Solar PV on garage - possible with this?

[ex_directory]

My garage is 10m from the house and has south facing roof, my house does not!

Had a solar chap around and he thought the garage would be perfect for a new installation, asked if the garage has it's own CU, which it does, a small one.

After he left, it occurred to me that the Garage CU is connected to the ring main of the house, not the main CU on its own MCB. Basically on a spur from the lounge. This was as per new build in 2000 so must have been up to building regs.

The Main CU has a MEMERA 2000 MCB B32 ALB321 32AMP 6k CIRCUIT BREAKER feeding the ring main.

Will this work? A concrete patio between the house and garage otherwise makes new cabling back to main CU a nightmare/not really viable anymore.

 

[DetlefSchmitz]

In practice it would probably work, but it's a really bad idea. Ideally the inverter should feed directly into a henley block in the vicinity of the incoming mains. Feeding into a ring final will compromise the overload protection of that circuit as some of the load in some parts of the circuit will be offset by the generated current.

 

[ericmark]

As far as I am aware it is normal to go for 7 KVA seem to remember above this the tariff paid changes, and below this uneconomic, this would mean 30 amp, so as @DetlefSchmitz says it may work, but it would mean 62 amp could be drawn from the ring, which would not really be safe, and to get the government payments it would need to comply with all the rules.

So the question is where does it connect to the ring final, could a cable be run from the CU or henley block by CU to where the cable goes to the garage?

Last house had an East and West facing roof, and we inquired about solar panels, and it seems to be down to how the panels are rated, if two sets of panels are fitted, then the production is over a longer period to single south facing and the peak output at mid day is not so pronounced so in kWh the output is far better than South facing, however it depends if two 5 KVA units facing east/west which because neither will generate together will only produce 7 KVA will be rated at 7 KVA or 10 KVA.

When the installers arrived some said counts as 7 others counts as 10, it seemed it was a grey area. Here the mountains shield the sun, so there is a very limited window when they will give a reasonable output, so not really an option.

My father-in-law had two sets of DHW solar panels fitted, east/west again, they were claimed to most of the time produce all the hot water he would require, and he boasted about how much his electric bill had dropped, until he had a smart meter fitted, then he had no DHW at all. So we then went to have a look, seems pilot flame had gone out on the gas central heating boiler when the smart meter was fitted, and the immersion heater had been removed, so clearly the electric bill went down, and gas bill went up, and it seems the solar panels simply looked good, and increased the energy rating of the home, but did not do a thing, the company was called to fix them, but never did work, and house sold when he died still not working, new owners disconnected them all, still sitting on roof, but do nothing.

After that I am a little suspicious about solar panels, the early ones you were paid a fixed sum did not matter if worked or not, but today metered, so maybe OK down South which I suppose you are, but up in North Wales at least they seem to be just a decoration.

 

[ex_directory]

As far as I am aware it is normal to go for 7 KVA seem to remember above this the tariff paid changes, and below this uneconomic, this would mean 30 amp, so as @DetlefSchmitz says it may work, but it would mean 62 amp could be drawn from the ring, which would not really be safe, and to get the government payments it would need to comply with all the rules.

So the question is where does it connect to the ring final, could a cable be run from the CU or henley block by CU to where the cable goes to the garage?

Yes, it is 4kw system (roughly 7KVA)

The ring main has maybe 15-20 sockets on it along with the garage. No extra cable and it is through mulitple rooms, no easy routing to add extra cable.

Yes, I am down south.

Seems a shame but this may make the garage idea a non-starter.

 

[flameport]

Solar needs to be connected to it's own dedicated circuit, and if that circuit requires an RCD, it must only be for that circuit, not shared with anything else.
Connecting to an existing ring circuit is entirely unacceptable.
Connecting the garage CU to the ring was somewhere between pointless and dubious, even 20 years ago, but isn't likely to be dangerous.

The presence of a patio doesn't have to mean the whole project is cancelled, there may be options to get a cable there. Cables do not have to go underground.

Photos of the garage/house/patio and general info on the exact location of the consumer unit / metering relative to the garage and other structures may be helpful.

 

[AndyPRK]

here is an example of getting a cable over head.

