This type of solar panel typically consists of 3/4″ copper tubes (10 to 12) running vertically between a header and a footer pipe. The fittings connecting the tubes are braised in place in a vertical orientation, forming a 4′ x 8′ panel. Fluid flows into the header at the top corner and out through the footer in the opposite corner. Any number of variations of a reflective sunlight concentrator is used to focus as much sunlight as possible on the tube. This type of panel is the most common in the marketplace today. A 4’ X 8’ panel delivers approximately 20,000 BTUs per day. This is based on a six-hour solar day average for a one-year period. Approximately 3400 BTUs per hour times six hours equals 20,400. This is also known as a 1 kW panel, because 3412 BTUs per hour equals 1 kW.

One of the leading manufacturers of this type of panel, in this marketplace is Solargenix.

This panel design requires as many as 30 braised connections. Which costs between $10 and $20 per braise, including testing. This brazing in the manufacturing process is one of the most expensive factors of this panel design.

High-end panels designed this way achieve better solar concentration by employing increasingly more sophisticated and expensive mirrored reflectors. Special surfaces usually come from outside suppliers who manufacture materials for agencies of the federal government like NASA. Although increasingly, many cloning efforts have come to the marketplace, these reflectors add great expense to the panel.

2) Non-Concentrated Sunlight, copper tube, with special coating

Panels of this type are similar in many ways to the solar concentrated panels above with the distinguishing feature being a coating applied to the solar elements. This coating usually black, is often described in such a way that the coating is somehow a magnet for solar energy. Over the years, a lot of dollars have been spent in designing better and better films and coatings to increase solar absorption. Many of these coatings actually fail colossally, because although the sun’s rays do saturate into the coating, sometimes the coatings are so thick that they impede conduction of heat from the coating to the copper. The thickness sometimes actually reduces the efficiency of the coating. A lot of engineering has been applied to this concept and the resulting highest benefit has come from the simplest solution — the thinner and the duller the coating, the better the results. This is because the highest efficiency comes from the prevention of photon bounce or ricochet. Photons give some of their energy into the tubing and then of course subsequently into the fluid, through the process of convection.

3) Non-concentrated Sunlight, copper tube, without special coating

This panel is usually considered to be the high end of the low-end of the market. It is usually less then a half a kilowatt per hour for a 4 X 8 panel. The cost of production is far less than the previously mentioned panels, although it is only marginally less in retail costs. This is part of the market where gouging is most prevalent. We see these panels used most often to heat swimming pools and out buildings.

4) Non-concentrated Sunlight, copper plate, solar element

This type of panel is the newest addition in perceived mix of technical solutions and attempts improve efficiency by increasing the area of solar element. Theoretically quite simple, the tubing through which the fluid flows is sandwiched between a pressure fit solid plate material. While conceptually a good idea, in practical application this design has not delivered to its potential. The “envelope,” to be effective must be pressure tight, requiring exacting engineering and production standards to create a good bond between the tubing and the plate material. At USS we consider this to be the latest in “me to” thinking. This solution is characterized by unstable and insecure attachment of the plate to the tube. Expansion and contraction tend to cause breakaway issues, because the plate can be as low as 40 below zero and the water coming in can be 70° above zero as it enters. Separation, deterioration and subsequent malfunction have plagued this type of panel.