Mike McMillan <toodle.pip1@virginmedia.com> wrote:
BrritSki <rtilburyTAKEOUT@gmail.com> wrote:
Sorry to reply to self and top post, but this is LONG, so wanted people
to see the added bit.
So, any comment on this estimation ? And in particular Mike or others,
any comment on the 3 questions asked in the footnotes ?
TIA Rog
On 26/01/2024 16:52, BrritSki wrote:
On 24/01/2024 15:46, Mike McMillan wrote:
BrritSki <rtilburyTAKEOUT@gmail.com> wrote:
On 22/01/2024 16:11, Mike McMillan wrote:IrCOll give you the figures from my Octopus Energy app ...
https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
Thanks again Mike. You make some excellent points esp. about life
expectancy (I intend to keep going for a while yet, but 100 might be
pushing it), and the complexity of Agile rCo I am happy doing this myself >>> (and can see!), but waife wouldnrCOt although sherCOd be perfectly capable
(and can also see), and I will probably work up a simple flowchart of
things to check like next dayrCOs weather, state of battery, likely usage >>> etc. to help me.
Of course as things get SMARTer at both Tesla and Octopus ends, the need >>> to intervene will lessen, and with all these things I guess you have to >>> play with them for a while to learn the best approach.
I wasnrCOt aware of the COSY tariff and I have asked Octopus if you can >>> get that without a Heat Pump to feed electric storage heaters of some
description during the 2 minimum periods to shift from gas, to electric >>> rCo probably not, but worth an email.
The COSY rate was close to what I was assuming rCo that electricity
overnight would cost on avg. 20p/kWh and 30p for daytime, but with our >>> low use and a big battery like that we should hardly ever need to use
grid power during the day rCo under a fiver for the whole of Aug 21- Jul >>> 22 rCo so that figure is almost immaterial. The 20p is probably
pessimistic, but if there are to be any surprises I want them to be good >>> ones ! [3]
For Export, I have assumed 8p for daytime and 15p for the peak 4-6PM
hours. Again, very pessimistic I think, so thererCOs only an upside.
My spreadsheet has daily figures for what we actually generated,
exported and imported along with the figures for the smart switch (which >>> is only ever used with the fan heater/cooler so is not real usage
although it does reduce gas usage a tad in winter). I then work out how >>> much capacity is available for charging during each day to fill the
battery to 90% [1] and then what is available for exporting during the >>> peak rate 4-6PM assuming keeping 3kWh for our overnight use and battery >>> minimum [2].
I then did a guesstimate of likely gen the next day (based on a third of >>> todayrCOs and yesterday's actual generation total, so probably pessimistic
also, but a check against the known next day actual revealed most of the >>> errors were in the right direction) to determine how much to top up
overnight to keep us going the next day. The battery level is then used >>> to start the whole process off again the next day and on we go.
The results are surprising to say the least. Cost of daytime electricity >> FOR THE WHOLE YEAR
under -u5. Cost of electricity for overnight topup -u77, but last year we >>> spent about -u55 overnight already from using dishwasher when itrCOs not >>> sunny and is full. We also spent another -u500 on daytime electricity. So >>> overall werCOd save about -u500 when you add VAT back in. This is in line >>> with my original calculations which showed a 90% saving with a large
battery, but not considered worthwhile then because a much smaller
battery would save over 70%.
Export would earn us -u370 during the 4-7PM peak and another -u190 from >>> spare generation capacity during the day, but that would be offset by
the loss of -u150 deemed export FIT payment, so net income would be -u410.
The total saving therefore on a very pessimistic basis are over -u900, so >>> a payback period of 9 years which is much more acceptable. The thing I >>> havenrCOt accounted for is using our Smart switch to power a small fan >>> heater for free heating like today which saves a little on our gas bill. >>> Total smartswitch use for the 6 coldest months is around 250 kWh. I am >>> not sure how to account for that rCo should I charge it at the electricity
rate (day or night), or the gas rate, or the gas rate times 3 or 4 to
account for the greater heating efficiency of gas ? Either way it is
max. about -u75 to subtract from the gains, adding another year to the >>> ROI period. On the upside I havenrCOt considered any additional savings >>> from savings sessions (see [3] below) or the rare occasions when you are >>> being paid to import power.
