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Author Topic: Economics of domestic batts  (Read 2956 times)
Countrypaul
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« Reply #15 on: February 18, 2020, 10:11:02 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.

Can you run the gas boiler to just heat the one room and see how much gas is used to warm the room from 10C to 20C (or whatever temperatures your permitted to use  Roll Eyes ), then do the same with an electric heater obviously having similar outside conditions. That way you could show real world figures although not using the gas to its most efficient if just the one room. I don't have gas and never have had, so I have no idea how accurate the meter would be for measuring the amount used which could be a limitation.

You could also show that a heat pump would make the electricity 2-3 times as efficient - perhaps even more  Grin
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jtp10000
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« Reply #16 on: February 18, 2020, 10:42:28 AM »

Octopus Agility got me very excited as if you can bridge your energy usage for the peak evening hours (4-7 pm), then you unlock <10p/kwh rate for the rest of the day and even lower for your EV charge.

The maths is complicated and highly dependent on your usage patterns- EV, out in day, kids, PV, co-operative better half on running washing machine etc..

Longer term any maths is highly dependent on the Agility price profile staying roughly as it is now. What happens if lots of people change their usage patterns and / or Octopus realise Agility doesn't make them any money? It is certainly likely to change over the next 5+ years.

So my basic maths:-

1. I reckon I use 7kwh between 4 and 7pm.
On Octopus Go this costs:-
7kwh x .13= £0.91

If I can instead get this for free from the PV or charge up at night when Agility is the cheapest I reckon (pls correct me) I can get this 7 kwh for an average of 2p.
7kwh x .02= £0.14

This would save £0.77p per day or £280 per year.

2. Perhaps also on Agility my EV charge rate will come down from current 5p to something like 3p as on Agility it tends to be a bit lower at night, so add another 10kwh x 2p= 0.20 per day= £73/year

3. Finally I think that on Agility your general rate is likely to be less than 13p- especially if you have usage in the day, so perhaps the rest of my usage, estimate 20kwh / day comes down from 13p to average of 9p = 80p/day saving = £290/year

Total saving £650 / year.

I can't see the upside can get much better than this as everything else is equal. I have made some unscientific assumptions on effective rates likely with Agility. Also if you are away you effectively don't get the benefit that day. I could have overestimated.

SO what does a 7kwh battery fully installed cost (or do you need slightly more if you expect to use 7kwh / day?).
I doubt it is under £6k- is that right? At £6k that is a 9.2 year payback which starts to get interesting- especially if it is easy to add capacity to the system as prices comes down further.
 
I am very happy to be corrected if anyone spots a mistake in my logic / maths. I would love an excuse to get a battery.

What I would say is that it seems to me that when these batteries come down in price to the £3k mark that it really is a no-brainer for anyone with an EV, PV and spare funds. It will take a lower price still if you don't have PV / EV.



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daveluck_uk
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« Reply #17 on: February 18, 2020, 10:46:42 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/

If you haven't already, check out will prowse on YouTube. He does some fantastic stuff with these type of batteries.
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kdmnx
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« Reply #18 on: February 18, 2020, 11:41:30 AM »


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.

The point about the pipe from the boiler "leaking" heat is moot because that heat still goes into your house. Think of it less about heating a room and more about heating the house.
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Countrypaul
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« Reply #19 on: February 18, 2020, 12:24:57 PM »

He seems less worried about pipe resistance and losses in the pipe than mind resistance and losses in his wallet  Grin

He needs to get the "right" figures to overcome the resistance
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Countrypaul
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« Reply #20 on: February 18, 2020, 12:32:57 PM »

Octopus Agility got me very excited as if you can bridge your energy usage for the peak evening hours (4-7 pm), then you unlock <10p/kwh rate for the rest of the day and even lower for your EV charge.

The maths is complicated and highly dependent on your usage patterns- EV, out in day, kids, PV, co-operative better half on running washing machine etc..

Longer term any maths is highly dependent on the Agility price profile staying roughly as it is now. What happens if lots of people change their usage patterns and / or Octopus realise Agility doesn't make them any money? It is certainly likely to change over the next 5+ years.

So my basic maths:-

1. I reckon I use 7kwh between 4 and 7pm.
On Octopus Go this costs:-
7kwh x .13= £0.91

If I can instead get this for free from the PV or charge up at night when Agility is the cheapest I reckon (pls correct me) I can get this 7 kwh for an average of 2p.
7kwh x .02= £0.14

This would save £0.77p per day or £280 per year.

2. Perhaps also on Agility my EV charge rate will come down from current 5p to something like 3p as on Agility it tends to be a bit lower at night, so add another 10kwh x 2p= 0.20 per day= £73/year

3. Finally I think that on Agility your general rate is likely to be less than 13p- especially if you have usage in the day, so perhaps the rest of my usage, estimate 20kwh / day comes down from 13p to average of 9p = 80p/day saving = £290/year

Total saving £650 / year.

I can't see the upside can get much better than this as everything else is equal. I have made some unscientific assumptions on effective rates likely with Agility. Also if you are away you effectively don't get the benefit that day. I could have overestimated.

SO what does a 7kwh battery fully installed cost (or do you need slightly more if you expect to use 7kwh / day?).
I doubt it is under £6k- is that right? At £6k that is a 9.2 year payback which starts to get interesting- especially if it is easy to add capacity to the system as prices comes down further.
 
I am very happy to be corrected if anyone spots a mistake in my logic / maths. I would love an excuse to get a battery.

What I would say is that it seems to me that when these batteries come down in price to the £3k mark that it really is a no-brainer for anyone with an EV, PV and spare funds. It will take a lower price still if you don't have PV / EV.


