In the world of alternative energy, solar photovoltaics is king. In fact the pro-solar buzz here in the US has gotten so loud that confused bee colonies have been flying in from overseas expecting to find the Bee Mardi Gras in full session.
But bees and humans alike, listen up!
You need to know that there is more to the solar energy story than just photovoltaics. First, absorbing the sun’s energy and then converting it to electricity is one effective way to harvest it for practical purposes, which is not in dispute. But there is a simpler, more elemental option available called solar thermal  that can put the sun’s rays to equally good use while eliminating the need for any sophisticated capture-and-conversion process.
Our nearest star bathes the surface of this blessed planet with an inexhaustible supply of free energy each and every day. Solar thermal systems allow us to trap the heat contained within the sun’s emanations and transfer it directly into our homes, where it can be used to raise the temperature of water or even meet a portion of a family’s space heating needs. Solar thermal set-ups are ingeniously and somewhat intricately designed, but the way they function is easy to understand and is based on fundamental principles of physical science. If you have ever carried a pail of water out into the sunshine to warm it, you are already familiar with the basic idea, with the only real difference being that solar thermal technology actually brings the sun’s heat directly into your home instead of forcing you to go outside to find it.
Even though solar thermal systems are sometimes designed to heat homes, in the vast majority of instances they are constructed and installed as replacements for conventional water heaters. In fact the overall efficiency of solar thermal space heaters is somewhat in dispute, since heating systems are expected to warm interior spaces primarily during times when sunlight is at its most scarce (i.e. in the wintertime and at night).
If you live in a climate that does not experience bitterly cold temperatures even during the darkest days of January, solar space heating might be worth a closer look. But for most off-the-gridders in most locations, this technology probably doesn’t have much to offer. Consequently, in this discussion we will narrow our focus and concentrate strictly on solar thermal systems that are used to heat water, which is a subject that should be of great interest to grid-phobic homesteaders looking to reduce the burden on their home power-generating systems.
Why Solar Thermal?
It is estimated that water heating costs comprise approximately 20% of the average American household’s electrical bill. But studies indicate that switching from a conventional electric hot water heater to a solar thermal system can reduce the amount of electricity required for this purpose by 50-80% , which should certainly pique the interest of conservation-minded off-the-gridders everywhere. What makes these numbers even especially remarkable is that most solar thermal water heaters come with electrical pumps and a backup heating unit, the latter of which is necessary to help homeowners get through days when the sun is not shining or when water demand is excessively high. So even though they are not net-zero users of electricity, solar thermal set-ups are still energy savers extraordinaire, capable of paying for themselves in perhaps 5-10 years time despite their relatively high upfront costs.
Depending on the size and characteristics of the materials and equipment purchased, a solar thermal water heating system could cost you anywhere from $2,000 to $10,000, which obviously represents a significant expenditure for any off-the-gridder not lucky enough to have a gold mine on his land. But make no mistake, a solar thermal system will pay for itself over time through accumulated energy savings, and if you should ultimately decide to fork over a wheelbarrow’s worth of greenbacks in order to purchase one, you will never be sorry that you did.
Once a solar thermal water heater has been installed, it should last 30 to 40 years without breaking down or needing replacement. Moving parts in pumps and conventional backup heaters may occasionally have to be replaced, perhaps every few years, but the materials used in solar thermal assemblies are solid and durable and every part of the system is built for the long haul.
Solar energy set-ups require approval from local government authorities, meaning you will likely have to acquire building permits, plumbing permits, and electrical permits before you can proceed with a solar thermal installation. But if you purchase your system from an authorized dealer, this part of the process should be merely a formality, since regulatory agencies these days seem to be pretty favorably disposed toward alternative energy.
Solar Thermal Up Close And Personal
Solar hot water thermal systems generally include a solar collector, one or two storage tanks, a backup electrical heating element, and a network of pipes through which water or a non-freezing heat-transfer liquid can circulate to absorb and transport the sun’s warmth from outside to inside the home. In most instances, an electric pump will also be necessary to keep the system’s liquid contents flowing freely, but there is one type of popular solar water heater (the thermosyphon, discussed below) that does not require any extra power input to facilitate efficient liquid movement and heat transfer.
The solar collector  is the heart and soul of any solar thermal hot water system. Should you decide to go the solar thermal route, you would have your choice of the following collector options:
- Flat-plate collectors: The most common type of residential solar thermal collector, a flat-plate collector panel consists of a shallow insulated box containing a dark absorber plate protected beneath a glass or polymer plastic cover. Flat-plate collectors have very little vertical extension and are designed to unobtrusively merge with the roof of a home. A flat-plate collector relies on a heat transfer fluid to circulate and carry solar heat from the collector to a water storage tank installed inside the home.
