Cheapest heating ever

[Originaltwist]

Batteries getting cheaper and no VAT

15kWh for £2,500 from Fogstar next month and no VAT

Time shifted night rates running heat pump (with the COP uplift) make for an interesting comparison to the normal heating methods. I've tweaked a recent chart of the latest rates to show how good it could be. Of particular note is that the battery tweak elevates an existing heat pump from the worst spot on the chart to the best with a doubling of the output. Batteries used to reach the end of life before payback was reached but now ....?

[markharro]

Ive never heard of Fogstar before but on checking their website the price for 15kWh of batteries appears to be £3747 - that would be over £3000 net of VAT. Where do you get the £2500 from? Also would you not need an inverter too if plugging in to an existing solar PV setup?

[MikeGrahamT21]

The 15kWh version is only 48V, so you’d only get around 1.8kW output from it maximum.

 

Only VAT free with installation also

Edited January 7 by MikeGrahamT21

[Gill]

1 hour ago, markharro said:

Also would you not need an inverter too if plugging in to an existing solar PV setup?

I looked at this the other day. This should be the link to it https://www.fogstar.co.uk/products/fogstar-energy-15-5kwh-48v-battery?variant=41546193174587

Would need inverter and as @MikeGrahamT21 mentions the max output is pretty low. Would love to think battery prices are going to become more competitive as we're now at a point where I think I can at very worst break even and something like givenergy all in one would give us small backup power as an added bonus. Will be interested to see if any vat savings ends up added to install costs. 

[ProDave]

Have you properly costed the pence per kWh of storing electricity in a battery?

 

It is a while since I have done that, but I previously looked at batteries to store surplus solar PV (i.e free) electricity, and concluded when you properly costed the batteries by allowing for the expected life and replacement at end of life the "free" stored energy was barely much cheaper than grid electricity.

 

I would be interested to see properly costed up to date figures.

[Gill]

17 minutes ago, ProDave said:

Have you properly costed the pence per kWh of storing electricity in a battery?

 

It is a while since I have done that, but I previously looked at batteries to store surplus solar PV (i.e free) electricity, and concluded when you properly costed the batteries by allowing for the expected life and replacement at end of life the "free" stored energy was barely much cheaper than grid electricity.

 

I would be interested to see properly costed up to date figures.

 

I did some very very rough calcs recently more to decide if I should even entertain the idea of batteries. 

All In one givenergy. Around 5k ex vat. 13.5 kW. Install unknown especially with the new vat drop. 

0.17 pence difference between by peak /off peak. 

Assume I can for at least one third of the year (winter) get 12 kW cheap rate daily from battery. 

0.17×12×(365÷3)  =248.2

Not great value there over 10 years (assuming performance isn't impacted). 

Looking at time of use tarrifs with two shorter off peaks I think I can potentially double by charge and discharge twice in a day so closer to 500 a year. 

If I add solar into the equation then our summer use would all be solar or off peak. Probably a small saving of about £1 a day. 

I do need to spreadsheet something but the above was enough for me not to bin the thought. 

 

 

 

Edited January 7 by Gill

[ProDave]

So £5K for 13.5kWh assuming I can install myself for £0

 

The key to working out the economics is what is the rated number of charge / discharge cycles of the battery?  Google suggests 4000 cycles.

 

So assuming you can store the rated capacity and use it each day, that will be 13.5 * 4000 = 54,000 kWh of stored power before end of life.

 

Divide by the cost, £5000, then you get 9.2p per Kwh as the cost of storing your energy.

 

Assuming your off peak is 15p cheaper than peak, then the real world saving is barely 5p per kWh

[Originaltwist]

2 hours ago, markharro said:

Ive never heard of Fogstar before but on checking their website the price for 15kWh of batteries appears to be £3747 - that would be over £3000 net of VAT. Where do you get the £2500 from? Also would you not need an inverter too if plugging in to an existing solar PV setup?

The £2,500 job is plugged on their site as coming next month and can be reserved. Yes you'd need an inverter/charger. I got excited by the Victron Quattro-II because it has an extra AC input which could pull in an EV v2L feed. It's very expensive but opens up many possibilities and anyway a V2G charger is expensive too and this gets round that by using the V2L feature that many more cars have and the Leaf doesn't.

I hadn't twigged the 1.8kW output - is that on the spec?

[TonyT]

19 minutes ago, ProDave said:

So £5K for 13.5kWh assuming I can install myself for £0

 

The key to working out the economics is what is the rated number of charge / discharge cycles of the battery?  Google suggests 4000 cycles.

