Solar Hot Water 3

The water heater is completed and working. Finally. We’ve been enjoying hot showers now for several weeks after nearly three months of no water heater. Very nice! The photo above is a shot of the controller which compares the temperatures of the collector on the roof and the water in the storage tank. The upper display shows the temperature of the collector box as 165 degrees F. while the water in the storage tank is 128.9 degrees F. When the temperature difference is about 7 or 8 degrees, higher in the collector, of course, the controller turns on the two little pumps which circulate the water up to the roof for heating. The water continues on down into the heat exchanger in the storage tank and gives off some of its heat to the storage water. If the sun sets, or clouds cause the temperature of the collector to drop below that of the storage water, the controller turns off the pumps. The water in the pipes running up to and through the collector then drains back down into the cleverly-named drainback tank. This is all automatic, no human input needed once everything is adjusted.

The water needs to drain back down into the drainback tank because, otherwise, should the temperature up on the roof and in the collector box drop to freezing, catastrophic damage would be done to the piping. Every time the pumps turn off, for any reason, all the water drains back down into the drainback tank, where it is stored until the pumps turn on again. Very handy.

This is the drainback tank. On the upper right is the copper pipe coming down from the collector on the roof. On the lower left is the outlet pipe leading to the top of the storage tank, where the outlet is connected to that copper heat exchanger that sits down inside the water in the storage tank. The clear acrylic, vertical tube is called a sight tube. It shows the level of the water in the drainback tank. In this photo, the pumps are off, as the sun has set, and the level of water shown in the tube is near the top. Once the pumps start, that level drops as the water is pushed up to the roof to be heated. Thus, the sight tube is a visual check to see whether the system is in operation and whether the system is losing water somehow. The drainback tank itself is just a stainless steel, 10-gallon tank which is surrounded—beneath that gray, plastic covering—by an inch of polyurethane foam, for insulation.

Here are the two pumps. They are connected to the outlet pipe of the heat exchanger that sits down inside the storage tank. Each pump is only about the size of a clenched fist. They work in tandem to pump water out of the heat exchanger and up to the roof. As the water is pumped out of the exchanger, more water flows down from the drainback tank. So, the water that is being heated on the roof is constantly circulating from the roof, down to the drainback tank, down from there into the heat exchanger, then back up to the roof. As I mentioned before, if the pumps turn off, then the water simply drains down from the roof into the drainback tank.

Choosing the pumps to use took me some time and research. There are a number of very good pumps available, but most of them are 120-volt pumps and rather pricey. I decided to take the time to attempt to find a 12-volt DC pump that would work. This would save me some electricity, as some is used to invert the 12-volt current from my battery bank to the 120-volt AC current. Usually, not inverting is more efficient, as long as the DC pump is equal to the AC pump in efficiency and power rating. I finally found a pump, and it was much less expensive than the AC pumps I’d been checking. Plus, the electrical usage was a bare fraction of that needed by the most efficient AC pumps I saw. However, in corresponding with the DC pump dealer, I realized that the head, or the vertical distance the pump would be pushing the water up to the collector on the roof, was right at the maximum rating for the DC pump. So, I bought two of those pumps, as using them in tandem greatly increases the head they can handle. Even buying two of them, the price was still a quarter or less than the cost of the AC pumps and the electrical usage still a fraction.

Here is a photo of the indoor part of the system, all complete and operating in the corner of the greenhouse. So far, everything is going well. The storage tank is rated to lose about 0.7 degrees F. per hour, and after a couple weeks, that is about what I’m seeing. If the pumps turn off at sundown and the storage tank water temperature is, for example, 140 degrees, I am finding the water to be 125 degrees or so the next morning. The storage tank has two inches of urethane foam surrounding it, and as can be seen, I have covered most of the pipe and fittings with rubber pipe insulation. The white plastic [Pex] line on the lower right is the cold water input to the storage tank, and insulating it would serve no purpose.

