Tapping the Sun - Brief Article - Evaluation

The sun is the ultimate energy resource. It drives all life processes on earth. With the help of solar collectors, humans are gradually reacquainting themselves with this fact. Solar photovoltaic modules produce electricity from sunlight. Solar thermal collectors make hot water. Using solar energy is a practical way to offset our dependence on fossil fuels. Solar technology is ready for the mainstream energy markets now. In most locations off the utility grid, a professionally installed PV (photovoltaic) system is less expensive than a 1/8-mile utility line extension.

If federal subsidies that artificially support coal, nuclear, and large-scale hydroelectric generation could magically disappear, photovoltaics would be economically competitive immediately. Today, people who live on the grid and invest money in a PV system are making a great ecological statement and a lousy financial one. But think about it: people make "lousy" financial decisions all the time. Do I actually need a $30,000, four-wheel-drive sport-utility vehicle to run errands around town? Or how about spending $20,000 on remodeling my kitchen? Are these lousy financial decisions? People place different values on different things. The great news is that more and more people are investing in a clean energy future that only the sun can provide.

PHOTOVOLTAICS

PV modules are the most high-tech and perhaps the most elegant way to harness the power of the sun. PVs convert the sun's energy into a DC electron flow. Inverters then condition the module's output, creating standard 120- or 240-volt AC electricity used by household appliances. Many inverters can also synchronize their output with the utility grid and actually spin your electric meter backwards. This way, you can share clean, renewable energy with your neighbors.

PV modules have steadily grown in size, output, and efficiency. A typical module output is now 15-200 watts per panel; two by four or five feet in area. In less than two years, in a sunny location, a PV module can produce output equivalent to all the energy it took to manufacture it. PVs have no moving parts to wear out, require no maintenance (except in dusty climates where they must be cleaned off regularly), and can carry warranties of twenty to twenty-five years. Since PVs don't make electricity from heat and production actually drops with temperature, they are best placed on a tracking pole, not on the roof.

Most PV modules end up in "is the Ford better than the Chevy?"-type arguments. Pay attention to cost per watt of power produced, and the length of the module's warranty. Up at Home Power, we recently had our first PV failure in nearly two decades. The nine-year-old module was simply returned to the manufacturer, who replaced it with a new one.

The BP590 module by BP Solar and the SR200 module by Siemens Solar are the two leading single-crystal PVs. The BP590 is an 85-watt module with a twenty-year warranty. It converts 27 percent of the sun's energy into electricity--the most efficient PV you can buy. The Siemens SR100 is a 200-watt module, meticulously constructed. Its twenty-five-year warranty is the longest in the industry.

Because batteries have not changed much for half a century, they remain the dinosaur in the PV system, [in the boonies, the battery house replaces the outhouse and, emissions aside, it's a toss-up whether a diesel generator is more convenient than a shed full of batteries --Ed.] PVs are most convenient with grid-connected homes. Here, battery-less inverters allow a post-modern fusion of old utilities with the new.--JS

SOLAR HOT WATER SYSTEMS

Solar thermal (hot water) systems are a simple way to use the sun's energy in your home. A roof is hot, and is the ideal location to heat hot water for appliances and space heaters. Solar systems are typically used in conjunction with standard gas or electric water heaters, reducing the amount of fossil fuel required to keep you in hot water. They have two- to five-year warranties.

Several systems and products are available. In colder climates, closed-loop systems rely on freeze-proof glycol as the heat transfer fluid. These systems eliminate freeze damage to collectors or plumbing. In warmer climates, drain-back systems directly heat the water that is used inside the house.

Two types of solar collectors are available: evacuated-tube and fiat-plate. In southern Oregon, at Home Power, we run both side by side. In cold climates, the evacuated-tube collectors manufactured by Thermomax are the most efficient. Thermomax utilizes evacuated tubes to transfer the sun's heat to a closed glycol loop. Twenty- and thirty-tube units are available, and their appearance is as high-tech as their function. Flat-plate collectors, manufactured by Sunearth, are a less expensive and comparable alternative. In warm climates, flat-plate collectors can produce 90-100 percent of the hot water that evacuated-tube units can, for less than half the cost.--IS

SOLAR COOKING

Solar cookers do not couple well with the standard 9-to-5 "Honey will you microwave me some dinner?" lifestyle. [Even in "less developed" nations, women cannot get the roasted taste, the sanctity of the hearth, the double function of both heat and light, or the cloudy-day reliability that wood fires provide. --Ed.] Solar cooking can be fun and a small environmental statement, like riding your bike to work. These ovens use reflectors to focus the sun's energy and heat food. Solar Chef ovens can reach 500 [degrees] F, and provide real-time cooking in full sun. A less costly and solid-performing alternative is the Global Sun Oven manufactured by Sun Ovens International. --JS

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