by Noah Kaye
As conventional fuel prices continue to explore new and uncomfortable outerbound limits, public interest in renewable energy has soared and is stronger today than at any point since the Carter years. By renewable, I mean a resource that continually replenishes itself like wind, solar, or biomass. Although that definition doesn’t consider nuclear a renewable resource, there is one nuclear power plant that won’t come up for relicensing in several billion years, and it’s conveniently located far away from your home – ninety-three million miles away.
So, why don’t we meet all of our energy needs by directly using energy from the sun? How much solar power do we use? Does it even work? These are all questions I get asked over dinner, and when I stop chewing, I am happy to share useful information about the technology, its economics, and the outlook for the industry.
How do you “use” solar energy, anyway?
Aside from tanning? The fastest-growing solar energy application is photovoltaic solar cells (PVs), a US-developed technology that converts sunlight directly to electricity via an electronic process that occurs naturally in certain types of material. Electrons in certain types of crystals are freed by solar energy and can be induced to travel through an electrical circuit, powering any type of electronic device or load. Crystalline silicon (c-Si) is the leading commercial material for photovoltaic cells (see diagram below); although c-Si cells have been in existence since 1954, new innovations continue to be developed. Another subset of PVs are thin film photovoltaic cells, which use layers of semiconductor materials only a few micrometers thick, attached to an inexpensive backing such as glass, flexible plastic, or stainless steel. Semiconductor materials for use in thin films include amorphous silicon (a-Si), copper indium diselenide (CIS), and cadmium telluride (CdTe). PV devices can be used to power small devices (i.e. road signs, calculators or phone call boxes) as well as homes, large stores and businesses.
For the average U.S homeowner, the most convenient arrangement is to connect your PV system to the electricity grid. This type of system requires no energy storage equipment. From an economic viewpoint, this tends to be an optimum configuration because the owner utilizes all the electricity during the day and any surplus is exported to the grid. In most U.S. states, your utility will credit the daytime surplus against your electric bill, and your meter will actually spin backwards as the PV system feeds excess electricity into the grid. (This process is called net metering.) Meanwhile, the cost of storage to meet night-time needs is avoided, because the owner simply draws on the grid in the usual way. Also, with access to the grid, the system does not need to be sized to meet peak electricity loads. The crucial issue is the technical aspects of tying into the electricity grid; inverters must be used to change the electric current from direct to alternating current, and meet other requirements of the utilities.
For customers that cannot connect their system to the grid but require the guarantee of a certain power output at any time of the day or night, either some kind of storage device is necessary or the PV system should be combined with another energy supply (e.g. diesel. Most off-grid systems use batteries to store power during periods of low or no sunlight. Rechargeable batteries are the most effective storage mechanism available, though there is still an efficiency loss due to the electrochemical conversion process of the battery.
The other consumer technology is solar thermal heating, which gathers thermal energy to heat the water in your hot water tank, radiant heating system, or pool system. Solar heating devices directly absorb the sun’s radiation with specially-coated absorbers – normally made of copper or aluminum, which are good conductors of heat — to heat air or water for use in a building. These systems can be either “open loop,” in which the water to be heated flows directly through the rooftop collector, or “closed loop,” in which the collector is filled with an antifreeze solution that passes through a heat exchanger mounted in or around your normal water heater. Closed loop systems can be used anywhere in the U.S., even in freezing conditions, while open loop devices must be drained during freezing conditions. During the day, with good insulation, your water can be heated entirely by the sun! In any weather or temperature, the heating system can back up your existing heater, reducing overall energy costs. The comparatively lower temperature increase required for a swimming pool enables the use of simple, lower-cost open loop designs that can keep a pool open and usable for many more weeks in any given year, without the considerable expense and maintenance headaches associated with natural gas usage. 
How is solar power growing? Is solar power substantial enough for our energy dependent future?
Even the most fervent solar energy supporters would concede that solar power has a long way to go before it plays a significant role in our energy mix. Today, solar represents about 6/100th of 1 percent of the total energy consumed in the United States – enough to power about 300,000 homes.
However, based on current growth rates and technology trends, the global PV industry will achieve $10 billion in sales in 2005. Worldwide, PV has experienced robust growth at 35% annually for the last five years, driven mainly by subsidized markets in Japan, Germany, and California. In the last few years, some of the world’s largest electronics and energy companies have entered into the PV industry, including, GE, Sharp, Sanyo, Shell, BP, and Kyocera. As aesthetic considerations are quite important for most property owners, these consumer-savvy companies now offer products that better integrate into the home.
The global water heating industry, meanwhile, is worth $5 billion and has a generating capacity of almost 70 gigawatts. Israel, for example, derives thousands of megawatt-hours of energy from rooftop solar water heaters each year  and over 200,000 pools are heated by solar in the U.S. alone. 
Would solar power be an economical choice for my home or business?
The answer depends largely on where you live. While the cost of PV cells has dropped by 95% since the 1970s, the installation costs are still too high in most locations; a typical suburban home requires a 2.5 to 3-kilowatt system, which costs $19,000 to $22,500 installed . But in recent years, many US states have expanded tax breaks and rebates for businesses and homeowners who purchase PV systems – making solar energy more affordable. New Jersey, for example, offers a generous rebate covering two-thirds of the capital cost upfront and owners receive regular payments for producing clean electricity. The Jersey home buyer can expect to recoup the balance in four or five years and manufacturers generally warranty their systems for at least 20 years of production.
Most solar thermal systems cost between $2,000 and $4,500. Although this is usually more than the cost of a conventional gas or electric system, today’s solar heating systems are cost competitive when you consider your total energy costs over the entire life of the system. You will be earning an annual 6% to 25% tax-free rate-of-return on your investment, depending on how much hot water you use and how much energy you save. Investing in a solar thermal system could also increase the resale value of your home. 
Making a choice
Philosophically, I find “going solar” appealing because it affords energy consumers a choice. If you are tired of up-or-down fluctuations in your monthly energy bills (mostly up, these days), choosing solar enables you to do something about your personal energy future: take control. You can stabilize in your electric bills until 2030, enjoying a degree of protection from the threat of interruption, shortage, or price swings. And for the environmentally conscious homeowner or businessperson, solar energy has attractive qualities: pollution-free, quiet, and easy to put on your roof.
Bottom line: if the economics of investing in solar make sense for your situation, you can choose to put that nuclear power plant – conveniently sited – to work for you.
Noah Kaye works in policy and communications for the Solar Energy Industries Association (SEIA). SEIA is the national trade association of the solar industry, representing all solar technologies and more than 20,000 employees in all sectors from manufacturing to installation.
 “Solar Photovoltaics,” U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy
 “Solar Hot Water and Space Heating & Cooling,” U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy
 “The Power of the Sun,” South Florida Sun-Sentinel, July 3, 2005.
 “Solar Power Heats Up,” Wall Street Journal, June 2, 2005.
 “Solar Energy Types,” Solar Energy Industries Association
 “Worldwide capacity of solar thermal energy greatly underestimated,” press release, European Solar Thermal Industry Federation, November 10, 2004.
 “Using Solar Energy to Heat Swimming Pools,” Florida Solar Energy Research and Education Foundation, 2001.
 “Solar Power Heats Up,” Wall Street Journal, June 2, 2005.
 “Heat Your Water with the Sun,” U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, December 2003.
Originally posted in “On Eagles’ Wings” August 3rd 2005