The Boy That Cried PV Extension

[Krill]

Sorry Mart, in my first post I wasn't intending to disparage immersion heaters, I was taking aim solely at electric boilers. I should have explained mself better. Mea culpa.

How much does a small water tank with an immersion heater cost compared to an electric boiler? How much of a hammering does the battery stack take by an electric boiler (given the potential costs of AC>DC>AC inverting inefficiencies? To my eye, there will be a cross over point where the inverting inefficiencies (plus battery cycles) cost outweighs the benefit of cheaper power periods, but an immersion heater and an unvented hot water tank can work around that (at a cost of space and more comoplicating pluming. OTOH, get a water tank that can then have a heat pump plumbed in and it's essentially future proof. Don't have that with an electric boiler, just have the option to pull from the grid or from batteries.

I think it's easy to come to the conclusion that electric boilers are bad, and they tie the user into no win situation, but I think it is harder to work out a water cylinder versus heat pump, and I don't envy you the challenge. If you do only need enough that a 75 or 100 litre tank and an immersion coil would suffice, that's pretty cheap to fit in my understanding.

Ultimately though, if we pull from the grid to power this (even if we store it in batteries), we are beholden to tariffs. I'm looking at trying to get onto Octopus Cosy in October and swap back to Flux next March. The multiple cheap slots solve so many issues that it probably makes immersion heating work until the planning rules are changed for AHSP (The gov will simply have to change the boundary issue to meet their already stated goals of cutting off gas boilers from new homes).

[Mart]

Thanks Krill, it's all good. There are so many ideas, products and solutions out there, that I think we are living in exciting times.

Assuming I can minimise the needed energy via the A2A units and HP HW tank, I think I'm in the lucky position of having quite a bit of choice for the relatively small remaining space heating needs, as it isn't too much. Famous last words.

Tepeo do a drop in boiler replacement heat battery that might suit my needs. It's 40kWh, the idea again being to charge on cheap rate, so it might use 3x the energy of a heatpump, but all of the leccy is at the roughly 1/3rd cheap rate price - their argument, not mine. But at ~£6k plus install, it's not really cheaper than an ASHP, and doesn't atract any subsidy.

Saw a T-shirt recently that described me perfectly - "Give me a minute to overthink this."

[Adokforme]

Over thinking, heaven forbid :-)
Please excuse my over simplification but:-
Ditch the gas and save the SDC as well as the planet. If it works out your a few pence down each day then what the heck, isn't that a price worth paying to be FF free! If it's a bit chily on those rare winter minus nights there's always the old fashioned HWB to keep you warm in bed.
We have to do away with gas anyway so if you don't do it now you'll have to go through the whole process again at some future point.
Go on, you know you want too.

[Mart]

You know me too well.

[Moxi]

At one point I was looking at these https://www.mixergy.co.uk/solutions/ihp-x/

They also will be doing something called cube x shortly which is a bit like the heat geek mini cylinder that is traditional ashp ready for if you go that route later. There are a good number of integrated hp cylinders now available and with careful organisation of the air intake snd vent system they can provide some heating and cooling at different times of year.

They are a compromise though and as such have a niche where they are the right fit, you just have to determine if you fit the niche.

From what you have said so far it could be that you do fit that niche, mostly requiring DHW with an occasional boost to the central heating. The question is - is it worth maintaining a wet heating circuit for a few heating days per year ? Does that wet system represent a risk and will it work when you need it ?

Lots of detail to go through to get to a good solution.

Moxi

[Moxi]

I did mean to say one big positive for the hybrid hp cylinder is that in a power cut you can easily run the small hp from the battery stack off the auxiliary power out from the inverter thereby giving you some hot water and heating during an outage - always a positive to have alternatives for when your main energy supply fails.

Moxi

[Mart]

Thanks Moxi, the Mixergy HPHW tank is exactly what I'm pondering for the DHW side. Although I suppose for ~1,200kWh(t) pa even that gets a tad questionable at say £56pa for the extra 800kWh v's a resistive unit. [Overthinking again.]

So ...... based on the HP principle, and there being no outside unit, and crucially as you point out my niche low(ish) demand, are there larger devices that could also also offer a flow to the wet system?

I appreciate I'm asking a lot from a small power unit, maybe 1kW to 1.5kW on the input, but even at a very low COP of say 1.5, that's 36kWh(t) to 54kWh(t) which even after allowing ~5kWh(t) for DHW, would be enough ....... I think, on the worst days.

Am I describing a thermal store, I really don't know much about water tanks and their range of roles and names?

[Adokforme]

Thanks Moxi, the Mixergy HPHW tank is exactly what I'm pondering for the DHW side. Although I suppose for ~1,200kWh(t) pa even that gets a tad questionable at say £56pa for the extra 800kWh v's a resistive unit. [Overthinking again.]

So ...... based on the HP principle, and there being no outside unit, and crucially as you point out my niche low(ish) demand, are there larger devices that could also also offer a flow to the wet system?

I appreciate I'm asking a lot from a small power unit, maybe 1kW to 1.5kW on the input, but even at a very low COP of say 1.5, that's 36kWh(t) to 54kWh(t) which even after allowing ~5kWh(t) for DHW, would be enough ....... I think, on the worst days.

Am I describing a thermal store, I really don't know much about water tanks and their range of roles and names?

Think you might be getting closer Mart.
Just thinking back to when transitioning to a cleaner form of transport, was there an interim stage involving a PHEV?

[dan_b]

Late to this thread - Mart - what have you been playing at! Congratulations, epic. Not at all envious!

What's the problem with the 2nd battery have they said?

[Mart]

Late to this thread - Mart - what have you been playing at! Congratulations, epic. Not at all envious!

What's the problem with the 2nd battery have they said?

Hi Dan, yeah you know me, and how long I've been wanting to 'polish' the PV system.

It all keeps getting more messy unfortunately. The company have been great, they keep heading down and trying out anything and everything with Solaredge techs on the phone, but no luck. From what I've been told the batts don't (usually) fail, hence the focus on the inverter.

The company has copied me in on a lovely e-mail they've sent to Solaredge explaining how the saga (covered in data logs) has dragged on, and how I don't have a fully working system yet.

I'm actually, and surprisingly quite chilled about it. TBH I have to be as Long Covid raises anxiety levels through the roof, but I suspect I'm not upset because I finally have (partially) the 'super system' I wanted, and between issues, it has proven able to do everything I hoped. In fact, the ability to manage 200% capacity, so long as I have AC export and space in the batts, is more than I thought was possible at the start of 2024. So I may not have everything today, but I will eventually have more than I expected.

So, it's all good, we'll get there eventually, and whilst the two batts would make managing high gen easier, and less chance of clipping, it's really not until Dec(ish) when I'll need all the energy capacity when I launch my 'war on gas'.


Just realised, how many years ago was it that you dipped your toes into home storage, and I was living vicariously through you, with monthly stats? Doesn't time fly, got to be over 5yrs?