Considering adding another battery - inverter options

Magnitio

A relative has recently had an 8kW inverter installed with 9.5kWp of panels. All approved by the DNO, but it is causing regular overvoltage issues. They have been out to investigate, checking cables, digging up the road, installing voltage meters. Daily voltage ranges from just under 230 to 256 when the inverter shuts down for a few minutes. It could end up being a cabling issue, or the relatively small number of houses connected to the transformer. I suspect it is an expensive issue for this DNO to investigate and fix (if they can), so I can understand why they might be cautious elsewhere.

Qyburn

JKenH said:

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 reason is that export limitation is imperfect and takes time to respond. In normal operation they therefore have to accommodate brief periods of export above the limit and potentially up to the full system output. For example when a load is switched off the battery or inverter has no advance notice of this and can only respond after export suddenly increases. I believe it is supposed to react within 5 seconds but don't know if that's the time to detect, or time to correct and bring export back within limits.

I suspect that they may also consider fault conditions, what impact your system would have if export limitation failed altogether.

Qyburn

michaels said:

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.

I believe you will need to get prior approval from the FIT provider for any alteration, and if your proposed addition goes through the generation meter the best you're likely to get is a payment for the proportion of total size represented by your original install. Say you had 3kW panels originally, and added another 4kW, then you'd be paid for 3/7 of your total generation. You'd be short changed because them making no allowance clipping or the fact the panels generate at different times.

ed110220

michaels said:

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.

No FIT here to impact (2022 install), I'm mainly interested in a larger inverter to be able to charge up enough batteries on cheap off-peak electricity to run an ASHP. Though it has made me think about another 4.8 kW of PV on the NE side of the roof, but that would be a project for the future. 

On that subject, how would you go about calculating how many kWh I'd need to store per off peak slot for an ASHP? I've looked through our daily gas consumption for the last two winters and the highest was 50 kWh, but it was rarely above 40 kWh and much more often below 30 kWh. 

50 kWh of gas = 16 kWh ASHP consumption at a COP of 3. Currently our 15 kWh battery lasts us till the next off peak slot so I'm thinking ~ 30 kWh would be sufficient. We don't use has for anything other than the boiler (no gas cooker etc). Therefore with a 5 h off peak period we'd need a 6 kW charge rate... Increase that to 8 kW inverter to be safe (higher than expected consumption, off peak tariff with a shorter period in future). Sound about right or too crude?

69bertie

Magnitio said:

All approved by the DNO, but it is causing regular overvoltage issues. They have been out to investigate, checking cables, digging up the road, installing voltage meters. Daily voltage ranges from just under 230 to 256 when the inverter shuts down for a few minutes. It could end up being a cabling issue, or the relatively small number of houses connected to the transformer. I suspect it is an expensive issue for this DNO to investigate and fix (if they can), so I can understand why they might be cautious elsewhere.

If they are installing voltage meters, they will soon find the source of the problem. It might be a simple case of an HV transformer tap changer stuck. One works I attended some years back had 265v as a result of one such incident and yes, the export generator had shutdown. 

The voltage can go down to as low as 216v and up to 253v. And yes, I wouldn't be surprised if an inverter shut down as the voltage got too high. Most generators operate in exactly the same way. After all, if it is generating outside limits, where do you stop.

Cost is irrelevant. If it is outside limits, it needs and will be fixed. Reason? If your appliances start going bang due to very high volts, who picks up the bill for replacement?

michaels

ed110220 said:

michaels said:

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.

No FIT here to impact (2022 install), I'm mainly interested in a larger inverter to be able to charge up enough batteries on cheap off-peak electricity to run an ASHP. Though it has made me think about another 4.8 kW of PV on the NE side of the roof, but that would be a project for the future. 

On that subject, how would you go about calculating how many kWh I'd need to store per off peak slot for an ASHP? I've looked through our daily gas consumption for the last two winters and the highest was 50 kWh, but it was rarely above 40 kWh and much more often below 30 kWh. 

