[No longer] Going for a Givenergy 8.2 kWh AC Coupled battery

Solarchaser

Yeah I used this
https://bloglocation.com/art/water-heating-calculator-for-time-energy-power

And was going for 80c - 40c so a 40c delta

Reading about a bit most replies seem to say down to 40c should still be good for heating.... its a bit of suck it and see.

I'm going with a thermal store in the loft at 210L and I'm gonna patch it into the radiators with a heat exchanger as a top up.
But upstairs pipes are all 15mm, and having just replaced all of the floors and redone all the upstairs rooms, there is no chance of opening that up again.
Downstairs it's all 22mm pipe so if I heated from the loft, I think I may suffer with a lack of heat Downstairs, so instead going with 500l tank in crawlspace under house.

I've been using 50kwh gas in December and January, so I'm going with 75% efficient so needing 36-37kwh, but thats heating and water.
Also it seems a bit daft to size everything for 2 months of the year (that's my caveat for when it doesn't fully work) so if I heat both tanks with 12kw, I'll be grand for the 3 hours, (planning on 15kw of heating elements, but *normally* only using 12kw. if I take 7kw for the batteries, i'm a bit tight for doing any car charging in those 3 hours. But I expect to get around 30kwh of heat this way.

In reality I think I'll need to go for a 4 hour go period, but thats an increase in cost of 10%, so trying to avoid.

If I have to buy a bit more in those two months,(especially if you are right about the 50c) then so be it, it will definitely only be those two months, and if its what 5kw a day, that's livable for the moment, under a pound a day (though not next year) and the £80 I'll save from the gas line rental will cover that.

However my go faster period is 8:30-11:30 so I'll be actually using heating then too, so might get away with topping up then also, hence the 15kw instead of 12.

Trying to hedge my bets a bit I guess.

It helps my man maths that the 15 year old combi started making some weird noises last week... certainly no point spending 2 grand on a combi when I wanted to go gasless before the recent price hike.

It's also come to my attention that for the moment, octopus will disconnect the gas FOC so I feel like everything is telling me to do it now.

zeupater

QrizB said:

Solarchaser said:

I'm instead going with a 500l water tank that I'm gonna insulate the heck out of as my way of using tou and ditching gas.

I was wondering how big a tank I'd need to do this.

We get through 30kWh of heat on a typical December or January day. If I use the existing radiators they'll work acceptably down to 50C, and I wouldn't want to heat the tank above 85C, so that's 35C of delta-T.

I reckon (OK I used this) I'd need a ~750-litre tank, which is pretty big but not impossible (a cubic metre IBC would give me some headroom).

Wonder if I could tell Mrs QrizB it was a coffee table?

Hi

Old fashioned 'rule of thumb' simplicity would work on 1kW raises 1tonne of mass (ie 1000litres of water) by 1C in 1Hr ... basically close enough to get a feel before getting into the specifics related to materials etc ....

HTH - Z

Toogie

Tepeo accept that the brochure diagram 9=15 is misleading and will correct it to show max input and output rates but not simultaneously! 

The efficiency is 100% though whereas my gas boiler is at best, 85% so there’s a gain of 15% straight out of the box. 

I researched ASHP’s last year and got a local reputable company to work up a quote for my 4 bed 3 bath 12 radiator 2001 house. The answer shocked me; up to £20k and total internal disruption replacing micro-bore rad pipework (and possible the rads). I question ASHP 4x gain, more like 2.5-3.5 and dependant upon in/out temp differential. I also note the recommended blog link is talking about ashp’s supplementing gas heating for single rooms; that’s not what I want. 
Lastly, I don’t see gas rates coming down to reach parity with electric rates any time soon. Not whilst our morally bankrupt government turns a blind eye to 

Toogie

our broken energy market and allow producers to milk their cash cows for all they’re worth, extracting obscene profits knowing the end of the road for their businesses could be in in sight. 

Just saying…..

Petriix

Here's an update: even though the price I was quoted was better than anything else I've seen, the crazy delay in delivery gave me the chance to look at what my actual savings would have been since getting a smart meter in December.

I crunched the numbers with the help of the data downloaded from n3rgy and the Myenergi API and was totally surprised to see that my savings would be far lower than anticipated. This is entirely due to my peak rate imports already being far lower than anticipated - averaging just 2.9kWh per day.

