Considering adding another battery - inverter options

ed110220

michaels said:

ed110220 said:

Just had a reply back from National Grid (DNO, was Western Power Distribution) and they've said I can have 17 kW total and export! Can't quite believe it. Not that I'd be installing anything like that... Possibly 8 kW?

Not sure why it's so high, possibly because I know the local substation has had work on it recently and I'd estimate the number of PV systems in the area is lower than average (many housing association properties who unfortunately haven't had any, lower income, quite a few HMOs etc).

That is interesting, currently we have a 10kw G99 with a 3.6 solar inverter and a 6kw V2H but would like to add a battery too with its own inverter (V2H can not be retasked and the PV gets FIT) but was worried that I would not get DNO approval even if the new invertor was set up not to discharge if grid export exceeded 10kw.  So I will ask them if I can get an increase.  DO you need to have the new system in place or can you just ask for it in readiness for an additional inverter?

I don't know exactly how it works, I just emailed to ask and have had a reply. They said they'd call me on Mon with more information. I don't have a new system yet.

Qyburn

For G.99 you put in your request, receive an "offer" which you need to accept. Then once installed you submit details of the installation and the DNO confirms (we hope) that it complies with the offer.

ed110220

Qyburn said:

For G.99 you put in your request, receive an "offer" which you need to accept. Then once installed you submit details of the installation and the DNO confirms (we hope) that it complies with the offer.

Presumably this is a less formal check so you can have a better idea of what to request.

Martyn1981

ed110220 said:

Just had a reply back from National Grid (DNO, was Western Power Distribution) and they've said I can have 17 kW total and export! Can't quite believe it. Not that I'd be installing anything like that... Possibly 8 kW?

Not sure why it's so high, possibly because I know the local substation has had work on it recently and I'd estimate the number of PV systems in the area is lower than average (many housing association properties who unfortunately haven't had any, lower income, quite a few HMOs etc).

Damn I'm jealous. I got 5.9kW from WPD in 2012, and then when I asked about V2G in 2019, they told me no chance, and I think the choice of words when I rang was "no idea what idiot gave you 5.9kW". They did say they weren't minded at this time to take away my approval ..... so I've never asked anything since, don't rock the boat. 

ed110220

Martyn1981 said:

ed110220 said:

Just had a reply back from National Grid (DNO, was Western Power Distribution) and they've said I can have 17 kW total and export! Can't quite believe it. Not that I'd be installing anything like that... Possibly 8 kW?

Not sure why it's so high, possibly because I know the local substation has had work on it recently and I'd estimate the number of PV systems in the area is lower than average (many housing association properties who unfortunately haven't had any, lower income, quite a few HMOs etc).

Damn I'm jealous. I got 5.9kW from WPD in 2012, and then when I asked about V2G in 2019, they told me no chance, and I think the choice of words when I rang was "no idea what idiot gave you 5.9kW". They did say they weren't minded at this time to take away my approval ..... so I've never asked anything since, don't rock the boat. 

Maybe ask again, surely they can't take away what you already have? 

I forgot to say that my supply has been unlooped since the solar was fitted. The neighbours were going to get PV too so they had their supply unlooped from ours, but in the end they didn't get any.

Looking at PVGIS I'm half thinking about having an identical or similar array on the NE facing side (the roof is symmetrical). Given the shallow pitch the yield isn't actually that much lower, though of course the yield in winter is quite a bit lower and export prices will probably come down.

Does anyone have an idea what kind of cost to expect for an inverter move/install these days? Currently it's in the loft which I know isn't ideal. So when I did internal renovations I ran some DC cables from the current inverter position down to the utility room so that it could be moved in the future. Was thinking of buying an inverter myself and getting it fitted as they seem to come up fairly cheap eg bought for a project but not used.

