DNO Refused Tesla Powerwall - any advice ?

tiya1990

Hi ,

We are a power hungry household in the West Midlands - Worcestershire.

We have 7.05KW PV Panels generating around 5000KW per year . We exported 3000kwh last year and imported 6,600kwh ( 4,000kwh is consumed by the electric car alone - we would like to get a second electric car and an induction hob in the next 2 years ) .

We wanted to retrofit the Tesla Powerwall so that with the 11kw inverter , our energy needs would be met and we would not have to import from the grid most of the year.

DNO has declined and will only agree to 5kw inverter .

Is there any reason for this as we are not going to be putting a lot out to the grid and will be using it ourselves ?

Can we appeal or agree to some ' reparation work ' between our house and the grid so that they might agree ? ( I am with Octopus and they told me that DNOs sometimes agree to this )

How can a 5kw inverter meet our needs ?

Thank You for reading this far and grateful for your advice.

MattMattMattUK

https://forums.moneysavingexpert.com/discussion/6663914/dno-refused-tesla-powerwall-any-advice

It will be capped because you could put it into the grid, so the grid would need to be able to support that. You could go for G100 which means you can have more generation capacity and more battery storage and inverter capacity, but the export is capped at a pre-approved limit set by the DNO, the Powerwall 2 and 3 are both able to do this and are compliant for G100 purposes. This means you can use the full power of the Powerwall's 11.5kW inverter but just not export at any more than the agreed limit of 5kW.

The "reparation work", you refer to would be paying for the line upgrade, and potentially substation upgrade and a move to three phase, very occasionally not charged if they were going to be doing it anyway, normally thousands to tens of thousands so not work it, especially not when G100 would solve your issue.

Martyn1981

Are the DNO adding the PW3 export potential to your current PV export? I mean are they allowing an extra 5kW on top of current limit, or 5kW total? What is the current inverter rating, and DNO limit?

So, if you're not already planning this, can you replace the existing inverter with the PW3. Then cap the PW3 to 5kW export, keeping the DNO happy(?)

We have 2 BEV's, induction hob and leccy oven. And in the heating months there's also two A2A will running too (500W to 1,000W total). Our 2kWp west system can help a bit, but most demand is met by our PV/battery system which is 3.68kW limited. We only import about 2% day rate leccy, as the 3.68kW covers us most of the time.

The BEV's are charged overnight as that's a lower rate than the export rate we get paid.

NedS

I hear your frustrations. I had similar issues when applying for a PW3 with National Grid. I would suggest giving the person a call and having a friendly chat with them for advice as to what your options are.

NG do not want to refuse you, but their primary concern is ensuring the local grid is safe for everyone.

I assume they have agreed to a 5kW inverter setting and 5kW export limit? NG sometimes offer this as part of their fixed fast-track (5+5) scheme, it is what it is.

If it fits your needs, or is a better compromise, they may agree to the full 11.04kW inverter rating if you agree to reduced or no export (i.e, you can self consume all you generate by storing in the battery/cars what you don't use).

NG originally offered me a 7kW inverter rating (matching our 7.2kW array) with 1kW export and then told me about the 5+5 fast-track route when we rejected the 1kW export offer as this was too low for us to be financially viable. Unfortunately if you go the fast-track route to get the 5kW export, you are limited to the fixed 5kW (max) inverter.

My experience was that the NG guy was brilliant. He was prepared to explain how they arrived at their offer and listed to what I wanted to achieve before suggesting the 5+5 fast track route which ultimately worked better for us. He could so easily have been a jobsworth and said it is what it is.

I think I recall that the 5+5 fast track scheme actually allows for up to two 5kW max inverters and an export of 5kW, so you could theoretically fit two PW3s limited at 5kW output each allowing 10kW of inverter rating to feed the house, which may be a reasonable solution of you also need the extra storage.

Jemma01

Am I reading this correctly, did they decline the powerwall component itself? I thought these can be restricted to 5kw. Is the concern that owners can bypass the limit and configure it above the approved limit?

Qyburn

Under G.100 they apply a total system limit as well as a export limit. SSEN limit was 2.3% for total, ie the power that would cause 2.3% voltage rise if it was all exported. That goosed our original plan using an AC coupled battery (PW2) as it would mean an absurdly small inverter.

Screwdriva

I think there is a bit of miscommunication here. The DNO has restricted either your peak generation and/ or your peak export to 5kWh. They have not refused the PW3, as it can easily be set to adhere to any DNO limitations and they know this.

The "negotiation" between the DNO and the installer can be quite arduous, with little room for installers to maneuver. Two of the installers I use are known to fight tooth and nail to secure higher allocations from the DNO (as @JKenH has experienced firsthand). But sometimes they too have to accept lower outcomes.

Who is your installer ? A few suggestions for them to try:

1) Ask for any works that can be done to increase the allowance. Sometimes (rare) this isn't more than £1-3K.
2) Insist that export can be limited while generation to 11kWh remains permitted.
3) Ask for a linesman to visit the site to physically test their presumed voltage readings (DNOs tend to perform desktop assessments and do not like to send resources) and can allocate more export allowance in the hope of avoiding this.

Jemma01

https://forums.moneysavingexpert.com/discussion/comment/81961035#Comment_81961035

What would make them limit his peak generation if it remains within his house boundaries? Or why?

Qyburn

https://forums.moneysavingexpert.com/discussion/comment/81961073#Comment_81961073

My understanding is there are two reasons, (1) G.100 export limitation isn't instantaneous so it could be exporting over that limit for brief periods. (2) my speculation but they could be concerned about failsafe if the export limitation fails. The actual rather vague answer i got from SSEN was ..

"We do often get the question about why the total installed capacity even needs to come into consideration, but there just needs to be a limit as a safety precaution in case of any faults etc"

NedS

I also do wonder if there's a bit of old fashioned thinking here too, not fully understanding the PW3 and what it can do. I know Tesla provided DNO training when the PW3 was first introduced into the UK to address this.

Anyway, a 5kW inverter (and hence export limitation) would not have been uncommon or unreasonable for a 7kWp solar array a few years ago, but products like PW3 have moved the goal posts significantly.

JKenH

A few years ago I considered adding a battery and some more panels (to avoid VAT on the battery install) and the message I got back from my proposed installer was that the DNO would not accept any more panels or a battery as the potential existed for the export to exceed what the DNO considered a permissible limit. The DNO would not accept an export limiting device as it might potentially fail.

Last September @Screwdriva put me in touch with another installer who over 3 months successfully negotiated the installation of a further 5kW of panels and a Tesla PW3 battery with an export limit of 11.04kW. Although I have 12.8kW potential on my roof, as it is spread over 3 elevations I am unlikely to reach the 11.04kW limit. I don’t know if this is a factor. Whether or not this is relevant I do not know, but I have not yet found a way to force export from my PW3. It decides when and how much to export.

I live in a rural area and my house is one of a half dozen or so connected to a transformer on a pole in a field. One of my old inverters regularly cuts out (as many as a dozen times a day) when it reaches overvoltage condition (approximately 259v). It did this before my PW3 and additional panels were added to the system and I had a Northern Powergrid engineer out to investigate but he didn’t seem concerned.

Despite this the PW3 and 11.04 kW export limit were permitted.