DNO refusing solar with G100 0kW export

[joeka101]

Hi,

I've applied for G99 for 16kW solar PV and battery storage all behind a G100(2) export limitation device set to 0kW (zero export). Single phase 100a supply.

DNO has come back asking for a large payment (multiple thousands) for network and supply upgrades as they say this amount of generation will lead to unacceptable voltage rise (over 12%) in MY property due to the length and age of my supply cable. (1940 house in a residential part of a city - not remote or rural).

I don't understand. I thought significant voltage rise would only occur when exporting (due to the need to be 'higher' than the grid and overcome resistance of the supply cable). If 0kW G100 export limit surely there should be no generation limit?

Is DNO trying to pull a fast one?

Cheers for any comments.
Joe

 

[ericmark]

It would seem that is the case. But first 18 months I could not get paid for export, one needs a second MPAN number to export, which had not been raised, however although not being paid, I was still exporting, so would have raised the line voltage, I can't see how one would grid tie, and not export, my inverter would not allow me to do that.

On the other hand, there are plug-in solar panels

as yet not legal in the UK, but freely available, all the reviews tell you that you can't get export payment, but once you have the MPAN number, unless the export is above the declared output of the permitted panels, how would they know?

This guy did a video

there is another video where the DNO provided a three-phase supply, and it all worked OK after, but what he did here was crazy. The voltage optimiser as he calls it, I always called then an auto transformer will allow one to raise or lower the voltage, they were used years ago to run 220 volt equipment on the UK's 240 volt supply, before voltages were harmonized with Europe.

There was an auto stepping version for fluorescent lamps, before the electronic ballast came out, but now considered as snake oil, and no need for them.

But the DNO has to supply the home at 230 volts plus 10% minus 6% so 216.2 volts to 253 volts, a 36.8 volts difference, so 36.8/100=0.368Ω loop impedance maximum to ensure that is maintained. Well, not quite, auto stepping transformers could allow a higher loop impedance, but be it that or heavier cables, or three-phase, they all cost. And things like EV chargers use the voltage to detect loss of pen, so anyone on the same supply is likely to complain, as their car has not changed.

I have 6 kW, and a 5 kW inverter, I must be close to the supply transformer as I see very little voltage change, and never seen it drop to 230 volts, in fact as more and more homes are getting solar panels, I am seeing the voltage slowly raising. It must be a headache for the DNO, as they can't stipulate which homes have solar panels, so they may end up with one phase with high voltage and one will low voltage if home on the same phase all get solar panels.

I look at my panels, and summer yes 5 kW, but today 210 watts, not even 1 kW, to span the 19 hours between off-peak, I would need far bigger batteries, but battery life is shorter than solar panel life so for the 3 to 4 months when I can not work on solar and off-peak, it is not worth the outlay.

 

[joeka101]

Thanks for the reply.

My understanding is that the inverter can scale down it's generation and switch off entirely based on the G100 export limiting device's CT clamp (senses if current is flowing INTO or OUT of property at meter tails). They all talk to each other. I'm also planning a very large bank of batteries to soak up basically everything I can possibly produce from solar PV (supplemented by cheap charging overnight).

I should point out I'm asking for 16kW generation (from solar PV and batteries combined). Not 16kW of panels.

Cheers

Joe

 

[joeka101]

PS Yes thanks for the link - I'd just watched that Artisan Electrics video too! That situation is exactly what I think is the DNO concern but I don't see what the issue is if I am limited to zero export (the inverters won't have to got to a higher voltage than grid plus grid supply cable voltage drop in order to "force" the export).

 

[ericmark]

I should point out I'm asking for 16kW generation (from solar PV and batteries combined). Not 16kW of panels.

My panels and my battery use the same inverter, so 5 kW is my limit as that is the inverter limit.

Batteries do not generate, they store, OK there are exceptions, Electric Mountain for example. So have you quoted the correct figures to the DNO?

 

[joeka101]

The hybrid inverter generates the AC output from both the DC batteries and DC Solar panels. The hybrid inverters total max output is 16kW but can throttle down to zero as per G100 export limiter.

 

[aesmith]

My understanding is the limit, which our DNO referred to as "total installed capacity" is because export regulation is imperfect. From memory the G100 only requires response with seconds. So they need to take into account the effect of that total power, should it be briefly exporting or should something malfunction.

Just for reference SSEN gave a maximum allowed voltage rise of 1.3% for export, and 2.3% total installed capacity. Both figures for a supply at nominal 240V. Interesting their G99 offer also specified that voltage must not be caused to rise more than 6V at the supply point.

 

[aesmith]

The hybrid inverter generates the AC output from both the DC batteries and DC Solar panels. The hybrid inverters total max output is 16kW but can throttle down to zero as per G100 export limiter.

By the way what size of battery do you intend? At first glance having a system without export capability would be a massive waste, for example over 12 months we exported over 60% of our generation. In Summer if prioritising battery charge over export (system default) the battery would be fully charged by 09:00.

 

[ericmark]

I would agree with @aesmith my solar

is double my consumption in summer, so it does not matter what the battery size is, March to September I am producing more than I am using. For October to February, it is the battery and the off-peak tariff which saves me money.

The major problem, both summer and winter, is some days are very good, and others are very poor, so some days we make money with export, and other days we pay for electric, we do on balance make money in summer, but I would say without export payment it had halved my electric bill, but with it, on balance we are about net-zero. Not done a whole year with Octopus yet, so not quite sure how it will work out.

I at first did not have a big enough battery, but batteries have a lot shorter life span to the panels, so going over size is not really going to pay for its self. So don't want to go too big, at this time of year, we can just about on a good day only use off-peak, and I would say good v poor days around the 50/50 mark so we have 1/6th of the days when we use grid power on average, we can double or battery capacity, the inverter will allow that, but don't think the gain is worth the outlay on extra batteries.

But the volt excess is solely about solar, nothing to do with the batteries. And it seems likely the wrong info has been declared to the DNO. Once the DNO allow you to have the export MPAN number with G99, they are also guaranteeing you can export. Their system does not allow them to say you can export ½ the capacity of your system, or even zero, it is either all or nothing.

The G99 regulation does not impose a single "max size" limit, but rather requires a formal application and approval process for any system with an inverter capacity greater than 3.68 kW per phase (11.04 kW for three-phase connections). The actual maximum size depends entirely on the capacity of your local electricity network.

Export limitation is an option: If your proposed system's full capacity is more than the local grid can handle, the DNO may offer an G100-compliant export limitation scheme. This allows you to install a larger system (e.g., a 10 kW system with a 3.68 kW export limit), maximizing self-consumption while limiting the power sent back to the grid.

So it seems there is no limit to install size with G100.