 

So assuming you can store the rated capacity and use it each day, that will be 13.5 * 4000 = 54,000 kWh of stored power before end of life.

 

Divide by the cost, £5000, then you get 9.2p per Kwh as the cost of storing your energy.

 

Assuming your off peak is 15p cheaper than peak, then the real world saving is barely 5p per kWh

Pylontech are 6000 cycles

[JohnMo]

24 minutes ago, ProDave said:

Divide by the cost, £5000, then you get 9.2p per kWh as the cost of storing your energy.

 

Assuming your off peak is 15p cheaper than peak, then the real world saving is barely 5p per kWh

But if the off peak wasn't viable without the battery, you need to compare to full price normal tariff, i.e. 27p, so the saving becomes 18p per kWh.

 

You cannot self install (GivEnergy AIO) without be trained, you cannot commission without access to the commissioning tools. It does add to the cost.

Edited January 7 by JohnMo

[MikeGrahamT21]

9 minutes ago, Originaltwist said:

The £2,500 job is plugged on their site as coming next month and can be reserved. Yes you'd need an inverter/charger. I got excited by the Victron Quattro-II because it has an extra AC input which could pull in an EV v2L feed. It's very expensive but opens up many possibilities and anyway a V2G charger is expensive too and this gets round that by using the V2L feature that many more cars have and the Leaf doesn't.

I hadn't twigged the 1.8kW output - is that on the spec?

it’s based upon the voltage, to achieve 3kW I think from memory you need 52V and higher.

 

one thing which isn’t clear with battery storage is the inefficiency of converting from AC to DC and vice versa, I need to do an update on my blog about it at some point. Say, like I do, charge in the small hours at cheap rate, putting 5kWh into the battery would likely give me around 4.6kWh of available energy, and then by the time that’s made it back out to device’s probably be down to around 4.3 (from memory input efficiency is lower than output), so you are losing energy right from the off.

 

you only have to put your hand on an inverter after an hour of exporting at 3kW, they get rather hot, and the main chip in mine will operate up to 105C, which is classed as normal.

 

will try and find time to post a blog update this week

[JohnMo]

GivEnergy AIO charging last night - dark red area, charging 6kW.

 

[TonyT]

2 hours ago, ProDave said:

So £5K for 13.5kWh assuming I can install myself for £0

 

The key to working out the economics is what is the rated number of charge / discharge cycles of the battery?  Google suggests 4000 cycles.

 

So assuming you can store the rated capacity and use it each day, that will be 13.5 * 4000 = 54,000 kWh of stored power before end of life.

 

Divide by the cost, £5000, then you get 9.2p per Kwh as the cost of storing your energy.

 

Assuming your off peak is 15p cheaper than peak, then the real world saving is barely 5p per kWh

Don’t think you get 100% DoD.

maybe 90% which is still nearly twice as good as lead acid

[SteamyTea]

As batteries age, it is accepted they hold less charge.

If one assumes a 10% charging overhead for thermal losses (this may vary over times and is just a starting point), then a 15 kWh system will need 16.5 kWh to be fully charged (this is depth of discharge agnostic for this purpose), that is an initial efficiency of 91%.

If one then assumes that the battery capacity reduces by 5% each year, the efficiency then drops to 86% after a year, then 82% by end of year 3.  After ten years it is 54%.

 

I am not actually sure if a degraded battery still takes the same amount of energy to charge up to deliver lower amount of energy, and lightly discharged batteries may well fair better than heavily discharged ones.  I think this is called Coulombic Efficiency (CE).

Even if the charging energy levels are reduced over time, I very much suspect that the overall CE drops.  Even if it is half of what I have modeled (very basic model with assumptions), that still means after a decade near enough 30% of the capacity has gone.  This will also affect the power delivery i.e. initially say it can deliver 5 kW, after a decade it may be only to deliver 3.5 kW.

 

It would be nice if someone that has batteries can monitor the overall energy in and the overall energy out to see how good they are, it is too easy to fudge the numbers to make them fit an argument.

 

A chart.

 

 

 

[Kelvin]

8 hours ago, TonyT said:

Don’t think you get 100% DoD.

maybe 90% which is still nearly twice as good as lead acid

The All in One battery claims 100% DoD. 
 

The figures above assume electricity pricing will remain constant which they obviously won’t whereas your capital cost is fixed. The battery storage economics are marginal and I’m still not 100% sure I’ll do it. I have budgeted for it in our build though. 