As DetlefSchmitz said, if the existing cable is big enough, and you can disconnect it from the ring. (adding a new cable between meter area and existing entrance - that is another possibility)

 

[ericmark]

I would say it depends on where the buried cable runs, with my mothers house when re-wiring just kitchen ran SWA around outside of house. But this house built on a hill getting a supply to garage is not going to be easy.

However for you it is not the time but cost, on the video shown I would have followed the fence line, so cable where it will not be dug up, and dug across gate way, I was always intending to re-do parents and bury the cable as it always seemed to get entangled with caravan.

The normal is

Overhead conductors shall be at a height above ground of not less than 6 m in all areas subject to vehicle movement and 3.5 m in all other areas.

although that is for caravan sites and marinas etc. I consider that 3.5 m is the minimum height for overhead, however when I did a site induction they seemed to think 2 m was enough. But you can bet your life if you set to 2 m they will get a motor caravan or something that will foul it.

So likely any installer will fit an over head at least 3.5 m high. It is all well and good you saying it's OK at 2 m, but if his rule book says 3.5 then 3.5 it will be.

I think it is rare for any detached garage to have more than a 13 amp supply as standard. Yes when some one specially asks for a supply to weld with etc. But unless specially asked for 13 amp is enough for garage lights and charge the car battery for non EV car. So for any surveyor to expect a garage to have over that without checking he is not doing his job.

 

[ex_directory]

Solar needs to be connected to it's own dedicated circuit, and if that circuit requires an RCD, it must only be for that circuit, not shared with anything else.
Connecting to an existing ring circuit is entirely unacceptable.

Very clear and understood. Thanks.

Connecting the garage CU to the ring was somewhere between pointless and dubious, even 20 years ago, but isn't likely to be dangerous.

Arguably been useful over the years when I have needed to shut off electric in the garage but not affect the house.

The presence of a patio doesn't have to mean the whole project is cancelled, there may be options to get a cable there. Cables do not have to go underground. Photos of the garage/house/patio and general info on the exact location of the consumer unit / metering relative to the garage and other structures may be helpful.

See below.

House circuit diagram now


Garage on left


Same fence on left runs down side of house


Where the kitchen utilty is and CU about < 1m from the wall

 

[ex_directory]

So questions I would have please:

1, Can I run a new armourmed cable just under soil/pebbles attached to gravel boards and then finally under a sand laid slab just outside the kitchen back door, up 0.5m and in to the house above the damp proof course? The pebbles can fill with water sometimes.

2, If I wanted Garage Solar PV and Electric car hookup in the future, can the garage still be run off one circuit from the main CU or would this need 2 cables?

 

[flameport]

1 - very likely. Water doesn't matter, armoured cable is suitable for direct burial in the soil.

2 - EV charging will require it's own dedicated circuit as well.
Possible to have a single larger cable from the house to a consumer unit in the garage with several circuits in it, one for the solar, one for the car, others for sockets, lights and whatever else. House end should be connected to it's own switchfuse, rather than being supplied from the house consumer unit.
Cable would need to be sized appropriately for the total load, 10mm² being a likely size.
If that is done, the existing garage connection to the ring would be disconnected and removed.

 

[ex_directory]

House end should be connected to it's own switchfuse, rather than being supplied from the house consumer unit.

Sorry for silly question time...

Does that mean the feed goes to the meter or still to the CU in the house?

If it goes to the CU, the CU in the is full. Does this swicthfuse need then a new CU in the house?

I appreciate a electrician will need to inspect and confirm, but this is about judging whether I even continue with the Solar PV idea. The electric car has not been part of my thinking and was just throwing it in to try and think ahead.

 

[flameport]

Meter -> Switchfuse - > Garage.
House consumer unit isn't involved.

 

[SimonH2]

To clarify, the tails between the meter and CU (or between isolator and CU if there's an isolator fitted) are disconnected and big terminal blocks (often referred to generically as "Henleys" in the same way that vacuum cleaners get called "Hoovers") are fitted. These terminal blocks split the connection, so one set of tails goes to the CU as before, and an extra pair go to the new switch-fuse.
Examples of such connector blocks on CEF's web site - none of them made by Henley.