A solar project consists of several photovoltaic panels that absorb energy from the sun and produce electricity. The electricity travels on power lines and is distributed to homes and businesses at retail rates.
A local community can benefit from utility-scale solar projects because they create construction jobs, send business toward providers of operations and maintenance, and increase tax revenue.
Solar Power Towers
Solar power towers are an advanced form of concentrating solar power (CSP). These plants use a large array of computer-controlled mirrors, called heliostats, to focus sunlight on a receiver at the top of a tower.
Once the sun’s rays are focused, heat-transfer fluid is heated in the receiver and pumped to a steam generator that turns a turbine. Depending on the design, this fluid may be water/steam or molten salt.
Older solar power towers used water as their heat-transfer fluid, but this is not cost-efficient. Newer and more advanced designs utilize molten salts as the heating fluid.
Molten salt is believed to be the key to efficient energy storage, which is important for solar technology. The Planta Solar 10 (PS-10) in Sevilla, Spain, is the first utility-scale solar power tower to store its heat in tanks of molten salts, which gives the plant a storage time of up to an hour after the sun goes down.
Solar Thermal Power Plants
Solar thermal power plants collect and concentrate the sun’s energy using mirrors. The concentrated heat is used to generate steam, which drives a turbine that produces electrical power.
The heat can be stored for use in cloudy weather or at night when it is not sunny enough to produce electricity. This system can be very useful as a backup source of power for fossil fuels.
A solar concentrating plant consists of a field of mirrors aligned in a north-south direction to focus sunlight on a receiver tube located at the center of a parabolic trough. Alternatively, a Fresnel reflector can be used to achieve the same effect.
Concentrating solar power (CSP) is a promising renewable energy technology for low-cost electric power production and industrial processing that can operate independent of daylight hours. The Department of Energy has released a road map that will advance this new technology. It also awarded $24 million in research grants to 10 teams that are focused on industrial uses of CSP.
Solar Photovoltaic Power Plants
Solar photovoltaic power plants, commonly known as PV, use large areas of photovoltaic cells to convert sunlight into usable electricity. They consist of solar panels and an inverter which converts direct current (DC) into alternating current (AC).
The energy in the photons is converted into a flow of electrons by the cell’s semiconductor material. Free electrons are generated when photons collide with the material, dislodging them from their atoms and generating direct current.
In most cases, the cells are made of crystalline polysilicon (SiC) or monocrystalline silicon. Crystalline versions are generally more efficient, but they are also more expensive than their multi-crystalline counterparts.
The efficiency of solar panels degrades gradually, especially in the first year, but it slows down to a steady rate after 25 years or so. The degradation rates vary from model to model.
Solar Water Heating
Solar water heating is a good choice for homeowners who want to reduce their utility bills and cut back on their carbon footprint. These systems require careful planning and proper installation to maximize their benefits while avoiding disadvantages.
To determine if a solar project is a good fit for your home or office, use the Federal Renewable Energy Screening Assistant to assess the economic feasibility of various types of renewable energy projects, including solar water heaters. The NREL site also offers a number of useful maps and tables of solar resource availability throughout the United States and around the world.
When shopping for a solar hot water system, look for one that’s certified by the Solar Rating and Certification Corporation (SRCC). This independent organization provides performance ratings and efficiency equations for its products. These are free to the public and can be used for comparing solar collector efficiency between different manufacturers.