Second thoughts on batteries

[Joeboy]

Reading your thoughts, I'd overshoot on the PV and track down a 'generic' hybrid inverter that will allow you to revisit batteries at a later date for plug & play. They do close the circle nicely but If cost is truly weighing on your mind it could be better spent on more pv and an outgoing tariff.

They(batteries) are not 'nice to have's anymore' but neither are they profit makers. Well not 365 for sure. You are in a position to future proof without commitment to full costs. I'd go that way and see how it plays out. Good call on the 300ltr tank. I have a 200ltr one and often wish in the good months that I had 400ltr as the current set up could easily max that out too. All the best to you.

Edit - I have been to the pub with my son and was half sleeping/mulling over your last post and posted the above clean without seeing Nowty or Gus input. I think we all see this similar.

[nowty]

They(batteries) are not 'nice to have's anymore' but neither are they profit makers. Well not 365 for sure.

I'd second that quote from Joeboy.

Some of us are in an enviable position of having top rates on FITs, So I make £3k per year tax free + the savings on my energy bills which is probably another £1k and rising. So I re-invest that £3k every year into more PV, then batteries, more PV, more batteries, hot water diverter, heatpump, ripple wind turbine, etc.

But now I am done, no more room or need for more PV or batteries. But that £3k per year will now be paying a £20k loan over the next 8 years for a good portion of my Tesla I am picking up next week.

So some of our thinking with FITs can be very different for folk starting out when the easy low hanging fruit has already been picked.

[Joeboy]

Although Paul, just to be clear. It's 18.08hrs here in Inverurie Scotland and I am down to 160W output from the PV. .....

Doesn't matter as the stack is near full and we need know nothing of the grid through the night.

If I went to the trouble of building to Passivhaus standards there is no way I'd not be in it for the full 24hr cycle and I would massage the build spec to reflect this (somehow) . I post this for battery owner perspective only. Cheers!

[nowty]

I ain't got no passivhaus but its been a classic day here, 49kWh generated, EV 100%, Home battery 100%, 300 litre hot water tank fully hot, I've been running the water distiller and I've boosted the storage heaters till they cut out. Import from grid has been 0.06 kWh.

Tomorrow is not so good but with the batteries and a 6kW Battery Inverter, no problem.

But I think I went a bit too far boosting the storage heaters today.

[Joeboy]

I ain't got no passivhaus but its been a classic day here, 49kWh generated, EV 100%, Home battery 100%, 300 litre hot water tank fully hot, I've been running the water distiller and I've boosted the storage heaters till they cut out. Import from grid has been 0.06 kWh.

Tomorrow is not so good but with the batteries and a 6kW Battery Inverter, no problem.

But I think I went a bit too far boosting the storage heaters today.

Outstanding! We had a great day here too but not to that level. HWT is using gas now and woodstove is evening heat. End result pretty good though. All else incl EV PV powered.

[Paul_F]

If money is tight for the build, I would concentrate on getting as much Solar PV fitted first as a priority. A battery system can be retrofitted later once you know where you are once you are living in it.

In your position, If I had to make a choice of more PV vs less PV and a battery, more PV wins, especially when you can now get paid for export through the SEG scheme.

I have 1.7kW on my NE facing roof, helps you get through those cloudy summer days. It was a DIY job using a second hand inverter and was very cheap to install, at about £1000 all in.

There's room for about 17.5 kW in total (worth about 13 MWh per year) - parts for that cost about £10k and save between £4-8k in tiles or slates, depending on what we go with. Just the SW face is about 8kW and worth about 7.5 MWh per year - parts cost about £5k and save £2-4k in roofing.
Realistically given that we're going to have a pretty efficient house and a NE facing array will be mostly producing in summer, I'm not at all sure how helpful it would be - essentially it's a cheap way of setting up an array to export to the grid in summer.

We did exactly as @Nowty suggests. Money was tight for our passive house build, so I dropped the idea of installing batteries and prioritised installing solar. I managed to get 25 panels into the South facing roof, as many as would physically fit, using all the roof area, but went for in-roof panels, so saved around £2,000 worth of slates, and the associated cost of fitting the slates.

I think we've got margin, but I'm wary that everything gets more expensive once you actually start building so want to keep a lid on it. One thing I'm wary of is that we've got the potential for a vast amount of PV - if we fill both sides that's ~13 MWh of generation per year versus ~4 MWh of consumption, and potentially gets us to the Passivhaus Premium target. At that point you start questioning whether you're adding more for the sake of it...

Reading your thoughts, I'd overshoot on the PV and track down a 'generic' hybrid inverter that will allow you to revisit batteries at a later date for plug & play. They do close the circle nicely but If cost is truly weighing on your mind it could be better spent on more pv and an outgoing tariff.