Of course we will have to withdraw some money from an ISA to pay for
this and looking at the performance report it shows an annual return of >>> 8%, so we would be rCLlosingrCY -u640 of returns. This is less than we are
saving, so not a problem and of course the addition of the battery to
the house will improve its EPC Rating and also the eventual resale value. >>>
I should really do this exercise again using last yearrCOs data so I donrCOt
make the mistake of the Climate Change Committee and just use a
favourable year to get the right result. Problem is I cannot remember
how I extracted this data from SolarEdge and loaded it up into a
spreadsheet. My memory is that it was a PITA, so I have just done a
monthly check comparing the data I used against 2023 to find that last >>> year was 5% worse. 2020 and 22 were good years, 21 and 23 a bit worse, >>> but not wildly wrong, so I think my pessimistic assumptions would cover >>> most of this and of course everything is based on current prices which >>> long term are likely to be exceeded.
I would appreciate your comments on this long post Mike, or anyone else >>> with experience of Solar and/or spreadsheets or this sort of estimating >>> generally. I hope I have been realistic and not just modelled things to >>> get the answer I wanted rCo I am actually surprised at the result which I >>> think is a good thing !
[1] Do you restrict the max. on your batteries ?-a I know for battery
longevity itrCOs recommended for EVs and phones (my phone (and laptop) >>> lets you stop charging at 85%), but I have read mixed opinions on
whether this is necessary for Powerwalls either because they have a
smarter (slower) (dis-)charging algorithm and/or there is a hidden max.
As I replied before, Tesla allow a charge up to 100% whether this is a notional limit or genuinely the full capacity I donrCOt know, they certainly
supply the full 13.5 kW/h from full charge anyway. It seems that there is no rCLwarningrCO or zone at 80%.
The Tesla actually allows setting of a reserve level; this can be any percentage one wishes, when the battery drops to that level of charge, it will reserve the rest for power outages. When I have wished to extract as much capacity as possible, I have set this to 5% and then it just sits and waits for a charge - no harm done to battery longevity to the best of my knowledge; I suspect the battery management system is watching over the state of charge and the true capacity though the app is mum on that point.capacity.
[2] Same question for keeping minimum above a certain level rCo worthwhile
?-a If I reduced my minimum charge level to 2 instead of 3 and used 100% >>> of the capacity instead of limiting to 12, it would generate another
-u100 of income approx..
I have only had full control over rCyeverythingrCO as Tesla call it since early[3] I have seen a claim elsewhere that you can quite legally game the
Octoplus system whereby you get very high payments for ALL the
electricity exported during a Saving Session (the -u2.25 per kWh you
mentioned Mike), but I donrCOt really understand how this works. AIUI the >>> savings session (SS) looks at what you normally use during the period vs >>> what you do during the saver session. So if you are regularly exporting >>> a lot during the 4-7PM period, you will not export MORE during a SS so >>> donrCOt benefit surely ?-a The only thing is if the SS is always 5-6, you >>> can set your normal export to be 4-5 and 6-7, so when there is an SS you >>> change the 4-5 to an hour later or something. Or have I got it wrong ? >>>
December as it had to be set up by the network by Tesla. I am not normally importing or exporting any energy at the designated SS times (well, not at this dark cooler time) so any activity at that time will be me exporting and they pay me for all of it. Not only do I receive the full SS rate as credit towards my bill, I also get my normal export 15 p. per kW/h on top of this. I have not set any times for my exporting as I have been happy to carry this out mandraulically. Before Tesla toggled my control system to allow export from the battery, it was purely PV power being sent to the grid - and that is unlikely to be available during SSrCOs at this time of year!
I might also add that were I using umpteen kW/hrCOs during the SS timeslot slot on other days and this happened to be a day they used for their rCytypical usagerCO statistic, I would benefit by that usage even if I used nothing on the SS day itself during that time. With a crystal ball, one
would ensure you used as much power at that time on a few non-SS days(charging up a battery of course!) to enhance the statistics on SS
days. Imagine, using (say for arguments sake) 10 kW/h less than usual AND exporting 10 kWrCOh too - all within the SS slot and being paid for 20 kW/h!
On Wed, 31 Jan 2024 17:45:26 -0000 (UTC), Mike McMillan wrote:
Mike McMillan <toodle.pip1@virginmedia.com> wrote:Just a little headsup for those who were interested in this thread:
BrritSki <rtilburyTAKEOUT@gmail.com> wrote:
Sorry to reply to self and top post, but this is LONG, so wanted people >>>> to see the added bit.As I replied before, Tesla allow a charge up to 100% whether this is a
So, any comment on this estimation ? And in particular Mike or others, >>>> any comment on the 3 questions asked in the footnotes ?
