Beginner's guide to solar PV

Not really an answer, but you could ask the same question in the relevant section of the Money Saving Expert forums: https://forums.moneysavingexpert.com/categories/green-ethical-moneysaving

What's feasable and what's cost-effective aren't always the same thing.

Thank you Simon, but that is not really what I am asking. I can happily write a spreadsheet to look at cost-effectiveness.

So, we have panels, an inverter, a battery, and a connection to the LV AC installation. How are they connected, what voltages are involved, etc?

How do you want to use the system? Some things to consider:

1) Will you have an EV charger?
2) Do you plan to include battery storage? If so, do you want to be able to run from the battery during a power outage (a lot of systems don't support this)?
3) Do you plan to run a heat pump? If so, do you want to use a battery to cover some of the heating during the day from "cheap" over-night rates?

1) Eventually - we all will!

2) Yes. Not necessarily.

3) No.

Some general information here: https://cat.org.uk/info-resources/free-information-service/energy/solar-photovoltaic/ (scroll down to the bottom for some more detailed Q&As)

The electrical design details can bit a bit variable - there are many options. Traditionally (for a simple grid-tied install)  you had a string of panels feeding DC to an inverter that then connected to the CU pretty much the same way as any other AC circuit (bi-directionality of RCDs notwithstanding). I've a string of 9 panels (in series) and they're currently producing about 270V - it's higher in summer (from memory 370-380V ish) - DC wiring is double insulated (specialised PV cables). AC side all 230V nominal of course.

Alternatively you can take AC onto the roof and have a little inverter on the back of each panel - tends to be more expensive (and potentially more awkward to maintain), but can be good if some panels are subject to shading (panels in DC strings wired in series all suffer reduced output even if only one panel is shaded).

Batteries can also be done in different ways. These days you can simply buy an inverter with a (small) battery built-in - the system then looks from the outside pretty much as a traditional setup - although there might be some extra instrumentation - e.g. wiring to a CT on the incoming mains so the inverter can regulate the AC output to match demand and avoid exporting.

Alternatively you can have a separate battery system (i.e. only connected to the PV via the AC installation) - again it can take account of PV generation (and possibly also cheap rate tariffs) to give the "best" overall results.

Some battery systems are grid-forming - i.e. will allow you to power the installation from your own personal mini-grid if the mains fails, and/or can be used to peak lop the mains supply (initially designed for generator fed off-grid systems, to avoid over-sizing the generator to cope with peaks). There's a lot of imagination from all sorts of areas off grid buildings, RVs etc)  that's now combining into AC connected battery systems with some very interesting results.

It might be worth looking at some manufacturer's information - Victron for example have quite a wide range and a fair bit of advise (some aimed at off-grid but the same physics applies).

   - Andy.

A simple question, but Uncle Google does not help.

I gather that there is normally an a.c. isolator means of isolation adjacent to the inverter. What sort of cable is normally used to connect that to a CU please? T&E?

I ask simply because I want to get my installation "solar-ready" as far as possible.

Mine has standard T&E.  It's no different to any other circuit. For some reason the installer decided to add isolators next to the inverter and also in the meter cupboard near the consumer unit. I don't know why, as I could isolate it by flipping a breaker.

Could be T&E but depending on your installation the volt drop (rise) requirement is likely to be more onerous in order to avoid "nuisance tripping" of the G98 overvoltage protection.

But often its run in SWA to avoid needing an RCD due to the circuit route or hazards.

Isolation by the inverter is recommended for maintenance and testing of the equipment, including functional switching, but not necessarily mandated.

Simon Barker said:

I could isolate it by flipping a breaker.

Simon, Jam, thank you.

I am hoping that my inverter (and battery) will be in the same store room as the top floor's DB. I had thought of using an MCB for isolation, but shouldn't both live conductors be isolated?

I believe it is standard practice to have a proper AC isolator close to the inverter, for maintenance.  If nothing else, it's sometimes necessary to reset the inverter if it gets in a mess.