@jamespa i guess you're on FIT exports? With a high rate.. inflation linked?

If so... highly doubtful you can round trip battery exports to increase income further? Presumably you would retain deemed export but bulk of FIT would have to change to actual exports at Fixed/Flux etc. Net result is likely to be better to stay on FIT?

Unless you're also adding significantly more PV solar?

In which case the calcs may be simpler? With no round tripping. 

But would get you cheapest overnight charging of EV and filling battery for daytime usage inc heat pump. 

• Increasing your self-use of solar 
• Maximising EV charging at overnight rates. Obviously depends on usage. Say 1000kw/pa. Round figure saving 20p/kwh? 
• Filled battery at overnight rates for day usage. Say 20kw/day for 100 days? Round figure saving 20p/kwh? 

Saving circa £600/pa? Possibly making ROI taking into account depreciation hard to justify... but....

Potentially adding in part or whole home emergency power supply capability? 

Potential resilience for grid planned outages? e.g. if grid becomes overloaded or interconnectors fail for any reason? Low wind? Russia? Etc!

Not necessarily a purely financial decision? Or is it?!

@toodles 

But that’s the deal with the devil, they are paying a premium to use your battery to balance the grid/makes some profit too. I estimate the balance of advantage is 95 in your favour. But, it’s not for EVs or heat pumps.

The autumn was good too, for those free electricity sessions they paid a flat bonus of a full battery, regardless of whether you did anything at all. It really added up nicely, for doing squat. 

@jamespa 

If you have no nett export then don’t do IOF as it is, by definition, impossible to profit. You need profit to cover the cost of the additional investment for fancy batteries. I’d suggest in your situation you need the cheapest possible battery system, or maybe none at all.  

Posted by: @papahuhu

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@jamespa 

If you have no nett export then don’t do IOF as it is, by definition, impossible to profit. You need profit to cover the cost of the additional investment for fancy batteries. I’d suggest in your situation you need the cheapest possible battery system, or maybe none at all.  

Reduced cost (as opposed to profit) is equally a motivation.  However you are right about batteries; I simply cant get the business case to work with any likely tariff however I try.  Its close if I am content with payback in say 8 years, but not close enough.  I guess if you either self-build or install a battery and solar at the same time the case is easier, the latter because the inverter part of the cost serves both.  If, like me, you already have solar then the added cost of buying and installing a new inverter tips the balance.  

@jamespa 

Hope it works out for you, revisit it in 6 months and you may find prices are down or maybe sodium chemistry is mainstream. Lithium extraction and processing is dirty and polluting, folks that go on about their environmental credentials have clearly never seen the devastation that sits upstream of their green tech. Indeed there is some credibility to the argument that oil extraction is considerably less damaging to the planet than lithium.

Posted by: @papahuhu

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@jamespa 

Hope it works out for you, revisit it in 6 months and you may find prices are down or maybe sodium chemistry is mainstream. Lithium extraction and processing is dirty and polluting, folks that go on about their environmental credentials have clearly never seen the devastation that sits upstream of their green tech. 

I am not sure if it had to be that way with Lithium... but then how could a virtual monopoly be built unless these things would be overlooked?

Anyway, there are more focused threads for these sodium vs lithium technology topics elsewhere. 

Posted by: @tim441

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Potentially adding in part or whole home emergency power supply capability? 

Potential resilience for grid planned outages? e.g. if grid becomes overloaded or interconnectors fail for any reason? Low wind? Russia? Etc!

We made this work (2 day protection can be reassuring).

But not easy achieve for under £3k with install costs, for a 16kwh system. 

I am currently doing the paperwork for SEG with export Flux - seems better than other octopus tariffs.

And the EV allows me Intelligent Go, so it will pay off even without solar.

I would gladly sweat the battery and keep an 8 hr protection from outage... Or let Solis AI decide..

@batpred Fair enough, if the usage of these materials is solely coupled to financial gain then that is at least honest. I designate myself to the camp of absence of empathy and callousness to the harm to others I’m causing, hard to define it as anything other than textbook psychopathy.

Posted by: @jamespa

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Reduced cost (as opposed to profit) is equally a motivation.  However you are right about batteries; I simply cant get the business case to work with any likely tariff however I try.  Its close if I am content with payback in say 8 years, but not close enough.  I guess if you either self-build or install a battery and solar at the same time the case is easier, the latter because the inverter part of the cost serves both.  If, like me, you already have solar then the added cost of buying and installing a new inverter tips the balance.  

