Concentration of CO2 in the Atmosphere

Solar Hot Water in the Age of Solar Electricity

The Tin Mountain Renewable Energy Initiative (TIMREI) solar raiser team prepares to install a flat plate solar hot water collector. These plates are heavy and require lots of muscle power. (Photo TIMREI).

Russ Lanoie

For many years, the best way to capture the energy of the sun, other than by inviting it through south-facing windows, was to use it to heat domestic hot water. The advantage to solar hot water is that it does not require very sophisticated technology to capture the energy of the sun and transfer it into water for either residential or commercial use. There are lots of do-it-yourself schemes, such as bread box heaters, that involve almost no technology by simply placing a black-painted water tank inside of an insulated box glazed with any of several available transparent or translucent glazing materials, sometimes as simple as old storm windows. I had a hose connected to an old water tank with no glazing and fully exposed to the sun for use as an outside shower for summertime. Sometimes the water would almost reach scalding temperatures on warm sunny days.

On the other end of the scale are hot water systems that are used for space heating with storage tanks connected to pumps and controls that circulate hot water through pipes imbedded in a floor or other distribution system. These are generally engineered systems requiring a lot of technology and hardware.

The most common application has been for residential hot water similar to the evacuated tube system shown in the photo or simple “flat plate” collectors that consisted of a glass or other type of glazing covering an insulated box with an “absorber plate” generally made of copper with a series of pipes running through it that connect to a storage tank much like a conventional water heater. I will explain the system that has successfully served my own home since I installed it in 1978.

As my wife and I operated a business we called Alternative Systems in the mid-70s, we built a house that incorporated much of the technology we sold at the time. A Fisher woodstove, still in use, a composting toilet that served for many years, Window Quilts, and a Daystar solar hot water system. The Daystar system came as a complete package, and I sold several of them, some to DIYers and others to customers who had plumbers do the installation. A few were roof mounted, but several were mounted closer to the ground, generally at a 45-degree angle to optimize their ability to capture the sun year-round. A friend mounted his so they could be tilted with the seasons to gain even more sun.

My own system was the subject of a federal monitoring program that consisted of metering hot water and backup electricity and a run time meter on the circulator pump. A researcher visited my house periodically to take readings that showed that our system provided 85% of our hot water even with two little ones in reusable diapers! To optimize the system, we even had a switch that would allow us to turn off the back-up electric power on mornings when the sky was clear to the west, indicating that the day’s washing would be in sun-heated hot water.

The system did require some maintenance, as the water from our municipal system tends to rot out water heaters very quickly. Our biggest expense was to replace the stone-line tank a couple of times until we finally installed a “lifetime” high-performance stainless-steel tank. One replacement control module and one or two circulator pumps were the other plumbing components replaced in over forty years of service, while the original collectors still gather the energy from the sun every times it comes out. The bigger issue is replacing the roof shingles on the south side of our roof, because the collectors will have to be removed and, hopefully replaced with a couple of spare collectors that I have. I’ve been able to get by with the original shingles by painting them with aluminum paint every few years but has finally run its course. Note that hot water collectors are MUCH heavier than the solar electric PV panels that are beginning to take their place which has been much of the reason for my procrastination.

It is not so much that today’s solar electric photovoltaic (PV) panels are so much lighter than solar hot water collectors, as it is their cost has plummeted and their efficiency increased while the cost of electricity is constantly climbing. There are many advantages to PVs over solar hot water systems, not the least is that there are no mechanical components to wear out or a heat transfer fluid to leak or need changing. PVs can be installed almost anywhere within reasonable reach of wiring, either from the roof down or underground from a ground mount system.

PVs, however, are not generally a DIY installation. PV installations usually will need the services of a licensed electrician to make the proper connection into the structure’s wiring system in conjunction with the local utility’s requirements, at least in grid-tied systems (not off-grid with battery backup).

Russ Lanoie is a long-time solar proponent in New Hampshire’s White Mountains and operated his Alternative Systems business in the 1970s—80s selling solar hot water systems, composting toilets and Window Quilts®. He lives in a passive solar home which has had Daystar solar hot water for forty years and 11kW of PVs on his barn since 2015.

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