Southern California Gas company is testing how well the sun can cool buildings.
The Los Angeles-based utility said on Tuesday that it has chosen two solar concentrators to measure how effective they are at cooling. The units will be installed on the roof of its Energy Resource Center (ERC) in Downey, Calif.
Both products--one from Hawaiian start-up Sopogy and another from HelioDynamics in the U.K.--reflect and concentrate incoming sunlight onto a pipe to heat water. That heated water is used in place of gas or electricity to power an industrial absorption chiller, which creates cold air using a heat exchanger and compressor.
(Credit:
Sopogy)
Using the sun for cooling has long been considered an excellent application for solar energy because the air conditioning load corresponds with daylight hours Concentrators can be more efficient and take less space than photovoltaic panels which make electricity, according to Southern California Gas.
Sopogy's MicroCSP is essentially a shrunk-down version of the parabolic troughs used in giant solar power plants. HelioDynamics' concentrators can produce both heat and electricity.
Southern California Gas chose these concentrators because they are small enough to fit on an office building roof and are modular, said Hal Synder, vice president of customer solutions. Each unit is capable of providing enough cool air for three average-size homes. Air conditioning can be half of a commercial building's electricity use.
The utility plans to test these concentrators for two years and will add electricity production to the site in a year.
There are already a handful of companies developing concentrators for cooling. Chromasun, started by one of the founders of concentrating solar company Ausra, has developed a solar collector designed for commercial and industrial customers which can reduce energy bills significantly by cutting peak-time usage.
Meanwhile, there is already a solar cooler in operation. Late last year, famed piano maker Steinway & Sons installed a solar cooling system that uses reflective troughs. Like the SoCal Gas systems, the heat feeds an absorption chiller to provide cool air and dehumidify Steinway's buildings. In the winter, it provides heat.
Skyline Solar has designed a solar concentrator that relies on more sheet metal and less silicon to cut costs.
The Mountain View, Calif.-based start-up on Monday introduced its product, called High Gain Solar (HGS) arrays, and said that it has raised an additional $24.6 million from New Enterprise Associates and other investors. It's one of six companies to get a Department of Energy grant worth $3 million for solar photovoltaics research.
Its arrays, expected to be available later this year, are targeted at commercial customers and utilities looking to generate from about 100 kilowatts to megawatts worth of electricity. The company has a 24-kilowatt demonstration facility at a plant in San Jose, Calif., with the Santa Clara Valley Transportation Authority.
(Credit:
Skyline Solar)
Skyline Solar's concentrator is built around a reflective metal trough that concentrates light onto strips of monocrystalline silicon cells. A tracking system follows the sun over the course of the day so that sunlight bounces onto the cells directly.
By concentrating the light onto these cells, Skyline Solar says it can deliver 10 times more energy per gram of silicon compared with traditional flat solar panels.
Because silicon is an expensive material, there are a number of solar companies using concentrators to squeeze more electricity from solar cells. Skyline Solar CEO Bob MacDonald founded the company after leaving SolFocus, a company that uses more expensive, high-efficiency solar cells and mirrors to concentrate light 500 times.
Skyline Solar's troughs concentrate the light by only a factor of 10 but its arrays use relatively few parts and those parts can be manufactured with existing equipment, such as that for car factories. An air-cooled heat sink is placed behind the solar cells to improve efficiency.
Skyline Solar concentrates light onto strips of monocrystalline silicon cells (bottom) rather than using traditional flat panels.
(Credit: Skyline Solar)The market for midsize solar arrays is growing, Travis Bradford, solar industry analyst at the Prometheus Institute for Sustainable Development, told Technology Review.
Utility giant Pacific Gas & Electric expects to install 500 megawatts worth of solar power in part through midsize solar installations. Other potential customers include industrial facilities with enough land and good sun.
But it's unclear that Skyline Solar's design will be much cheaper on balance because the tracking and mounting system adds costs and the prices for traditional flat solar panels are dropping, Bradford said.
Researchers at the Massachusetts Institute of Technology detailed a technique that can boost solar cell output and turn colored windows into solar panels.
Published in Science magazine on Friday, the researchers have developed a way to use dyes painted on glass to redirect light.
By stacking multiple concentrators, you can optimize plates for different wavelengths. Solar cells will be placed along the edges of the plates, reducing the amount of solar cell material needed, and thus the cost of a panel.
(Credit: MIT)By pushing light to the edges and filtering it, they can concentrate the light and squeeze more electricity from photovoltaic solar cells.
The cells are placed on the edges of the glass, rather than across the flat surface of glass, which would allow panel manufacturers to use less costly solar cell material.
It's a technique that was pursued in the 1970s but abandoned because not enough redirected light made it to the cells on plate edges.
By borrowing laser technology, the MIT researchers said they adequately direct and concentrate light to the point where they can boost solar cell output ten-fold.
The technology, which uses off-the-shelf dyes used in car paints, promises to be cheaper than traditional solar concentrators because it eliminates the need for mirrors, lenses, and trackers, said Marc Baldo, an MIT professor of electrical engineering who led the work.
Participants in the research are starting a company, Covalent Solar, to commercialize and improve the technology. MIT said that they expect to have a product available in about three years.
SolFocus has now raised a total of $63.6 million in series B funding to move into production of its solar power plants.
An extra $11.6 million in funding, announced Tuesday, complements the $52 million in series B funding the company announced in September. Altogether, the company has raised $95 million in venture capital.
SolFocus, which was spun out of Palo Alto Research Center (PARC) is perhaps the most high-profile company to pursue solar concentrators, where mirrors and lenses magnify light in order to squeeze more electricity from very efficient solar cells.
These solar installations--usually ground-mounted machines, are typically geared at utilities or large businesses. Concentrating solar power competes with solar farms of photovoltaic panels and solar thermal technology, which uses reflective troughs or mirrors to heat liquid that turns a turbine.
SolFocus also makes tracking systems that maximize the angle of solar concentrators and solar thermal systems.
As the company completes its funding, there are growing concerns over the valuation of public solar companies and whether a recent wave of solar start-ups can provide the products that utilities demand. Venture capitalists are poised to invest $1 billion in solar-related companies this year.
Pacific Gas & Electric--one of the most aggressive utilities in adopting renewable energy--told the San Francisco Chronicle this week that renewable energy companies "technically aren't able to deliver." Because many of the companies pursuing renewable energy technologies are start-ups and not fully tested, PG&E may not be able to meet its goal of using 20 percent renewable energy by 2010, CEO Peter Darbee said.
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