Domestic Solar. Battery requirement.

[Emmit]

Hi All,
Not van related but thought you 'sparky' specialists would know the answer.

We have 12 x375 watt mono panels on the roof.

I appreciate we would need a new inverter but can anyone crunch a number as to how much battery power we would need to install.

It occurs that with the cost of lithium batteries falling off a cliff, it might be the time to install the batteries.

 

[Bolti]

16kw coming in at £1,750 from fogstar

Fogstar Energy/Seplos 48V 16.1kWh Solar BatteryWhite

Fully assembled 314Ah 48V (16.1kWh) lithium battery from Fogstar Energy. Seplos BMS. Scalable, reliable solar storage for homes and small businesses.

www.fogstar.co.uk

 

[autorouter]

I appreciate we would need a new inverter

You probably have seen this already, but there are two types of inverter. The standard grid-tied inverter doesn't charge batteries. You want a hybrid inverter that can charge batteries. If you are buying all the items separately, make sure you get a hybrid inverter.

The minimum battery power depends on the inverter power. For a 5kW inverter, you would want about 5 times the battery kWh, so about 5 x 5 = 25kWh of battery. This will ensure that the batteries are not stressed when giving full power to the inverter. In a commercial setup about twice that is better, but for domestic use the 5x figure is fine.

 

[Howard B]

We had 16kwh in our last house and used on average 10kwh per day. If you charge them from the mains during winter on a cheap overnight tariff as well as claiming FIT you will need a new export meter.

 

[MisterB]

If you charge them from the mains during winter on a cheap overnight tariff as well as claiming FIT you will need a new export meter.

We do that and didn't have a new export meter, in fact to do so might have meant we lost our FiT payments of 50% deemed.

Our set up is 4Kw of solar installed under the second phase of FiT, with it's own inverter.
An additional Sunsynk 5kw inverter feeding 2 x 14.3Kw Seplos upright batteries.

We are all electric and have overnight storage heaters, so we charge those and the batteries up overnight. I have my inverter set to charge to 50% at the moment, but because of the weather, the solar charges it well above that level so it hasn't been using any overnight or daytime electricity for a while now other than @10kw for the hybrid car overnight.

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[Howard B]

We do that and didn't have a new export meter, in fact to do so might have meant we lost our FiT payments of 50% deemed.

Our set up is 4Kw of solar installed under the second phase of FiT, with it's own inverter.
An additional Sunsynk 5kw inverter feeding 2 x 14.3Kw Seplos upright batteries.

We are all electric and have overnight storage heaters, so we charge those and the batteries up overnight. I have my inverter set to charge to 50% at the moment, but because of the weather, the solar charges it well above that level so it hasn't been using any overnight or daytime electricity for a while now other than @10kw for the hybrid car overnight.

OK. Ill try and explain our situation.

When we moved in to our last place we a had a one way meter measuring the electric produced by the 4kWh PV system. We were paid for what we produced and another 50% for deemed export. When we added the batteries the original meter would have recorded the PV generated, plus added any electric from the grid to be stored in the batteries. Our installer told us the system met the current requirements for FIT and signed a document to that effect ,so we though all was well. We had to sign a document for out FIT provider (EON) that any changes made would not be in contravention of the FIT rules & regulations. A that time we thought we were compliant.

However, I subsequently noticed that we had unusually high readings on the meter over the winter months which prompted me to investigate further. Thats when I found out the meter was also recording the import from the grid as well as the PV generation. This was also confirmed when we had our annual independent readings by an EON agent.

We informed EON who suspended our account until we installed the import/ export meter. The import/ export meter will work out what you have imported from the grid to store in the batteries and take it from the PV generated plus any electric from the grid for battery storage only. This will give you a Net reading for FIT purposes and we still got the 50% from our PV generation. It doesnt count anything for direct household use.

The installer was still adamant that what he had done was compliant for FIT, however I showed him my research which he investigated and subsequently agreed he should have fitted the import/export meter. He was blaming Givenergy for giving him incorrect information. He fitted the import export meter for free and our FIT account was reinstated by EON.

If you have the PV & batteries installed at the same time, then the installer should fit an import/ export meter at the time to ensure you are compliant.

This was our situation and how it was resolved. After speaking with the EON FIT teams and a number of discussions with Emlite who make the import/ export meter we installed, I suspect there are plenty of other out there who may not be compliant with the FIT rules after retrospecively fitting battery storage .

Hope this makes sense.

 

[MisterB]

I think Its one of those scenarios that appear to be the same but aren't.

I was making the point that I didn't need the additional meter and perhaps someone else might not either.....I have two inverters, one original to the PV and one totally separate that doesn't feed into the grid at all, it's there just for charging the batteries overnight. When I finally get around to adding additional solar, then it will also feed directly to the batteries and will NOT export. At that stage I could then go on to export all my FiT solar as opposed to deemed 50%, but I would need to do the sums first !!

My export meter is the original and is checked every couple of years.

It sounds to me as though your installer didn't go down the easy route of simply adding another inverter for whatever reason, possibly commission from the supplier? Or he didn't understand what he was doing in the new to most people environment of battery storage, which from your experience may be the reason.