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March 19, 2007

The solar variety show

Category: Concentrating Solar,Photovoltaics – Dan 7:38 am

Like many people, what I knew about solar power was limited, and in particular was limited to knowing about flat panel solar collectors. Oh, and one article that I’d read years ago about a “power tower” being built somewhere in the southwestern US with a bunch of heliostats (sun tracking mirrors).

Turns out that solar is an area with not only vast potential, but extensive innovation on a number of different approaches to turning solar energy into useful power. Here’s my list:

  • Flat panel technologies – All flat panel technologies have some key characteristics. They do not require direct sunlight, and generate energy regardless of where the light source is located. As a result, they don’t need to track the sun (although efficiency will be higher if they do), and they generate some power even on cloudy days. There are several types of flat panel collectors:
    • Flat panel crystalline silicon solar cells – These are what most people think of when they think solar. Cystalline silicon is grown into rods, which are sliced into wafers that form the cells. Arrays of the cells are built into flat panels.
    • Thin film technology – The high cost (both dollars and energy) of crystalline solar cells prompted development of a new approach where thin films of semiconductor materials are deposited. Although these generally have lower efficiencies than crystalline cells, the costs are also significantly lower, both in terms of manufacturing the active material, and in terms of the required support structures (thin film cells are much lighter). Thin film cells are also flexible, and can therefore be bonded directly to roofing materials; an example of this is the BIPV Solar Electric Roofing produced by SolarIntegrated.
    • Non-traditional photovoltaics – There is a new generation of semiconductor solar cell devices that work differently than the above two options. Companies doing this development include Konarka Technologies, Nanosolar and Nanosys.
  • Concentrating Photovoltaics – If the most expensive component of a traditional solar cell is the collector itself, then why not use mirrors or lenses to concentrate sunlight on the collectors. The advantage of this approach is lower costs. This does, however, make it more important that the collectors track the sun, and this technology clearly works better in southwest locations that have relatively cloudless skies. Companies working on concentrating photovoltaics include SolFocus, Silicon Valley Solar, and Sharp Electronics.
  • Solar Thermal Technologies – If what you need is heat and hot water, why go to the trouble of converting sunlight to electricity? This is the theory behind various solar thermal technologies. Solar thermal has been around for generations, and unfortunately this seems to be the unglamorous stepsister of solar technology. Solutions range from basic arrays of black tubing on the roof to help heat swimming pools, to modern sophisticated devices using glass evacuated tubes coated with advanced materials and integrated with ethanol-filled heat pipes. This is worth an entire article, so I won’t write more here.
  • Concentrating solar power – If you think big, it’s possible to create facilities that gather sunlight over a large area to create high heat that then is used to generate electricity. The three primary types of facilities here are:
    • Parabolic Trough – Long parabolic trough-shaped mirrors focus sunlight on tubes that heat a fluid to well over 500 degrees F; this heat creates steam to power a turbine generator and produce electricity.
    • Power Tower – A circular array of sun tracking mirrors focus sunlight on a central receiver on tower, heating a fluid which powers a generator.
    • Dish Engine systems – A mirrored dish focuses sunlight on a stirling heat engine at the focal point that directly generates electricity.

Why so much investment in PV?

Category: Photovoltaics – Dan 5:46 am

Photovoltaics (PV) have always baffled me. While they clearly make sense for applications in remote locations, other options like wind and concentrating solar power are far more cost effective for industrial scale power generation. Why then is there so much venture capital investment in PV? Looking through the publications, there are at least a dozen companies developing new PV technology, and major investments are being made in fabrication facilities to create hundreds of MW of PV panels each year.

Then I saw my copy of “Inside the Tornado” on the bookshelf an the the light went on in my head.

Most alternative energy sources — Wind, concentrating solar power, geothermal, and biomass — are industrial scale sources. If your not a utility, you’re not likely to be making a major investment in any of these sources.

Photovoltaics are entirely different. An individual can install them on his home. A business can install them on the roof of their warehouse. PV panels can work anywhere there is sufficient light. And while having a grid connection is useful, you don’t need the utility’s permission or cooperation to generate PV power.

The analogy I’d use here is the automobile. There were other ways to get around in the early 1900’s, and public transit was highly developed in many parts of the country. Although early automobiles were a pain (they weren’t reliable, gas stations were few and far between, the roads were poor), they offered a way to take transportation into your own hands and not rely on the railroads and public transit agencies. In the terms of “Inside the Tornado”, cars were a disruptive innovation. They changed the paradigm, and the result was huge growth of the automotive industry, and the decline of the railroads.

PV has the same potential — to change the entire nature of the energy supply business. If PV became cost competitive, companies and consumers could take control of their power generation away from the utilities. The upside opportunity for companies here is far greater than the upside of other alternative energy sources (wind, CSP), which rely on existing organizations (utilities, oil companies, etc) to drive adoption and investment.

What do you think? Is this what’s driving PV investment? And will it work?