https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home

Please excuse the (not my( typos, the Webmaster was using a Merkin spill
chicken which went through my article and nuggered a few worms. They left
me intact and krect!

--
Toodle Pip, Mike McMillan

On 22/01/2024 16:11, Mike McMillan wrote:
>
> https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
>
> Please excuse the (not my( typos, the Webmaster was using a Merkin spill
> chicken which went through my article and nuggered a few worms. They left
> me intact and krect!
>
Very interesting. I'll read in full tomorrow.

In message <l17v2cF5cfsU1@mid.individual.net> at Mon, 22 Jan 2024
19:47:24, BrritSki <rtilburyTAKEOUT@gmail.com> writes
>On 22/01/2024 16:11, Mike McMillan wrote:
>>
>>https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-
>>sustainable-and-energy-efficient-home
>> Please excuse the (not my( typos, the Webmaster was using a Merkin
>>spill
>> chicken which went through my article and nuggered a few worms. They left
>> me intact and krect!
>>
>Very interesting. I'll read in full tomorrow.
>
I just have. Thanks Mike - obviously a Lot of Thought (and money) is
involved.

One thing - the shots of your roof (with the chimney and aerial)
reminded me: I've wondered for some time, why triangular solar panels
don't exist, for the ends of rows (of rectangular panels) where a 45
degree roof edge is present. As well as using otherwise wasted space,
they'd be - IMO, anyway - more aesthetically pleasing.
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Try to learn something about everything and everything about something.
-Thomas Henry Huxley, biologist (1825-1895)

On 22/01/2024 16:11, Mike McMillan wrote:
>
> https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
>
> Please excuse the (not my( typos, the Webmaster was using a Merkin spill
> chicken which went through my article and nuggered a few worms. They left
> me intact and krect!
>
Well written and balanced and very interesting.

Funnily enough at the weekend I had drafted a post asking questions
about batteries but hadn't sent it obvs, so I will post it now below.
Some of my ?s have been partially answered by your article but I'll
leave it unchanged for now. What I would be interested in knowing Mike
if you are willing to share, is how much you earn from selling back to
the grid thru Agile ? I would guess our numbers would be similar as
although we have a smaller array and only 1 Powerwall, we don't have a
heat pump and our use was a bit lower than yours too at avg. 6.5kWh/day
vs 8 for you pre-installation.

I am looking again at batteries as our solar panel installer from 5
years ago has advised that battery installations will soon be VAT free
so they can install a Tesla Powerwall 2 with Home Backup Gateway for
around £8K.

My original calculations at the start of last year, that showed that for
us a much smaller battery was the most cost effective, are still correct
as far as they go, but they are based on old energy prices and I need to
rework them at the new rates. On the face of it with a £670 (according
to Octopus) annual electricity bill though, even elimination 100% of
that would still mean a 12 year ROI which is too long for me.

However what I hadn’t considered back then was the opportunity for
selling back to the grid, but I am unclear what the Octopus Flux tariffs
really mean, so any advice or input from people who have batteries would
be appreciated - Mike, Sally, ??? – I’m looking at you.

1. I understand the principle is that you store your solar in the
battery and then sell it back at the most advantageous time which is
1600-1900, but Octopus only seems to have 3 rates for Flux (and 2 for
Intelligent Flux whereas I thought the price paid fluctuated every half
hour ?

1a. Is there a rate for that ? How does this work with the special
offers occasionally from Octoplus to save money by reducing consumption
4-7PM ?

1b. The Flux/IF tariffs mean I would lose part of my FIT worth around
£150 a year – are there any tariffs that would still allow that ?

[I think Mike must be using Agile which I hadn’t considered, but the
Octoplus and FIT ?s remain]

2. What is the approach for minimum battery level ? I understand you
don’t want it to fall below 20%, so given that we use around .7kWh
overnight we would need to keep a minimum level of 3.5kWh in the
battery, meaning the most we could sell would be 10kWh.

3. Is that possible in 3 hours during the peak period – in other words
is there a max. rate at which you can transfer back to the grid ?

4. What happens during a nice sunny day when the battery is full by
lunchtime but I am still generating – does that get sold directly to the
grid at the non-peak rate or what ?

5. Intelligent Flux seems good as it allegedly understands my needs and
decides what to sell and when to maximise my income and also doesn’t
topup overnight if the forecast is for sun the next day, but does the
Tesla have all those smarts too ?

6. If so, can you switch back and forth between IF and Flux depending on
time of year to benefit from much lower topup rates in winter when you
use them more and higher selling rates in summer when you rarely need to
topup ?

