Clean Power Traditional photovoltaic panels

Published on March 1st, 2012 | by David L Roberts


What’s the Best Solar Technology for Your Home, Community, Business or Farm?

March 1st, 2012 by  

Because of all the media attention about solar power, most people think of photovoltaic (PV) solar panels. People in or on the fringe of the clean energy business might 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 about how the California solar panel maker Solyndra went bankrupt after receiving a $500 million grant from the Department of Energy (DOE). Many of these headline stories even make network TV news, but much is misunderstood.

What is solar energy? What are the differences in different types of energy technology in existence today?

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.

Hybrid Solar Energy

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.

SunScience hybrid solar Energy Managment System

SunScience hybrid solar Energy Management System

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

Traditional photovoltaic panels

Traditional photovoltaic panels

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 PV panels

Concentrated PV panels

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)

Concentrated (thermal) Solar Power

Concentrated (thermal) Solar Power

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:

Solar thermal panels

Solar thermal panels

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. Ancient iterations of this technology have been around for thousands of years (roman baths in Ephesus, Turkey). Today’s applications do not involve the large land use arrays of CSP systems, but 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. Many 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 heat space, as described above. These can be added to a home or building after it is already built, but are 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 them. 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 south-facing to allow the sun’s heat into the rooms. Or, in warmer climates, to have smaller windows facing south and larger windows north-facing. Here’s a good explanation of active and passive solar energy usage.

Admittedly, this is but a simplistic 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 of 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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About the Author

is a marketing consultant to renewable energy startups.

  • Wink

    Question: We on a lake (30 feet above water level) w/ lots of shade. Southern exposure (150 feet from house) calculates 95% access to the sun. Can photovoltaic panels be mounted on private property butting up to water?

    • Bob_Wallace

      You’d want to check the zoning/permitting issues. You may not be able to install close to the lake due to some regulation. I recall someone having problems getting permission to mount panels over his dock. Don’t recall the details.

      150′ from panels to house is a long way. Shipping 12/24/48 volt electricity would take some large (expensive) wire to avoid too much resistance loss. You’d probably want to either put in a higher voltage DC system or put your inverter near the panels and run 120 vac (better 240 vac) to the house.

      Assuming the water is south (south-ish) of your panels, that could be a good thing. You’d have extra sunlight reflected off the water, increasing your output.

  • opalstey

    if you sell solar power to the grid do they still use petroleum to distribute electricity to their customers

    • Bob_Wallace

      Almost no petroleum is used to generate electricity in the US. Some countries/places, especially islands, rely on diesel generators for a good portion of their electricity.

      In the US diesel is used in Hawaii and remote villages. And some for emergency backup.

  • ahmed said


  • omar

    i want to ask a question, what happened if its raining or its cloudy, does the solar system save energy for that time?

    • Bob_Wallace


      Most people are going to be ‘on the grid’. Any extra power they generate when the Sun is shining gets fed into the common electrical grid and used by someone else.

      Then when the Sun is not shining they pull electricity from the grid just like others. Generally solar owners get credit for the electricity they send to the grid and use the credit for power they use at other times. People size their systems so that they produce during the sunny hours as much as they use on a 24/365 basis.

      This works great for everyone (except coal and nuclear plant owners). When the Sun is shining is generally when demand for electricity is the highest (lots of AirCon) and solar feeding in from rooftops reduces the need for the utility to purchase expensive “peak” power. Then utilities get to pay back with cheap “off-peak” power.

      Other people (like me) are “off the grid”. We run our personal free-standing power companies, storing extra power in batteries for the dark hours and generally resorting to a generator if there are a number of cloudy days in a row.

      Off the grid is more expensive. Batteries are sort of pricey and have to be replaced every few years, but if you live some distance from the nearest power line it can be cheaper to set up your own system.

      Depending on the amount of cloud cover you do get some power from solar panels. I’ve seen people claim 30%, but I find that hard to believe. Perhaps with a very thin cloud cover, but my panels give me very little power in heavy cloud conditions.

  • Dave Roberts

    Many U.S. solar manufacturers, especially German Solar Power (w/plant in Oregon), are upset over Chinese PV panel pricing. Are protective tarrifs called for or is it, in the end, good for the market, despite the increasing number of bankruptcies?

  • Stan

    I LOVE the CPS! Most any geo area qualified land owner can put up a tower and make a 1MW generation system.
    But remember, we don’t poduce at night, so 1/2MW… take 500 homes for example, and if you’re doing $.18 per KWH to the grid…deduct the tax incentives from your capitalization/ ammortization….and ya got something.But, unlike PVs, these are mirrors…..put a dusting of…well…dust on a mirror, and use it to reflect sunlight…not too bright, huh? Use your hand held if you want an actual rating. So, there is going to be a labor expense to clean the panels withing a time period, AND, if weather conditions are facilitating dust… the time of need…..but 100 panels can be cleaned by one person in one day. Let’s call it an expense of about 10 to 20 homes per month in revenue (about $4000)
    Also, the CPV’s main advantage, is on homes with too small of a usuable area to allow for enough standard panels. So, if they’re twice the price….who cares?

    • Dave Roberts

      Hey Stan, Not instead of, but additional advantages of CPV, and the related smaller required footprint, is portability. Consider a residential system on wheels on the ground that can be moved — to your next home. Or consider military or disaster applications where urgent trucking or helicopter transit of pre-assembled CPV units is called for. The mind boggles 🙂

  • I found hybrid solar panels are best working solar panels for office. It also works well for home. Thanks

  • Mlandersmd

    CPV systems do not require less land, despite their higher efficiency. The need to avoid inter-array shadowing requires the spacing of CPV arrays farther apart than the PV elements of a fixed-tilt or single-axis tracking PV system. On the other hand, pole-mounted CPV arrays leave 99% of the site ground accessible/usable to a height of 3 feet. This allows native flora and fauna to thrive on CPV sites in a way that can’t happen on fixed-tilt or SAT PV sites.

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