Solar collectors capture radiant energy from the sun and deliver that energy as heat. They can only capture that energy that falls on them - this seems obvious once said, but does need to be said.

No solar collector will collect all of that energy. Some will be reflected away and will then be unavailable for delivery as heat. A good design and good materials will minimize reflective losses - but there will be some reflective losses no matter what.

Heat always flows from hot to cold and the greater the temperature difference, the faster the flow. The solar collector itself, because it's warmer on its inside than on its outside will lose some of the collected heat to the outside by conduction. Again, a good design and good material choices can minimize these losses.

Every object warmer than absolute zero radiates energy. The warmer the object, the higher the energy level of that radiation. By designing a solar collector to operate at the lowest possible temperature, it's possible to minimize these radiation losses. Note that heat (energy) and temperature (energy density) are very different things - and that the most common mistake made by uninformed builders is an attempt to achieve the highest possible operating temperature (which will result in maximizing conduction and radiation losses!)

The effective solar gain is the difference calculated by subtracting all losses and energy overhead from the incident energy (energy falling on the collector). The ratio of gain to incident energy is a panel's efficiency. While no collector can deliver 100% efficiency, it's not unreasonable to expect efficiencies better than 70%. As you might guess, the cost of improving the efficiency from 70% to 75% is a lot less than the cost of improving the efficiency from 85% to 90%.

It is possible to maintain a normal comfort level in a structure using solar heating only - but only if three conditions are met:

• The structure must be well-insulated.
• The structure must be tight to prevent warm air from escaping.
• The structure must incorporate some form of heat storage from which heat can be drawn when there isn't sufficient solar energy being added.

The importance of solar collectors is that each bit of heat they deliver will reduce the use of the conventional heating system by exactly that amount. For example, if solar panels deliver half of the needed heat, then the fuel consumption of the conventional heating system will be cut in half.

About DeSoto Solar Heating Panels

One of the most frequently asked questions has been: "How much solar collector should I install?" A good rule of thumb for estimating appears to be one square foot of panel area for every 125 cubic feet of space heated, which can be calculated by multiplying the floor area in square feet by the ceiling height in feet.

It's not unreasonable to install one or a couple of collectors with the thought of adding more later. More is better, but it need not all be done at one time.

Attempting to store heat makes sense only if the heat being collected significantly exceeds the immediate requirement; and in the real world this frequently isn't the case. I'll note in passing that it only make senses for structures that have, by today's standards, good thermal efficiency.

That evaluation led to the conclusion that the design trade-offs were in favor of a simple panel that efficiently trapped energy and transferred that energy as heat to air flowing from the structure, through the collector, and back into the structure.

Experience has shown that it's possible to store a useful amount of heat in a slab or basement floor by blowing warm air from near the top floor ceiling across the concrete. You can see a simple example of such an arrangement in the photos of a sample installation.

The design priorities have been: affordability, efficiency, reliability, longevity, ease of installation, simplicity of operation, and consumer maintainability in a product that could be built using existing technology and the best of readily available (off-the-shelf) materials, with a minimum labor content.

The results have been gratifying. It took precision computer-controlled (CNC) machinery to produce a consistant high quality result. A lot of different materials and finishes were tried and discarded along the way. More than a half-dozen panel design generations were created, learned from, and discarded - but the current design is well worth that cost.