Evacuated solar panels

The Navitron site

On Sun, 20 Jul 2008 14:21:57 +0100 someone who may be Bill Taylor wrote this:-

Seconded.

However, as they were, IIRC, mentioned in a recent thread on the subject I assume that they are not " *good* " enough.

Not sure about 'on the web' but I installed a system back in the UK. Bought the equipment from a supplier who also gave me a 'diy manual' - and came to check / commission the system...

It had three temperature sensors - one in a specially-formed 'pocket' set in the side of the hot-water cylinder, one on the manifold (where the solar 'tubes' were mounted ion the roof, and the third sensor on the return pipe from the tank coil (again - mounted in a 'pocket')

The controller had very few adjustments - it was possible to set the differential temperature between the panel and the tank at which point the circulating pump would stop/start - also there was a preset 'frost' temperature at which point the pump would start to prevent the system icing up (don't think it was ever activated).

More or less a 'fit & forget' installation. Clever controllers would also data-log - so you could see how long the pump had run per day.

Without getting into the holy war - the system was backed up by an immersion heater - but without the intervention of our immersion it supplied out dhw requirements for a family of 2 between march and september (location - Suffolk)...

Any questions - feel free to email me - email address works...

Regards Adrian

why mot leave them permanently off? or On..won't make much difference either way ;-)

My system has three sensors, one at the top of the collector, one about 1/4 way up the cylinder in a pocket, and one near the top of the cylinder also in a pocket. When the collector is 10 degrees above the temperature of the lower cylinder collector the pump starts. It runs until the temperature difference drops to 5 degrees when it stops and waits for the differential to rise again. The top cylinder stat acts as an overheat preventer to reduce risk of scalding if the top of the cylinder rises above 60 degrees. This range works fine for me. You could if you wanted have a higher top level setting and use a thermostatice blending valve but why fix what isn't broken? The whole kit (panel, sensors, pump, cylinder, controller, high temperature lagging, inhibited antifreeze for the circulating circuit and an expansion vessel kit) cost me circa =A31000 from an ebay shop with some pipe from my local supplier. With the ever increasing prices of energy I reckon the payback time is progressively reducing :-) I didn't charge myself for installation!

simplest option with vac tubes is to run the pump from a solar pv panel. Doesnt work so well with flat plate.

NT

PV cells are much less efficient than evacuated tubes though. Evacuated tubes will still collect a reasonable amount of heat in overcast conditions, but the PV cells to drive the pump circuit won't work very well in such conditions. Such a system will need to include a battery backup - use a larger than required PV panel to charge the batteries during sunny periods, and run off the battery when overcast.

dan.

Nothing simple about that at all.

• It runs the pump at the wrong time. Midsummer, and that's about it. You need pumping over much more of the useful solar year than you can expect useful PV output. That's why we in the UK bother with solar water heating, but not PV!

• Cheap commonplace pumps need AC, PV is DC. You can provide a sensible controller for much less cost than an inverter.

• If you do want PV pumping for an off-grid solar system, at least provide a good batter backup.

I take it that's a sledge hammer permanently roped to the roof to smash the bloody things up when they fail to deliver what the salesman promised?

You mean they don't. I'm shocked.

I must invite one of these guys round next time I'm in need of some evening entertainment. I wonder if they sell to the man of the house, the lady or both. That would be an opportunity for practising my favourite unnerving technique. Chair at each end of the room, couch in the middle in between, forming a shallow angle. Salesman sitting in the middle finds it very awkward.

A couch? How decadent. No salesman worth his salt would fall for that old chestnut.

Some are not very professional.