Harnessing Solar Energy

The sun showers Earth with an unfathomable amount of energy every minute. In fact, more solar energy hits our planet in one hour than the entire global population consumes in a year. Of course, this statistic is outrageous because the vast majority of the sun’s energy is impossible to harness without covering the planet in an uninterrupted layer of super efficient solar panels. Though meaningless on its own, however, this factoid is still quite telling. The sun, as the primary energy source of our solar system, offers powerful alternatives to conventional energy sources. Today, a range of technologies exists to harness substantial amounts of solar energy and use it to power society. Below I’ve provided a brief overview of several; I’ll be exploring each more in-depth in future posts.

Perhaps the most popular of these technologies comes in the form of photovoltaic (PV) panels. Most commonly referred to as solar panels, they comprise numerous small PV cells made from carefully selected semiconductors. The electrons in these materials become excited when they come in contact with light and produce an electrical current, essentially converting sunlight directly into electricity. While PV is often associated with deserts and other regions that offer intense sun exposure, their performance is more dependent on sunlight than extreme heat (PV uses both direct and scattered sunlight, which includes light that’s been affected by clouds and other obstructions). And although the temperature at which they achieve maximum efficiency varies depending on the specific panel, they operate less efficiently in extreme heat. The materials also tend to break down more quickly in very high temperatures. For these reasons, PV cells will last longer (and ultimately generate more electricity over their working lives) in a place like Georgia than the Mojave Desert. Solar energy that hits the earth is generally measured in terms of solar radiation using kilowatt-hours per square meter (kWh/m2) as the metric. The catch here is that the areas that experience the most solar radiation also tend to have the hottest temperatures, generally above the optimal range for most PV panels.

NREL’s map of the average annual solar radiation in the US.

If light is the sun’s most obvious property, then heat is its most fundamental. Another way to generate electricity using the sun is through Concentrated Solar Power (CSP). This technology makes use of the sun’s heat, and utilizes a range of systems to concentrate that heat on a working fluid (most commonly water). From this point, the system operates much like a traditional thermal power plant, where the heated fluid drives an engine, which generates electricity. Though the basics remain largely the same, four very different types of systems are currently being deployed: parabolic troughs; Fresnel reflectors; dish Stirling; and solar power tower. Unlike PV, which utilizes direct and scattered light, CSP requires as much direct sun as possible. These systems work best in areas with clear skies and intense heat and aren’t very effective in places with more moderate climates. This is your best option for the Mojave. As mentioned above, I’ll be going into more depth about CSP in a later post.

In addition to generating electricity using the sun, we can also use it to heat air and water in controlled ways. In many sunny cities, it’s becoming common to find roof-mounted water tanks and solar collectors on buildings. Although the collectors often look like PV panels from afar, this is in some ways a much more intuitive technology. Again, numerous types of systems exist, but the concept is simple: pump cold water into the collectors where it is heated by sun and then pumped into a thermal tank. Some are designed to work for most of the year, but require a back-up energy source for the winter and during cloudy or cold stretches.

The sun’s energy can also be used passively to heat buildings. The degree to which interior spaces can be heated by the sun is primarily dependent upon the design and construction of the building. Building orientation, maximizing sun exposure with south-facing windows (in the Northern Hemisphere), is critical. The use of insulating materials is also important to maximize the effect of the harnessed heat. This starts getting into building standards and LEED certification, which plays an important role in energy conservation, but reaches well beyond the scope of this too-long post.

These are some of the popular ways that solar energy is being harnessed. Each technology takes advantage of the sun’s energy in different ways, and each requires a specific set of conditions to function optimally. While some technologies, like passive solar space heating, can be utilized in a broad range of climates and regions, others are much more limited in terms of where they will be reasonably effective. These conditions also directly affect cost-effectiveness, a survival test for emerging technologies.

The Verdict: No single technology or energy source will be able to meet our energy needs in every circumstance. The range of solar technologies available, however, offers a number of ways to harness the sun, each with its own specific set of strengths and weaknesses. There is no silver bullet here, but by focusing on regional needs and resource availability, solar energy can play a prominent role in our energy future.

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5 responses to “Harnessing Solar Energy

  1. It seems that, with the possible exception of the nuclear tecnologies, all earthly sources of energy – fossil fuel, bio-fuel, wind, geothermal, tectonic, magnetic, tidal and wave energies – are all derivatives of solar power. It has long seemed obvious to me that the greatest harvest of energy will come from our cultivating solar technology and focusing directly on the sun itself for power. We know that solar cells are increasngly efficient at converting sunlight into energy for uses other than illumination. Still, the development of solar technology has been slow, and progress has been disappointing.
    For decades, I have heard stories that the petroleum companies have been buying up solar energy patents and ideas in order to keep them off the market. I would like to know whether you or your followers are aware of specific examples of where this has been done. Thanks for a great post.

    • You’re right that to some degree many energy sources result indirectly from the sun (fossil fuels and biofuels are actually similar in this regard, only separated by a few million years). And the sun does provide vast opportunities that we aren’t taking advantage of.
      With respect to oil companies gobbling up patents, you might be interested in this: http://en.wikipedia.org/wiki/Free_energy_suppression – a related conspiracy theory. While oil companies may very well have purchased alternative energy patents over the years and sat on them, there’s very little evidence to suggest that this happened on a scale that would alter our energy landscape. But they may be hindering these technologies in other ways, such as through political avenues (their recent involvement in the failed attempt to overturn California’s climate change law – AB32 – comes to mind).

      • Thank you. The wikipedia entry was informative. I hope that your readers and followers realize what a helpful resource you are. Many “unbiased” sources of environmental information are thinly-disguised fronts for some broader interest. I appreciate your efforts at objectivity and your measured language. Educators might comfortably refer their classes to your blog. Keep it up… Rome wasn’t built in a day.

  2. Pingback: Photovoltaics and Our Energy Future « CleanTechVerdict·

  3. Pingback: Concentrated Solar Power: Focusing the Sun « CleanTechVerdict·

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