Don't you a 4kWp PV system which should knock a portion of your usage down before the savings (mainly in spring/summer of course).

Have you considered how that will affect your calculations? Just wondered what effect it would have on your calculation other than making them even more complex  Smiley
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jtp10000
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« Reply #21 on: February 18, 2020, 01:38:13 PM »

I tried to include the PV in my assumption that the battery would charge up at an average of 2p.
The Smart meter will only track your net import so of course to do a proper detailed analysis you would also need PV production data you could subtract from it.
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pantsmachine
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« Reply #22 on: February 18, 2020, 08:09:25 PM »

Sadly in this case no, across a cold loft, 8 foot drop of internal wall then under a suspended timber floor. I get your point though.


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.

The point about the pipe from the boiler "leaking" heat is moot because that heat still goes into your house. Think of it less about heating a room and more about heating the house.
« Last Edit: February 18, 2020, 09:23:35 PM by pantsmachine » Logged

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Justme
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« Reply #23 on: February 18, 2020, 08:54:18 PM »

When people are working out if its cost viable are you using claimed efficiency stats?

The claims seem to be mains to bat 90+% & bat to mains 90+%.
On a 4kWh mains used charge thats 3.24kwh actually usable on the output.


Empirical data suggest that those numbers are optimistic.
More realistic is mains to bat 80% & bat to mains 80%.
Resulting in a 4kWh charge giving just 2.56kWh for the end user.

We are currently looking at getting mains installed to use instead of the genny.

That will reduce our input per kWh costs but is it still worth using the inverter & battery bank?
The genny is making a kWh for about 25p.
In summer the solar covers our full use. In winter it does not scratch the surface.

As we are low users I cant see a break even point.



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kdmnx
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« Reply #24 on: February 18, 2020, 09:29:08 PM »

Sadly in this case no, across a cold loft, 8 foot drop of internal wall then under a suspended timber floor. I get your point though.


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.

The point about the pipe from the boiler "leaking" heat is moot because that heat still goes into your house. Think of it less about heating a room and more about heating the house.

If your central heating pipe really does go through the loft then that is a HORRIBLE system. You’re paying to heat the moon. No competent heating engineer would do that.
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kdmnx
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« Reply #25 on: February 18, 2020, 09:34:06 PM »

When people are working out if its cost viable are you using claimed efficiency stats?

The claims seem to be mains to bat 90+% & bat to mains 90+%.
On a 4kWh mains used charge thats 3.24kwh actually usable on the output.


Empirical data suggest that those numbers are optimistic.
More realistic is mains to bat 80% & bat to mains 80%.
Resulting in a 4kWh charge giving just 2.56kWh for the end user.

We are currently looking at getting mains installed to use instead of the genny.

That will reduce our input per kWh costs but is it still worth using the inverter & battery bank?
The genny is making a kWh for about 25p.
In summer the solar covers our full use. In winter it does not scratch the surface.

As we are low users I cant see a break even point.





Have you thought about wind? If you’re off grid and have enough solar to cover summer but struggle in winter then a kW or two of wind will make a big impact on your winter genny use.
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RIT
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« Reply #26 on: February 18, 2020, 10:06:18 PM »

The complication is that a year ago we were all doing this type of calculation based on electricity costing 15p a unit and rising fast. The Octopus Agile tariff has reset this expectation, with my average cost now around 9p a unit.

Two other changes seem to be due in the future that will complicate things even more

  - The possible switching of some of the electricity costs from the per-unit fee to the standing charge - which will keep the per-unit cost lower than expected.

  - The mad dash we now seem to be starting towards electric cars which will most likely keep the cost of batteries high and cause the issue of do you want to end up with both a set of static batteries and a set of batteries on wheels.

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pantsmachine
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« Reply #27 on: February 18, 2020, 11:53:31 PM »

Sadly in this case no, across a cold loft, 8 foot drop of internal wall then under a suspended timber floor. I get your point though.


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.

The point about the pipe from the boiler "leaking" heat is moot because that heat still goes into your house. Think of it less about heating a room and more about heating the house.

If your central heating pipe really does go through the loft then that is a HORRIBLE system. You’re paying to heat the moon. No competent heating engineer would do that.

A fairly broad sweeping statement there pal, thanks for the input though.
To answer- I did not say the pipes through the loft were bare, nor did I imagine their route and as you do not know the house layout you cannot make a  legitimate condemnation of said engineer.

Typing my thoughts last night helped clarify my decision and direction and you've entertained me, thanks.

RIT, I like the idea of an EV that can be plugged in and the remaining charge of the day used for house. Although in agile that user would be exposed to the 4pm to 7pm high rate if they were on the commute home with no residential battery to discharge? Might not be enough reason to go to the expense.

  With my next chemical battery install I will have covered the entire days use from four hours off peak charging which appeals to me. Will that ever stack up and go beyond break even? I think so but there are faster ways to a financial return than waiting to break even in under 6,000 cycles!

I will buy a few hive smart sockets and link them to the storage heater and fridge/freezers to shift their cycle out of 4pm to 7pm peak.
« Last Edit: February 19, 2020, 03:14:23 AM by pantsmachine » Logged

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TT
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« Reply #28 on: February 19, 2020, 07:54:24 AM »

Is there not a lead acid system available to do this at significantly cheaper outlay, I admit it may not be one packaged unit?

I would like batteries, but think more Lead Acid would be the way for me in a static environment.



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pantsmachine
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« Reply #29 on: February 19, 2020, 09:15:10 AM »

I think a lot of guys go for deep cycle lead acids from forklifts?
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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
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