50 kWh of gas = 16 kWh ASHP consumption at a COP of 3. Currently our 15 kWh battery lasts us till the next off peak slot so I'm thinking ~ 30 kWh would be sufficient. We don't use has for anything other than the boiler (no gas cooker etc). Therefore with a 5 h off peak period we'd need a 6 kW charge rate... Increase that to 8 kW inverter to be safe (higher than expected consumption, off peak tariff with a shorter period in future). Sound about right or too crude?

Can you get your half hourly usage for the gas as that will obviously show you how much was used in the peak hours rather than the daily total.  With a heat pump you are likely to use a smaller (or even no) night time set back which transfers some of your usage from peak hours to off peak hours, specifically any morning peak where the gas boiler gets the house back up to the daytime temp.

I would probably chose worst day and assume a cop of 2.5 on that day rather than 3 - but against that it may not be cost effective to go for 'zero' peak import if you then have to add another 5-10 kwh of battery that you will only use on 2 or 4 days a year (although there might be some offsetting of the cost if you get a good SEG rate and can make a profit on the round trip on the days where you don't need to use all the storage for your own consumption)

ed110220

michaels said:

ed110220 said:

michaels said:

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.

No FIT here to impact (2022 install), I'm mainly interested in a larger inverter to be able to charge up enough batteries on cheap off-peak electricity to run an ASHP. Though it has made me think about another 4.8 kW of PV on the NE side of the roof, but that would be a project for the future. 

On that subject, how would you go about calculating how many kWh I'd need to store per off peak slot for an ASHP? I've looked through our daily gas consumption for the last two winters and the highest was 50 kWh, but it was rarely above 40 kWh and much more often below 30 kWh. 

50 kWh of gas = 16 kWh ASHP consumption at a COP of 3. Currently our 15 kWh battery lasts us till the next off peak slot so I'm thinking ~ 30 kWh would be sufficient. We don't use has for anything other than the boiler (no gas cooker etc). Therefore with a 5 h off peak period we'd need a 6 kW charge rate... Increase that to 8 kW inverter to be safe (higher than expected consumption, off peak tariff with a shorter period in future). Sound about right or too crude?

Can you get your half hourly usage for the gas as that will obviously show you how much was used in the peak hours rather than the daily total.  With a heat pump you are likely to use a smaller (or even no) night time set back which transfers some of your usage from peak hours to off peak hours, specifically any morning peak where the gas boiler gets the house back up to the daytime temp.

I would probably chose worst day and assume a cop of 2.5 on that day rather than 3 - but against that it may not be cost effective to go for 'zero' peak import if you then have to add another 5-10 kwh of battery that you will only use on 2 or 4 days a year (although there might be some offsetting of the cost if you get a good SEG rate and can make a profit on the round trip on the days where you don't need to use all the storage for your own consumption)

I have got the half hourly records but I haven't been through them all because the amount of gas we use from 00:30 to 05:30 is insignificant as we never have the heating on at those hours. Using a smaller night time setback is going to increase overall consumption - any idea how much?

Here's the half hour consumption for a typical colder winter day: 

ed110220

I've just had a call from National Grid (ex WPD) and they said I could have the full 17 kW. When I said I was surprised she said she was too, that 17 kW is the maximum possible and it's because I live close to my local substation. She also said it's fairly rare for them to get an enquiry like this, because installers usually submit a specific request rather than asking what they can have.

QrizB

ed110220 said:

I've just had a call from National Grid (ex WPD) and they said I could have the full 17 kW.

That's a result, then 🥂

ed110220

QrizB said:

ed110220 said:

I've just had a call from National Grid (ex WPD) and they said I could have the full 17 kW.

That's a result, then 🥂

16 kW inverter, 7 Seplos kits for 112 kWh of storage, import 100 kWh each night for £6.70 and then export 90 kWh each day for £14.85

No, realistically am looking at an 8 kW inverter and another Seplos kit.