Zero PV generation allowed by DNO

[Dreadnaught]

Following this discussion with interest.

Tempted by a cheap DC only PV setup for my passive build with an electricity-only solution for space heating and DHW. Have a shaded site but might be able to justify some east/west panels.

[ProDave]

Re the FIT.  I have always thought the system we have is bonkers.  Initially the FIT rate was way too high (not complaining I am still benefiting from it)  Now it is way too low. (I AM complaining about that)

 

I also object to having to have an MCS contractor install it to claim the FIT which we all know pushed up the price a LOT.

 

A far better system would be no equiment subsidy, no need for a special installer, just a normal electrician who will issue an EIC as he would when wiring a new house, and a fair payment for exported power with a meter that actually mesures export and pays an actual metered rate, not far below the import rate.

 

Reading this thread, and on the basis I am almost certainly going non FIT, I will probably just install mine and say nothing to anybody.  I will be doing my damned best to use it all so not much will "escape" anyway.

[willbish]

Had some futher correspondence from the DNO,

 

I told them I would be installing a large electric combi ~14kW

Asked if I could limit PV export to 16A

 

Their response:

 

Hi Will

 

I’m sorry that you were unable to reach me yesterday, I was out of the office all day.

 

As the area is quite rural the number of customer’s connected to the transformer is very low and therefore the load being pulled is insufficient to counteract the voltage rise caused by your PV.

That said, if you were to install only 16A per phase of PV you could do this by the fit and inform process whereby you simply notify us post-installation and therefore it would be up to Western Power to pay for any reinforcement costs. I have done a study on a 16A installation and it would actually only require yours and your neighbours service cable to be upgraded. We would do this free of charge.

 

If you are installing an electric boiler this is classed as a disturbing load and we would need to conduct a network analysis on this also. I have attached the relevant form to be completed with regards to the boiler. Unfortunately any reinforcement costs associated with this installation would be chargeable to you.

 

So to clarify, with regards purely to the PV, if you only install up to 16A per phase of PV we will cover any reinforcement costs. This 16A applies to the whole installation, not just the export.

 

I hope this makes sense, please do not get in touch should you have any further questions.

 

Kind regards

 

(the do not get in touch bit has not been edited by me! ?)

 

So at least I can have some PV.

I've got space for more than 4.0kWp though, what are my options now?

 

-Standard 4.0kWp MCS system 

-Diy 4.0kWp system

-Either of the above plus additional panels on DC configuration

-Whole array DC 

 

Any input much appreciated

[ProDave]

So install the PV, wait for them to do the free upgrade work, then install any high power loads.

 

Sorted.

[willbish]

You think I should just settle for 4.0kWp, what about my slightly irrational desire for loadsa PV

 

Is a duel AC & DC system worth the extra configuration hassle?

Will a sole DC system lead to a waste of excess generated electricity if I don't have additional storage on top of the Sunamps

[ProDave]

Well the easy way is install 4KW and notify them. Let them upgrade the network, then add more and you might forget to notify that.

 

I am not yet convinces of the economics of battery storage. Every time I look at it, the cost of the "free" stored power is not much cheaper than just importing it when you factor in battery life and replacement costs.  That has to change for the better and I am sure it will, I just don't think we are there yet.  I am pretty sure with HW heating and use of big appliances in the daytime it is not hard to self use most of what you generate.

[willbish]

The DNO says that after the upgrade only 4.0kWp is permissable. Before the upgrade zilch.

 

My offer to limit the export to 16A was refused. So I was thinking that anything on top of 4.0kWp would have to be DC. Happy to be a little inconsistent with the truth if that's what you're saying but might struggle to persuade my sparky 

 

[Temp]

5 hours ago, willbish said:

That said, if you were to install only 16A per phase of PV you could do this by the fit and inform process whereby you simply notify us post-installation and therefore it would be up to Western Power to pay for any reinforcement costs. I have done a study on a 16A installation and it would actually only require yours and your neighbours service cable to be upgraded. We would do this free of charge.

 

Presumably if you installed a <16A array (and they only upgrade you and your neighbour) they could still refuse a G58 later on the grounds that..

