Solar PV AC supply

[Richard]

Good evening gents,

Client having PV on out building. The supply to the outbuilding is a dubious 2.5 SWA of about 40mtrs via a DB of the main DB. So to clarify the run has 3 dbs in series.

I'v disregarted this and opted to quote for a new run straight to the intake with relavent AC isolators either end. Other companys I feel have probibly opted to go straight into the garage DB as it would save quite a bit of work. Would that be complient in your eyes as I didn't even consider it to start?

thanks in advance

 

[Eco Chap]

Size of PV system? Do your vd and cc calcs to clarify that the cable is no good. If its not best you can do is explain too the client as clear as you can why you intend to run a new feed to the incoming. Chances are they won't like the thought or cost of digging up their garden and some mukka will say the existing installation is fine and get the job anyway. Great industry eh!

 

[Richard]

I also came accross another issue which relates to the OP: IET Forums - Disconnection times - PV an a shared RCD

 

[shanky887614]

remember a 4kw pv array will put around 17amp load on the cable.

mighy not conply on a 2.5 garage supply if its backed by up by a b20

need to calc it

 

[Gavin A]

impossible to comment without knowing the proposed array size, but there's nowt wrong with installing to sub boards in principle.

 

[Richard]

Ok sorry gents i'll ellaborate. 4kw array. In terms of volt drop, Iv guessed from memory and the run is probs about 30mtrs so in terms of volt drop that seems to come back around 3.4% passable for a power circuit I think.

Currently, the property has a TT earthing arrangment, so all circuits are covered via RCD. At the front end. The house is quite long and narrow. The sub board is located towards the garage end of the house, and feeds alot of circuits from there including showers ect. Currently there is also a 30ma RCD there (in series). If the PV was put in as is on the garage DB, then the PV would be sharing the same RCD's as the shower, sockets ect? I feel this would compromise disconnection times as even if the rcd disconnects, the fault could still be supplied by the PV for however long that takes to stop producing.

Hense why I opted to price for a seperate submain!

Any POV would be apprichiated.

Thank you

 

[SibertSolar]

You did the right thing imo, sharing and RCD is not advisable and sub/sub board arrangements increase propensity for issues with perceived grid voltages, monitoring and troubleshooting. Also, 3.5vd may cause over voltage issues for the inverter

 

[Gavin A]

3.4% volt drop would very rarely be acceptable for solar PV. RCD arrangements can usually be adjusted to work around that issue if it's simpler than digging an entire new cable in IME.

 

[Sunshine777]

For a 4000TL SMA recommends 6.0 mm2 cable for runs up to 23.3m and 10 mm2 for runs up to 38.8m. So how could the existing 2.5 SWA possibly be used?

 

[shanky887614]

For a 4000TL SMA recommends 6.0 mm2 cable for runs up to 23.3m and 10 mm2 for runs up to 38.8m. So how could the existing 2.5 SWA possibly be used?

it actually goes on to mention that the grid impedance of the ac cable must noy exceed 1ohm.

otherwise the inverter will disconnect at full feed capacity due to excessive voltage at the feed in point


the conductor cross-section should be dimesnsioned such that cable losses do not exceed 1% at nominal voltage

download link for installation guide below

https://www.google.com/url?sa=t&sou...QFjAA&usg=AFQjCNEsx18G-KZsvY4G93ulkamslh0dQQ

 

[marc8]

Have you considered using micro inverters feeding sub board? Or am I missing something if the voltage is within range for micro inveter the you won't have a problem with 1% volt drop to inverter.
Then you could split power just before RCD unit & you are on the mains surely?