+4kwp ok If you don't get the NOD from the DNO?

[volzhskyboy]

Hi all,
Can someone enlighten me on a question I have, some have advised to go for as big a system as allowable by funding or space available and I can see the sense in this, but, others have said that the DNO may put a limit of a 16A @ 230V = 3.68Kw system being fitted to the grid. Is the size of the installation therefore limited by the DNO's decision or is there a practicable and cost efficient way around this?
Bill.

[BruceB]

If you want to have an installation above 16A per phase then as you say you need the DNO's permission, via a G83/1-1 Stage 2 application.  Their response is likely to be either:
- no problem, go ahead and inform us when completed; or
- the local network cannot cope without reinforcement at a cost of £x,000 (which may include re-cabling and/or replacing a transformer).
Regards
Bruce

[volzhskyboy]

Thanks Bruce,
Hmmm, "per phase" you say.... so is there some way or even such a thing as a 3 phase inverter that would allow you to potentially supply 3 x 16A back to the grid and would it be an expensive option?
Bill.
 

[BruceB]

Google sunny tripower for an example of a 3 phase inverter.  Allows you to connect up to 11kW without prior permission, eg using 10000TL model.  They are an economical way to do it.
Regards
Bruce

[marshman]

Thanks Bruce,
Hmmm, "per phase" you say.... so is there some way or even such a thing as a 3 phase inverter that would allow you to potentially supply 3 x 16A back to the grid and would it be an expensive option?
Bill.
 

It will only be expensive if you don't already have a 3 phase supply to the site. The cost, and extra "standing charge", for connecting a new 3 phase supply to the property may be prohibitive.

Roger

[volzhskyboy]

Ahhh,
I wouldn't of thought a normal domestic supply would be 3 phase though?
And there was me thinking it was just a matter of choosing an alternative inverter, there's always a down-side!
Thanks for the info Bruce & Roger.
Bill.

[EccentricAnomaly]

... but, others have said that the DNO may put a limit of a 16A @ 230V = 3.68Kw system being fitted to the grid.

Actually the limit is 16 A at whatever the voltage happens to be at that moment:

https://www.navitron.org.uk/forum/index.php/topic,13316.msg155905.html#msg155905

My guess would be that the idea that there's a 3.68 kW limit comes from the DNOs accepting that that much PV is not going to produce enough power that the local voltage will go too high - i.e., that if the voltage is above the nominal 230 V (as they aim for it to be) it's within the 16 A limit and if the voltage is below the nominal (legally it can be down to 230 - 6% = 216.2 V, but they don't like to do that) then any voltage increase due to going over 16 A is good.

[GavinA]

... but, others have said that the DNO may put a limit of a 16A @ 230V = 3.68Kw system being fitted to the grid.

Actually the limit is 16 A at whatever the voltage happens to be at that moment:

https://www.navitron.org.uk/forum/index.php/topic,13316.msg155905.html#msg155905

My guess would be that the idea that there's a 3.68 kW limit comes from the DNOs accepting that that much PV is not going to produce enough power that the local voltage will go too high - i.e., that if the voltage is above the nominal 230 V (as they aim for it to be) it's within the 16 A limit and if the voltage is below the nominal (legally it can be down to 230 - 6% = 216.2 V, but they don't like to do that) then any voltage increase due to going over 16 A is good.

that's not how I read it.

Declaration of phases, frequency and voltage at supply terminals

27.—(1) Before commencing a supply to a consumer’s installation, or when the existing supply characteristics have been modified, the supplier shall ascertain from the distributor and then declare to the consumer—

(a)the number of phases;

(b)the frequency; and

(c)the voltage,

at which it is proposed to supply electricity and the extent of the permitted variations thereto.

(2) Unless otherwise agreed in writing between the distributor, the supplier and the consumer (and if necessary between the distributor and any other distributor likely to be affected) the frequency declared pursuant to paragraph (1) shall be 50 hertz and the voltage declared in respect of a low voltage supply shall be 230 volts between the phase and neutral conductors at the supply terminals.

[source

therefore, unless you have it agreed in writing in advance with the DNO, the declared voltage of the installation must be 230V, and the declared output of the system must also be at 230V, so 16amps at 230V = 3.68kW.

I'm fairly sure it also explicitly states this in the G83 regs, but my other laptop with the regs on it has died and I don't fancy forking out again for a copy until I know if the death is permanent or temporary.

