Changing system capacity - FIT

Martyn1981

Ferdy147 wrote: »

What's the highest reading a 3.92kw system should produce?

Looking at my inverter (SMA 4000TL) then the reading is sometimes (although not for too long) at about 4100 - should that be possible?

Hiya Ferdy. Don't worry too much about the spikes/peaks, cold panels with the sun 'popping' out from behind a cloud, can cause short-term output higher than the panel ratings.

The DNO's are concerned about sustained outputs, and have drawn a permission line at 16A (which at a nominal 230V = 3,680W). Basically if too many systems were outputting too much power, for too long, without enough houses locally to 'mop it all up' then there could be problems. By recording all installations the DNO's will know when they need to 'harden' the local infrastructure to cope.

For your system, 3.92kWp, I don't think 4,100 watts sounds surprising for short bursts, perhaps 20 seconds or so? But it does mean that the inverter isn't limited (physically capped) to 3.68kW, as many weren't. These days I think the 4000TL's are capped.

Using the rules set by my DNO (as detailed above), they would take your panels (3.92kWp) and multiply that by the efficiency rating of the SB4000TL (Euro rated at 96.4%) giving a potential sustained output of 3.78kW.

Today, a very picky DNO might decline 'deemed permission' as being in excess of 3.68kW, or G83/1 permission. No worries for you, as this obviously got passed. But if this did happen to someone after installing, then for SMA inverters, they could simply get the inverter dialed down to 3,680W as this can be done in 1W increments, and (I believe) 3.68kW is an actual setting on them.

Mart.

EricMears

Martyn1981 wrote: »

The DNO's are concerned about sustained outputs, and have drawn a permission line at 16A (which at a nominal 230V = 3,680W). Basically if too many systems were outputting too much power, for too long, without enough houses locally to 'mop it all up' then there could be problems. By recording all installations the DNO's will know when they need to 'harden' the local infrastructure to cope.

Really not sure what you mean by "harden the local infrastructure" ?

FWIW, I insisted that we apply for any necessary permission(s) to output the full 4.00kW (+ positive tolerance) and didn't seem to have much bother getting consent (although in 'real life' we very seldom get there anyway).

There are no local houses to use my output - at least not till it's been boosted to 11kV at our nearby poletop transformer and back down to 230v at the next one along the line.

Martyn1981

Eric, don't forget that 3.68kW is not really a problem, it's the sum of installations (or potential installations) that the DNO's are worried about. 3.68kW is just the line in the sand that they've drawn.

I don't know if it's true, but apparently Western Power Distribution (my DNO) have got the reputation for being tough, as one of their transformers burnt down due to too much 'backwards' leccy, before they were really on the ball recording all SSEG's.

Quite what 'harden' means (the term described to me when I was chatting to WPD) I don't know, but I suspect it means upgrading transformers to cope with larger amounts of power making it all the way back, when (if) generation exceeds total local demand.

A year ago nobody really seemed too bothered with 4kWp v's 3.68kW export, as in reality there is very little difference, but things are getting more regulated as the number of PV installs grow.

My current set-up can sustain about 4.2kW from noon to 2pm (though this is dropping fast, in line with the sun's height). So if an empty house was only consuming 200W, my install alone could supply 20 additional houses. It's the worst case scenario that the DNO's have to plan for. Glad I don't have their job.

Mart.

EricMears

Martyn1981 wrote: »

I don't know if it's true, but apparently Western Power Distribution (my DNO) have got the reputation for being tough

We used to be EMEB who got taken over by Central Networks and are currently (sorry !) calling themselves WPD

Martyn1981

EricMears wrote: »

We used to be EMEB who got taken over by Central Networks and are currently (sorry !) calling themselves WPD

'Times, they are a changing'.

Can't remember if I've already mentioned this, but when EDF were checking my FITs application, the 'bod' was surprised that I'd got permission for an extension. He then said, 'you wouldn't get permission from our guy's, we're with WPD'. Very funny moment.