TIA Rog
On 26/01/2024 16:52, BrritSki wrote:
On 24/01/2024 15:46, Mike McMillan wrote:
BrritSki <rtilburyTAKEOUT@gmail.com> wrote:
On 22/01/2024 16:11, Mike McMillan wrote:IrCOll give you the figures from my Octopus Energy app ...
https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
Thanks again Mike. You make some excellent points esp. about life
expectancy (I intend to keep going for a while yet, but 100 might be >>>>> pushing it), and the complexity of Agile rCo I am happy doing this myself >>>>> (and can see!), but waife wouldnrCOt although sherCOd be perfectly capable
(and can also see), and I will probably work up a simple flowchart of >>>>> things to check like next dayrCOs weather, state of battery, likely usage >>>>> etc. to help me.
Of course as things get SMARTer at both Tesla and Octopus ends, the need >>>>> to intervene will lessen, and with all these things I guess you have to >>>>> play with them for a while to learn the best approach.
I wasnrCOt aware of the COSY tariff and I have asked Octopus if you can >>>>> get that without a Heat Pump to feed electric storage heaters of some >>>>> description during the 2 minimum periods to shift from gas, to electric >>>>> rCo probably not, but worth an email.
The COSY rate was close to what I was assuming rCo that electricity
overnight would cost on avg. 20p/kWh and 30p for daytime, but with our >>>>> low use and a big battery like that we should hardly ever need to use >>>>> grid power during the day rCo under a fiver for the whole of Aug 21- Jul >>>>> 22 rCo so that figure is almost immaterial. The 20p is probably
pessimistic, but if there are to be any surprises I want them to be good >>>>> ones ! [3]
For Export, I have assumed 8p for daytime and 15p for the peak 4-6PM >>>>> hours. Again, very pessimistic I think, so thererCOs only an upside. >>>>>
My spreadsheet has daily figures for what we actually generated,
exported and imported along with the figures for the smart switch (which >>>>> is only ever used with the fan heater/cooler so is not real usage
although it does reduce gas usage a tad in winter). I then work out how >>>>> much capacity is available for charging during each day to fill the
battery to 90% [1] and then what is available for exporting during the >>>>> peak rate 4-6PM assuming keeping 3kWh for our overnight use and battery >>>>> minimum [2].
I then did a guesstimate of likely gen the next day (based on a third of >>>>> todayrCOs and yesterday's actual generation total, so probably pessimistic
also, but a check against the known next day actual revealed most of the >>>>> errors were in the right direction) to determine how much to top up
overnight to keep us going the next day. The battery level is then used >>>>> to start the whole process off again the next day and on we go.
The results are surprising to say the least. Cost of daytime electricity >>>> FOR THE WHOLE YEAR
under -u5. Cost of electricity for overnight topup -u77, but last year we >>>>> spent about -u55 overnight already from using dishwasher when itrCOs not >>>>> sunny and is full. We also spent another -u500 on daytime electricity. So >>>>> overall werCOd save about -u500 when you add VAT back in. This is in line >>>>> with my original calculations which showed a 90% saving with a large >>>>> battery, but not considered worthwhile then because a much smaller
battery would save over 70%.
Export would earn us -u370 during the 4-7PM peak and another -u190 from >>>>> spare generation capacity during the day, but that would be offset by >>>>> the loss of -u150 deemed export FIT payment, so net income would be -u410.
The total saving therefore on a very pessimistic basis are over -u900, so >>>>> a payback period of 9 years which is much more acceptable. The thing I >>>>> havenrCOt accounted for is using our Smart switch to power a small fan >>>>> heater for free heating like today which saves a little on our gas bill. >>>>> Total smartswitch use for the 6 coldest months is around 250 kWh. I am >>>>> not sure how to account for that rCo should I charge it at the electricity
rate (day or night), or the gas rate, or the gas rate times 3 or 4 to >>>>> account for the greater heating efficiency of gas ? Either way it is >>>>> max. about -u75 to subtract from the gains, adding another year to the >>>>> ROI period. On the upside I havenrCOt considered any additional savings >>>>> from savings sessions (see [3] below) or the rare occasions when you are >>>>> being paid to import power.
