten oxide-based electrochromic layer for its first windows. Tungsten oxide can endure repeated cycling between ion-rich and ion-free stages-which makes it durable, says Delia Milliron, a Lawrence Berkeley National Laboratory (LBNL) researcher in electrochromic materials. However, using tungsten oxide can heat up a window until it's too hot to touch; it also doesn't block infrared light very well, meaning it lets plenty of heat through.
Soladigm has licensed research from LBNL that could solve these problems. The research came from Tom Richardson, a researcher at LBNL's Advanced Energy Technologies Department who found novel alternatives to tungsten oxide. In one, a magnesium-based electrochromic layer reacts with hydrogen ions to reflect light. In another, an alloy of antimony with materials such as copper or silver is used with lithium ions to do the same. The reflective approaches not only prevent heat buildup, but also can precisely control the amount of visible and near-infrared light that the window blocks, Richardson says.
Either approach could better control the amount of heat from near infrared, making it possible to significantly warm up a room in cold days. "There might be time when you want light blocked but you want the near-infrared to get in. In the winter, you want light and the heat to warm up the house, so having the ability to switch both or independently will be ideal," Richardson says.
The ability to manage the amount of light and heat that gets into a room sets electrochromic windows apart from low-emittance, or low-E, windows. Low-E windows have a metal oxide coating that reflects near-infrared light and allows most visible light to pass through. These windows generally cost around $10 per square foot.
Some experts say that installing electrochromic windows could cost considerably more than installing low-E windows for certain types of buildings. "To do a whole facade, you would have to run electricity to each window, and that might be cost-prohibitive," says Aaron Smith, a researcher in the Lighting Research Center of Rensselaer Polytechnic Institute. "It also would be more difficult to install them when retrofitting older buildings."
Applied Materials Moves Solar Expertise to China
The company says its future is in energy products for the Chinese market.
The world's biggest supplier of solar-manufacturing equipment has opened a research and development center in China, and its chief technology officer will relocate from Silicon Valley to that country next month. Applied Materials, founded in 1967 as a semiconductor company, has manufactured in China for 25 years, but is expanding its presence to be closer to its customers and develop products suited to the country's urban population.
"We're doing R&D in China because they're becoming a big market whose needs are different from those in the U.S.," says Mark Pinto, Applied Materials's CTO. Going forward, he says, "energy will become the biggest business for the company," and China, not the U.S., "will be the biggest solar market in the world."
Indeed, the move by Applied Materials is just the latest sign that China is rapidly moving to the forefront in adopting renewable energy technologies. China is no model for addressing climate change -- its greenhouse-gas emissions are expected to nearly double by 2030. The lion's share of demand for photovoltaics comes from Europe, which accounted for 82 percent of the photovoltaics sold in 2008, according to a report by Solarbuzz. China currently makes up less than 1 percent of the demand for photovoltaics, but its demand for photovoltaics is expected to grow; Beijing aims to produce 20,000 megawatts of solar energy by 2020.
Its strategy, says Pinto, is to "help drive down costs through scaling." The company developed equipment for building amorphous-silicon solar cells on thin glass panels the size of a garage door, 5.7 square meters. These sheets can then be sliced into smaller panels or left as they are. Working at this scale saves money; Applied Materials made it work by developing equipment that can coat the huge panels with uniform silicon films just nanometers thick.
To compete in both the U.S. and Chinese markets, says Ken Zweibel, director of the George Washington Solar Institute, the company will need to increase the efficiency of the solar cells that can be made using its equipment. "Amorphous silicon has a relatively low cost, but its efficiency is the lowest of all the thin-film solar cells," says Zweibel. Cells made of cadmium telluride that are sold by U.S. thin-film company First Solar have an efficiency of around 11 percent. The amorphous-silicon solar cells made on Applied Materials's equipment are at just over 8 percent. "The 3 percent difference in efficiency is a 30 percent difference in terms of overall cost," Zweibel notes.