NedS

You are lucky with your DNO offer. We have an existing 3.68kWp on a 3kW inverter, and applied for more solar (up to 7.2kWp) and a Tesla Powerwall 3 battery/inverter. They agreed to the install, but offered only 1kW total on the export, thus significantly limiting us to less than the 3.68kW we can currently export. Without the export, the numbers simply do not add up to make the install financially viable.

ed110220 said:

Martyn1981 said:

ed110220 said:

Just had a reply back from National Grid (DNO, was Western Power Distribution) and they've said I can have 17 kW total and export! Can't quite believe it. Not that I'd be installing anything like that... Possibly 8 kW?

Not sure why it's so high, possibly because I know the local substation has had work on it recently and I'd estimate the number of PV systems in the area is lower than average (many housing association properties who unfortunately haven't had any, lower income, quite a few HMOs etc).

Damn I'm jealous. I got 5.9kW from WPD in 2012, and then when I asked about V2G in 2019, they told me no chance, and I think the choice of words when I rang was "no idea what idiot gave you 5.9kW". They did say they weren't minded at this time to take away my approval ..... so I've never asked anything since, don't rock the boat. 

Maybe ask again, surely they can't take away what you already have? 

Correct, they cannot take away what they have previously approved, but you could make a new application and receive a lower offer than what you already have (see above). Of course you do not have to accept the offer. I should note that when receiving a G99 offer, you must install and notify the DNO within 3 months of the received offer for final approval. If you don't install and connect to the grid within 3 months, the offer expires. If you don't take up the full offer, the approved install is what you have as any 'excess' also expires after 3 months (e.g, they offer you 10kW but you install an 8kW inverter on a 10kWp array, you can't then later upgrade to a 10kW inverter without a new G99 application).

The concern on my local substation is voltage rise. The NG are responsible for making sure the grid voltage does not exceed a permitted maximum of 253v AC. When lots of homes are all exporting at the same time (sunny midday), the voltage rises. When everyone is importing power (dark evening in winter), the voltage drops. You can see this at home by checking the AC voltages reported by your inverter or by simply measuring the voltage at a wall socket. I've seen my voltage rise to 250v during the day indicating my area (connected to my local substation) is likely already saturated with solar. When I pull electricity overnight, the voltage can drop back to ~235v (although I've not paid as much attention to this), which would be further exacerbated by EV drivers charging overnight.

Anyway, the upshot is they do not want my export on an already saturated substation, so made me an offer well below the standard G98 amount everyone would be entitled to. The guy at the DNO explained the put the numbers into a spreadsheet to calculate the voltage rise for the 11kW we applied for, and then keep dropping the value 10, 9, 8kW... down to zero until the grid is happy with the voltage rise, which in my case was 1kW, so that's what they offered me.

It really is a crap shoot, and first come first served. My local substation has ~150 properties connected on 5 feeders, so around 30 properties per feeder. The first properties to apply on any given feeder will get near unrestricted offers and as more properties apply, the restrictions increase until such time they effective become a no. The only hope I have is more of the remaining 30 properties without solar install under G98 rules and notify the DNO, who then see that the substation is at it or about to exceed it's limits and they need to upgrade it - then I can apply again and the result will be markedly different (I don't think they are allowed to hold back capacity for potential future G98 installations)

Qyburn

ed110220 said:

Qyburn said:

For G.99 you put in your request, receive an "offer" which you need to accept. Then once installed you submit details of the installation and the DNO confirms (we hope) that it complies with the offer.

Presumably this is a less formal check so you can have a better idea of what to request.

I guess that will depend on the DNO. Our installer applied for the capacity we really wanted, and we got an offer conditional on us paying quite a substantial sum to upgrade the cable from our transformer. They also indicated lower values for total system size, and for export, that would be acceptable without that work. However each of those took two months of so to come back with SSEN's response.

michaels

ed110220 said:

Martyn1981 said:

ed110220 said:

Just had a reply back from National Grid (DNO, was Western Power Distribution) and they've said I can have 17 kW total and export! Can't quite believe it. Not that I'd be installing anything like that... Possibly 8 kW?

Not sure why it's so high, possibly because I know the local substation has had work on it recently and I'd estimate the number of PV systems in the area is lower than average (many housing association properties who unfortunately haven't had any, lower income, quite a few HMOs etc).

