Economics of charging at 7p and exporting at 15p

[Stinsy]

My main reason for the batteries was to import at cheap rate to prevent import at peak rate and for them to have enough capacity to power the whole house for at least a day.
During the summer and shoulder months I can export quite a bit but overall the target is to be cost neutral for electricity over the year.

Sure, charging on off-peak then offsetting peak prices is much more compelling, still not amazing though:




Let me know if you think I've added it up wrong...

[nowty]

I generally don’t specifically charge just to discharge (except if there is a special reason, saving session, crazy experiment, etc), but use as much cheapslot leccy as possible and let the solar PV export as much as possible. The solar diverter is now redundant.

So far this year I’ve exported 10872 kWh so thats a credit of £1,630.
And imported 10943 kWh practically all at cheapslot price so thats a bill of £766, well maybe £800 as the leccy was 0.5p more earlier in the year.
So still a nice profit, and all leccy free, 2 EVs charged, all hot water and house typically at 23 to 25 degrees all year round.

[Fintray]

My main reason for the batteries was to import at cheap rate to prevent import at peak rate and for them to have enough capacity to power the whole house for at least a day.
During the summer and shoulder months I can export quite a bit but overall the target is to be cost neutral for electricity over the year.

Sure, charging on off-peak then offsetting peak prices is much more compelling, still not amazing though:




Let me know if you think I've added it up wrong...

I suppose the biggest difference is that I am now heating my house with the heat pump and not having to buy oil at £1000-£1500 or so a year, obviously my electricity consumption has increased but like Nowty this charges my car, powers everything and keeps the house at around 24C.
Since the heat pump went in (mid March) my average daily consumption and export figures have been:



That's compelling enough for me.

[Colin Deng]

I think we are on 6,000 80% warranty Lifepo4's. About 2 grand for 30kWhs. Export 70% of that to allow for 10% losses and 20% remaining in stack. At 8p per kWh profit that's.

30/100x70×0.08/100= £'s x365x16 =£9,808 less 2k build cost. Rough as hell and massively open to interpretation as well as a 16 year slide from 100%soh to 80%soh.

I have had 2 pints though but that's £7,808 across a battery set lifespan.

Thanks for the calcs.

Here is my back of fag packet effort:



I have to admit, it isn't particularly compelling!

What is the going rate for 15x LF280K cells these days? @colin?

Sorry been busy these day
Customer from Poland will be at our factory tomorrow, busy prepare for that
The price now is at the range 51.5-53$ range

Thanks

[Yuff]

My main reason for the batteries was to import at cheap rate to prevent import at peak rate and for them to have enough capacity to power the whole house for at least a day.
During the summer and shoulder months I can export quite a bit but overall the target is to be cost neutral for electricity over the year.

Sure, charging on off-peak then offsetting peak prices is much more compelling, still not amazing though:




Let me know if you think I've added it up wrong...

I’m assuming your figures are 1 cycle a day?
If you take a mixture of the export income and peak rate savings and do 2 cycles a day then the figures become more compelling.
I’m either charging or exporting 24/7 and have the system set up to accommodate that albeit I need to manually do IOG schedules when needed.
But we have 4 EVs and over the past couple of weeks have done several long journey and a 50 mile commute twice a day ( not the norm as SWBMO is visiting her mother in st Mary’s hospital london)which is probably averaging out at 150 miles a day conservatively and the net daily cost has been approximately £3.
The only gas we use is for a gas fire.

[sharpener]

My main reason for the batteries was to import at cheap rate to prevent import at peak rate and for them to have enough capacity to power the whole house for at least a day.
During the summer and shoulder months I can export quite a bit but overall the target is to be cost neutral for electricity over the year.

Sure, charging on off-peak then offsetting peak prices is much more compelling, still not amazing though:




Let me know if you think I've added it up wrong...

6 year payback is not at all bad. But you should either include depreciation of the batteries over their warranted lifetime (which might be as short as 6 years) or set aside some of the "profit" into a sinking fund to provide for their eventual replacement (and you would have to make a guess as to how much prices have further to fall). Either way it would reduce the "profit" quite a bit!

[Stinsy]

My main reason for the batteries was to import at cheap rate to prevent import at peak rate and for them to have enough capacity to power the whole house for at least a day.
During the summer and shoulder months I can export quite a bit but overall the target is to be cost neutral for electricity over the year.

Sure, charging on off-peak then offsetting peak prices is much more compelling, still not amazing though:

Let me know if you think I've added it up wrong...

I’m assuming your figures are 1 cycle a day?
If you take a mixture of the export income and peak rate savings and do 2 cycles a day then the figures become more compelling.
I’m either charging or exporting 24/7 and have the system set up to accommodate that albeit I need to manually do IOG schedules when needed.
But we have 4 EVs and over the past couple of weeks have done several long journey and a 50 mile commute twice a day ( not the norm as SWBMO is visiting her mother in st Mary’s hospital london)which is probably averaging out at 150 miles a day conservatively and the net daily cost has been approximately £3.
The only gas we use is for a gas fire.

I think you've nailed it!

My batteries were not purchased with the intention of charging on cheap electric and discharging to the grid for profit. They were purchased with the intention of self-consuming back when the rate for export was derisory and I couldn't even get a ToU tariff (no smartmeter). Now I primarily use them to avoid paying peak rates.

My small (12kWh) pack isn't big enough to get me from one cheap period to the next however a bit of solar and some generous provision of additional cheapslots on gloomy days gets me through. I only bothered doing the admin required to get paid for electric so that I could max out the saving-sessions. However I found this made summer much less stressful because I could charge the battery to 100% every day rather than 50 or 75%. This was more of an ambivlelence about exporting rather than trying to export as much as I can.

However now we have the possibility to deliberately charge on cheap rate to export that energy back to the grid. And I was wondering if it was worthwhile. Your post has made me think I was too quick to dismiss the miserly 6.31% ROI. Sure, if you were to buy the batteries with the intention of profiting in this way, it isn't worthwhile. But the point I was missing was that this is ADDITIONAL money on top of the self-consumption/ToU shifting! And an extra £20 a month when you've already got an efficient setup IS worthwhile...

[Stinsy]

Right!

The game is afoot! My bill gets cut today. I've set up my inverter to max out buying-low-selling-high-for-fun-and-profit. I'll report back in a month...

[Joeboy]

Right!

The game is afoot! My bill gets cut today. I've set up my inverter to max out buying-low-selling-high-for-fun-and-profit. I'll report back in a month...

[dan_b]

"miserly 6.31% ROI"

I think there are a fair amount of people who would bite your arm off for an investment plan that returned 6.3% tax free every year - but I get your point it's a lot of capital investment and those returns are not guaranteed (tariffs may go up, as well as go down, battery cycle life, equipment failure etc)