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Author Topic: Economics of domestic batts  (Read 2957 times)
brackwell
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« on: February 15, 2020, 11:27:51 AM »

I am interested to hear from people who have had domestic batts FOR MORE THAN 1YR  to hear their views on the economics and savings and a view on the longer term.  These are changing times so we need to keep doing a rain check.

Ken
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freddyuk
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« Reply #1 on: February 15, 2020, 05:43:29 PM »

I have 5kWp of PV installed with some winter shading.
25kWh of battery capacity. Background loads around 400w.
Grid connected with import/export meter (net metering payment of 9cent per kWh & Import cost of 10c per kWh nightime)
System is using ESS firmware.
Batteries are recharged each night up to 95% soc unless weather is extreme and clearly no sun forecasted then switch to 100% SOC before 08.00 wintertime.
Using normal kitchen appliances including electric oven, washer, dryer, toaster, microwave etc. Obviously try to use dryer night rate only. Washing machine off peak only or sunny days.
Water heated by oil boiler or immersion on night rate. Wireless diverter installed and removed as unreliable. Basic Apollo Gem installed but will not handle the battery system with proportional control. Immersion timer can be used during off peak.
Numbers in VRM tell me how much energy I need from generator when I go off grid.
We can do better but only by making daily lifestyle changes to maximise available solar.
Net metering gives us effective potential to profit from solar generation in summer if export exceeds import.
Fixed costs of standing charges make lower bills harder to achieve. Low usage policy means charges for using under 2kWh per day.
Installation costs were mitigated by my ability to get wholesale rates and "bankrupt" battery stock.

« Last Edit: February 17, 2020, 04:19:35 PM by freddyuk » Logged
Scruff
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« Reply #2 on: February 16, 2020, 09:31:51 PM »

I've had many flavour batteries for donkeys years. I can't beat the cost of imported utility power on any variant I've tried when I pay myself for my time, the installation cost, and the involved hardware.
Batteries are efficiency reduction devices to grid network power.
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pantsmachine
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« Reply #3 on: February 16, 2020, 10:10:42 PM »

I think they are epic. I have ran the sums based on pre solar, pre battery and I will see my investment In batteries returned in 6 years. I then and only last month added octopus agile which brings the batteries back into play in the winter months. Let's put it this way. SSE would happily charge me 19p per kwh on an open contract last time I looked. Agile will charge my batteries at around 4p per kwh and on occasion for free. I'm buying another battery next month to take me up to 8.3kw storage, 80% of this dischargeable.
« Last Edit: February 16, 2020, 10:46:19 PM by pantsmachine » Logged

8.045kWh PV system with Solar edge
9.6kWh Pylon tech battery storage
18kWh Heater Storage
Solar I boost charging 12kWh 210 ltr OSO system tank
Deep insulation, air leak controlled home
Zoned CH wet system & Hive 2
Burley W/Stove
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kdmnx
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« Reply #4 on: February 17, 2020, 06:56:19 AM »

I think they are epic. I have ran the sums based on pre solar, pre battery and I will see my investment In batteries returned in 6 years. I then and only last month added octopus agile which brings the batteries back into play in the winter months. Let's put it this way. SSE would happily charge me 19p per kwh on an open contract last time I looked. Agile will charge my batteries at around 4p per kwh and on occasion for free. I'm buying another battery next month to take me up to 8.3kw storage, 80% of this dischargeable.

I’m interested as to your logic for choosing “agile” most people seem to agree that “go” is better for batteries. Maybe your use-case is different.
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pantsmachine
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« Reply #5 on: February 17, 2020, 09:25:30 AM »

I will I'm sure have a go at go as it's no penalty to change but quite happy with the prices on agile and no disturbance to how we live. SWMBO is a good egg but only so far. Smiley

Maybe try go when I buy an EV. Apart from the 4 hours at 5p what is the rate on go?
« Last Edit: February 17, 2020, 09:31:20 AM by pantsmachine » Logged

8.045kWh PV system with Solar edge
9.6kWh Pylon tech battery storage
18kWh Heater Storage
Solar I boost charging 12kWh 210 ltr OSO system tank
Deep insulation, air leak controlled home
Zoned CH wet system & Hive 2
Burley W/Stove
Low energy bulbs
24 kW Leaf
Veg patches & wood fired hot tub
dc
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« Reply #6 on: February 17, 2020, 10:53:30 AM »