Damn I'm jealous. I got 5.9kW from WPD in 2012, and then when I asked about V2G in 2019, they told me no chance, and I think the choice of words when I rang was "no idea what idiot gave you 5.9kW". They did say they weren't minded at this time to take away my approval ..... so I've never asked anything since, don't rock the boat. 

Maybe ask again, surely they can't take away what you already have? 

I forgot to say that my supply has been unlooped since the solar was fitted. The neighbours were going to get PV too so they had their supply unlooped from ours, but in the end they didn't get any.

Looking at PVGIS I'm half thinking about having an identical or similar array on the NE facing side (the roof is symmetrical). Given the shallow pitch the yield isn't actually that much lower, though of course the yield in winter is quite a bit lower and export prices will probably come down.

Does anyone have an idea what kind of cost to expect for an inverter move/install these days? Currently it's in the loft which I know isn't ideal. So when I did internal renovations I ran some DC cables from the current inverter position down to the utility room so that it could be moved in the future. Was thinking of buying an inverter myself and getting it fitted as they seem to come up fairly cheap eg bought for a project but not used.

Our PV array is about 10 degrees south of west.  We were thinking of adding panels to the East facing roof and putting it through the same inverter and accepting about 10-20% clipping for an hour or so around mid day on peak output days, seems to work out better return than adding another inverter - however there are FIT implications as the inverter output goes to the generation meter.

JKenH

We were very lucky to get our 7.3kW export limit but we never approach that as our solar array is split over ENE and WSW roofs. A couple of days ago the inverter on our WSW roof tripped out and on investigation I could see a voltage of 256v. I switched on an immersion heater and that dropped the voltage sufficient for the inverter to restart. This was the first time this year I had noticed this and the sun was particularly strong between clouds. We are on the edge of a village and a transformer on a pole three houses away serves just a handful of properties. Three of us have solar panels so our generation can have a massive impact on generation. I have seen voltages as high as 259v and as low as 212v. 

Inconvenient as it maybe, there is a reason for export limits. I had tried to get the go ahead for a battery but the DNO, Northern Powergrid, said no as they factored in the potential output from the battery and were not prepared to consider export limiting devices. I felt aggrieved at the time but, on reflection, can understand their stance.

NedS

JKenH said:

We were very lucky to get our 7.3kW export limit but we never approach that as our solar array is split over ENE and WSW roofs. A couple of days ago the inverter on our WSW roof tripped out and on investigation I could see a voltage of 256v. I switched on an immersion heater and that dropped the voltage sufficient for the inverter to restart. This was the first time this year I had noticed this and the sun was particularly strong between clouds. We are on the edge of a village and a transformer on a pole three houses away serves just a handful of properties. Three of us have solar panels so our generation can have a massive impact on generation. I have seen voltages as high as 259v and as low as 212v. 

Inconvenient as it maybe, there is a reason for export limits. I had tried to get the go ahead for a battery but the DNO, Northern Powergrid, said no as they factored in the potential output from the battery and were not prepared to consider export limiting devices. I felt aggrieved at the time but, on reflection, can understand their stance.

The over-voltage tripping could have been caused by 'cloud enhancement', which apparently is a thing where there is strong direct sunlight between interspersed white cloud cover:

https://protonsforbreakfast.wordpress.com/2024/07/20/holiday-trip-part-2-cloud-enhancement/

Regarding the over-voltage, it may be worth contacting your DNO/NG to report the high voltage. The maximum allowable voltage is 253V AC (I'm not sure over what time period), and if it is above this threshold then the Grid is responsible for taking corrective action so it sounds like it's time your substation/cabling is upgraded to cope with the demands being placed upon it.

It seems from a previous post in 2022 that this is not a new situation. I'd be pushing the DNO to take corrective action:

https://forums.moneysavingexpert.com/discussion/6359328/solar-inverter-over-voltage-reports

Both voltages you have observed are outside of allowable range of 230V -6%/+10%