To date, the highest temperature I’ve seen in the storage tank has been 144.7 degrees F. This is in November. Mixing that hot water with some cold for our showers means we have more than enough for the two of us to bathe. More experience will be needed to determine how well all this serves us over a longer period of time. Already, there have been a few cloudy days during which we heated no water. Summers here will, of course, have longer sunlight hours; but over the past ten or fifteen years, we have seen cloud build-up by late morning during the summer, clouds which hang around til mid-afternoon. It is entirely possible that, because of this sky condition, we will not see much hotter water on a regular basis. However, time will tell.

As to the cost, when I began looking into a solar water heating system, I first researched entire systems, package deals including the tanks, pumps, collectors, and so on. I was advised by dealers, and read in various online and magazine sources, that a modest system such as we wanted could easily reach $7,000 to perhaps $10,000, once all the pipes and fittings and insulation were purchased.

I then began to look for collectors, as I had already purchased my storage tank anyway. The hooking up of everything is time consuming, but it isn’t an extremely technical project. Gravity, sun exposure, electricity. However, I quickly found that simply purchasing a collector locally was probably out of the question. Dealers who had them would only sell to contractors. And few dealers had them. I found a number of makes and models of collectors listed online. Several of them told me the same thing: they would ship to dealers. I was advised to make nice with a dealer and try to talk one into ordering one for me. I did find a couple of sources who were willing and ready to sell me a collector, but then I found out the next problem: shipping. These items are over-sized, many of them in the range of four feet by eight feet and others four feet by ten feet. They all have a transparent face, naturally, either of glass or polycarbonate or some other breakable substance. Shipping, therefore, was estimated to be about the cost of the collector itself. The collectors I found were either roughly $800 to $1400 or were less expensive than that but smaller, necessitating two or more to get the water-heating job done. The shipping averaged $750 for a collector, which included a crating charge to protect the fragile glazing. Therefore, I was looking at $1500+ to have a collector delivered here to the house.

So. I made a constuction list of the components of the collector I might want to build, instead, and went to various retailers to get prices for copper fittings, pipe, wood—everything I could think of. The web site, BuildItSolar.com, was invaluable in this task, as I was able to visualize the entire building process. Not only that, but there are any number of ways to construct a collector, and quite an array of materials to use [copper pipe or plastic pipe, glass glazing or plastic, wood frames or aluminum or galvanized metal or....]. The BuildItSolar site has articles, with many photos, of what others have tried and how well their collectors performed.

I built my own. The final tally came to $370. Far less than the $1500 or more for a commercially-built collector. That total does not count my time, labor, and gas to drive to buy parts, but it isn’t bad at all. I could have cut down that cost by using less-expensive glazing [such as single-walled polycarbonate rather than double-walled] and a few other things. But $370 is ok.

The system itself cost me $2,200. Far less than the $7,000 or far more I was told to expect. Of course, again, my labor was free, and that made a big difference. The $2,200 includes the cost of the collector. I had a few copper fittings, pieces of sheet metal, and some PEX pipe around from previous projects, but all together, those items probably came to less than $50, if I had needed to purchase them, though I made no attempt to try to figure that into my summary of total cost. I also had all the hand tools needed to construct the system. I used a Sawzall, an electric drill, sheet-metal snips, soldering supplies, various wrenches, files, screwdrivers, sawhorses, and so on. My table saw, bench vice, and saber saw came in handy but were not necessary. The one tool I purchased, and which I highly recommend, was the modified ViceGrip clamp for snugging the aluminum fins around the copper pipes in the collector. I paid $22 for it, and I saw the clamp itself for $21 at a Lowe’s—I’d have had to weld a pair of steel plates to it if I’d made my own. For $1, it was a bargain.

Would I recommend building one’s own collector? Sure, I saved more than a thousand dollars, considering shipping. How about the system itself? Again, sure, I saved several thousand dollars there, at least. The drawback was that it took me quite a while, and we waited to have a water heater for over two months. Then there was the pleasure of doing it myself….