Part of this is behaviour. It would be great to have the convenience of running the oven or whatever appliances without having to think about it, but it's a massive expense without the financial return.

The overriding thing that tipped the balance for me was throwing the £4k into a mortgage overpayment calculator. That showed an interest saving of £1400 over the 12 years remaining on my mortgage; obviously that's on top of the immediate capital repayment. According to my spreadsheet it would take over 28 years (at current prices) for the battery to return £5400 in savings.

If prices more than double in the next year or so then I'll run the numbers again to see how things look.

Boffinboy24

I went through a similar thought process recently. What eventually made me stop going for the battery is seeing the stats for someone on octopus outgoing on this forum - at the moment the SEG payments they are getting were averaging 16p per kWh. You can’t be on Go at the same time, but even so it makes the case for battery much weaker as export is actually worth something. If prices fall then the SEG payments will fall… but so will the savings with a battery. 

arty688

Batteries are sold as a no brainer but it very individual thing depending on usage, tariff etc. Overpaying your mortgage may seem like a no brainer to but its more complicated than that as ATM mortgages are cheap money.

JKenH

What any calculation on battery payback fails to take into account is the satisfaction factor of having a battery - the feeling of being more self sufficient.  All of us on here are nerdy to a degree and the extra statistics a battery generates just adds to our fun. Just look how many of us record our PV generation daily.

There is also the (usually unrealised) benefit that having a battery may provide us with back up in the event of a power cut saving the contents of the freezer or keeping the central heating running. It might never be needed but it’s a form of insurance. 

We don’t expect to see a return of our investment on every device we buy; a bigger more expensive household good/car doesn’t necessarily add any extra utility or save us any more money but we hope to get satisfaction from the extra money spent. Perhaps look at a battery like that. 

Instead of replacing my 16 year old plasma TV (400w consumption) I bought a £1200 portable power station (2.4 kWh battery/MPPT charge controller/1 kW inverter) and a £200 340w solar panel on the basis that I would get more satisfaction from that than changing my TV. I probably won’t ever see payback but the fun I have had playing with different orientations and inclinations of the panel is priceless (to me). Until my Octopus rate goes up the most I can expect to save is 26p on a good day. If my Octopus rates double then the saving might be more like 50p/day so payback is still a minimum of 8 years.

Petriix

JKenH said:

What any calculation on battery payback fails to take into account is the satisfaction factor of having a battery - the feeling of being more self sufficient.  All of us on here are nerdy to a degree and the extra statistics a battery generates just adds to our fun. Just look how many of us record our PV generation daily.

There is also the (usually unrealised) benefit that having a battery may provide us with back up in the event of a power cut saving the contents of the freezer or keeping the central heating running. It might never be needed but it’s a form of insurance. 

We don’t expect to see a return of our investment on every device we buy; a bigger more expensive household good/car doesn’t necessarily add any extra utility or save us any more money but we hope to get satisfaction from the extra money spent. Perhaps look at a battery like that. 

Instead of replacing my 16 year old plasma TV (400w consumption) I bought a £1200 portable power station (2.4 kWh battery/MPPT charge controller/1 kW inverter) and a £200 340w solar panel on the basis that I would get more satisfaction from that than changing my TV. I probably won’t ever see payback but the fun I have had playing with different orientations and inclinations of the panel is priceless (to me). Until my Octopus rate goes up the most I can expect to save is 26p on a good day. If my Octopus rates double then the saving might be more like 50p/day so payback is still a minimum of 8 years.

Well I had loads of fun modelling what the battery would have done, without actually having to buy it.

I'd need rates to at least double (or prices halve) before I look at batteries again. 

Reed_Richards

JKenH said:

What any calculation on battery payback fails to take into account is the satisfaction factor of having a battery - the feeling of being more self sufficient. ... 

There is also the (usually unrealised) benefit that having a battery may provide us with back up in the event of a power cut saving the contents of the freezer or keeping the central heating running. It might never be needed but it’s a form of insurance.... 

I agree.  I would waste a lot more of my generated electricity if I did not have a battery and I find the fact that I don't hugely satisfying, even if having a battery does not ultimately save me any money.  I was just in time to catch the end of the FIT and I don't have a smart meter so don't have an accurate measure of what I export - so for me it is deemed export or nothing.  And I do have battery backup, even though I have only been caused to use it once in 3 years.