Cincinnatus BLOG *** Political Commentary - Social Commentary

There are two basic types of solar electricity plants: Solar thermal, also called Concentrating Solar Power (CSP), and Photovoltaic. CSP generates high-temperature heat through the use of various mirror configurations, which is then used to make electricity utilizing traditional heat-conversion technology. Photovoltaic solar power in contrast, converts sunlight directly into electricity.

Concentrating Solar Power

Solar thermal electricity is an attractive renewable energy option in the southwestern United States and other Sunbelt regions. Concentrating Solar Power (CPS) systems can be sized at a capacity for village power (10 kilowatts), or a number of smaller systems can be connected to a larger grid. According to the Solar Energy Industries Association, solar thermal electric systems operating in the U.S. today using parabolic trough design meet the needs of over 350,000 people and displace the equivalent of 2.3 million barrels of oil annually. To put this in perspective, the United States consumes approximately 20.7 million barrels per day of petroleum products, making us the world’s largest oil consumer.

Parabolic trough solar systems that date back to the 80’s track the sun using parabolic curved, trough-shaped reflectors to focus the sun’s energy onto a receiver pipe running at the focal point of the reflector.  Because of their parabolic shape, troughs can focus the sun at 30-60 times its normal intensity on the receiver pipe.  The concentrated energy heats a Heat Transfer Fluid (HTF), flowing through the pipe.  This fluid is then used to generate steam that powers a turbine that drives an electric generator. Some systems are also configured to use thermal storage to provide electricity at night or on cloudy days.

Source: National Renewable Energy Laboratory (NREL)

Although Concentrating Solar Power (CPS) plays a small role in the nation’s energy supply, several factors have caused a resurgence of interest in the sunbelt states, notably the high cost of fossil fuels, environmental concerns, government mandates and incentives, technological advances, and short lead times.

In addition to parabolic trough systems, other CPS technologies include a dish/engine system that uses a mirrored dish to collect and concentrate sunlight onto a receiver. The receiver absorbs the sun’s heat and transfers it to a gas or fluid in an engine. The heat causes the gas or fluid to expand and drive a piston, which is connected to a generator that produces electricity.

Source: National Renewable Energy Laboratory (NREL)

There are also power tower systems that utilize a field of mirrors to concentrate and reflect sunlight to a receiver on the top of a centrally located tower. The receiver absorbs the sun’s heat through molten salt, and the heat is released to generate steam. The steam then powers a conventional steam generator to produce electricity.

Source: National Renewable Energy Laboratory (NREL)

Although Concentrating Solar Power (CSP) technologies are not expected to make a major contribution as an energy option, they are making a comeback after nearly 20 years of indifference. The Arizona Public Service’s 1-megawatt Saguaro solar thermal power plant came on line in December 2005 and the 64-megawatt Nevada Solar One went online in June 2007. Numerous larger-scale projects are in the development stage; e.g. Southern California Edison is developing a 500-megawatt solar power project using Stirling dish technology. Stirling will build a 1-megawatt test facility using 40 of the company’s 37-foot diameter dish assemblies. Assuming the test is successful, a 20,000-dish array will be constructed between January 2009 and December 2012. Part of the renewed interest is related to the relative simplicity of the CSP technologies. They can be built with commodity materials such as glass, steel, and concrete, and standard utility power generation equipment, making it possible to scale-up and rapidly deploy new power plants. This is not the “big solution”, but it could make a significant contribution to future clean energy generation in states like California, Florida, Arizona and New Mexico.

Solar Thermal for Heating

Solar Thermal can also harness the power of the sun to provide solar heat for solar hot water, solar space heating, and solar pool heaters. A solar heating system saves energy, reduces utility costs, and produces clean energy.

Photovoltaic

Photovoltaic (PV) is the term used for solar panels that create electricity directly from the sun without any moving parts.  The most commonly used PV material is highly purified silicon that converts sunlight directly into electricity. When sunlight strikes the material, electrons are dislodged, creating an electrical current that can be captured and harnessed. Photovoltaic cells are often connected together to form PV modules that may be up to several feet long and a few feet wide. Modules, in turn, can be combined and connected to form PV arrays of different sizes and power output.

