Harvesting energy with home made solar thermal collector

Nearest star from Earth is Sun. And it emits huge amount of energy which is free. No surprise many people try to get most of it with minimal cost. Photovoltaic solar panels still have low efficiency and yet are quite expensive. Everyday we hear how their efficiency is increased by introducing new technologies. Anyway solar panels require direct Sun which in some regions doesn’t appear very often. So how we can get this energy with almost no initial cost? The easiest way to do so is to build a solar thermal collector. You can find lots of high efficient commercial collectors. They look great and at some level works in winter time when Sun shines. I decided to go simpler. I need hot water only in spring, summer and fall. In winter time I burn wood to heat the house an so water. In summer time I usually heated water using electric boiler which generates nice bills at the end of month. No more…

So I started this project which is still in testing phase. But seems to work fine. Lets go through build process how I made a simple solar collector using old window frame. First of all I was lucky I’ve got this old window frame which area is about 1 square meter.

It has two glasses in both sides. I removed one glass and replaced it with OSB sheet. Then placed about 30mm of stone wool for thermal resistance:

Luckily the window frame opens like a book. Four screws holds it together. Depth from glass to the middle is about 30mm – enough space for insulation in one side and for placing heat carrier pipe on another. OK next step was to place a tin sheet which will accumulate Sun radiation energy.

Tin is reflective and reflects most of energy like a mirror. We need to absorb as much energy as possible. Best solution for this is to cover it with black paint. I covered it with non glossy paint so it would not reflect any light. The darker is better. I found that paint coating works great as it is non glossy.

After this is done we can proceed to pipe which will remove heat from black tin absorber. Here you can argue that metal pipe will work best (maybe copper or aluminum) if you have one around – use it. I had several meters of PP-R plastic aluminum 18mm diameter pipe (7 meters of it). Didn’t want to waste money on new one so I used it. Painted it with same black color and bended it to form serpentine shape:

Painted non black spots at fixture places and covered with top part of window with glass.

Now fun part begins. I wanted to integrate solar collector it in to existing home water system. So I attached pipes to same water heater that works with home heater. I used three-way pipe connector with valves so I could disconnect any of it at any time. In summer time I just want only solar heater, so I disconnect boiler from house heating system and leave only solar to circulate hot water. I used 20mm plastic pipes to connect collector to boiler as they are cheap and easy to assemble:

We all know that best place to put solar collector is roof. Here it gets most of sun and is in safe place. I decided to go different way. When you put solar collector on the roof it is higher than water boiler. You will definitely need a water pump to circulate hot water down. I wanted natural flow when water from collector flows upwards without any pumps. So I decided to put it lower than boiler which is on the ground. You can see that pipes are going up from collector. I insulated hot water pipe to preserve hot water from cooling until it reaches water heater tank.

I found spot where sun sines most part of the day and is convenient to put. Still considering about flowers on the ground, but it seems that they don’t have significant effect on collector. Might be I’ll leave them for a while.

Set up is still fresh and in testing phase. Probably one collector won’t be enough to heat 120L of water. There is another same size window frame lying in the garage so probably I will assemble another one to put aside. I will give updates on how it works pretty soon.

16 Comments:

  1. It would be interesting to see how this works since you can’t be at the optimum angle to the sun. 45 degrees off collects half the energy, which is why good solar arrays track eth sun.

  2. very nice diy, really

    do you think that doing more rubber turns would increase collected heat or is it just enough ?

    regards 🙂

  3. Tom, I agree, the angle isn’t optimal. Just didn’t want collector to stand out as it sits on the ground. I plan to compensate this with additional same panel. But it already works fine (I’m not the first one who is doing this way). Yesterday we could already enjoy warm shower 🙂
    imayada, by saying rubber you have in mind the collector pipe? Actually there could be more turns of it, but this is what I could do with my hands. Besides this is why painted tin sheet is used. It accumulates sun energy and then transfers it to collector.

  4. What temperature does the water get to?

  5. Temperature actually could be better. Didn’t have a chance to measure it but seems to be about 40 degrees of Celsius. Enough to take a shower. I am working on second collector where I will increase the number of turns using different technique.

  6. 40 degrees is still pretty impressive. If anything, I hate the hot water being too hot. If water can come out hot enough to scald you, it’s a waste of energy and money.

  7. I’ve been thinking about doing something siimilar; I’m thinking about going for a water reservoir in the form of an old oil drum or something. This I will paint matte black to collect heat in the water.

    I’ll not use that water itself, though, but run a spiral of copper wire through it to transfer heat to the water going into the electric boiler. I don’t live on a place where the weather will allow me to use solar heated water only, but I’m thinking that every degree C I can heat the water before putting it into the boiler is a degree I don’t have to gain by electricity.

    Also, having a reservoir like this should provide at least some heating, as the reservoir water should not be colder than the ambient temperature, while the water in the pipes is about 4-5 degrees.

  8. You will really want to watch out with Legionella, though. When you use the water daily, there is little build-up of legionella cultures, but when you are out for a long weekend, the water can get severely infected.

    To avoid this, collectors typically have some (automated) backwash. The simplest form that I made was with two extra threeway valves: on the cold side and one on the hot-side. The one on the hot-side has a garden-hose coupling. You can then connect the garden hose to it, and push water trough it, washing the collector (and in your case the pipes leading to it) clean. Five minutes of cleaning before taking a shower to avoid getting Legionnaires’ disease 🙂

  9. why not runn it in series with the heater… cold >> solar >> electric.. that way the electric heater will take up the slack when its not as sunny… since i assume the eclectic heater has a regulated outlet… itll just turn itself off when its sunny, fit a bypass so you can bypass the solar side if you want to work on it.

  10. @Ber – I used to have a collector exactly like this at my last place (but 3 x the size and pump driven as it was on the roof), you’re unlikely to get Legionella as the water has chlorine in to kill the Legionella. Backwashing the collector won’t help if there is Legionella in the system, as it will be in the tank and all the pipes too!

  11. I think he is using an heat exchanger isnt he?
    If not, you realy should think about it, cause the legionnaires and also there is a big problem that plastic pipes contains plasticizer.
    When you use them for cold whater (which they are made for) its no problem, but if you put them directly into the sun and put hot water through them, they will put these substances into the whater, which results that you drink water enriched with poisonous and DNA-changing substances.

    Greetings Michael

    PS: I am planning such an construction and will try to evaluate if i could put the bassin next to the panel on the roof and not under the roof

  12. oh no please someone let me out of this HTML-Tag O.O

    xD

  13. Wait, I thought I understood this until the very end.

    Of course I’m using heat exchanger.

    Where is the heat exchanger? Does the water heated in the solar collector come out of your hot water tap or does it just loop through a heat exchanger to warm the tap water indirectly?

  14. Indirectly. See image bellow:
    collector sketch

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