DIY: Collecting solar, hot water


  1. Used electric boiler, 50 l;
  2. Spiral black pipe, inner volume 5 l max; Frame it (opt. / recomm. );
  3. TWO Thermostats, used in same boilers;
  4. Solar panel 10W;
  5. Mill type water pump 5W;
  6. Three pipe taps (keys), some T connections;

Below, more detailed description and scheme.
I have ~0,1 bar in pipes. In case of city pressure, ~2 bar, I have no idea how little pump would circle water.

Solar hot water collector, active system. Scheme.

1: Connect spirals outlet to boiler’s hot water outlet (inner, long pipe) RED. Connect boiler’s inlet BLUE to spiral’s inlet. Connect T fork below RED for hot water outlet. Connect T fork for immediate pump and spirals BLUE?

2: Not needed long pipe. Shorter it is, more frequent pump switch, shorter pumping. Instead, good idea to frame it, to collect more heat.

3: Ideal would be to use electric, programmable (but still two) thermostats, but quite more electronics needed, esp. if this meant be running exceptionally from solar panel only. No battery is needed.
The first trick, is to remake one of t-stats. Be default, they switch-off when are hot. Have to remake it in to switch-on. Might take a nerve. Make sure the click remains when touching contacts. Slow touch makes contacts oxide very fast.
This t-stat needs to be injected in to pipe of spiral, at the outlet. It switch-on the pump to rotate hot water. It cuts power when cold water (from boiler) reaching this, 1st t-stat.

Second t-stat stays as it is in the boiler. It is needed to cut the power, when collected water in heater is hot. Without – it will be circling the pipe continuously, when temp. in pipes and boiler are equal.

Will take a nerve to adjust them both for the most efficiency. Otherwise, circling of hot water in pipes will be cut only when water will get chilled to cut the 1st t-stat;

4 / 5: Solar connected straight to the pump. Such a single pump serves me already for two years, never failed, once cleaned b/c of little stones blockage. A filter before it would be preferable. Overcast conditions are still generate enough power to run the pump. Cover exact part of solar, so it stops the pump when is shady, but still enough to pickup when sun comes back. Place the solar nearest spirals;

6: In order of proper flow of water in pipes, when hot water from the boiler needs to be taken, flow in spirals should be cut. See the scheme.

Pipe spiral. Mechanical thermostat. Solar 10W.
Mechanical rod thermostat. Rod installed through the hole in L connector.
Tiny (45x35x25mm) mill water pupm. 5W.
El. Boiler. Collecting water circles in opposite directions: in-hot-“outlet” and out-cold”inlet”.