 

..a significant stretch of the overhead main will also need upgrading

 

 

[Temp]

I wonder if the government consulted the DNOs before deciding that we were all switching to electric cars in 2040 (or is it going to be 2030 as some are pressing for)?

 

I've been thinking of installing a charger, even though I don't have an electric car yet, just in case the DNO have to start refusing installations in my village.

[SteamyTea]

7 hours ago, Temp said:

I wonder if the government

It is not the same problem; the grid was set up for centralised and coordinated generation.

But it may be an interesting way of getting your line upgraded.

11 hours ago, ProDave said:

use of big appliances

My biggest load is my kettle, and that is only on for a few seconds.

On 30/05/2018 at 13:14, ProDave said:

and a fair payment for exported power

Pre FiTs and the ridiculous 41p/kWh + 5p/kWh deemed export rates, people with PV wanted 'net metering', then it was about 10p/kWh which is close to what we get now.

The MCS scheme was not just about payment rates.  It was also meant to protect householders from dodgy traders and unsafe installations.  May not have worked in all cases, but generally most people are satisfied with their installations.

On 30/05/2018 at 11:55, Dreadnaught said:

Tempted by a cheap DC only PV setup for my passive build with an electricity-only solution for space heating and DHW.

Remember that switching DC is a lot harder than switching AC, and there may be some other safety implications to take into account.  You are not dealing with an ELV.

https://electrical.theiet.org/media/1425/low-and-extra-low-voltage-direct-current-power-distribution-in-buildings.pdf

Edited June 2, 2018 by SteamyTea

[Nickfromwales]

2 hours ago, SteamyTea said:

Remember that switching DC is a lot harder than switching AC, and there may be some other safety implications to take into account.

If a DC setup is available on the market then those implications will have already been considered and mitigated against in the design of the end equipment ? No consumer should have to consider such safety implications, thats down to the manufacturers is it not? 

[dpmiller]

it does mean that the control gear (switches etc) are more expensive and bigger for a given number of Amps than their AC equivalent.

[SteamyTea]

5 hours ago, Nickfromwales said:

If a DC setup is available on the market

Is there one that is available, or is it a jumble of parts.

I don't think it is like buying a computer, speakers, mouse printer, monitor.

 

I once saw two qualified electricians test the short circuit voltage of a 3.5 kW_p system on a very sunny April day.  They did this by putting a short circuit loop in after the DC isolator.

When I say I saw it, what I meant was I smelt it.

Dopey pillocks.

They never had a chance to measure the voltage.

[Nickfromwales]

Some waffle here.

[willbish]

My negotiations with the DNO continues.
I'm reviving this thread as I'd like a bit of inspiration or possible directions to take the discussions.

Their latest position is that after upgrades have been completed (at their expense) following a 'fit and inform' of 16A per phase, the network can then
support a massive 3.8kWp of PV.

In previous discussions last year they said that 16A limit applies to the whole installation, not just the export. Is there any way I can convince them otherwise?

What methods of export limitation are there that I could propose?

[ProDave]

New rules apply now. a <16A system is now under the G98 rules. Make sure any inverter you buy is now G98 compliant. you cannot now register a new install with a G58 inverter.

 

That will limit the generation to 16A.  You can have more that 4KW of panels connected to the inverter and it will never output more than 16A so will be compliant.

[willbish]

7 minutes ago, ProDave said:

You can have more that 4KW of panels connected to the inverter and it will never output more than 16A so will be compliant.

 

So where they've previously said the 16A limit applies to the whole installation not just the export, that is now irrelevant? As long as the inverter is G98 compliant I can crack on with a decent sized array and don't need to continue any further negotiations?

 

Because my roof is E/W split I would prob put something like 3.0kWp on each side. Being limited to 16A isn't going to affect my overall generation significantly, if at all.

[Onoff]

14 minutes ago, ProDave said:

New rules apply now. a <16A system is now under the G98 rules. Make sure any inverter you buy is now G98 compliant. you cannot now register a new install with a G58 inverter.

 

That will limit the generation to 16A.  You can have more that 4KW of panels connected to the inverter and it will never output more than 16A so will be compliant.

 

Is this to put the brakes on home generation, because the grid can't cope or a bit of both?