I explained it was with WPD, and that's when he told me the transformer story. Apparently a large number of PV installs had gone up in one area, and nobody had really been worrying about it. They were all regular sized installs and self commissioned like most PV installs. Then one sunny day the local sub station / transformer burnt down, costing WPD a 6 figure sum to replace.

(Again, I don't really understand the full details, but apparently the sub-stations can't go backwards, so they have to be hardened to cope with (get rid off?) the power.)

Since then they've kept a much closer eye on the rules and the sum of SSEG's in any given area. To be honest that sounds perfectly reasonable, especially as SSEG's of all kind will keep increasing as the years go on.

As 'Mr helpful' at WPD, who was very patient with me, explained, 'two years ago had you mentioned PV, I'd have thought you were talking about double glazing, we're all still learning'.

Mart.

Ferdy147

Martyn1981 wrote: »

For your system, 3.92kWp, I don't think 4,100 watts sounds surprising for short bursts, perhaps 20 seconds or so? But it does mean that the inverter isn't limited (physically capped) to 3.68kW, as many weren't. These days I think the 4000TL's are capped.

Using the rules set by my DNO (as detailed above), they would take your panels (3.92kWp) and multiply that by the efficiency rating of the SB4000TL (Euro rated at 96.4%) giving a potential sustained output of 3.78kW.

Today, a very picky DNO might decline 'deemed permission' as being in excess of 3.68kW, or G83/1 permission. No worries for you, as this obviously got passed. But if this did happen to someone after installing, then for SMA inverters, they could simply get the inverter dialed down to 3,680W as this can be done in 1W increments, and (I believe) 3.68kW is an actual setting on them.

Mart.

Thanks for that Mart.

You are correct that 4100 is only for a short burst and is the max I've seen it at. Have seen it at over 3.7kw for much longer periods though...

Martyn1981

Ferdy147 wrote: »

Thanks for that Mart.

You are correct that 4100 is only for a short burst and is the max I've seen it at. Have seen it at over 3.7kw for much longer periods though...

Hiya Ferdy, I think you've made a typo, didn't you mean you've seen it holding (just) 3.68kW? :rotfl:

I do (sadly) find this stuff very interesting, especially as things change and adapt for the future. Not sure if the DNO's find it fun!

Mart.

Ferdy147

Martyn1981 wrote: »

Hiya Ferdy, I think you've made a typo, didn't you mean you've seen it holding (just) 3.68kW? :rotfl:

I do (sadly) find this stuff very interesting, especially as things change and adapt for the future. Not sure if the DNO's find it fun!

Mart.

Yes you're right again a typo on my part of course!

Seriously tho, I didn't know anything about this limiting the inverter to 3.68kw business till I read this thread. Wondered why some people here had 3.6kw inverters on a 4kw system.

Dave_Fowler

I'm considering adding a further 2.6kWp to my system by putting more panels on a separate detached, brick built, tiled roofed garage. I understand that as this is an extension, I'll need an EPC rating of D or better. I take it that it's the EPC of my house that is calculated, not the building to which the panels are attached. The garage is not insulated in any way.

I would need a separate generation meter as the garage is detached by quite a distance (but does have a 30A electricity supply connected to the house consumer unit).

Dave F

tunnel

I'm considering adding a further 2.6kWp to my system by putting more panels on a separate detached, brick built, tiled roofed garage. I understand that as this is an extension, I'll need an EPC rating of D or better. I take it that it's the EPC of my house that is calculated, not the building to which the panels are attached. The garage is not insulated in any way

Yes your correct,the EPC is on the house,not the garage. I've just extended my system,adding another 2.04 onto my newly built garage with no insulation. An EPC lasts for 10 years too,so if you've moved in in the last 5 years or so then there should be a valid one on the property. If its worse than a "D" then a new one will be required(bear in mind the solar you now have in will contribute to any new EPC)

Tunnel