7. In the Tesla app how much control do you have over all this ? I
cannot find a good description or demo of it, only that it takes account
of weather forecasts for the next day, and no doubt uses some clever AI.
But no matter how clever it is, it will still not know all that I know
e.g. that I am going away for a week so usage will be low, so sell,
sell, sell, or that we are having a family do tomorrow so the oven will
be in use a lot.

8. Does anyone know of any spreadsheets available that will model all
this based on real data rather than a salesperson’s rosy projections ?
I am going to give it a try in my spreadsheet where I already have the
actual generation/usage data for a whole year, but it will be hard, esp.
the weather forecasting bit – I can be 100% accurate as I know what
actually happens the next day but what was the forecast saying the night
before ??? There’s also the question of how you handle the fact that you
are still generating between 4 and 7 (and indeed much later with our
unshaded SW facing array) so would not have to worry about the 3.5kWh
reserve, at least at the start of the peak rate payback.

I also would need to reconsider our heating strategy – currently we use
our gas CH set at 19C for a morning warmup and 20C in the evenings,
supplemented by a fan heater on a smart switch to heat the living room
(which has been great the last few days), a fire in the woodburner on
cold afternoons (also the last few days !) or a 30 minute blast from the
gas CH. If you have free/cheap power in the battery though, you can use
electric heating in the places and at times you actually need it and
keep the CH at much lower background levels. I am currently using
max/min thermometer to measure how warm/cold each room is on the current
schedule to see what would make sense.

Although I disagree profoundly with Net Zero on the basis of its
feasibility (and it seems from today’s news that the Royal Society also
questions the CCC models) I am not against renewables per se and am
happy to add a battery to help smooth the load on the grid, but only if
it makes financial sense for us personally. I know it would add to the
value of the house, but we’d have to pay for this out of our savings
which means we’d lose interest on that sum for the rest of our lifetimes
and of course a battery is not likely to last as long as a solar panel.

The great unknown is where prices are going – not down very much for
sure (although Cornwall Insights has doubled down on their price drop
forecast for 2024), but how high over the next 10 years ? And if we
persist with this NZ madness with no sign of the 100TWh of storage the
RS estimates is needed, power cuts are going to be much more likely so a
battery will be a good thing to have….

Many questions – hope someone can help… TIA

BrritSki <rtilburyTAKEOUT@gmail.com> wrote:
> On 22/01/2024 16:11, Mike McMillan wrote:
>>
>> https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
>>
>> Please excuse the (not my( typos, the Webmaster was using a Merkin spill
>> chicken which went through my article and nuggered a few worms. They left
>> me intact and krect!
>>
Find a cup / glass of your favourite beverage / tipple, sit back and be
prepared to lose a few minutes of your valuable life - I hope the loss will
nevertheless, be of interest and a form of gain into the bargain.;-)))

> Well written and balanced and very interesting.
Most kind!

>
> Funnily enough at the weekend I had drafted a post asking questions
> about batteries but hadn't sent it obvs, so I will post it now below.
> Some of my ?s have been partially answered by your article but I'll
> leave it unchanged for now. What I would be interested in knowing Mike
> if you are willing to share, is how much you earn from selling back to
> the grid thru Agile ? I would guess our numbers would be similar as
> although we have a smaller array and only 1 Powerwall, we don't have a
> heat pump and our use was a bit lower than yours too at avg. 6.5kWh/day
> vs 8 for you pre-installation.
>
I’ll give you the figures from my Octopus Energy app as that gives me the
overall figures in an easily digested form. I buy my energy on the Cosy
Tariff and I ‘sell’ my excess back on the Outgoing Tariff. The Cosy is used
during the 6 cheapest hours and fills the battery so that (normally
speaking anyway) we don’t draw anything from the grid during the more
expensive and the very much more expensive hours. Our Cosy hours cost 17.27
p. kW/h and Outgoing brings in 15 p. kW/h. Previously, we had been using
the ‘Agile’ tariff and the ‘buy’ price varied by the half hour and I would
look them up in advance and set my Tesla App to charge at the cheapest
time. The rate could vary between about 20 p. per kW/h down to 00p. or
even minus a few pence per kW/h which meant they paid me to use energy at
those times. I felt that as I was having a lot of horsepiddel appointments
and am still undertaking treatment for my fuzzy vision, I would change over
to Cosy where the tariff can be set and forgot about so less worry for Mrs.
McToodles if I have a stay at the NHS’s pleasure - I may revert to Agile if
and when they sort out my sight for me.

