Solar energy, quite simply, is energy that comes from the sun. (Simple.) But there are now many types of solar energy technology focused on making use of that energy and turning it into usable electricity or heat (or both).

The scale of energy generation ranges from the home water heater to serving 100,000+ homes. Below is an outline of the many solar energy forms, starting with hybrid solar power, since it is the least understood and publicized.

By definition, “hybrid energy” includes combinations of clean energy sources such as solar power, wind energy, or geothermal heat pumps, combined with engines or generators. Many in operation are do-it-yourself projects for off-grid use. Sunwize (CA) combines PV solar power and diesel engines, while N. Arizona Wind & Sun incorporates both solar and wind sources. Cogenra Solar capitalizes on the inefficiency of PV solar panels (ranging 15-20%) and captures the wasted heat thrown off to heat water, resulting in 4-5 times the amount of total energy versus PV panel systems alone. Its best “cogeneration” customers are industries or institutions where significant hot water is needed.

Another hybrid solar energy company is SunScience, whose Energy Management System integrates both a concentrated photovoltaic (PV) capability (for electricity) and a thermal component (for hot water), on a compact footprint. Its systems architecture incorporates data from a network of sensors that measures temperature, humidity, and other environmental elements. Proprietary software monitors—and controls—the elements of energy output, storage and environmental elements for total systems management. SunScience’s first application is “controlled-environment agriculture” within greenhouses, to achieve year-round farming in cold climates. Technological “proof of concept” was achieved at a formal “harvest” event late January.

Photovoltaic (PV) panels. This is what most people think of to lower their electricity bills or supply clean power to communities. Examples of large solar PV companies are Sunpower (CA) and SunTech (China). Glenn wrote a post in September on how PV solar panels work, and Wikipedia has much more about this decades old technology, but essentially PV panels are made of silicon semiconductors within solar cells that convert sunlight (photons) to electricity (electrons). Scientists at national labs are experimenting with organic materials and “quantum dots” to achieve this process, but most PV panels are still being made with crystalline (or wafer) silicon, with manufacturing now dominated by China. Cost per watt is falling under $1.00, but efficiency is still only 20+%, resulting in large land areas needed for significant electricity output.  PV roof panels are the predominant technology for home use, whereas huge multi-acre arrays of PV panels are required for utility-scale projects, mostly in remote locations.

Thin-Film Photovoltaic. Once touted as the next generation of PV because of a) lighter weight, b) less of the expensive silicon material needed, and c) other forms of photovoltaic material (amorphous silicon) can be used. The result is a lighter, thinner product with a greater variety of applications, such as its own rooftop material, on top of shingles, or even on windows. But the dramatic price reduction of traditional PV panels out of China slowed market acceptance of thin-film PV. Other disadvantages include higher manufacturing costs, lower efficiency, and greater corresponding space needed for energy equivalency. The top thin-film company in the world, in terms of market share, is First Solar.

Concentrated Photovoltaic (CPV). In a broad sense, this newer form of electricity production competes directly with utility-scale PV and CSP (described below) solar arrays. The CPV advantage over these other systems involves a smaller footprint because the solar panels are made of multi-junction solar cells with concentrating lenses, rather than flat silicon cells. The result is increased efficiency anywhere from 2-3 times greater than traditional PV panels, ranging upwards of 43%.  Therefore, corresponding less land space is required. Disadvantages include greater complexity of cell manufacture and price per kilowatt hour. Current thinking is that in order to be competitive, CPV systems need to be larger, approaching 100 MW, and located in high-DNI (direct normal irradiance) areas such as the southwest U. S., Mexico, Chile, Mediterranean countries, etc. But now, with PV panels from China becoming dramatically less expensive, economic challenges for CPV only increase. Some successful companies include Amonix and Semprius.

Solar thermal energy. Most thermal energy news is about Concentrated Solar Power (CSP) because of the billions of dollars involved and the tens of thousands of homes served with electricity, from one project. America’s first and the world’s largest CSP project is being completed near Tonapah in eastern Nevada. Technically, this highly efficient thermal energy system creates electricity with huge arrays of mirrors (flat, parabolic or troughs) that track and reflect sunlight onto a solar tower that heats fluid to over 1000 degrees F, creating steam that turns a generator, in turn creating electricity. SolarReserve’s Crescent Dunes project of 10,000 mirrors has the capacity to generate 110 megawatts and will serve 75,000 homes. And due to an accompanying molten salt storage system, electricity can be delivered 24/7. Another example company is Brightsource Energy (CA) and here’s a video from the Dept of Energy on the technology.