Flat Plate Collector Structure

You are here

The oldest, simplest and most common solar thermal collectors are flat plate collectors. They have a robust design that can withstand temperatures falling well below zero and rising well above most climate norms (they work fine at around 180°F or 82°C). It's no surprise that they're the base to which all other, more complex collectors are compared.

Like most renewable energy equipment, flat plate collectors are designed as cells which can be connected together to create large arrays, depending on your needs. In this case, the collector boxes are usually 4 feet wide, 8-10 feet long and 4-6 inches deep. If you live somewhere metric, they're commonly available in a 1 meter by 2 meter format.

Flat Plate collector schematicFrom the outside, the box looks like a glass-topped container with a couple of copper tubes sticking out at the top and bottom and, to be honest, basic flat plate collectors aren't much more complicated than that. They are insulated on the inside (sides and bottom) and contain an absorber plate which gathers the sun's heat after it passes through the glass.

Although the name suggests otherwise, the absorber plate is not literally flat: to improve energy collection, it's usually either corrugated or dimpled.

The absorber plate is not attached to the collector box, but sits on top of a series of copper or aluminum fins which carry the gathered heat down to a set of riser tubes (or one long tube which snakes back and forth inside the box). The fins are soldered, welded or roll-bonded to the risers to ensure the heat is transferred efficiently. The risers themselves are packed between three and six inches apart – the closer the better.

The riser tubes (or snaky single tube) connect to two half-inch or one-inch manifolds which transfer the heat out to wherever it's needed: the manifolds are the bit that's visible from outside the box and are held in place by rubber grommets.

These boxes, often called "internally manifolded collectors" snap together to create big arrays. It's important to note that each manufacturer produces their own mounting hardware, depending on the materials they use, so make sure you buy the right type for the collectors you're installing.