How Much Do Solar Reflectors Help

Reflector panels which bounce rays back onto a collector should reduce the amount of collector surface you need. In fact, a small collector can receive more radiation than a much bigger one if it's helped by properly arranged reflection surfaces. Good reflectors should boost the performance of any flat plate collector by at least 25% (Figure 44).

Figure 44. Sometimes banks of solar collectors and reflector panels can be made to work in combination. Reflectors can increase the performance of flat plate collectors by 25% or more. It's best, of course, if the reflector is adjustable, so it can be moved to shed light on the collector at all times of the year.

Figure 44. Sometimes banks of solar collectors and reflector panels can be made to work in combination. Reflectors can increase the performance of flat plate collectors by 25% or more. It's best, of course, if the reflector is adjustable, so it can be moved to shed light on the collector at all times of the year.

Insulated Shed Rool Addition

Figure 43. When the ridge of a house runs north and south, it can be difficult to design a collector system that works well without having to use many panels on both the east and west roofs. A cheaper alternative might be to plan a simple addition with a shed roof that puts the collectors at just the right tilt.

Insulated Holding Tank

Insulated Holding Tank

Figure 31. A thermosyphon solar water heater uses a free-circulating panel. Notice how the direction of the fluid flow is upward and that there are no pumps to keep the water moving. This is because hot water naturally rises, while cold water seeks the lowest point in the system.

efficient, but it requires a thermostatic control mechanism to turn the pump off when the sun is too weak to give the collector energy.

The upward flow of liquid through a solar panel can be directed in a couple of different ways. The tubing, which is integral with the plate itself, might be a single line that zig-zags across the absorber like a serpent. Experts refer to this as a series pattern. The advantage of this flow path is that the liquid takes a long route through the collector and gets quite hot. The plumbing involved also is quite simple (Figure 32).

In a parallel flow collector, fluid comes into the bottom of the panel through a single in-flow manifold, then is diverted through a number of parallel tubes for one pass across the collector plate, before it's re-collected again in the out-flow manifold (Figure 33). Most prefabricated tube-in-sheet absorber plates are designed to use this flow pattern. Although liquid spends somewhat less time in the collector — and is heated less per pass as a result — more heat will be collected in a day's time.

The third type of collector — the open-water type — has an absorber plate made of corrugated steel or aluminum roofing material. Open water collectors are called tricklers in the solar trade because water starts at the top of the panel and trickles down the open channels in the corrugations.

The best-known panel of this type is the Thomason collector, developed some years ago in Washington, D.C. The whole Thomason system is well protected by patents, but the collector v/orks very simply. Cold water is pumped to headers along the ridge of the house above the

Figure 32. Tubing in a "series" configuration is easiest to put together and gets water hottest.

Figure 32. Tubing in a "series" configuration is easiest to put together and gets water hottest.

Figure 33. A "parallel" tubing configuration, although it's more complex, causes less pressure loss in the systfem because there's less friction in the pipes.

collectors. It then seeps from carefully spaced holes in the header and runs slowly down the black metal absorber plate (Figures 34-35).

At the bottom of the corrugated sheet there is a gutter to collect the water which has taken heat from the sun. This gutter runs into a pipe, which in turn, transports the water to the storage tank. Variations on the open-water collector include the "series dribble" system (Figure 36), which directs water back and forth across the collector plate, and the Shore system, which runs water between two sheets of blackened corrugated roofing. There is apt to be lots of evaporation from the open-water in a trickier and this can

Cold Water Pipe

Cold Water Pipe

Figures 34-35. Water in a trickling collector, such as the one designed by Thomason (top), starts at the top of the collector and runs to the bottom. The water is heated as it runs down valleys in black corrugated roofing.

In the system designed by Shore (bottom), there are two layers of corrugated metal and the water trickles between them.

Figures 34-35. Water in a trickling collector, such as the one designed by Thomason (top), starts at the top of the collector and runs to the bottom. The water is heated as it runs down valleys in black corrugated roofing.

In the system designed by Shore (bottom), there are two layers of corrugated metal and the water trickles between them.

Figure 36. A "series dribble" system is another variation of the open-water solar collector.

cause condensation on the underside of the glazing. The Shore collector, with its double layer of roofing, is better in this respect.

Flat plate collectors, for the most part, are either ready-made or built at home. The homemade varieties are built from scratch or put together from a kit. Prefabricated collectors tend to be expensive, as we have already seen. If you're an amateur plumber, you may want to start at ground zero and make collectors entirely on your own. If not, you may opt to buy the collector plate but build the rest of the collector box yourself. It's simple, really. All you have to worry about is keeping the collector box watertight (more on this in Chapter 5). The third option would be to build your collector completely from ready-made parts — available from several manufacturers. (See appendix.)

Whatever you decide to do, build or buy collectors that are small enough and light enough to be handled easily. Remember, there's a big difference between moving a panel on level ground and getting it into place up there on the roof. If the collector is too unwieldy, mounting it properly becomes a balancing act and a wrestling match all rolled into one.

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