Playing with some Evacuated Tubes

An Eccentric Anomaly: Ed Davies's Blog

My House Sketch shows evacuated-tube solar-thermal panels along the bottom of the south roof. An offer came up which would save at least £1200 relative to possible alternatives so, with a bit of prodding by skyewright, I ordered them the other week and they arrived on Tuesday. I had to have a play, of course.

Monday and Tuesday were beautifully warm - it felt uncomfortably hot walking around the harbour in Wick on Monday afternoon before a hospital appointment. (Actually, the temperature wasn't that high but it's probably a matter of adaption.)

Nice 22 kW PV array on the roof of that harbour building. Did somebody say “obsessive”?

I took a tube out with a heat pipe in on Tuesday afternoon. The copper top of the heat pipe got pretty hot though I didn't keep it out long enough for it to be untouchable. It did surprise me, though, how long it took before heating at the top end started. I guess it takes a while for the heat transfer material to start to evaporate - perhaps it has to melt first.

Wednesday was horribly dark and I didn't bother.

This morning (Thursday) it was pretty grey though the clouds were intermittently thinning enough to show where the Sun was and occasionally to cast shadows. My little PV panels were mostly about breaking even with the 2 W self-consumption of the MPPT charge controller with the odd forays to 8 W or so (compared with typical bright sunshine output of high 30s watts).

I propped two tubes outside, one proper tube with a heat pipe in it and one spare glass envelope filled with water with a bread-wrapper stuffed in the top to reduce evaporation.

By early afternoon the cloud was persistently thick and there were the odd spots of light drizzle with a brisk northerly wind at about 8 °C. I went out wondering if there would be any detectable heating at all so was quite impressed to find that the top of the heat pipe was quite noticeably warm (despite being exposed to the wind) and the water in the other tube had reached 26 °C.

It is, of course, worth remembering the difference between the temperature reached and the amount of power available. Still, an encouraging start.

Just for interest I pulled the heat pipe part way out of its tube:

As my neighbours commented, all I have to do now is build a house to put them on. In the mean time I'm busy squirrelling away boxes in odd corners of this house.