What's the best solar energy system for your home, community, business or farm?

Because of all the media attention about solar power, most people think of photovoltaic (PV) solar panels.  People in the clean energy business know about the Chinese' so called"dumping" of low cost PV panels onto the U.S. market.

About how schools and universities are installing PV panels to save on their electric bills, but also to educate tomorrow's future decision makers.  And how the California solar panel maker Solyndra went bankrupt after receiving a $500M grant from the Department of Energy (DOE).  Many of these headline stories even make network TV news, but much is misunderstood.  There are many technologies to create energy form the sun, some to create electricity, some to create heat and some, as hybrids, can do both.  The scale of energy generation ranges from the home water heater to serving 100,000 homes.  Below is a high level outline of the many solar energy forms, starting with hybrid solar power, since is the least understood and publicized.

Hybrid Solar Energy.  By definition, "hybrid energy" includes combinations of clean energy sources such as solar power, wind energy, 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 Solarcapitalizes 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.  Their 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 PV capability (for electricity) and a thermal (hot water) component, on a compact footprint.  Their 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-around farming in cold climates.  Technology "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 are Sunpower (CA) and SunTech (China).  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 surface 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 is 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 onto 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.  Examples are First Solar and Solyndra.

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 100MW, 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.  The 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.

Medium to lower temperature forms of thermal energy creation -- well under 1000 degrees -- are best suited for heating water and are not efficient for converting heat to electricity.   Early iterations of this technology have been around for literally hundreds of years.  Today's applications do not involve the large land use arrays of CSP systems, rather employ on site flat panel solar heat collectors.  Applications include direct heating of residential or commercial air spaces, water heaters, swimming pools and now soil within greenhouses.  These systems are available locally through your telephone book or thru the Solar Energy Society.

Active versus Passive solar energy.

"Active" solar energy includes installing electrical or mechanical devices such as solar panels or thermal energy set ups to create electricity, heat water or space as described above.  These can be added to a home or building after it is already built, but best when incorporated into new construction.   "Passive" solar involves recognizing the sun's radiation properties to either increase the natural heating benefits of the sun or, conversely, to minimize it.  This is best achieved when a structure is being built or window renovations are planned.  The basic idea for colder climates is for windows to be situated to be south-facing to allow the sun's heat into the rooms.  Or in warmer climates to have smaller windows facing south and larger windows facing north.  Here's a good explanation of active and passive solar energy usage.

Admittedly, this is but a top line discussion of the solar energy forms that are out there.  But it does show the innovation, the breadth and perhaps even demonstrates why solar is the fastest growing or the various clean energy forms available.  And, according to recent job growth data, is the fastest growing of any U.S. industry.

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