A solar heating panel is a device that traps solar radiation and delivers that energy as usable heat inside a structure. This radiation includes everything from infrared through the visible spectrum to ultraviolet.

What's a passive solar heating panel?

A passive solar heating panel requires only the sun - no fans, blowers, or pumps are needed for it to operate at peak efficiency. It uses the heat produced to provide a convective flow that moves the heat from the collector into the structure. This means that the installed panel has a zero operating cost - and that it will continue to operate at full efficiency even through power outages and fuel delivery interruptions.

Do solar panels replace my furnace system?

It's possible but, in general, not unless the structure is well-insulated, snug, and there is some provision for storing enough heat to maintain comfort through nights and dark days. Otherwise, solar heating panels simply reduce fuel consumption, with a corresponding reduction in operating costs and emissions.

How does it work?

The DeSoto Solar heating panel has an efficiently combined radiation trap and heat exchanger. The radiation trap absorbs solar energy and the exchanger releases it into the air inside the panel. The heated air rises and is heated continuously until it flows out of the collector and into the structure. As heated air flows out of the collector, cool air is drawn into the collector from near the structure's floor. The greater the amount of energy collected by the radiation trap, the higher the temperature of the heat exchanger and the faster the resulting airflow. The DeSoto Solar heating panel is designed to produce a maximum temperature between 110°F and 115°F. Unlike some solar panels, the airflow inside the collector body is controlled in such a way that the heating panel can't run in reverse at night in extreme cold.

The vertical orientation produces two important behaviors: [1] The panel operates most efficiently in mid-winter. In mid-summer, when the sun is high in the sky, most of the radiation is reflected (downward) by the polycarbonate glazing; and [2] if the ground in front of the panel is snow-covered, the snow reflects a significant amount energy (up to an additional 90%) into the panel's radiation trap.

How much heat is produced?

As Mark Twain (mis)quoted: "There are three kinds of lies: lies, damned lies, and statistics." The only honest answer to this question is: The quantity of heat produced depends on [1] orientation, [2] shading, [3] latitude, and [4] prevailing weather patterns. Let's briefly examine each of these variables:

Our collector is designed to be installed vertically. It will trap the greatest amount of solar radiation if it faces true (not magnetic) south; and the least if it faces true north. If it faces a little east of south it will trap more energy in the morning; and if it faces a little west of south it will trap more energy in the afternoon.

Shading occurs when solar radiation is blocked from reaching the collector by plants, other structures, an object, or even the planet itself (night). The collector can only trap the energy that reaches it.

The collector is only useful in the temperate zones. In the equatorial zone the sun is too directly overhead; and in the polar regions the sun remains below the horizon throughout the heating season. Within the temperate zones, efficiency will be highest as the distance from the equator increases.

Some areas like Southern California, Arizona, Minnesota, and Florida normally receive above average amounts of solar radiation while other areas such as Seattle receive below average amounts. Although this is a form of shading, it's unlike the clear-cut behavior of object shading because the weather is a difficult-to-predict variable.

How much solar collector is enough?

If the goal is to go with solar heating only, this question should be directed to a local architect with substantial experience with solar heating systems. However, if the goal is to produce substantial savings using solar in conjunction with an existing system, a workable rule of thumb is have one square foot of panel area for each 125 cubic feet of heated space.

How long will it last?

If installed properly and not subject to salt spray, our solar panels should have a service life at least equal to that of the structure into which they are installed. It may be necessary to replace the polycarbonate glazing 2 to 4 times per century, but our 20-year old sample is still in pretty good shape...

How do I control the temperature?

Vertically mounted solar panels naturally produce a maximum amount of heat at the winter solstice and a minimum amount of heat at the summer solstice as a result of the same axial tilt that produces winter and summer. If there isn't enough panel area to satisfy the heating requirement, then the conventional heating system is used to make up the difference. If the panels are producing too much heat, then the temperature can be lowered by allowing warm air to escape outdoors (by opening a window, for example.) During warm seasons the panel is designed to shut down automatically, but a cover or shutters can be used to completely block sunlight and absolutely prevent heat production.

Does the solar heater only heat air when the daytime hours are not overcast?

Nope. It does an effective job of converting any incident radiation (with a wavelength longer than ultra-violet) to heat. It doesn't make much difference whether that radiation is from a point source (sun in a clear sky) or scattered (passed through diffusing clouds). The amount of heating that takes place is a function of solar flux.