Edited January 8 by Kelvin

[TonyT]

I think it’s a no brainer, charge with off peak, some solar time shift consumption to cheaper energy import.

 

all good.

 

[MikeGrahamT21]

10 hours ago, JohnMo said:

GivEnergy AIO charging last night - dark red area, charging 6kW.

 

 

This seems to show an inefficiency, much in the same way mine does, unless you are actually consuming power at that time?

 

This is what mine shows during charge, with an evident "load" during the charge, this isn't a load, its just in fact the inefficiency. I'm in talks with Solis regarding this at the moment, as to me it seems to be too much, and they advised me to speak to Pylontech, i'm waiting for their response

[JohnMo]

The colours are

Green, power going to the house, running MVHR, heat pump etc. this is also represented as import electricity in the light red/pink section below the dark red.

 

The way mine works, during off peak, it charges battery and any consumers take electric direct from grid, not the battery. At the end of the off peak period the battery is at 100% charged, then house consumption comes from battery, until departed to 5%, then grid power is taken by the house.

Edited January 8 by JohnMo

[Bramco]

12 hours ago, Originaltwist said:

I hadn't twigged the 1.8kW output - is that on the spec?

 

This could also be the input rating as well, so it would take a long time to charge up the 15kW capacity.

Also the 4000 cycles might mean that the Fogstar batteries are recycled cells, which might account for the pricing. Most of the other battery suppliers are at least 6000 cycles, afaik, Tesla is unlimited.

Key things on battery specs are obvs the size but also, cycles, DoD and the output.

 

Hopefully the transport co will be delivering our Sunsynk batteries today - then the fun starts with the installation - although it all looks pretty straightforward. We'll be charging on the Octopus Go 9p rate for 4 hours at night unless of course the sun has been shining in which case the batteries should be almost full.

 

Simon

[Originaltwist]

12 hours ago, MikeGrahamT21 said:

it’s based upon the voltage, to achieve 3kW I think from memory you need 52V and higher.

 

one thing which isn’t clear with battery storage is the inefficiency of converting from AC to DC and vice versa, I need to do an update on my blog about it at some point. Say, like I do, charge in the small hours at cheap rate, putting 5kWh into the battery would likely give me around 4.6kWh of available energy, and then by the time that’s made it back out to device’s probably be down to around 4.3 (from memory input efficiency is lower than output), so you are losing energy right from the off.

 

you only have to put your hand on an inverter after an hour of exporting at 3kW, they get rather hot, and the main chip in mine will operate up to 105C, which is classed as normal.

 

will try and find time to post a blog update this week

Mike - I've checked the Fogstar specs. It can deliver 200A so as a 50v battery that's 10kW. Being gentle with it and using 100A will match the 5kW on my favoured Quattro inverter.

Re the comments on handling charges and inverter losses - totally relevant - I would point out that we are looking at a battery + heat pump argument, so all gains are multiplied up by the COP and losses are similarly mitigated. Putting away the spreadsheets for a mo, It looks like heat pump running costs are roughly halved with a battery (see chart above) so if you spent £5k on the rig and knocked £1,000 off your bill you'd be paid back in 5 years. Life expectancy is nearer 10 years (insert joke here).

Losses - If all the kit is inside your heated envelope then they are more like efficiency setbacks but not really losses.

I'm with @TonyT it's looking like a no brainer for heat pump owners.

[Originaltwist]

A few negative comments above drove me back to the Fogstar site for a closer look at the £2,500 15kW.hr battery.

The cells are different from their more expensive 15kW.hr offering being the EVE prismatic ones but they are grade A.

The charge rate and the discharge rate are the same at 200A. I doubt if anyone would use 200A either way.

I can't find any stats on round trip efficiency.

The life span is lower at 3,500 cycles on an 80% DOD yet there is an 8 year guarantee. Presumably if not drawing 200A the cycles might be extended but anyway once a day for about 10 years looks acceptable.

BTW  I have no affiliation here – just a curious potential buyer, so any negative comments are more than welcome.

 

The following is clipped off their site.

Unwavering Confidence in Quality: We stand behind the exceptional design and construction of our batteries, offering an industry-leading 8-year warranty and a 15 year shelf-life.

Premium Grade A EVE Cells: The Fogstar Energy 15.5kWh Battery utilizes 16 premium LF304 Grade A EVE cells, renowned for their exceptional lifespan of 3500 cycles at a discharge rate of 200A per cycle.