We love the sun! The way we appreciate this gift of nature is by harvesting it whenever we can. One way is by heating water.
We have three solar water heaters that we cobbled together from items at salvage yards, auto part stores, as well as manufactured solar collectors. One is made from a pigmat (I’ll explain below), one includes an imported Swiss panel with a selective surface (I’ll explain that too), and they all can heat water to scalding temperatures. Thankfully we have cold water too.
There will always be a special place in my heart for my first solar water heater, so I’ll start with that one.
My first was a batch heater, made in 2004, our first year on Ampersand’s property. At a salvage yard in Los Alamos, the much beloved Black Hole, I scored a tank. Ten gallons, black, no leaks. And I was glad to find an already constructed box to retrofit as the heater’s shell, because my carpentry skills at the time were minimal.
Some call this design a breadbox heater. The design is simple, much like a solar oven. A dark tank holds the water. The tank is housed in a box, with a window, tilted towards the south. The box is insulated. Simple, right?
A ten gallon tank was perfect size for us. We’re frugal with our water. And the smaller the tank, the less time for the sun to heat the water.
Salvaged materials, whenever possible is one of our key design principles. A salvaged double paned window retains heat. We also insulated the inside of the box with two inches of foam board. Then we lined the inside with reflective mylar. Sun shines through the glass. That which doesn’t hit the tank reflects off the mylar towards it. The dark tank absorbs all that heat.
When I show this to folks on a tour of Ampersand, they usually ask How does the water get into the bathroom?
People see that the water heater is below the window and they wonder how could there be any pressure when it comes out the tap. Here’s the secret. The water line feeding into the bottom of the batch heater actually originates way up the hill at our large rain catching cistern. The bottom of this cistern is above the roof of the bathroom. The water line is buried underground to prevent freezing, so it’s not visible. But there is plenty of pressure that goes right through the heater into the bathroom just from using gravity.
A few details worth sharing. The pipes in and out are wrapped with insulation. The pipe out from the heater goes through a wall into our community bathroom, where the water is used. We installed a valve and a drain on the inlet. In case the tank should need to be drained for repairs or any other reason.
A couple years ago Passive Solar architect Mark Chalom (who has supported Ampersand for years) donated a sheet of selective surface for us to install on our batch heater. A selective surface is a material with high absorbence (of sunlight) and low emittance (of heat) applied to the surface of solar absorbers. In this case, that’s the water tank. It increases the efficiency of a solar heater. This selective surface came as a film and it required a high temperature adhesive to install. We wrapped the tank with the selective surface and, lo and behold, the water temperatures increased.
This batch style heater is still not as efficient as our thermosyphoning ones. But it was easy to construct with salvage materials and a few extra plumbing parts.
Reflectors would increase the sunlight and therefore the heat entering the water tank. I keep thinking I’ll build reflectors for it, someday. Ones that can withstand our high winds
I recently inspected the batch heater to get started on the reflector project, but then realized other work was needed. The wooden box needed more screws to hold it together, the window was sagging. Basically there were air gaps where we were losing heat. And the hose connecting the heater to the bathroom plumbing inside? That needed better insulation. When we have bitter cold spells in the winter, down to 10 degrees F or below, this is where the water freezes. When it does it blocks the warm water in the tank from coming inside. So that was the last round of repairs for the batch heater, and again I postponed the reflectors.
Over the years, we’ve upgraded this heater bit by bit. And I’m impressed that it has served us for so long. In the summer it provides hot water pretty much all the time. In the winter you may have to wait till noon if you want your shower hot.
The winter nights are so long and the outside temperatures are so cold that the heater will lose much of it’s heat by morning. Removable insulation helps retain that heat. In the past we’ve just thrown a blanket over the heater at night. That does make for earlier hot water. But we didn’t always remember to remove it in the morning. And then, when that happens, the blanket doesn’t help at all! It’s a ten gallon tank though, so it heats up pretty quick once it gets some sun.
With anything solar, placement is important. Tall structures that cast a shadow will decrease the amount of solar gain available. We constructed a garden arbor nearby, with some interns and used that task as a design exercise. Together we calculated how to not obstruct the early morning winter sun.
That’s a lot of solar design for one day, but there’s always more. Here’s a glimpse of our fancy thermosiphoning solar water heating systems, a whole other concept.
Six years ago Steve Baer and Zomeworks helped us install a solar thermosiphoning heater on our main house. Thermosiphon is a way of saying that water rises from the panel into the tank above by using the natural qualities of water as it heats. There is no pump needed to circulate the water. It happens on it’s own because heat rises.
This panel also has a selective surface. Our friend Steve Baer imported it from the Swedish company Energie Solaire. It’s not sold by that company to install the way we did. But Steve is a solar pirate and he helped us get it together anyway.
At low pressures (under 32 psi), the Swiss panel (as we like to call it) can freeze and expand with water in it without breaking. That means no need for glycol solution and a heat exchanger, which many solar heaters employ. If the Swiss panel is frozen outside, we can still access the hot water from the tank indoors (a re-purposed 20 gallon electric water heater tank) just by turning on the tap. Once the sun comes out again, the reflectors around the distribution tubing (we used truck radiator tubing) help the ice to thaw and permit the thermosyphon to work again.
The black pigment has worn off over the many seasons. This year I repainted the panel with high temperature barbeque paint. It’s important that the panel rest on a layer of insulation so that it doesn’t lose heat to the ground through the back.
We love the Swiss panel. This photo of our on-demand propane heater, the backup water heater in the house, should explain how well it works. Honestly we have not turned the propane on once since installing the thermosiphoning heater.This is our other thermosiphoning water heater. We use it in the summer for outdoor showers. It’s a great system for demonstrating the thermosiphon set-up because you can see it all in one place.
The panel is below the storage tank. Whenever the sun is shining the water in the tank gets hotter and hotter. This mold for producing this panel was originally constructed to warm nursing sows, that’s why we call it the pigmat. The white tank above (also a re-purposed 20 gallon electric water heater tank) is the gravity feed tank. The hash marks on the vinyl tube tank gauge mark one gallon of water, allowing those using the shower to track their water usage.
I know many of you will want to know how to get the pigmat or the Swiss panel. All I can say is to contact Steve Baer at Zomeworks. I can’t guarantee he will be able to help you, but the inquiry will put a smile on the face of this true solar inventor genius. He will be pleased to hear that there is interest in these simple products, and happy to know that people are interested in using direct sunlight rather than focusing on photovoltaics and pumps when they are not needed. I’ll leave it to him to tell you about the downfalls within the solar industry and why these simple products are not readily available. Happy tinkering!
Ampersand has posted our Spring Schedule! We are excited to offer a Geology Hike, Archeology Hike, Floodplains and Flowforms Hike (new!), as well as Picnics, a Volunteer Day, Homeschool Day, and an Open House. We would love to see you!
Written by Amanda Bramble (with help from Andy Bramble- any incomplete sentences are included because he insisted)