[Ted]

But sub-section 3 goes on to say:

(3) For the purposes of this regulation, unless otherwise agreed in writing by those persons specified in paragraph (2), the permitted variations are—

(a)a variation not exceeding 1 per cent above or below the declared frequency;

(b)in the case of a low voltage supply, a variation not exceeding 10 per cent above or 6 per cent below the declared voltage at the declared frequency;

But I have so far failed to get ENA to explain whether the "16A at 230V" varies within the accepted voltage range, but they have said "it is 3.68kW".

[EccentricAnomaly]

...and the declared output of the system must also be at 230V...

Good luck getting any power into the grid when its voltage is almost always well above 230 V.

I think the maximum power you can put in is 16 × 253 = 4048 W in the case where you're lucky and the grid voltage, with your 16 A current, is 230 + 10% = 253 V.

On the other hand, if your voltage is on the lower limit, 230 V - 6% = 216.2 V, and doesn't even rise when you feed in 16 A then the maximum power you have, in theory, the right to be able to produce is 16 × 216.2 = 3459.2 W. Still, it seems likely that in those circumstances nobody is going to bother if you produce a little more than 16 A to help hold the grid voltage up and it seems entirely plausible that the DNO would accept a power limit corresponding to 16 A at 230 V (i.e., a tiny bit over 17 A at the minimum voltage).

The most likely case, of course, is that the voltage is around 240 V and you can produce about 3840 W.

Whatever, my mind still boggles that there don't seem to be inverters that can be set up to simply limit at 16 A - ideally doing something vaguely useful with any excess. What would be really cool would be an an inverter with a remote sensor which limits the export from the building to 16 A allowing any excess to be used internally in the normal way. Remotely sensing the voltage as close to the main fuse as possible would also be good.

[climber]

Good luck getting any power into the grid when its voltage is almost always well above 230 V.

When you say "well above", how much above 230V?

[EccentricAnomaly]

When you say "well above", how much above 230V?

Legally for European harmonization reasons it's 230V -6%/+10% (216.2 to 253 V) but in practice they still aim for the "old" 240 V standard. The odd times I've measured it in various places it's typically been within a couple of volts each way of that but others here (e.g., marshman) have seen higher, particularly when they're generating themselves.

[ecogen]

I think the maximum power you can put in is 16 × 253 = 4048 W in the case where you're lucky and the grid voltage, with your 16 A current, is 230 + 10% = 253 V.

I too believed this to be what G83 allowed. However I am no longer so sure.
16 A per phase is the maximum under all operating conditions. Maximum rated true power is 3680W. Scope and definitions can be used to calculate this, although there is no specific power limit figure stated anywhere in the doc.
A power factor of 0.95 lead / lag and a power load of 3680W (clause 5.6.) gives 3874VA. Under this load the voltage is 242V.

[climber]

When you say "well above", how much above 230V?

Legally for European harmonization reasons it's 230V -6%/+10% (216.2 to 253 V) but in practice they still aim for the "old" 240 V standard. The odd times I've measured it in various places it's typically been within a couple of volts each way of that but others here (e.g., marshman) have seen higher, particularly when they're generating themselves.

G83/1 Overvoltage Limit is 264 V though?

[EccentricAnomaly]

I too believed this to be what G83 allowed. However I am no longer so sure.
16 A per phase is the maximum under all operating conditions.

Agreed. Even 400 V three phase (19.2 kW).

Maximum rated true power is 3680W. Scope and definitions can be used to calculate this, although there is no specific power limit figure stated anywhere in the doc.

Sorry - I don't know where that comes from. I don't think it was in the text you PMed me.

A power factor of 0.95 lead / lag and a power load of 3680W (clause 5.6.) gives 3874VA. Under this load the voltage is 242V.

Again, there being not quite on phase would reduce the amount of power you can transfer while staying within the current limit. What you mean by "Under this load the voltage is 242 V"? Surely the voltage is whatever it is.

There are two "power limits" to consider:

1. The maximum power you could put in under your particular grid conditions while staying within the 16 A limit.

2. The maximum power you can produce and still reasonably expect to stay within the current limit whatever valid grid conditions apply (or at least with nominal grid conditions).

Staying within the first, higher, limit is a legal requirement. Staying within the second, lower, limit is a conservative piece of engineering needed in order to achieve the first if your system can't limit the current but can only limit the power.

(Unusual case of actual grid voltage being below nominal ignored for simplicity here.)

Anyway, I thought earlier on in this thread people were conflating these two limits and my sole intention in posting was to try to point out the distinction.