I do have an EV and did the maths using eon next drive (7 hrs at 6.5p) and my measured consumption form my heat pump. 

I couldn't get the business case to work either, even if I played arbitrage games in summer by importing at 6.5p to charge the batteries at night and exporting at 16.5 p during the day to discharge them.

I don't think the EV affected the case as it happens, it's 100pc charged at night anyway.

For me battery prices need to come down by 20% or more for them to be viable

If my 13yr old solar inverter fails, and thus I have to buy a new inverter anyway, it might just work then.

Others do claim to have a business case, even though I (and it seems you) appear not to.

@adamk will OVO accept you? Several months ago the initial “trial” closed to new entrants. And of course it is limited to make of ashp. Our Vaillant did but not all makes do.

Similar situation here (we have a PW3 and ASHP+solar), with a strategy of using Octopus Cosy during the winter with the battery allowing us to achieve all our import at the Cosy cheap rate. Without a battery, we averaged 19-20p import last winter, and may average 13p with a battery, so a saving of 6-7p per kWh. On that basis the battery does not pay for itself within the 10 year warranty period.

However, as alluded to by @jamespa, owning a Powerwall gives us access to Intelligent Octopus Flux, which in summer allows us to almost double the credit we can build each month over the 15p SEG export, and the more you export (the bigger the solar array you have), the more you make. This can have a significant impact on the calculations.

We went ahead and bought the battery anyway as (a) we wanted to max out our solar and would have needed a new inverter anyway which can be offset against the cost of the PW3 which comes with built in inverter, and (b) comfort was a major consideration allowing us to run the heating constantly (and cook in the evenings at peak rate times) as I could simply not bring myself to turn stuff on at peak rate without a battery. Last year we turned heating off for the 4-7pm peak and tried to avoid using the oven/microwave/air fryer which caused much marital unrest, so battery == happy marriage!

The net result for us is that we will accumulate sufficient credit in the summer on IOF to cover winter usage on Cosy == no bills.

We chose the PW3 as we only had suitable locations that were outside, fully exposed to the elements, so any battery had to be fully outdoor rated and also perform well in cold temperatures, so active thermal management was a must. My research indicated the Tesla was the market leader in this respect. No point having a battery that cannot fully recharge in 3h when it's -5C outside and then having to heat the house with expensive electricity exactly when you are using the most. If we had suitable indoor locations such as a warm garage / utility room / plant room etc, then we may have considered other options, but our only suitable location was on an exposed east facing wall.

I must confess to not understanding the need to justify the business case for investing in renewables.  What other capital expenditure is subject to the same scrutiny?

What's the business case for buying a house, or a car or going on holiday?  People who say they can't justify an EV or a heat pump or solar or batteries frequently buy /lease an expensive new car every 3 years and then use it for at most 5% of the time.  Where's the sense in that?

If you want to invest in renewables, then go ahead.  There's no need to justify it.

Posted by: @downfield

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I must confess to not understanding the need to justify the business case for investing in renewables.  What other capital expenditure is subject to the same scrutiny?

What's the business case for buying a house, or a car or going on holiday?  People who say they can't justify an EV or a heat pump or solar or batteries frequently buy /lease an expensive new car every 3 years and then use it for at most 5% of the time.  Where's the sense in that?

If you want to invest in renewables, then go ahead.  There's no need to justify it.

Hmm.

I must admit at least one of our car purchases was based on the cost saving of the better fuel efficiency outstripping the purchase cost in a relatively short time. Our move to an EV was based on a similar argument.

I would more generally say that all our purchases are based on whether the benefit we get is worth the cost we have to pay, so in that sense all our capital purchases go under the level of scrutiny you describe.

All that said, I still agree with what you wrote. I can’t see the sense in paying on the never-never rather than saving up and buying later - unless, of course, there’s no choice but to buy immediately.

I also agree that people will sometimes be scrupulously logical about one thing and whimsically inconsistent about something else. And, of course, they’re allowed to.

