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Harvesting energy with home made solar thermal collector

2017-12-21 08:47  
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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.


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