Solar thermal/PV systems

[liberti]

I would like to ask for advice on using PV panels to run the pump and controller. From a practical point of view am I better off generating and inverting to drive the standard 240v pump & controller and what wattage panels would be required?

Would I be better using 12v  pump and controller (assuming controller exists in 12v form) Can anyone recommend a supplier?

Are the PV and evac tubes 'balanced' - by that I mean are the PV panels able to produce the power to enable the energy captured by tubes to be circulated on say a cloudy spring day?

Thanks,
Geraint Hughes.

[filipinobrian]

I am sure the professional renewable engery folks here will reply soon, but I've got to tell you its a very bad idea! The evac tube systems get very hot even on a cloudy day, when there isn't enough sun to power the pump through even a large pv solar panel.

I experimented last month whith a home made flat plate collector, a 32 watt solar panel & a 12v dc computer cooling pump. The pumped worked on sunny days and I got hot water. It didn't work on cloudy days, but that didn't mater because the water in the collector didn't get more than luke warm anyway, so no damage done. It did prove to me that if you want reliable solar hot water in the Uk you have to go with the tubes. (I've often wondered about a thermosyphoning evac tube system, with the tank higher than the collector & no controls or pump at all......)

[liberti]

Thanks filipinobrian.

My knowledge of electrics is limited so this next bit may be total nonsense!! Could the PC cooling pumps you mention have a high starting current(?) requirement, which they have access to being connected to mains - unlike solar, especially when cloudy etc.

Maybe pumps with lower starting needs may be more suitable?

The likes of Solartwin and Imagination Solar use DC pumps - anyone know what pumps they use?

[Much]

Not that I'm an expert in the solar thermal field, but aren't both the solartwin and imagination solar systems of the non-tube (ie. panel) variety? Thus the previous comments about the lack of flow probably not causing an problems (ie. overheating / damage) to such due to the panels not reaching a damaging temperature still holds.