On-grid domestic battery storage

EVandPV

It can be as simple as ‘fit and forget’ or you can tinker with it like some of us either to squeeze every last penny of savings out of it or just because you enjoy hacking/modding  things.

For me, it’s a bit of both. I have a script running which charges the batteries when Agile prices are low and another running on a Raspberry Pi controlling a relay using the batteries as a ‘buffer’ when diverting spare pv to our immersion heater. 

We had our system installed last December so it’s given me something to play with during lockdown while I’ve had some spare time on my hands.

In the summer, you can pretty much just leave them to do their thing.

In the winter, you’ll probably want to at least set up a grid charging schedule to take advantage of cheaper leccy at different times of the day (assuming your on a time of use tariff).

But that’s about it really if you don’t want to go any further than that.

joefizz

Pile_o_stone said:

From reading this thread and battery threads on other forums, it almost seems that people need to have a degree in Electrical Engineering when they have a battery installed. I was therefore wondering if it's the case that batteries are as 'fit and forget' as solar panels but that, as the forums are frequented by people who are hobbyists, they like to tinker with the tech. Or is it the case that this is a new technology and a lot of refining and technical knowledge is required to get them to work?

Thats sort of chicken and egg ;-) I tinker with it because I have  a degree in electrical engineering and know if I duck it up I can probably recover it. Probably!

Most are install and forget and the vast majority of people will do it that way. The types of battery and your background knowledge will ultimately decide the price you pay for install. If you can do the work yourself and are happy with a modular system that either needs a bit of tinkering/fettling or can be installed piecemeal then you are going to pay less than one of the out of the box install and forget systems. Its probably because this is a moneysaving site that you get a lot of the former ;-)

I havent tinkered with mine in ages but it was useful (and ultimately more expensive) to build it up and measure my usage and the 'value' I was getting from my system. 2 years on and 2 'upgrades' later Im pretty much at the leave well alone part. I could have just bought the entire thing in one go and saved myself the extra VAT and shipping to NI charge but wanted to see if half my current capacity would have been enough. It would have been but what I have now allows me to do so much more in the summer, but I needed a full years data to make that decision.
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.

Solarchaser

Its been a wee while since I updated on my figures for my lux system.
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 🤔😁

joefizz

Solarchaser said:

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.

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).

Ive moved back to corded power/garden tools in the main from petrol driven and moving away from battery powered ones where possible (even spent an hour a day this week sawing wood with a bowsaw, had enough, chainsaw to do the next lot in probably less than an hour total!)

Is there anything you have done with the batteries that you wouldnt have considered? Ive been looking at more ways to reverse years and years of decreasing electric use now I have this 'free' resource but have run out of ideas for the minute.

Solarchaser

Good question, I would like to do ashp,  especially as air con in the summer, but I cannot justify it, on any given day there are 3 windows open in the house, im not gonna get the wife to change that, I've tried convincing her on the merits of a PIV, but she is not for it. So ashp will not work.

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.

mickyduck55

Air to air ASHP interests me as well and had a couple of quotes for a split system one unit in bedroom and one in lounge mainly for AC in summer.  Considering the cost of the hardware the installation costs seem very high

joefizz

Solarchaser said:

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.

Yeah, at lower power levels the battery response time really isnt up to it. On the other side at those levels they do seem to use less power than normal hobs so maybe swings and roundabouts? Found myself on my hob (up to 9 levels) using level 6 and above gets round the switching problem, but then theres the possibility of burnt food to deal with ;-) I did wonder why some hobs had half and half induction/normal, not a solution I know ;-)

joefizz

mickyduck55 said:

Air to air ASHP interests me as well and had a couple of quotes for a split system one unit in bedroom and one in lounge mainly for AC in summer.  Considering the cost of the hardware the installation costs seem very high

If I had the choice again Id go for the split system, I went for single self install with quick connectors but looked at the dual output system for a long time. In retrospect it was no more difficult to install than ac in a car or replacing the brake lines and then just pay someone to inspect and certify it afterwards.
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!

Solarchaser

joefizz said:

Solarchaser said:

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.

Yeah, at lower power levels the battery response time really isnt up to it. On the other side at those levels they do seem to use less power than normal hobs so maybe swings and roundabouts? Found myself on my hob (up to 9 levels) using level 6 and above gets round the switching problem, but then theres the possibility of burnt food to deal with ;-) I did wonder why some hobs had half and half induction/normal, not a solution I know ;-)

I think you misunsderstand,  its not the power levels, its the way induction hobs work. They dont supply constant power, they ramp up for 2-5 seconds then switch off for 2-5 seconds, on again for 2-5 seconds then off again and so by the time the inverter is starting to respond to the ramp, its already switched off, so the inverter pushes export, drops off and I import, pushes export and then drops off and I import, over and over again.

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. 

EVandPV

Solarchaser said:

joefizz said:

Solarchaser said:

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.

Yeah, at lower power levels the battery response time really isnt up to it. On the other side at those levels they do seem to use less power than normal hobs so maybe swings and roundabouts? Found myself on my hob (up to 9 levels) using level 6 and above gets round the switching problem, but then theres the possibility of burnt food to deal with ;-) I did wonder why some hobs had half and half induction/normal, not a solution I know ;-)

I think you misunsderstand,  its not the power levels, its the way induction hobs work. They dont supply constant power, they ramp up for 2-5 seconds then switch off for 2-5 seconds, on again for 2-5 seconds then off again and so by the time the inverter is starting to respond to the ramp, its already switched off, so the inverter pushes export, drops off and I import, pushes export and then drops off and I import, over and over again.

Our electric oven works much like that. Pain in the butt, especially if your on Agile and cooking during the peak period.
Brings tears to a Scotsman's eyes watching the smart meter ticking over.