They(batteries) are not 'nice to have's anymore' but neither are they profit makers. Well not 365 for sure. You are in a position to future proof without commitment to full costs. I'd go that way and see how it plays out. Good call on the 300ltr tank. I have a 200ltr one and often wish in the good months that I had 400ltr as the current set up could easily max that out too. All the best to you.

Thing is, PV - and particularly roof-mounted PV on a new build - is actually really cheap at <£500/kW. That means it makes sense to put a lot on, and the real question becomes how much is too much.
Intention with the tank is to run hot feed as much as possible (at least dishwasher and possibly washing machine), and set the thermostat relatively cool to maximise heat pump COP. Mixergy enable charging from the top with a heat pump, which is a significant consideration with only 3kW of heat to play with - and they only go up to 300 litres. A 300l tank is already storing ~25 kWh, or 8 hours running with a heat pump (less if preheating with a shower heat exchanger).

If I went to the trouble of building to Passivhaus standards there is no way I'd not be in it for the full 24hr cycle and I would massage the build spec to reflect this (somehow) . I post this for battery owner perspective only. Cheers!

I've not yet seen someone who got batteries and has regretted it, which is one of the reasons I've started wondering...

[Tinbum]

I have about 12kW of panels on a north east facing roof with a shallow 19degree pitch. The inverters limit output to a max of 10Kw. (2x 4Kw inverters and a Growatt SP2000 with 8Kwh storage). I did debate hard as to whether it was worth doing but am pleaded I did. The reason for doing it was purely for the winter output and to help to try and cover my base load. Even on duller winter days the output is not too bad as the light bounces off the clouds. During the summer I use the extra output to run heat pumps for an above ground pool for the kids.

[Joeboy]

Assuming this is the forever house, an EV or 2 are likely to appear on the timeline? Maybe you'll want a heated greenhouse or a tub or even a pool in time?

I certainly found that our life adjusted around the power we generated as we lived through it. Continues to today. I don't think that massive amounts of self generated power can have a downside. Obviously, good homework to be done on the outgoing side and it's tariff. Exciting times for you! At £500 per kWp you won't have that chance again. I suppose their will also be bidirectional charging in EV's. A quick way to transport and storage down the road?

[Paul_F]

I have about 12kW of panels on a north east facing roof with a shallow 19degree pitch. The inverters limit output to a max of 10Kw. (2x 4Kw inverters and a Growatt SP2000 with 8Kwh storage). I did debate hard as to whether it was worth doing but am pleaded I did. The reason for doing it was purely for the winter output and to help to try and cover my base load. Even on duller winter days the output is not too bad as the light bounces off the clouds. During the summer I use the extra output to run heat pumps for an above ground pool for the kids.

Looking like a 30-35° pitch for us. Interestingly I've heard back from GivEnergy - the 10kW 3-phase system isn't available in the UK, they don't sell anything between 5kW single-phase and 30kW 3-phase. I'll check again when we start building, but I think that's enough to knock the idea of a battery on the head - the other alternatives are a lot more expensive.

Assuming this is the forever house, an EV or 2 are likely to appear on the timeline? Maybe you'll want a heated greenhouse or a tub or even a pool in time?

I certainly found that our life adjusted around the power we generated as we lived through it. Continues to today. I don't think that massive amounts of self generated power can have a downside. Obviously, good homework to be done on the outgoing side and it's tariff. Exciting times for you! At £500 per kWp you won't have that chance again.

I'm more than a bit wary of that argument - it's basically the same as the medieval sale of indulgences, with having PV giving you a license to pollute more.

I suppose their will also be bidirectional charging in EV's. A quick way to transport and storage down the road?

Assumed to be, yes - but since we tend to buy older cars and the house is a much higher priority, the assumption is that an EV is at least 5 and probably 10 years away for us.

[Joeboy]

Assuming this is the forever house, an EV or 2 are likely to appear on the timeline? Maybe you'll want a heated greenhouse or a tub or even a pool in time?

I certainly found that our life adjusted around the power we generated as we lived through it. Continues to today. I don't think that massive amounts of self generated power can have a downside. Obviously, good homework to be done on the outgoing side and it's tariff. Exciting times for you! At £500 per kWp you won't have that chance again.

I'm more than a bit wary of that argument - it's basically the same as the medieval sale of indulgences, with having PV giving you a license to pollute more.
[/quote]

Oh not at all. If anything it pushes you the other way as you are more aware of generation and thus your own use. Although you may wish to live the aesthetic lifestyle which is of course fine. At the same time in that lifestyle you will be exporting more to the grid and will be helping the carbon balance outwith your own home. Just another way to look at it? You'll know your own mind on this one, its personal.