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Where Can Solar Energy Devices Be Applied Cost Effectively?
Many people believe solar energy can't compete economically in countries like Canada and even the US where fuel prices are low and the availability of solar energy is not great over parts of the year. These people are not fools. Most potential solar energy applications other than pool heating don't make good economic sense. Its important to understand what makes for a worthwhile solar energy application at least in terms of economic return on investment.
First we must understand that there is only at most about 1 kw of energy available for a one square meter surface exposed to the sun. No matter how high tech a solar gizmo is, the most you can collect is about 1 kw per square meter. You have to combine a low cost solar collector with an operating condition that allows the collector to operate at a high efficiency if you want the system to pay for itself in a reasonable time frame. Any solar heating panel will have an operating curve that depends on the temperature of water being heated (this is the temperature the collector operates at (slightly higher as water moves through the panel) relative to the air temperature the collector is exposed to. If this temperature difference is small as it is in a swimming pool heating situation then collectors like Powerstrip will have high efficiency. That's the power produced per area relative to the amount of energy available over that area from the sun. As the temperature of the water gets hotter (as it can in a domestic water pre-heating system) a collector with glass over it and boxed in insulation will maintain good efficiency at the high end of the temperature when an unglazed pool collector like Powerstrip will not unless protected from wind. Boxed and glazed collectors are about 4X the price of pool panels per area. If the load is small (as in a domestic situation) there will be a high cost of balance of system so the extra cost of using boxed and glazed collectors is usually justified for the higher performance. As the load gets large, however, the system cost becomes more dependant on collectors and this is where Powerstrip can be applied cost effectively where other collector types cannot. Large scale solar water heaters for laundries and fish hatcheries and condo complexes with central water heating can pay for themselves in reduced fuel consumption in 5 years, whereas small scale domestic systems, no matter which collector type is used, will take at least 20 years to pay back (this is better in warm climates).
Warning: You should be very careful using boxed and glazed solar panels in a pool heating application. The high stagnation temperatures can melt pool plumbing! Unglazed panels like Powerstrip are self limiting in temperature and cost much less and will usually outperform more expensive collector types in low temperature applications like pool heating.
History is repeating itself in Canada in 2010 as municipalities rush to take advantage of stimulus funds and other government incentives. Cities the country over are installing boxed and glazed collectors systems on their pools. The following studies were done by us in an effort to try to counter attack but mostly what we are encountering today (December 9 2010) is that Canadians foolishly are believing that boxed and glazed collectors make more sense on pools that swimming pool heating solar technology, the technology that has been around for 40 years proving itself over and over.
Saskatoon's solar mistake simulation study
Richmond, BC's near solar mistake simulation study
Another type of high temperature solar panel worth mention is the evacuated tube. These will maintain 70% efficiency even in arctic air temperatures and hot water being heated. They are super-insulated in a vacuum. The drawback is very high cost but if you want to heat your space in winter these may be your best bet. Forget about them ever paying for themselves but space heating with solar won't pay for itself anyway. In a very cold climate with sun these are probably the best choice for domestic water pre-heating as the size of collector required is small so the cost relative to the rest of the system is warranted.
If Powerstrips can be protected from wind we find that their operating curve gets pretty close to a boxed and glazed collector as long as air temp doesn't get too low. If you have a shelterred location that sees good sun Powerstrips are your best choice for collectors even on small scale systems. In California 80 sq ft of Powerstrip will match the year round performance of 2) 4'x8' boxed and glazed collectors in a residentail water heating application and Powerstrip can be attached to the roof properly and Powerstrip is about 1/4 the price per area.
If you are heating large volumes of cold water Powerstrip can be applied to the low temperature end of the heating very economically and the higher the load the quicker the payback period. Powerstrip will perform well right up to high temperature if the collectors are protected from wind. If the roof is flat wind loss is minimal because the collectors are protected naturally in the boundary layer. Wind factor is very low if the sloped roof surface is facing a direction other than that of the prevailing wind direction. Finally the highly profiled collector cross section means that as long as the wind isn't directly in line with the flow cores, the collector protects itself naturally from wind losses.