On-grid domestic battery storage

EVandPV

ASavvyBuyer wrote: »

Worked out some figures based on our average normal rate (14p/kWh) consumption to see if it would be worthwhile charging from Solar PV in Summer & 5p/kWh rate in Winter.

Average in the Spring/Summer normal rate savings would be 4kWh/day = Approx £90/6months

Are you sure your average is only 4kwh a day in spring/summer ? Sounds a bit low for a 4kw system.
Ours is only 3kw but our average is more like 7-8kwh a day.
Also, you can charge at night at 5p if the forecast isn't suitable for pv charging the following day.

ASavvyBuyer

EVandPV wrote: »

Are you sure your average is only 4kwh a day in spring/summer ? Sounds a bit low for a 4kw system.
Ours is only 3kw but our average is more like 7-8kwh a day.
Also, you can charge at night at 5p if the forecast isn't suitable for pv charging the following day.

Yes, I have figures from Octopus of how much we buy at 14p/kWh for every day of the year.
Average in the summer is 4kWh/day. In the winter the average is 6kWh/day.
Maximum the Solar PV system could put into the battery a day (in the summer) is approx 6kWh, as we either use the PV generated electric or it goes into the grid.
Even though our system may generate over 20kWh/day some days, the max that could go into a 6kW battery system is 6kWh's.

EVandPV

ASavvyBuyer wrote: »

Yes, I have figures from Octopus of how much we buy at 14p/kWh for every day of the year.
Average in the summer is 4kWh/day. In the winter the average is 6kWh/day.

Sorry, my mistake, misread your post. I thought you meant your average generation was 4kwh in the summer.

EVandPV

ASavvyBuyer wrote: »

Even though our system may generate over 20kWh/day some days, the max that could go into a 6kW battery system is 6kWh's.

There will be days when the battery cycles more than once.
For instance, the sun is out and the battery charges fully by late morning. The sun goes behind cloud for a couple of hours so the battery discharges. Then the sun comes out again and starts charging the battery again.
It's not easy to figure this out, for sure. I've looked at various calculations and the results vary wildly.

ASavvyBuyer

EVandPV wrote: »

There will be days when the battery cycles more than once.
For instance, the sun is out and the battery charges fully by late morning. The sun goes behind cloud for a couple of hours so the battery discharges. Then the sun comes out again and starts charging the battery again.
It's not easy to figure this out, for sure. I've looked at various calculations and the results vary wildly.

Agree, yes it could, but as we know we only buy 4kWh/day on average, at 14p/kWh in the summer months, that is the most we could save.

EVandPV

ASavvyBuyer wrote: »

Agree, yes it could, but as we know we only buy 4kWh/day on average, at 14p/kWh in the summer months, that is the most we could save.

No worries, I'm sure you've done your homework.
I'm having enough trouble working out my own figures without telling anyone else how to do it.
We don't have a smart meter so there's a bit more guesswork involved. :think:

Solarchaser

Just for a real world comparison.
My sofar system is literally about 5 days away from being installed for a year.
The batteries have done 210 cycles.
That's full cycles, I dont know the cumulative effect of the micro cycles, so I can only go on full cycles.

I pay 13.2p / kwh and batteries have only been charged from solar so 13.2 x 6 x 210 = £166

As Savvy buyer mentioned the system would be around £3k so that's around a 17/18 year payback which is why I'm second guessing (more like twentieth guessing) my plan to have 24kwh.... but I still want to.

If I was to use an off peak rate tariff saving 8p/kwh over the say 150 days of winter it's potentially another £72 bring it to £244, which then makes the payback around 12 years.

But I still want more batteries

1961Nick

ASavvyBuyer wrote: »

Worked out some figures based on our average normal rate (14p/kWh) consumption to see if it would be worthwhile charging from Solar PV in Summer & 5p/kWh rate in Winter.

Average in the Spring/Summer normal rate savings would be 4kWh/day = Approx £90/6months (based on 12p/kWh saving)

Average in the Autumn/Winter normal rate savings would be 6kWh/day = Approx £90/6 months (based on 8p/kWh saving)

Therefore total saving for a 7.2kWh (6kWh usable) battery system = Approx £180/year

Cost of 7.2kWh battery system is approx £3k. Therefore payback period approx 16.6 years.

Looks like, for us, it is better to just buy the RE generated electric for now until battery costs come down further.

My batteries (12kWh) have saved £218 since the 1st of Feb. With off peak charging during Nov/Dec/Jan plus a bit of solar charging, the saving should be just over £300 annually. That's a 13-14 year ROI assuming no hardware catastrophes.

EVandPV

Solarchaser wrote: »

Just for a real world comparison.
My sofar system is literally about 5 days away from being installed for a year.
The batteries have done 210 cycles.
That's full cycles, I dont know the cumulative effect of the micro cycles, so I can only go on full cycles.

I pay 13.2p / kwh and batteries have only been charged from solar so 13.2 x 6 x 210 = £166

As Savvy buyer mentioned the system would be around £3k so that's around a 17/18 year payback which is why I'm second guessing (more like twentieth guessing) my plan to have 24kwh.... but I still want to.

If I was to use an off peak rate tariff saving 8p/kwh over the say 150 days of winter it's potentially another £72 bring it to £244, which then makes the payback around 12 years.

But I still want more batteries

You've just depressed the hell out of me.
But I still want batteries.

1961Nick

EVandPV wrote: »

....But I still want batteries.

Put one on your Christmas list.:santa2: