Solar energy uses radiation from the sun for heating or electricity generation. “Passive” solar heating utilizes building design and construction to minimize the use of heating fuel. Passive solar design employs windows, thermal mass, and proper insulation to enable a building itself to function as a solar collector. For example, by orienting windows to the south, the sun’s energy is transferred into the house through natural processes of conduction, convection, and radiation. “Active” solar heating systems use pumps or fans to circulate heat (water or air) to a point of use, such as a domestic hot water tank. Solar water heaters use the sun to heat either water or a heat-transfer fluid in the collector. Heated water is then held in the storage tank ready for use, with a conventional system providing additional heating as necessary. Indirect-circulation systems are the best type of water heating system for Alaska. They work by pumping an intermediary heat-transfer fluid through the solar collectors, which then circulates through a heat exchanger and warms the potable hot water being held in a tank. In warmer climates, the water is pumped directly through the solar collectors without an intermediary fluid. Despite short winter days, solar water heaters can be used about 9 months out of the year in Alaska, making them one of the most practical applications of solar energy for domestic use. Photovoltaic (PV), or solar-electric panels, are used to generate electricity from the sun. They are commonly used to power homes or communities that are “off the grid”, or not connected to an electric utility’s power grid. Another emerging technology in solar electricity generation is concentrated solar power, which uses mirrors to concentrate sunlight onto receivers that collect the solar energy and heat a thermal oil. That thermal energy is then used to produce electricity via a heat exchanger that vaporizes water to drive a steam turbine. The 64 MW Nevada Solar One that went into operation in 2007 uses concentrated solar power to generate electricity at $0.15 – $0.17 per kWh. While this rate is more expensive than fossil-fuel derived power in the area, long-term contracts help to reduce rates over time while providing clean energy to America’s southwest.
Solar energy in Alaska
Although Alaska’s northern location presents the challenge of minimal solar energy during the long winter when energy demand is greatest, solar energy fulfills an important role in space heating and off-grid power generation. A $600,000 grant from the Alaska Energy Authority will allow the Alaska Village Electric Cooperative to assess performance of utility-scale PV systems in villages. The proposed PV-diesel hybrid systems would provide solar-powered energy for much of the summer and some days during the spring, fall, and winter, with a diesel generator as backup to provide a stable energy supply. The largest amount of solar-electric generation in Alaska comes from the Golden Valley Electric Association’s Sustainable Natural Alternatives Program (SNAP). Members of the electrical coop install their own renewable energy producing systems, the vast majority of which are solar. Non-producing members can choose to donate to an escrow account to support such renewable energy development. The donations are used to pay the producers of the renewable energy. SNAP was launched in 2005 and now has 27 producers, with solar panel systems ranging from about 700 watts to 15 kW. In 2008, 29 solar producers and one solar-wind hybrid producer had a total solar capacity of 111kW and produced 77,500 kWh of solar electricity. As of June 2009, Golden Valley Electric Association has 574 customers, or about 1% of their members, participating in the SNAP program and hopes to raise that number to 3%.