Solar Thermal Islands: Cool Concept or Pipe Dream?

Solar Concept Design

I ran across this article at The Oil Drum and thought it was too tasty to pass up. It describes a new design to help concentrated solar power (CSP) increase efficiency and reduce cost.

Here’s the problem: solar thermal collectors focus the sun’s heat onto a clear tube of fluid (see: Intro to Solar Thermal). The collectors generate the most energy when the sun’s rays are parallel with the tube of fluid.  Since the sun moves across the sky throughout the days and seasons, it only reaches this “sweet spot” certain hours each day. But, if the solar collectors could move to track the sun, their power output could increase dramatically. Keep in mind that CSP is one of the most efficient forms of solar power.

Other solar technologies already track the sun through the sky, so why not CPS? The simple answer is in the clear fluid tubes: one long tube is mounted over a row of collectors, fixing the collectors into a straight line. This design reduces cost and increases efficiency. It also limits which direction the collectors can move. They can’t tilt left-to-right towards the sun, for example, because of the rigidity of their construction.

Solar IslandDr. Thomas Hinderling of CSEM (Centre Suisse d’Electronique et de Microtechnique SA) suggests that instead of moving each collector (an expensive feat), why not move a platform beneath the concentrated solar farm? That way, in theory, all of the collectors would simultaneously generate the maximum possible amount of electricity, and you would utilize existing and inexpensive technology. Everyone wins! But to make it possible, you have to build a solar island.

Wouldn’t it be expensive to build an island? If something went wrong, you would endanger the entire installation. CSEM has a solution. They propose constructing a large round platform (5 km!) on an airtight frame, and filling the enclosed space with gas, effectively floating the bulk of the weight on air. If you’re having trouble visualizing that (I know I did), think of it this way: they want to build a fancy air mattress to support the platform. Using gas ensures an equal distribution of weight across the entire structure - assuming you don’t spring a leak like my air mattress. By controlling the pressure of the gas, you could build a flat or slightly convex surface and mount the solar collectors accordingly. Anyone who doubts the power of pressurized gas should watch Jaws or perhaps Jumangi (for a slightly scientific explanation).

In water, you would attach the platform to a floating ring and program motors to spin it in the desired direction. This style of solar collector doesn’t require a great degree of precision so no expensive equipment required. On land you would use the same technology, but you would build a moat to float the circumference of the platform. Water or oil in the moat would reduce the amount of energy required to spin it. (I propose a circular rail system that it could be fueled by the steam or electricity generated by the CSP. I’m not an engineer; perhaps that solution is too expensive?)

As concepts go, this one is certainly big, but a number of problems must be overcome to make it a reality. One potential problem could be high winds. Could air moving over a flat membrane produce enough lift to cause damage? In the desert, where CSP works best, there’s a lot of dust and sand. In the ocean you must contend with salt water and rough seas. How big must your platform be before it can withstand a hurricane?

photo of pilot projectAnother concern central to renewable energy development is transmission lines. If you build these platforms in the ocean, as this article suggests, how will you transfer the heat or generated electricity to land?

Despite technical difficulties, the promises of this concept are tempting enough to draw in investment. A pilot project is under construction in Ras al Khaimah, a member state of the United Arab Emirates(UAE), to work out the details. (See picture, taken May 2008) If this technology proves feasible, it will be one more weapon against increasing renewable energy demands. Hopefully these platforms will be scalable so that the cost of the platform decreases as its size increases. For details and some rudimentary calculations, see the original article.

Written by Michelle Bennett

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