- Integral collector-storage systems: ICS water heating systems  are relatively simple devices that hold metal or plastic tubes inside a glazed, insulated box. Cold water circulates directly through these tubes, picking up the sun’s warmth from the collector before moving back inside to be stored for later use. Many ICS collectors only preheat the water that flows through them, thereby reducing the heating loads on conventional electric water heaters used in conjunction with the ICS. Because ICS systems require water to be piped outside, they are not appropriate for use in areas of the country where frigid temperatures are common during the winter, since the tubes inside the collector do not insulate the water that flows through them and thus are incapable of preventing it from freezing.
- Evacuated-tube collectors: Often found in commercial settings but not frequently used for residential applications at this time, evacuated-tube collectors feature parallel rows of metal absorber tubes encased in glass and surrounded by a vacuum on all sides. The absorber tubes have fins attached on the bottom that soak up solar energy and transport it to interior spaces via the circulation of a non-freezing liquid, and because they are surrounded by a vacuum, heat loss through conduction and convection is eliminated. This is undoubtedly the most powerful and efficient type of solar thermal collector available on the market, but because of its advanced design it does not come cheap.
- Thermosyphon: This is a specialized type of passive solar collector (meaning no electrical pumps are used) that relies on the heat of the sun, the laws of gravity, and the tendency of warm water to rise while cold water sinks to make magic happen. With a thermosyphon, the solar collector must be installed below the storage tank so that as water heats, it will move up through the collector pipes and into the tank while colder water flows back into the system from above in an endless cycle of gravitationally-inspired movement. Thermosyphons are obviously not well suited for colder climates since they circulate water through their collectors instead of a non-freezing heat transfer liquid. Additionally, if the collectors are to be installed on a roof, the storage tank will have to be put up there as well, so anyone putting in a thermosyphon will have to make sure that the roof of his home is strong enough to support all of that weight.
As we have already mentioned, a solar thermal system can indeed cost a pretty penny and that isn’t pretty at all. But if you are intrigued by everything about solar thermal except the price, you can always channel your inner MacGyver and try to build a system all on your own. There are oodles and oodles of people who have designed and built their own fully-functional solar thermal water heating systems, using a wide variety of innovative ideas and concepts, and if you would like to try to build one yourself you should have no trouble finding guidance and instruction on helpful websites all across the Internet. Thermosyphons have proven especially attractive to DIY’ers because they don’t have moving parts, depend on simple principles of operation, and can often be put together with scavenged or recycled materials.
A home-made thermosyphon  can be a good choice if you just want to satisfy a modest percentage of your household hot water needs with solar thermal. But if you would like to provide your family with all the hot water it could ever hope to use and then some, you would be wise to invest in a ready-made thermal system. It might cost you more than you want to pay, but keep in mind that such a system will most certainly give you a positive return on your investment in just a few years time, while also freeing up valuable energy resources that can be used for other purposes.
The total cost of a pre-fab solar thermal system will depend largely on how much solar collector area is required and on the size of the solar water storage tank. Assuming for the moment you would like to meet all of your hot water requirements with your solar thermal set-up, you should plan on purchasing at least 20 square feet of solar collector panel for each of the first two members of your household, and then you will need to add an extra 8 square feet for each additional person residing in your home (if you live in the Sun Belt) and 12-14 extra square feet if you live in the northern United States or Canada. Regardless of whether you plan to install your collector panels on your roof or on the ground, it is important that they face the south during the daytime and be completely un-shaded during all hours when the sun is visible and above the horizon.
As for the water tank, you will need approximately 1.5 gallons of storage capacity for each square foot of collector that you install. Solar thermal storage tanks are frequently sold with storage capacities of 66, 80, or 120 gallons, and the size you choose will essentially be a function of how many people you have living under your roof. To put it in terms that will be easily understood by fans of classic television series, Andy, Opie, and Aunt Bee would likely do just fine with a small 66-gallon tank, while the Cleavers would require the 80-gallon version and the 120-gallon model would be ideal for the Waltons or the Brady Bunch.
Harvesting The Stars
Could a solar thermal water heating system be right for you? Only you can answer that question for certain, since only you know for sure if there is room for one in your current home improvement budget. Even if you don’t think you can afford a full-sized solar thermal set-up at this time, however, you should still take a closer look at some of the clever DIY designs  available for your perusal on various websites that cater to the self-sufficient and independent-minded.
Perhaps a small do-it-yourself unit would be a good place for you to start, and if you like the results you obtain, you could either expand that system or replace it with a high-efficiency pre-fabricated model. Regardless of what you decide to do, just remember that your homestead is being bombarded each and every day (even on the cloudy ones) with astonishingly abundant supplies of free solar energy, and if you install a solar thermal water heating system on your property, it will allow you to finally make the most of the electromagnetic bounty that God and nature have so generously provided.