I have had a Powervault system for last 21 months. My export has been reduced from 75% to 47% of my generation, approx 4200KW/yr. This gives me a payback of some 12yrs, not helped by recent reductions in cost of electricity.
System generally reliable, it has hung a couple of times but reset without issue. An extra battery, I have room in the cabinet,  would improve performance but current cost of upgrade is not attractive.
My research suggests that heating of domestic hot water offers best return.
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Sharp NU-E235 x 17 = 3.995kWp, SB4000TL, 4KWh Powervault, Essex CM8 3NR  Lat - 51-46'41"
bleem2k
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« Reply #7 on: February 17, 2020, 10:59:22 AM »

@pantsmachine GO 'peak rate' is approx 13p/kWh (depending on where you live) - check here - https://www.energy-stats.uk/octopus-go-tariff/

On our usage profile, agile is currently working out cheapest -



Agree that heating the home/water is probably the better use to begin with, certainly it could provide the biggest carbon reduction with removing the gas boiler. Batteries are certainly less disruption to install as a 'bolt on' but I think bigger changes may be needed, i.e. heat pumps, heat batteries, first. Although each household will have different requirements and different usage profiles.
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dan_b
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« Reply #8 on: February 17, 2020, 11:10:31 AM »

Had my 4kWh PowerVault since December 2016 - so just over 3 years now.  It has discharged 4300kWh in that time.  I got it subsidised through a DNO trial, so paid less than £2000 for it, which will alter the sums somewhat.

The first year of ownership I ran it just from charging with excess solar.
Moved to Economy 7 in January 2018 and started doing limited overnight charging on cheaper rate during the dark months, but switched off during summer/autumn.
Moved to Octopus Go in October 2019 and then switched to Agile in December 2019.

2017 - 874kWh
2018 - 1742kWh
2019 - 1486kWh

I can't make a reliably accurate calculation of how much the battery discharge in 2018/2019 was "free" from solar-supplied electrons, or simply time-shifted lower-rate electricity from E7/Go/Agile, but a rough guess would be 800kWh of solar and 800kWh of timeshift.

Batteries were replaced under warranty in the first year.

On that basis,
I've avoided 2400kWh of import at a grid average of 18p, so that's £430 saved
and I've time-shifted 2000kWh of import at say a cost of 5p in vs 18p in so that's another £260 saved in time  shift.

So in the 3-ish years I've avoided £700 quid in imported electricity costs.
At that rate I'll be heading for break-even in another 6 years I guess - 9 years pay-back assuming it doesn't fail completely by then.

Man maths needed to justify it from a purely financial point of view - but I've enjoyed being able to learn about batteries and energy efficiency and how the grid works and changing my behaviours to suit the times when solar and battery provide the most support.

The Powervault I have is limited by capacity and charge/ discharge rate compared to what you can get now, but the acquisition cost was low relatively speaking compared to a a Powerwall 2.

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3.06kWp SolarEdge system with a split array:
2.18kWp 10x South facing, plus 4x West facing 880W

Mk1 ImmerSUN DHW diverter
4kW PowerVault Battery

Tesla Model 3 Long Range
brackwell
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« Reply #9 on: February 17, 2020, 08:37:06 PM »

Dan,
Very interesting.
I thought/hoping you might have been able to do more than 4300kwh in 3 yrs   What kind of limits this uptake as cleary a larger through put would help the economics.

What do you think would be the retail cost of your kit.

Ken



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pantsmachine
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« Reply #10 on: February 17, 2020, 09:29:48 PM »

Thanks Bleem2k,  with the flat rate andx25ppd sc i think I'll stick with agile and continue to roll the dice for plunge pricing. Horses for courses but I feel more plugged in to RE by riding the waves of agile. We have a number of storage heaters that we bought as spares for properties.

We have toyed with the idea of trying the smallest most discreet unit in a hidden corner of the big room and charge it on 2p power 01.00 to 05.00 hrs.

Do any of you guys know of the comparison between a kwh of gas and same in electricity re heating? I guess it comes down to losses, boiler, pump, pipework etc vs full efficiency in the red hot heating element?