I'm always intrigued when you make this statement, as my view is that a home battery, coupled with a time of use tariff, is the biggest value element within the "renewables package", even in the absence of solar PV.  I know that you're very analytical, so have no doubt in the fundamental maths behind the calculations, so this reaction is more in surprise that the answer it generates doesn't shout massive value back at you when you crunch the numbers.

Are you restricting your choice to specific high-cost batteries in your calculations, or is there some specific non-obvious constraining factor being reflected, as it's the only way that I can think that you'd conclude that the payback wouldn't work?

The only 'regret' I have about my entire setup is that the original 10kWh battery storage (now 15kWh via a spot of good fortune) is still about half of what I'd ideally like to have, especially now that there's a heat pump running within the household.  I would love to replace the batteries with a couple of 16kWh Fogstar replacements, or the cheaper 32kWh unit as a less practical 2nd preference, at current prices, which seem to have remained consistent for the last 12 months or so.  It's a more marginal situation where I'm replacing an existing element of the system 'like for like' as it only extends the existing economies being obtained with half of the capacity, so is very much a 'nice to have' currently.  However, if I was starting from a scenario of existing PV, EV, heat pump with no battery storage then the option of 32kWh of storage for circa £3,400, plus installation costs, then I'd be astonished if the maths didn't work in my case.

For clarity, I'm not doubting your assessment of your own calculations.  I'm more intrigued as to the factor that is different in your assessment, and why.  The logical one is that you've ruled out Fogstar batteries, and would be intrigued as to why, if that's the case.

Posted by: @sheriff-fatman

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Are you restricting your choice to specific high-cost batteries in your calculations, or is there some specific non-obvious constraining factor being reflected, as it's the only way that I can think that you'd conclude that the payback wouldn't work?

I dont know TBH.  Quotes for installed batteries seem very similar, a bit more than: 2.5K=5kWh, 5k=10kWh, 8-9K=20kWh.  I am including cost of capital.  I am assuming 4% interest but also accounting for tax on the interest (which is favour of the investment).

If I stretch things I can just about get payback = 8 years, mostly its 10 years.  This is based on EON Next Drive (2025 edition) which has a large differential between cheap rate and nighttime rate (6.7p vs 25.4p)  Roughly speaking I do 50% of my import at night rate and 50% at day rate.   

Does that answer your question.  Im trying to make it work, I'm not trying to find reasons not to do it!

We have solar, batteries and ASHP.

We use seasonal tariffs. In the summer We use Intelligent Octopus Flux (we generate more than we consume, thus are net exporters) and in the winter we use Octopus Cosy (high ASHP usage, low generation, net importers)

We generally export in the summer at 25-26p per kWh and import in the winter at 15p per kWh. Annually, we roughly generate what we consume. The leverage between summer export (25-26p) versus winter import (15p) of 10-11p per kWh means we can purchase 1.7kWh of heat in winter for every 1kWh of excess solar we export in summer, and results in negative bills for us. Long may the current tariffs continue.

Posted by: @jamespa

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Posted by: @sheriff-fatman

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Are you restricting your choice to specific high-cost batteries in your calculations, or is there some specific non-obvious constraining factor being reflected, as it's the only way that I can think that you'd conclude that the payback wouldn't work?

I dont know TBH.  Quotes for installed batteries seem very similar, a bit more than: 2.5K=5kWh, 5k=10kWh, 8-9K=20kWh.  I am including cost of capital.  I am assuming 4% interest but also accounting for tax on the interest (which is favour of the investment).

If I stretch things I can just about get payback = 8 years, mostly its 10 years.  This is based on EON Next Drive (2025 edition) which has a large differential between cheap rate and nighttime rate (6.7p vs 25.4p)  Roughly speaking I do 50% of my import at night rate and 50% at day rate.   

Does that answer your question.  Im trying to make it work, I'm not trying to find reasons not to do it!

So, assuming any technical issues could be overcome, if you factored in a 16kWh battery cost at £2,000 or a 32kWh battery at £3,400 and added on a cost to install (they've been described as 'plug and play', but this is generally referring to swapping out Sunsynk batteries for these, so that might be an oversimplification), does that price level make a big enough difference in your overall calculations?

I'm an accountant, so am very familiar with opportunity cost type calculations, and DCF analysis, which I assume yours are if you're figuring in interest lost and tax on interest saved, but the underlying price of the batteries appears to be the big constraint in your calculation.  The Fogstar ones seem to be generally acknowledged as being the best value cost/kWh of reliable storage options currently available so if the calculation doesn't work at those prices, then I guess it won't work at all.