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On-grid domestic battery storage
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7.2kwh Pylontech battery storage with Lux ac inverter
Raspberry Pi immersion controller
Raspberry Pi Lux charge controller
Renault Zoe 40kwh, Zappi EV charger and Octopus Go
In real terms most of the tinkering doesnt amount to much, although things like upping capacity to allow full battery use to power the immersion led to savings in oil usage which then led to installing an ashp. The higher capacity has also allowed stuff like running a hot tub for the last 2 weeks without making a dent in my imported electricity. The month before I did 4 beer home brews with the same result. My 2 monthly electricity bill has just come in at 3.12 yes three pounds and twelve pence....
...which is great if you gloss over the almost 10k everything electrical has cost me... ...but thats about 50-70 quid every 2 months I no longer need to find and all part of the plan to FIRE.
The new lux parallel inverters have finally arrived and so I'll be swapping them over soon, and likely lose all the data I've gained from lux till now.
The inverters went in mid March and are coming out in the last 3rd of September, so roughly in the brightest 6 months, and so the time you would expect them to shine (pardon the pun)
So before that happens I thought I'd put down the figures i have for the last 6 months.
Fit system total solar generation according to fit meter 2638kwh
According to lux 2654kwh (I'm actually stunned its so close 99% accurate)
Export to grid from smart meter 2006kwh
Export from lux 1793kwh so 89% accuracy (or 11% adrift if you prefer)
Total battery discharge 1072kwh at 14.7p/kwh a saving of £158
This is for 4 x 2.4 kwh pylontech batteries discharging to 10% so around 8.5kwh of storage.
Total imported electricity for this time is 632kwh.
My non fit system total solar generation 3590kwh (definitely a fudge factor here as the ct clamp is on the line for my garage, so on a sunny day if im working in the garage welding, grinding etc, then the generation figure will be lower as I'm using some of it, on a dull day the generation figure will be higher as I draw leccy into the garage, but the ct sees it as generation rather than supply)
Unfortunately I didn't take the figures off the inverter to compare
Total battery discharge 1269kwh at 14.7p/kwh a saving of £187
Also 4 x 2.4kwh pylontech batteries discharging to 10% so around 8.5kwh of storage.
So total saving should be £158 + £187 = £345
However this would ignore the inverter taking some of the power when discharging, in the change from dc to ac, which im putting a finger in the air at ~10% as sometimes its around 3% but sometimes its almost 25%
So this takes my £345 to a more realistic saving of £310.
Which sounds pretty good, until you realise that makes my roi around 20 years.😥
Now there is more to this, as its only half of the year, this was all solar charging, and with lockdown the kids have been in the house during the days, so the meals tv's and game systems have been drawing power on days id expect normally to just come home to full batteries, so there's definitely an argument to say they would have done better in "normal" times.
There is also an argument for getting a good saving on winter electricity using octopus go.
So at 5p with a round trip on the inverters say 6p instead of the 15p rate, id save 9p/kwh and since I'm likely as the nights get darker to wipe out the batteries every day, I could argue a reasonable 150 days of 17kwh (both systems combined) at 9p saving is an extra saving of £229.
I think most people would see this as reasonably achievable since I'm drawing around 28kwh a day or 10000kwh /year
(Total solar - total export +total import)/182(x365)
Yes its rough, but quickly illustrative.
So at £229 + £310 = £539/year the roi is more like 12 years.
So are batteries gonna save you money..... hmm would be my answer at this point.
I picked up several of my batteries on the cheap, coming to around £6k for batteries and inverters, but if you had to buy all new id expect to pay around £8k.
I think its gonna be hard to justify batteries unless you use a lot of electricity
And id suggest most members of this forum have already tried to reduce their energy bills in various ways, so I think you will find it difficult to make batteries wash their face right now.
So if purely on money saving.... as its the money saving forum... id say maybe not.
Assuming the inverters die before roi is achieved, then likely not.
But if the question is, do I regret getting batteries, absolutely not, for me its been a wee project, both in money saving, electricity management and also to test theories.
I would advise that probably 8 batteries is the wrong number, for most folk 6 would probably be about right.
For me, 20 would be great 🤔😁
4kw sse since 2014 and 6.6kw wsw / ene split since 2019
24kwh leaf and Lux 3600 with 17kwh useable storage
Is there anything you still want to do? Im pretty much stuck now, got my oil consumption down to around 600l a year from 1200 or so, put an extra tank in and topped up at this months prices, so thats about 4 years of winter heating/hot water locked in at about 700 quid total (including extra 2nd hand tank and all new wiring/connectors). Should bring me up to around the serviceable life of the boiler (although working on that too).
I will (maybe... I think) be putting in a hot water cylinder and using the excess solar (which there is not that much of now) to heat it for hot water, to move away from gas, but I can't see what else I can do, that wouldn't involve major upheaval.
I did work out through the course of the post last night that I've spent over £10k over the last 2 years between batts and more solar.
I'm certain the wife would have preferred two weeks in disney instead, which costs about the same for a family of 5
Edit. Anything I've done, that i wouldn't have considered, I dont think so.
Been pretty happy with what the batteries have done in general, but disappointed in how poor they are with induction hobs, so going back to when I put in the new kitchen, id probably have went with normal hobs.
4kw sse since 2014 and 6.6kw wsw / ene split since 2019
24kwh leaf and Lux 3600 with 17kwh useable storage
One output in a central hallway (bungalow) is ok but at night does involve closing all the other doors to 'direct' the air into the bedroom. The PIV inadvertently does a good job of circulating the air in there but I didnt have much choice in unit placement with planning laws here and house layout.
On the very few days here that it gets too hot, the AC is a godsend, no more hanging bags of ice over a large fan!
You are correct in that under a couple of hundred Watts they don't respond as well, but this is with a 1.8kw hob, so its the ramp rate that's the issue rather than the power drawn in this case.
4kw sse since 2014 and 6.6kw wsw / ene split since 2019
24kwh leaf and Lux 3600 with 17kwh useable storage
Brings tears to a Scotsman's eyes watching the smart meter ticking over.
7.2kwh Pylontech battery storage with Lux ac inverter
Raspberry Pi immersion controller
Raspberry Pi Lux charge controller
Renault Zoe 40kwh, Zappi EV charger and Octopus Go