Flat Plate Collector Parts

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Flat plate collectors are the simplest type of solar thermal collector. They consist of several basic parts, as described below.

The box

The frame which contains all the equipment needs to be very tough and durable to resist strong winds and all sorts of weather. Generally speaking, frames are made of extruded aluminum which can be quite heavy and thick for heavy-duty collectors. There are some collectors which have rolled aluminum or extruded fiberglass frames, but they're a definite minority.

All collector frames are fastened together with stainless steel fasteners. This is because it's really important to use compatible frame and fastener materials – plain or galvanized steel just don't work with aluminum. Remember that when you're buying your mounting gear, too, as the same rule applies.

The absorber plate

As you would expect, the absorber plate's coating directly affects how efficient the collector is. Coatings always have two important rating figures: how much they absorb and how much they emit.

Almost all absorber coatings have an absorption rating of between 90 and 98, which is the percentage of sunlight they soak up. Traditional flat black paint has an emission rating of anything from 15 to 30 percent, whereas new high-tech alternatives like physical vapor deposition (PVD), sputtering, black chrome or black crystal have lower ratings which are between 5 and 10 percent.

To figure out how efficient the collector is, you simply subtract the emission rating from the absorption rating: the higher the outcome, the better!

The insulation

The back and sides of the collector are always insulated to retain as much heat as possible inside the box. Most modern collectors use standard insulators such as fiberglass, rock wool, rigid expanded polyurethane (PUR) or polyisocyanurate. As long as the material can withstand prolonged high temperatures, it's acceptable.

The glazing

Funnily enough, the collector glazing – the glass side – is the one part that can't be modernized yet. Although loads of different plastics and other materials have been tried, it's old-fashioned low iron tempered glass that outdoes them all. It's pretty much the only material that doesn't fail with the long-term high temperature setup.

That's not to say that collectors haven't been modernized, of course. The glass itself is always a single pane – adding a second reduces the collector's efficiency – and is generally patterned on one side to reduce glare. It is usually seated with a rubber gasket around it to keep it in place and make a good seal with the frame, though some collectors use silicon caulking. That works fine, too, but it's almost impossible to remove the glass for maintenance.

There's one important safety tip here: tempered glass is very fragile around the edges. If you ever have to remove the glazing from a collector, make sure you wear safety gloves and goggles. Even a slight tap on the tempered glass edge could cause it to literally explode!