[ProDave]

The change from G59 to G98 was the result of an EU directive that imposed further technical details.  The current limit of 16A remains the same.  It is total generation that must be limited to 16A on the assumption if nothing is using power in your house, all 16A could be exported.

 

I see nothing wrong with an E/W split with 3KWp each side as long as the inverter is g98 and can handle the voltage and current that each string can output.

[willbish]

3 minutes ago, ProDave said:

I see nothing wrong with an E/W split with 3KWp each side as long as the inverter is g98 and can handle the voltage and current that each string can output

Great, thanks for the info

[Ed Davies]

For reference, here's the actual law: http://www.legislation.gov.uk/uksi/2002/2665/regulation/22/made

 

It seems to me that there are three possible interpretations of the 16 amp limit:

 

1) 16 amps per source of energy (so you could have two separate PV systems producing a total of 32 amps).

 

2) 16 amps total generation per installation.

 

3) 16 amps maximum export from the installation, so you can generate more so long as you can convince the DNO that not more than 16 amps will be exported.

 

1 is obviously silly but looking at the wording of the SI isn't obviously ruled out. 2 seems to be @willbish's DNO's interpretation. Assuming 1 is eliminated it's not a mad reading of the legislation. However, 3 is what's been widely understood on other forums. How you convince them has been a bit DNO dependent. IIRC, Western Power used to accept one particular diverter for this purpose. I think there are now inverters which operate with a current clamp so they'll limit export, i.e., they'll generate more than 16 amps so long as you're using the excess in house, which are accepted by some DNOs.

 

My understanding of the reasons for the change from G59 to G98 (I'm assuming @ProDave's got the numbers right here, I can't remember them) is that under the old rules the inverters would all drop out simultaneously when the frequency got low. The worry, particularly in Germany, was that if the grid was struggling as indicated by low frequency and voltage, it could happen that all the PV (and small-scale wind) could drop out together resulting in a cascading failure. Under the new rules they drop out more slowly likely resulting in a more managed and local failure.

[joth]

17 minutes ago, Ed Davies said:

change from G59 to G98 (I'm assuming @ProDave's got the numbers right here, I can't remember them)

 

Near enough.  G59 was actually replaced by G99 (being the rules for >16A installs)

G83 was replaced by G98 (rules for <=16A)

 

https://33kv.com/news/the-impact-of-moving-from-g59-to-g99/

https://www.ssen.co.uk/G99G98Requirements/FAQ/

[joth]

btw I've been on a similar (but different) voyage of discovery. Got PV quotes in January, G99 approved for 8kW in August, G99 expired this month, looking to start on site in the new year so eventually need to re-apply for G99 in... May? and have it commissioned by July.

In the mean time things move along (end of FiT, addition of VAT, G99 process bedding in...) I just had a look and there's a fresh wave of G99 certified ("type approved") inverters that didn't exist when I started. e.g. Solar Edge SE8000H. Which should make the whole G99 process a bit simpler at least.

 

Also it has "HD Wave" technology which is apparently revolutionary change in inverter efficiency and reliability. ("Like flat screens replacing CRTs"). Not sure what to make of this:

 

 

[joth]

http://www.ena-eng.org/gen-ttr/TTf1l3s/SOETC_00165_190606024212.pdf
"The inverters of the SExxxH series consist of the high power models: SE4000H, SE5000H, SE6000H, SE8000H and SE10000H. 
All the models use the same hardware and software. The different powers are realized by software derating. "

 

Interesting: it's just a software tweak to convert the 4kW inverter into a 10kW model.

[Nickfromwales]

11 hours ago, Ed Davies said:

so long as you can convince the DNO that not more than 16 amps will be exported.

You can go one better as they are able to insist that a representative from the DNO actually attends site to carry out a witness of such export limitation. The DNO charge sometimes ( incontestable ) but often don’t.

@willbish are you putting DC batteries in with the PV at the outset? You may never get permission to put them on the AC side,  now or retrospectively, if they’re already so particular over this. 
Export limitation should suffice here so I don’t see you having a big problem. 3kWp on each roof sounds a good amount and would generate a good spread of Pv through the day, without the midday ‘peak’ that can knock the inverter off when the local voltage rises to 253v.