Home batteries *Can* save you money

Petriix

I understand your pain. While my kids are beginning to learn that a jumper or pair of jeans can be worn multiple times before being washed, Mrs Petriix calls me the 'door police*' and insists on 'letting some fresh air in'. You know when we've had an argument because the dishwasher or washing machine will go on at a random time because 'it needed doing'

*I prefer to think of myself as 'The Free People's Door Army', fighting against the evil 'Heat Wasters' in the eternal 'Energy War'.

Solarchaser

Ahh the old "fresh air".
Drives me bloody mental that.
And of course all the internal doors are open too, just to make totally sure every bit of heat escapes out the door.... then complains it's cold and turns the heating up 🤬🤬🤬

Verdigris

Suddenly living alone seems like bliss.

Meatballs

Petriix said:

I understand your pain. While my kids are beginning to learn that a jumper or pair of jeans can be worn multiple times before being washed, Mrs Petriix calls me the 'door police*' and insists on 'letting some fresh air in'. You know when we've had an argument because the dishwasher or washing machine will go on at a random time because 'it needed doing'

*I prefer to think of myself as 'The Free People's Door Army', fighting against the evil 'Heat Wasters' in the eternal 'Energy War'.

The coming apocalypse shall be heralded by furious hoovering in our household.

nottsphil

pete-20-11 said:

You also use more electric converting from AC to DC and back to AC again - vs using it live?

Something like 90% efficiency on a round trip? Some lost to heat? 

Hi. I'm thinking about batteries but does this mean they can't be charged directly from my solarPV? DC>AC>DC>AC doesn't seem  very efficient to me! 

Verdigris

nottsphil said:

pete-20-11 said:

You also use more electric converting from AC to DC and back to AC again - vs using it live?

Something like 90% efficiency on a round trip? Some lost to heat? 

Hi. I'm thinking about batteries but does this mean they can't be charged directly from my solarPV? DC>AC>DC>AC doesn't seem  very efficient to me! 

You can have DC side batteries which have a better round-trip performance but the downside is you can't export. If you think you can use it all then that is the better option, probably. However, summer peak production tends to go with low consumption, so it may be better to suffer the lower efficiency of AC side batteries but be able to sell your surplus.

Having an EV to charge and air-conditioning may favour DC side batteries.

EVandPV

Solarchaser said:

Ahh the old "fresh air".
Drives me bloody mental that.
And of course all the internal doors are open too, just to make totally sure every bit of heat escapes out the door.... then complains it's cold and turns the heating up 🤬🤬🤬

Tell me about it !
Nobody in our house thinks to close the back door when the dog goes out for a pee.
So in the summer, they let all the flies in, and in the winter, 6 hours worth of heating goes out the ruddy door. 🤦

Solarchaser

Apologies for the thread revival, but I thought it important to provide figures when talking about the batteries, in terms of how much I have saved.

Octopus have been 90-95% great, and when I initially did this thread they told me I'd have all the year figures within a week, then it was a month, then it was March and here we are.

So I ended up going through my bills individually and on the crossover months taking the actual day by day cost to get to a final figure of what the batteries have saved or cost me in terms of bought electricity 

My total electric bill from October 26th 2020when new parallel inverters went in, to October 26th 2021 was £349
Of that £86.90 was the daily standing charge.
So the total electric charge was £262.10 for 4239 kwh which equates to 6.18p/kwh

For those of you looking thinking that can't be right for 4.5p and 14.2p bought in fairly equal measure, well you are right, because for the first month or two with octopus I messed about switching tarriffs to go to agile when it was negative pricing etc, so the waters become somewhat muddy because of that.

With that in mind I'll put up figures for March 2021 to March 2022 in the next post

Solarchaser

For March 16th 2021 to March 15th 2022 I used 3689kwh from my smart meter confirmed by the bills.
I have paid £318 for this.
£86.9 was standing charge, so £231.1 in electricity 
Average price of 6.26p (rate of 14.2 and 4.5p/kwh)

Batteries have discharged a total of 4093kwh

I've exported 2084kwh excess solar in this time
A total of 7139kwh of solar was generated, (had some issues, should have been more like 7500) and so generated minus exported equals 5055kwh used, plus the 3689 bought brings the total usage up to 8744kwh

Arguably some of that wasted in round trip of the inverter, say 20% of the 4093 would bring it to 3274, or another way of saying it would be that I used 818kwh less than I would if I didn't have batteries.
So without batteries my consumption would be more like 7926kwh.

Using that all at 14.2ppkwh would cost £1125.49 I've paid £318 a saving you could say of £807.49 so for me around an 11 year payback.
At the more recent prices of 30ppkwh it would be £2377.8
Assuming my cost would roughly double as well, as that's going to happen at the end of my fixed term then the difference would be £1741.8 and around a 5 year payback.

I've deliberately been conservative with this, adding in the daily charge to correct price, but not adding it to future as I'd rather be on the side of caution rather than being some sort of salesman selling solar, as we all have seen.

So anyway my point is, without the recent price increase, solar definitely makes sense, with the recent price increases, if you are a fairly high user of electricity... and as we shift away from fossils, we are all going to be.. then solar plus batteries makes sense, though I'll caveat that by saying I still dont think the tesla offering does.

JKenH

Solarchaser said:

For March 16th 2021 to March 15th 2022 I used 3689kwh from my smart meter confirmed by the bills.
I have paid £318 for this.
£86.9 was standing charge, so £231.1 in electricity 
Average price of 6.26p (rate of 14.2 and 4.5p/kwh)

Batteries have discharged a total of 4093kwh

I've exported 2084kwh excess solar in this time
A total of 7139kwh of solar was generated, (had some issues, should have been more like 7500) and so generated minus exported equals 5055kwh used, plus the 3689 bought brings the total usage up to 8744kwh

Arguably some of that wasted in round trip of the inverter, say 20% of the 4093 would bring it to 3274, or another way of saying it would be that I used 818kwh less than I would if I didn't have batteries.
So without batteries my consumption would be more like 7926kwh.

Using that all at 14.2ppkwh would cost £1125.49 I've paid £318 a saving you could say of £807.49 so for me around an 11 year payback.
At the more recent prices of 30ppkwh it would be £2377.8
Assuming my cost would roughly double as well, as that's going to happen at the end of my fixed term then the difference would be £1741.8 and around a 5 year payback.

I've deliberately been conservative with this, adding in the daily charge to correct price, but not adding it to future as I'd rather be on the side of caution rather than being some sort of salesman selling solar, as we all have seen.

So anyway my point is, without the recent price increase, solar definitely makes sense, with the recent price increases, if you are a fairly high user of electricity... and as we shift away from fossils, we are all going to be.. then solar plus batteries makes sense, though I'll caveat that by saying I still dont think the tesla offering does.

Hi @Solarchaser just a small point. Presumably, without a battery, some of your usage would be at the cheaper Go Faster rate. I have solar but don’t have a battery so shift what usage I can to the cheaper rate (including my car charging) so my average rate on Go Faster works at around 9p/kWh plus VAT so say 9.5p. I realise you have a different use profile but I imagine if you didn’t have a battery you could perhaps move more of your use (or perhaps just your car charging into that cheap rate window so you could use your solar to cover household usage). 

Edit: just reread your post and realised that the calculation is the saving with both solar and batteries so please ignore my comment about using solar to cover household usage.

Also I believe there is a diy element to part of your installation which perhaps not all of us would have the skills to manage so this might make a difference to the  payback period for the average householder.

I notice you haven’t included the earnings from your FiT payments in the payback calculations - doing so would shorten the payback period.