The Flat Plate Solar Collector



The flat plate solar collector is the type of collector mostly seen.

It is one of the two major types of solar collectors . The other one, more fitted to cold weather regions is the solar evacuated tube collector (also known as vacuum tubes collector). The solar collector is the most important element of the solar hot water heater

The Construction of a Flat Plate Solar Collector

Solar collector flat plate is a layered structure; the layers top to bottom are:

  • The top layer is a glass sheet
  • Bellow the glass there is a winding pattern of pipes(the idea is to use the available layer surface area to get the maximum pipes’ peripheral area)
  • Bellow that is a black sheet absorbing material attached to a bottom metal plate.

All these goodies are assembled in a rugged sealed insulated case, the entire assembly is sometimes called flat panel solar collector.

This solar collector like any other type of solar collector uses the greenhoose effect. Visible light penetrates through the top glass sheet but after it is converted to heat by the absorbing sheet, the heat radiation in the infrared range is locked inside the casing because the glass is opaque to infrared radiation

In regions where the temperature never drops bellow freezing (32 degrees)(day and night, winter and summer) the pipes run water. This arrangement is called an open system (or a direct system)

In regions where the temperature drops bellow freezing (32 degrees) the pipes run anti-freeze liquid (glycol). This is called a close system (indirect system)

Cost of Solar Flat Panel Collector

Flat panel solar collectors can cost around 700-900$ for 20 square feet size and 1100-1300$ for 40 square feet size (not including shipping and installation)

Schematic Drawing

You can view a schematic drawing of a flat plate collector bellow

flat plate solar collector

Corrosion and Corrosion Prevention

A direct system (open system) that runs water through the collector is prone to oxidization and to the development of rust in parts made of plain vanilla steal or cast iron. The practical way to avoid corrosion is to use materials like stainless steel, copper or bronze, glass and plastic and to avoid bi-metal effects (two different metals touching each other). As a buyer, find out what are the materials the manufacturer is using and insist on corrosive resistant materials.Use a water filter on the water entering the open system. The filter protects the system from debris and softens the water (preventing the deposit of scale)

Pipes Cross Section

There is an academic discussion about what is the optimal cross section for the pipes in the solar flat panel collecter. There are 3 alternatives: circular cross section pipes in the flat plate solar collectors, elliptical pipes in the flat panel solar collector or semi circular pipes. Practically, buy what ever is available on the market, unless you want to build a collector.


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