Of course we will have to withdraw some money from an ISA to pay for >>>>> this and looking at the performance report it shows an annual return of >>>>> 8%, so we would be rCLlosingrCY -u640 of returns. This is less than we are
saving, so not a problem and of course the addition of the battery to >>>>> the house will improve its EPC Rating and also the eventual resale value. >>>>>
I should really do this exercise again using last yearrCOs data so I donrCOt
make the mistake of the Climate Change Committee and just use a
favourable year to get the right result. Problem is I cannot remember >>>>> how I extracted this data from SolarEdge and loaded it up into a
spreadsheet. My memory is that it was a PITA, so I have just done a
monthly check comparing the data I used against 2023 to find that last >>>>> year was 5% worse. 2020 and 22 were good years, 21 and 23 a bit worse, >>>>> but not wildly wrong, so I think my pessimistic assumptions would cover >>>>> most of this and of course everything is based on current prices which >>>>> long term are likely to be exceeded.
I would appreciate your comments on this long post Mike, or anyone else >>>>> with experience of Solar and/or spreadsheets or this sort of estimating >>>>> generally. I hope I have been realistic and not just modelled things to >>>>> get the answer I wanted rCo I am actually surprised at the result which I >>>>> think is a good thing !
[1] Do you restrict the max. on your batteries ?-a I know for battery >>>>> longevity itrCOs recommended for EVs and phones (my phone (and laptop) >>>>> lets you stop charging at 85%), but I have read mixed opinions on
whether this is necessary for Powerwalls either because they have a
smarter (slower) (dis-)charging algorithm and/or there is a hidden max. >>>
notional limit or genuinely the full capacity I donrCOt know, they certainly
supply the full 13.5 kW/h from full charge anyway. It seems that there is >>> no rCLwarningrCO or zone at 80%.
The Tesla actually allows setting of a reserve level; this can be anycapacity.
[2] Same question for keeping minimum above a certain level rCo worthwhile
?-a If I reduced my minimum charge level to 2 instead of 3 and used 100% >>>>> of the capacity instead of limiting to 12, it would generate another >>>>> -u100 of income approx..
percentage one wishes, when the battery drops to that level of charge, it >>> will reserve the rest for power outages. When I have wished to extract as >>> much capacity as possible, I have set this to 5% and then it just sits and >>> waits for a charge - no harm done to battery longevity to the best of my >>> knowledge; I suspect the battery management system is watching over the
state of charge and the true capacity though the app is mum on that point. >>>
I have only had full control over rCyeverythingrCO as Tesla call it since early[3] I have seen a claim elsewhere that you can quite legally game the >>>>> Octoplus system whereby you get very high payments for ALL the
electricity exported during a Saving Session (the -u2.25 per kWh you >>>>> mentioned Mike), but I donrCOt really understand how this works. AIUI the >>>>> savings session (SS) looks at what you normally use during the period vs >>>>> what you do during the saver session. So if you are regularly exporting >>>>> a lot during the 4-7PM period, you will not export MORE during a SS so >>>>> donrCOt benefit surely ?-a The only thing is if the SS is always 5-6, you >>>>> can set your normal export to be 4-5 and 6-7, so when there is an SS you >>>>> change the 4-5 to an hour later or something. Or have I got it wrong ? >>>>>
December as it had to be set up by the network by Tesla. I am not normally >>> importing or exporting any energy at the designated SS times (well, not at >>> this dark cooler time) so any activity at that time will be me exporting >>> and they pay me for all of it. Not only do I receive the full SS rate as >>> credit towards my bill, I also get my normal export 15 p. per kW/h on top >>> of this. I have not set any times for my exporting as I have been happy to >>> carry this out mandraulically. Before Tesla toggled my control system to >>> allow export from the battery, it was purely PV power being sent to the
grid - and that is unlikely to be available during SSrCOs at this time of >>> year!
I might also add that were I using umpteen kW/hrCOs during the SS timeslot >> slot on other days and this happened to be a day they used for their
rCytypical usagerCO statistic, I would benefit by that usage even if I used >> nothing on the SS day itself during that time. With a crystal ball, one
would ensure you used as much power at that time on a few non-SS
days(charging up a battery of course!) to enhance the statistics on SS
days. Imagine, using (say for arguments sake) 10 kW/h less than usual AND
exporting 10 kWrCOh too - all within the SS slot and being paid for 20 kW/h! >>
An umrat (Chris J Dixon, I'm looking at you) has started a thread over in uk.d-i-y about the possible future of the FIT. It might be worth other umrats' while to take a look and/or contribute over there.
THBAPSA
Nick
On 17/11/2025 19:55, nick wrote:<big snip, better late than never>
Just a little headsup for those who were interested in this thread:
An umrat (Chris J Dixon, I'm looking at you) has started a thread over in uk.d-i-y about the possible future of the FIT. It might be worth other umrats' while to take a look and/or contribute over there.
THBAPSA
Nick
Why on earth didn't you go the full gilliver and crosspost this?
john
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