Solar Thermal - what labelling, if at all?

Are you sure thet are actually generating electricity? I would have thought any wiring would be a supply, perhaps to a pump.

As a second supply it still needs mentioning at the origin, as it’s presence is not expected - even more so, as it is independent of the public supply. It should also have a method of isolation, as you would expect to find with a grid tied PV system. 


Regards,


Alan.

As sure as I can be, a large tank, with 2 immersion heaters, one, the top, connected to the mains supply, the bottom, connected to a junction box which leads to a pump, a lot of piping and pressure guages.

It rather depends as to whether it's just a solar thermal system or a PV installation (which may be providing heat via the thermostat).


As Simon Barker‍ says if it's just solar thermal it's not generating electricity* so I'm not sure why it would need to be treated any differently to any other heating controlls / pump.


*Unless there's a small cell/module providing power to the pump or irradiance meaurements to the control, which some do have, but these are islanded systems as with no mains connection and again no notices at the DB required.


If there's also a PV system with inverter connected to the electrical installation then I agree with Alan Capon‍ and the usual notices per G83/G98 (depending on age) and likely also MCS are required.

There were some experiments with combined thermal and PV panels a while ago (being that PV panels are only something like 10% efficient there's still a lot of heat to be had) - but they had some significant problems - not least that the temperatures needed for a good thermal solar system tend to reduce the lifetime & efficiency of the PV cells considerably, plus the all the difficulty in mixing water and electricity in a module that's difficult to access for maintenance as well as being exposed to the worst of the weather. I wasn't aware that they'd got into any significant commercial production.


There was one system that had a separate PV panel alongside the thermal panels - the idea being it would generate a suitable amount of electricity to drive the circulating pump for the thermal panels (stronger sunshine needs more pumping to carry the heat away from the thermal panels, and PV panels produce more electricity with more sunshine - so you can see the logic) but I don't think that really took off either - although it was offered as a commercial product for a time.


Having PV panels solely to supply an immersion (without the benefits of FIT payments) sounds to me like a non-starter - PV panels are significantly more expensive than simple thermal ones and far less efficient. If you wanted more heat, it's far more sensible to add another thermal panel instead of a PV one.


Anything is possible though - and it's an area that has attracted a lot of DIY experimentation - so rule nothing out, but my guess would be that both immersions are powered by the normal mains, but the lower one is additionally controlled by the solar control system - perhaps switching it on over night if the panels haven't produced sufficient heat during the day, or something of that nature.


   - Andy.

Any solar PV system that is not connected to the mains has a real control problem. Too little sun and the voltage drops, stalls the pump and burns it out, too much sun and the voltage rises and burns out the pump.

It would be possible to connect a fancy controller that cuts off with low voltage and dumps the electricity in the immersion heater when there is too much but what happens when the tank is all hot, is it allowed to boil?

If this is what you say it seems to be, then it is a rather clever system. Any name plates around?

Any solar PV system that is not connected to the mains has a real control problem. Too little sun and the voltage drops, stalls the pump and burns it out, too much sun and the voltage rises and burns out the pump.

It would be possible to connect a fancy controller that cuts off with low voltage and dumps the electricity in the immersion heater when there is too much but what happens when the tank is all hot, is it allowed to boil?

If this is what you say it seems to be, then it is a rather clever system. Any name plates around?

What I was referring to were the various systems out there (Immersun is one, but I personally have never implemented it so cannot recommend) that have a conventional grid connected inverter with a second immersion either simply switched or modulated. Normally this is in conjunction with export monitoring and arranged so that rather than exporting to the grid, excess energy after other electrical loads is diverted to the hot water cylinder. Idea being that it's better value to offset the gas than to export.

And no, it shouldn't be allowed to boil... there ought to be a stat!

As for pumps, solar pumps have been around for a long time. Varying levels of quality from cheap water fountains upward, but some are actually decent and are used for essential things like pumping drinking water in remote villages in developing countries, f'example.

And no, it shouldn't be allowed to boil...

Many solar thermal systems are intended to boil - as a last resort safety feature - e.g. during a power cut or pump failure - since no thermostat will turn off the sun. As long as the panel is at the highest point of the system, turning a small amount of water to steam will push all the rest of the water out of the panel itself and so prevent any more boiling (the panel is then allowed to reach it's stagnation temperature, dry). You just need an expansion vessel that sized large enough to take all the displaced water (which is why most solar systems have quite large expansion vessels even though there's often only a few litres of fluid in the solar circuit) - or as a further failsafe via the pressure relief valve.  There was an alternative approach where the circuit was pressurised to such an extent that the boiling point of the fluid was raised beyond the stagnation temperature of the panel - but that required maintaining the solar circuit at over 6 bar and as far as I know was never popular outside of Germany.


   - Andy.

Thanks all, further to this, I spoke to the Guy who usually inspects these houses today.

The panels were originally PV and Solar Thermal when built , 10-12 years ago. The PV side was pretty useless, so was decommissioned after a few years.

The solar thermal was kept, as it was performing OK.

There are 2 immersions, but only one is connected, the other was left in place, as it was easier then removing it.

So no labelling required,as no wires coming from the panels.

The residents think it works well, though I'm not sure they really know, one of them had turned off the controller, so was getting no benefit from it.


The controls are now Glowworm Fluropro, there is a good diagram of the system in the .pdf linked below:
https://www.wolseley.co.uk/wcsstore7.00.1066.925/ExtendedSitesCatalogAssetStore/images/products/AssetPush/DTP_AssetPushHighRes/std.lang.all/ic/al/Glowworm_Solar_Technical.pdf