Pinto says research at the Xi'an center will focus on products suited to the way that country's population is concentrated, in cities with tall buildings. "Cities in China don't have very much rooftop" on which to place solar cells, says Pinto. The company plans to develop technologies such as electrochromic windows, which save heating and cooling costs by changing color with the weather. Solar cells embedded in windows might act both as a shade and an energy source. The company is also researching LED lighting and plans to work on thin-film batteries.
U.S. Solar Market to Double in the Next Year
Government incentives and lower solar prices are starting to pay off.
In a few years, the United States is likely to be the world's largest market for solar power, eclipsing Germany, which has taken the lead as a result of strong government incentives in spite of the relative paucity of sunlight in that country. A number of factors could make growth possible in the United States -- especially changes in legislation that give utilities incentives to create large solar farms.
Last year, the U.S. solar industry got off to a slow start, but sales rebounded in the second half of the year, largely because of a drop in the prices of solar panels of up to 40 percent, partly caused by an oversupply due to the recession. Revenues for many solar companies were likely flat, but the megawatts of solar installed in the United States overall grew by 25 to 40 percent last year, says Roger Efird, the chairman of the Solar Energy Industry Association and the managing director of Suntech America, a branch of Suntech Power, the largest maker of crystalline silicon solar panels in the world.
This year, Efird says, solar installations could double, reaching a gigawatt of capacity. "That's a big number," he says. "If you are in the solar business, you were talking watts 15 years ago, you were talking kilowatts 10 years ago, and you have trouble even talking megawatts today."
The growth had several likely causes, including decreasing prices for solar panels and installation costs, as well as increasing state incentives, which can make solar far more attractive. According to Harry Fleming, the CEO of Acro Energy Technologies in Oakdale, CA, these changes mean that the cost of a typical five-kilowatt rooftop solar system has dropped from $22,000 after state incentives are applied ($40,000 without them) to $16,000 in the last 18 months. Prices are expected to fall to $13,000 by the end of the year ($25,000 without incentives). "This is going to make solar a middle-class product," he says.
At the same time, it seems likely that projects funded through the federal stimulus package will get underway this year. The U.S. General Services Administration and the U.S. Department of Defense, for example, are both ready to start solar projects, Efird says. "A big kick for us in 2010 will be these stimulus funds we've been waiting for," he says.
Another key could be solar projects undertaken by utilities. Efird says that a small change in the tax code has allowed utilities to take a tax credit for solar investment. After that, "we began to see, really for the first time, utilities starting to get interested in solar as a way of generating wholesale electricity that they could then resell." His company has done demonstration projects in the past, he says, "but we've never looked at the utility sector and said that's a market in itself." About a third of the new installations next year could come from utilities.
It's unlikely that a climate bill that puts a price on carbon dioxide will pass this year, but other legislation could further help the industry. A jobs bill, for example, might include incentives that were originally included in a climate and energy bill passed in the House last year. These incentives could include a renewable energy standard, which would require utilities across the country to use renewable energy. Just as important could be a national standard for connecting solar installations to the grid. Right now some states don't have laws that allow people to connect rooftop solar panels to the grid and receive credit for the power they generate, and the laws that do exist vary from state to state. A uniform standard could speed sales and installations.
Some experts, however, expect that a large number of the solar projects planned for the next several years will fall through -- perhaps as many as 75 percent -- because of the relative "immaturity" of the industry. Few large projects have been built so far, and so there will likely be large cost overruns.
For many solar companies, regulations, land-permit requirements, and the need for transmission lines have slowed down projects. In some cases, smaller solar projects located close to substations have a better chance than large solar farms that require special new transmission lines, even though the latter could, in theory, be more economical. One thing that could help with this would be designated areas that are preapproved for solar farms, and equipped with transmission lines that would serve a cluster of such farms. "But that would require a degree of strategic thinking that's currently absent," says Jim Barry, the chief executive of the Dublin, Ireland-based NRT, a company that's currently developing large solar projects in the United States.