PV is already a ubiquitous part of our lives powering many small consumer devices such as calculators and wristwatches. More complex systems provide power for satellites, water pumps, appliances as well as traffic signs and parking meters. PV use is expanding rapidly and major US companies are positioning themselves to take advantage of this new opportunity e.g. Tokyo Ohka Kogyo Co., Ltd. (TOK) and IBM (NYSE: IBM) announced that they are collaborating to establish new, low-cost methods for bringing the next generation of solar energy products to market. Intel Corporation announced that they are spinning off key assets of a start-up business effort inside Intel’s New Business Initiatives group to form an independent company called SpectraWatt Inc. SpectraWatt will manufacture and supply photovoltaic cells to solar module makers. In addition to focusing on advanced solar cell technologies, SpectraWatt will concentrate development efforts on improvements in current manufacturing processes and capabilities to reduce the cost of photovoltaic energy generation.

PV is expanding in the following areas:

• PV Systems with Battery Storage: are especially practical in areas where utility power is unavailable or line extension impractical and can be used to power devices such as telephones, televisions and power tools.
• Net Metering: is a policy that allows homeowners to receive the full value of the electricity that their solar system generates. Homeowners with a PV system can offset their electric bill by feeding the excess electricity not needed to power their homes into the utility grid. Under federal law the utilities must purchase any excess electricity these homeowners produce. At the end of each month, if the customer has generated more electricity then they used, the utility credits the net kilowatts produced at the wholesale power rate. But if the customer uses more electricity than the PV system produces, the customer pays the difference. In effect the power grid acts as a battery backup, saving individual customers the expense of purchasing and maintaining a battery system.
• PV Systems with Generators: are used in situations where non-grid power is needed, but power must always be available e.g. rural clinic or communications equipment that must be constantly available. The generator only kicks in when the sun is no longer shining and the battery system has been drained.
• PV in Hybrid Power Systems: In addition to a PV system, engine generators, wind turbines, or small hydro plants can be added to an integrated system to supply the power needs of a small community.
• PV for Utility Power Production: Although the technology may not be sufficiently developed to make a major contribution to power generation, it can be useful to utilities in a variety of ways. Utilities are able to build modular PV facilities more quickly than conventional fossil or nuclear plants, place them where they are most needed in the grid and expand them incrementally as power demand increases. In order to offset the higher costs of PV power generation, several utilities are experimenting with placing systems in locations where they have greater inherent value, e.g. in locations where electricity must be sent long distances over conventional power lines resulting in significant power loss during the journey.

With the advent of the transistor and accompanying semiconductor technology, the efficiency of photovoltaic power has increased dramatically. Photovoltaic power has become more practical.  Commonly available solar panels are 7-17% efficient at converting sunlight into electricity, which is four times greater than only a few years ago.  Newer technologies may raise the efficiency of photovoltaic panels to as high as 30% to 50% or more.

Scientific American reported in August 2008; “The amount of solar photovoltaics harnessing electricity from sunshine in the U.S. will more than double by 2013, thanks to plans to build 800 megawatts (mW) worth in California. The two vast solar farms - covering more than 12 square miles - will be among the largest ever built in the world and dwarf the current U.S. record holder: Nellis Air Force Base in Nevada with 14 mW. In fact, the total amount of solar photovoltaics connected to the grid in the entire U.S. is just 473 mW at present.” When operational in 2013, the two farms could provide 1.65 billion kilowatt hours of electricity per year. Sounds good, but let’s put it in perspective; after devoting 12 square miles to photovoltaic panels this project would contribute four-tenths of 1% of our nation’s energy needs by 2013.

Solar is the ultimate clean source of energy and although research is being conducted by the largest corporations in the world, and major advances will undoubtedly be made, we are not there now.  Any prediction as to when a major breakthrough could be deployed to generate a significant proportion of our energy needs is pure guesswork.

Solar power is also expensive at $.15 to $.30 per kilowatt-hour, as compared to $.04 -$.06 for coal, natural gas, or wind. Technological breakthroughs such as artificial silicon or an inexpensive replacement will be needed to bring the cost of solar into line with traditional power generation. Solar power plants have also been criticized because extensive tracks of land are needed to generate utility scale electricity. The Japanese, for example, are trying to overcome solar’s earthbound limitations by entering into a 20-year project that would place solar panels in space and beam energy back to earth with either a laser or microwave system. In space, without the limitation of the atmosphere, solar irradiance is 5 to 10 times greater than on earth’s surface, so generation is more efficient and can be collected 24 hours a day regardless of the weather.

The limitless power of the sun will make a significant contribution to our clean energy future. But if it is to supply more than 10% of our requirements (including electricity at night and when the weather does not cooperate), research is needed to develop cost-efficient, land-sparing systems that are attached to energy storage facilities.