This is very much a "lets-just-see-if-it-works"-type test, and thus has all sorts of caveats and problems built in from the word go. The first one being that as soon as the plastic piping we used to connect it up warmed up slightly, its flexibility increased, and it sagged, immediately preventing the thermosyphon effect from taking place.
(A quick lesson: In order for the water to circulate by itself, the piping must be 'uphill' all the way from the lowest point of the loop to the highest. Then, as the water is heated in the panel, it becomes less dense and rises up, whilst the denser, colder water in the tank sinks down the other side of the loop into the bottom of the panel. The water heats up a little more on each cycle through the panel, gradually raising the temperature of the tank water. The neat thing about this setup is that at night the circulation stops naturally once the panel temperature drops below the tank temperature, thus preventing the panel from radiating away all that heat you've carefully collected - and no valves or pumps required.)
Problem 1 solved (for the time being at least):
A most encouraging sight (hot water entering the tank - click on the picture for a larger, clearer view):
Problem number two. This impromptu water tank is made from a polystyrene cold box I found lying around. I knew it was going to leak, but it managed nearly a day-and-a-half before it became a problem - more than enough for the first try:
It's also a very small volume for this panel, around 13 litres including the water in the pipework. The next step will be to make a tank bigger than this, yet smaller than the big blue behemoth - perhaps around 50 litres, with decent insulation, so we can gather some more useful data from it.
And on that subject, oh for a nice datalogger and some thermistors! At the moment I have 3 glass/liquid thermometers of slightly dubious accuracy, which I obviously have to directly observe every time I want a reading.
Still, we hit 63°C after a couple of hours, which is nice. It was too hot for me to rescue my thermometer by hand when I accidentally dropped it into the tank.
Projects for the next few weeks:
- make a ~50 litre insulated tank.
- move panel another 20 yards so it's not shaded at certain times in the afternoon.
- give it some legs to prop it up at the right angle so it's actually pointing at the sun.
- build a platform for the water tank to sit on.
- connect it up with some proper pipework.
- run some day-long and week-long tests.
- work out how on earth to strip about 50% of the weight out of the design!
