Solar System with Battery - Electrical Diversity

derek_bartram · Post by **derek_bartram** » Sat Nov 18, 2023 12:43 pm

Obviously this is something the PV installer will deal with, however as I'm doing the plans for the rest of the house then it would be useful to be able to factor it into the calculations/layout...

I'll be getting a 6kW PV system installed, with a 9.5kW battery. The solar inverter/battery controller will be 15m from the consumer unit.

With a 10mm^2 TC&E cable, I have 44-64A max current capacity based on Reference Method A/C.

Question 1) Searching 6kW Solar Inverter maximum current, gives various results up to 40A maximum, therefore my 10mm^2 should be sufficient?

Question 2) When calculating diversity for the consumer unit, as the device is nominally only providing current, then presumably I give the diversity current as 0?

Thanks!

ericmark · Post by **ericmark** » Sat Nov 18, 2023 3:10 pm

If anything like mine, it is not as simple as that. The supply will be split into two, there will be an UPS supply which even with power cut will not fail, and standard supply, there will be an array of isolators, some AC and some DC, and also a load of CT coils which need to be a set distance apart.

Some may be wireless, but likely some wired, each make of Solar inverters will be slightly diffrent, so you would need to down load the instructions for yours.

I am not pleased with my install, the boiler is no longer RCD protected, and the iboost+ was not running when it should, and it seems clear the thermostat is too short, likely also the immersion heater.

It has over discharged batteries, and one has failed within 2 months, since the installers did all the work, it is their problem to solve, also found law has changed and now need a smart meter to be paid for exported power.

You do not want arguments about who does what, so let the one installer do all.

Neelix · Post by **Neelix** » Sat Nov 18, 2023 4:07 pm

One thing to remember is that PV must not be protected by a shared RCD

derek_bartram · Post by **derek_bartram** » Sat Nov 18, 2023 4:26 pm

Thanks both!

Every time I speak to anyone about PV, they always grumble about installation or reliability - my own previous experience including one replacement inverter, with a second starting to fail as we moved out (thankfully all landlord's responsibility). Neighbour up the road is having similar grief too.

@ericmark Totally get the comment about the one installer bit - really all I'm trying to do is ensure a) I have sufficient capacity in the consumer unit, and b) sufficient capacity through a couple of bits of metal earth trunking under the floor. How many spaces in the consumer unit does yours use up?

@Neelix Hadn't clocked that, however I confess I've opted to solve all those problems by using RCBOs - slightly more expensive option certainly, however a) makes this stuff simpler, and b) increases the amount of slots available.

ericmark · Post by **ericmark** » Sat Nov 18, 2023 6:28 pm

No spaces used in orignal CU, new one fitted with SPD, MCB for that, and one device for the panels.

The two double RCD sockets and FCU direct from the inverter.

London mike 61 · Post by **London mike 61** » Sat Nov 18, 2023 8:10 pm

Shortly after our solar panels were installed we had a problem where the batteries ( 5 of them ) would completely discharge and because they were so low , they wouldn’t charge back up. So after many phone calls the installer sent out a engineer and he installed some new software upgrade that would only allow the batteries to go down to 15% and if needed they would automatically be topped up from the grid.
We haven’t had any issues since the upgrade but this time of year we don’t generate a lot of electricity through the panels but the money we get in the summer for what we sell to the grid.

Mike

Neelix · Post by **Neelix** » Sat Nov 18, 2023 8:54 pm

derek_bartram wrote: ↑Sat Nov 18, 2023 4:26 pm
@Neelix Hadn't clocked that, however I confess I've opted to solve all those problems by using RCBOs - slightly more expensive option certainly, however a) makes this stuff simpler, and b) increases the amount of slots available.

Only uneducated fools fit dual RCD boards

I really think you need a local spark on board …..

derek_bartram · Post by **derek_bartram** » Sun Nov 19, 2023 8:19 am

Could you elaborate on that please? As far as I'm aware, I'm using a design recommended by the BS7671 On Site Guide?

Neelix · Post by **Neelix** » Sun Nov 19, 2023 10:31 pm

derek_bartram wrote: ↑Sun Nov 19, 2023 8:19 am Could you elaborate on that please? As far as I'm aware, I'm using a design recommended by the BS7671 On Site Guide?

The onsite guide is no where near enough to give anybody enough information to design an installation with little or no experience

It’s a site guide of useful reminders of a very small part of what is required

derek_bartram · Post by **derek_bartram** » Mon Nov 20, 2023 9:06 am

I'm aware of that, however the purpose is to 'guide'.

You mentioned:

Neelix wrote: ↑Sat Nov 18, 2023 8:54 pm Only uneducated fools fit dual RCD boards

Could you elaborate a) why? and b) how you think I'm doing that please?