Other solar panels are made of metal, what are the advantages of your largely wood design?

Wood is universally available, structurally strong, a good insulator, easily machined, a renewable resource, and requires a minimum of energy to produce, and provides the same service lifetime as the structure into which it's installed. Having said that, beginning in 2010 the exposed wood surfaces will be covered with a stainless steel "skin".

Why is there no BTU rating for your solar heater?

To date, no one has been willing to guarantee a BTU input figure. If I provide an output rating, it will be taken as a guaranteed minimum - and I'd rather not mislead any customers.

Why do you use polycarbonate instead of glazed glass in your panel?

It's considerably safer and (overall) works better. There is glass that transmits radiation better, but the polycarbonate glazing I use makes up the difference by being a much better insulator - it retains more of the collected energy than glass.

Why do you offer no "flow rate" information for your panel?

Flow rate is variable and dependent on solar flux and altitude. There is no single number that could be true for everyone. Again, it's a question of not misleading customers.

What is the CO₂ reduction for each size panel?

Hmm - this is just question #3 in disguise. The actual reduction is the same for all panel sizes: 100% of the CO and CO₂ that would have been released by burning enough fuel (of whatever kind) to produce the same heat energy.

Why is the design of your panel better than other products on the market?

Because I focused on producing a design to fulfill my customers' needs rather than my desire to produce revenue.

If there were a fire in a structure in which your panel was installed, what effect would it have on the fire, if any?

The wooden parts would contribute fuel. The polycarbonate glazing would begin to soften noticeably at approximately 800°F, which would lead to ventilating the structure - but at that temperature, the structure would have lost integrity anyway. The aluminum and stainless steel would have little, if any, effect.

What is the daytime energy rating of your panel?

Eh? This looks like the Btu question in disguise. See above.

How do I overcome the aesthetic objections of my partner to installing solar heating panels in our residence?

If warm, clean, green, and economic benefits aren’t enough, then you're probably better off with a conventional heating system and a generator to keep it running during power outages.

What are the field reports from your customer base on the average Return-on-Investment on your solar heaters?

I don't have much data to work from, but it looks like a 3-year break-even is a reasonable expectation. Of course, it depends on location, energy costs, etc.

Friends tell me that at night solar heaters can produce a back draft, which pulls the warm air out of a structure in which it is installed. How does your design deal with that?

Your friends are poorly informed, or have been looking at cheap "no-brainer" panel designs. There is no good reason for such behavior. I made the solution to this non-problem available to the general public years ago, and show it at this web page.

Why don’t you put insulation between your panels and the structure in which it is installed?

Re-read the third paragraph at this other web page.

Why don’t you have an electric fan in your solar heater?

Because a fan can't produce better performance than the panels already deliver. B'sides, I favor machines with no moving parts.

Are there advantages to installing a panel into the wall, rather than hanging it on a wall like other manufactures suggest?

Sure - they're less inclined to fall off or blow away. :o) Aside from that, vertical panels deliver much better performance - especially in snow areas - and offer the additional benefit of shutting themselves off in the warm season.

Why don’t you offer a roof mount option with your solar heater?

Because that space is reserved for year-round DHW (domestic hot water) and PV (photovoltaic) panels, which really should be mounted on the roof.

Is there a reason your panel does not have an UL Certification? "I checked with an engineer in our HVAC group and he said that there is nothing in the product that would need testing or certification since it is without fans, compressed gasses, heating elements, etc." (Katie King, Customer Service Professional, Underwriters Laboratories Inc.)

Yuppers. I'm not much inclined to make customers pay for non-benefits. Did you price UL certification? Yikes!

Other companies claim their panels heat a number of square feet in a structure, DeSoto Solar rates its models on cubic feet heated. What is the difference and why do you rate yours on cubic feet?

Well, what we're heating is air. Just how many square feet of air are they claiming to be able to heat? Our two models heat either 3000 or 6000 ft³ (cubic feet) of air (ft³ = square footage × ceiling height). The average 2000 sq. ft. home has 15,500 ft³ to heat, which means that 2 large panels and 1 small panel should be enough keep the structure comfortable. Just to ensure comfort, I'd probably suggest 3 of the large panels.