@pantsmachine GO 'peak rate' is approx 13p/kWh (depending on where you live) - check here - https://www.energy-stats.uk/octopus-go-tariff/

On our usage profile, agile is currently working out cheapest -



Agree that heating the home/water is probably the better use to begin with, certainly it could provide the biggest carbon reduction with removing the gas boiler. Batteries are certainly less disruption to install as a 'bolt on' but I think bigger changes may be needed, i.e. heat pumps, heat batteries, first. Although each household will have different requirements and different usage profiles.
« Last Edit: February 17, 2020, 09:40:27 PM by pantsmachine » Logged

8.045kWh PV system with Solar edge
9.6kWh Pylon tech battery storage
18kWh Heater Storage
Solar I boost charging 12kWh 210 ltr OSO system tank
Deep insulation, air leak controlled home
Zoned CH wet system & Hive 2
Burley W/Stove
Low energy bulbs
24 kW Leaf
Veg patches & wood fired hot tub
Countrypaul
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« Reply #11 on: February 17, 2020, 11:23:27 PM »

Surely you can asume that resistive heating is near enough 100% efficient as the loses in the cables from meter to the heater will also contribute to houe heating (unless you have a long run outside the thermal envelope). For gas it will be much more difficult to work out, though if the boiler is within the thermal envelope along with the pipework and emtters than you are probably just looking at boiler efficiency. Is it a condensing boiler running at a low (<55C) temp and therefore most efficient (90%+?) or something much worse...
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dan_b
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« Reply #12 on: February 18, 2020, 12:52:38 AM »

My Powervault is limited to just 700w charge rate so it doesn’t fill very quickly. Discharge rate is higher at 1100W but again not sufficiently high to be able to cover all big draws like kettle or dishwasher hot cycle.  And at only 4kWh it cant take much anyway!

I think retail when I got it was at least £1000 more.  The trial was heavily discounted.   They did also do the 6kWh lithium version but it was a lot more and it would seem had no BMS to speak of.
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3.06kWp SolarEdge system with a split array:
2.18kWp 10x South facing, plus 4x West facing 880W

Mk1 ImmerSUN DHW diverter
4kW PowerVault Battery

Tesla Model 3 Long Range
pantsmachine
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« Reply #13 on: February 18, 2020, 02:36:17 AM »

Surely you can asume that resistive heating is near enough 100% efficient as the loses in the cables from meter to the heater will also contribute to houe heating (unless you have a long run outside the thermal envelope). For gas it will be much more difficult to work out, though if the boiler is within the thermal envelope along with the pipework and emtters than you are probably just looking at boiler efficiency. Is it a condensing boiler running at a low (<55C) temp and therefore most efficient (90%+?) or something much worse...

I agree yet I am up against a resistive (pun intended) mind that is playing catch up to the actual costs I now pay for E. My mind remains in gas good/electric bad for heating. Not the case now, the engineer side of my mind wants to chase down the losses as a percentage point which is impossible so I thought I'd throw it out for chat (no hijack intended Ken). In this case I'm looking at at least 100 ft circuit of 10mm pipe to that room on a 90% efficient when new (15 years old now) system boiler. Could easily be sub 80% of the gas kwh making it to that room? The timed discreet storage heater might just be the answer. I'll have wi fi timed control on that switch to bring the heater to the 21st century.....

That's not a bad idea, cheers lads! Smiley Another battery added in another form.
« Last Edit: February 18, 2020, 02:50:43 AM by pantsmachine » Logged

8.045kWh PV system with Solar edge
9.6kWh Pylon tech battery storage
18kWh Heater Storage
Solar I boost charging 12kWh 210 ltr OSO system tank
Deep insulation, air leak controlled home
Zoned CH wet system & Hive 2
Burley W/Stove
Low energy bulbs
24 kW Leaf
Veg patches & wood fired hot tub
GarethC
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« Reply #14 on: February 18, 2020, 09:48:03 AM »

What do you guys think of the batts this chap is recommending? Battery only but seems very cheap at £1.8k (although probably exc shipping) for 10.6kWh.

https://pushevs.com/product/etc-lfp-battery-cells/
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