@downfield unfortunately due to a low income I only look at roi. When I had solar installed back in 2014 the FIT was one of the main drivers. I consider batteries with some scepticism due to them relying on low unit rates for upto 10 years to get the money back at which point the warranty expires. If we started using other forms of fuel for generation our unit price might be more reasonable and people wouldn’t need to do this constant dance to get the best out of batteries and solar.

ive recently installed a 7kw Vaillant heat pump, but i was thought to be bonkers by most, if I can’t get a decent unit rate they may yet prove correct. But we wanted to move our boiler and hw tank so for £3800 (not including the pipe upgrades my plumber did) I thought I’d take the plunge and see if all the YouTubers pushing them are correct. So far I’m happy with the 4.4x each kw it consumes to heat hot water. The actual install is another issue on another thread. But unless I can load shift to reduce the obscene 22p kWh down to a lower rate it’s going to be a fag packet between the gas boiler and heat pump running costs.

Re our income I’m often said to be tight yet without being prudent I wouldn’t be able to look at these techs. The gov doesn’t help as it keeps increasing the min wage at a faster rate than my public sector job rises, why? I used to earn maybe £2 per hour more now it’s more like 30p. Regards cars, my wife had her last one 11 years and bought it for £3350 it got written off by another driver. The latest one cost £1000 5 years ago. I spend a bit more but did have my last Audi for 5 years and that cost £1000. My latest Audi is the most expensive car I’ve ever bought and cost £16.5k but I’m in my fifties and could afford to buy it outright. We never use pcp or loans.

Posted by: @adamk

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But unless I can load shift to reduce the obscene 22p kWh down to a lower rate it’s going to be a fag packet between the gas boiler and heat pump running costs.

Assuming you have a smart meter and given you have a Vaillant you should be able to get 15p/kWh for your heat pump consumption from OVO.  As I have an EV its better for me to be on EonNext (6.5p/kWh from midnight to 7am) and I average about 19p/kWh if I exclude the EV consumption (the average is lower still if I include the EV, but for the purposes of comparing heat pump running cost with my previous boiler I like to exclude it, and attribute all the cheap electricity consumed by the EV to the EV). 

Without an EV Id almost certainly be switching to OvO.  Loke you a cant convince myself about batteries, the financial case doesn't work for me and I haven't seen sound environmental arguments for them.

Having made the switch and unless something radical happens to electricity/gas prices Im content not to think about it again.  Im not switching back!

@adamk apologies if my comments appeared thoughtless and I should of course have qualified my final point with "and provided you have suitable funding".

I deliberately kept the comment general and wasn't aiming at anyone in the thread - perhaps I should have started a new thread.

It's just that folks who wouldn't in general terms know one end of a cost-benefit analysis from the other suddenly seem to get very hooked up on pay back when it comes to renewables.  And I just wonder why.

I completely agree with you on cars - my policy has always been to buy a 2 - 3yo and keep it for at least 10 years...

And why aren't battery prices coming down?  One reads about the massive production capacity in China and low car prices over there but it doesn't seem to be reflected in falls in home storage battery pricing in Europe.

@downfield I think the reason we pay more is import duties VAT and a high min wage. For comparison Germanys min wage is £11.05, France £10.23, ours is £12.21. This has an upward pressure on everything and is in part why inflation is being so stubborn.

Posted by: @adamk

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 I think the reason we pay more is import duties VAT and a high min wage. For comparison Germanys min wage is £11.05, France £10.23, ours is £12.21

Er, according to this https://www.destatis.de/EN/Themes/Labour/Earnings/Minimum-Wages/Tables/minimum-wages-germany.html

The min wage for roofers and electricians in Germany (the trades that are involved in fitting solar panels) is EUR14-16, about the same to simewhat above ours.  UK VAT is zero on installed solar, so unless Germany and France have negative vat, it's not that either.  I don't know about import duties perhaps you could clarify how ours compare?

@jamespa yeah I’m only showing the min wage we’ve set as a country not for individual trades. I’m surprised they are saying an electrician only gets £12.11-13.84, no wonder so many people want to work in the UK. No way you can find a sparks in the UK that earns that. My builder is on £27 per hour.