Last year, we consumed (according to Tesla app - results from the different
apps and the SmartMeter readings which I can’t read very easily, seem to
vary somewhat!) 6.7 MW/h. We had the heat pump installed in late February
so our gas consumption was supplying the space heating and domestic hot
water before that time. Some of the domestic hot water was heated via the
immersion heater which might have been fed from any excess solar power we
had day to day. As we had had the solar PV fitted in the previous August,
we had a power diverter fitted when the heat pump was fitted so that then
allowed us to select how and when the DHW was heated - solar or grid. The
Tesla app tells me that we produced 6.5 MW/h with our solar PV last year;
some used here and the rest exported. With 27 kW/h of storage capacity, we
should not need to import from the grid at all should the big yellow thing
in the sky put in enough appearances from March onwards until November!
>
>
> I am looking again at batteries as our solar panel installer from 5
> years ago has advised that battery installations will soon be VAT free
> so they can install a Tesla Powerwall 2 with Home Backup Gateway for
> around £8K.
Yes, my second Powerwall fitted late last year ‘enjoyed a VAT rate of 5%
(wrinklies concession) and was cheaper than the first one, just a few days
and they will be zero rated.
>
> My original calculations at the start of last year, that showed that for
> us a much smaller battery was the most cost effective, are still correct
> as far as they go, but they are based on old energy prices and I need to
> rework them at the new rates. On the face of it with a £670 (according
> to Octopus) annual electricity bill though, even elimination 100% of
> that would still mean a 12 year ROI which is too long for me.

Go on - we are all part of the living to 100+ movement!
>
> However what I hadn’t considered back then was the opportunity for
> selling back to the grid, but I am unclear what the Octopus Flux tariffs
> really mean, so any advice or input from people who have batteries would
> be appreciated - Mike, Sally, ??? – I’m looking at you.

I’m getting the Outgoing tariff which is 15p. Per kW/h at all times.
>
> 1. I understand the principle is that you store your solar in the
> battery and then sell it back at the most advantageous time which is
> 1600-1900, but Octopus only seems to have 3 rates for Flux (and 2 for
> Intelligent Flux whereas I thought the price paid fluctuated every half
> hour ?

It is Agile that varies by the half hour; there could be 48 different
prices in any one day with this tariff.
>
> 1a. Is there a rate for that ? How does this work with the special
> offers occasionally from Octoplus to save money by reducing consumption
> 4-7PM ?

My experience so far has been that they may start a ‘Saving Session’ at
17:00 or maybe 17:30 lasting from 60 to 90 or 120 minutes. One session
paid (ITIW) £4.00 per kW/h but most are about £2.25 per kW;h.
>
> 1b. The Flux/IF tariffs mean I would lose part of my FIT worth around
> £150 a year – are there any tariffs that would still allow that ?

Sorry, Dunno.
>
> [I think Mike must be using Agile which I hadn’t considered, but the
> Octoplus and FIT ?s remain]

The interesting thing is that not only do Octopus Energy pay the Saving
Session Rate, they still pay the agreed Outgoing rate on top!
>
>
> 2. What is the approach for minimum battery level ? I understand you
> don’t want it to fall below 20%, so given that we use around .7kWh
> overnight we would need to keep a minimum level of 3.5kWh in the
> battery, meaning the most we could sell would be 10kWh.

Because we are using up to approx. 40 kW/H per day for the Air Source Heat
Pump to work, we don’t have a great margin but I was paid (or credited)
some £223 for late Oct. - mid December Saving Sessions. I might add that in
this mild weather we are currently enjoying, the daily needs are less than
12 kW/h for heating the whole house to a very comfortable 22.5 degrees C.
>
> 3. Is that possible in 3 hours during the peak period – in other words
> is there a max. rate at which you can transfer back to the grid ?

I have the battery set up by Tesla (carried out remotely for me) to allow
me to export ‘everything’ and this enable me to push up to 10 kW/h to the
grid.
>
> 4. What happens during a nice sunny day when the battery is full by
> lunchtime but I am still generating – does that get sold directly to the
> grid at the non-peak rate or what ?

OE pay me the Outgoing rate of 15 pence per kW/H (but I don’t have any FIT
contract to complicate things).
>
> 5. Intelligent Flux seems good as it allegedly understands my needs and
> decides what to sell and when to maximise my income and also doesn’t
> topup overnight if the forecast is for sun the next day, but does the
> Tesla have all those smarts too ?

Without an EV, certain tariffs are out of my reach. I understand that OE
are in the throes of adding the Powerwall to their list of addressable
equipment then all the ‘smarts’ should come on line I suppose.
>
> 6. If so, can you switch back and forth between IF and Flux depending on
> time of year to benefit from much lower topup rates in winter when you
> use them more and higher selling rates in summer when you rarely need to
> topup

IAW, Yes. Unless any restrictions are applicable when moving between
certain combinations.
>
> 7. In the Tesla app how much control do you have over all this ? I
> cannot find a good description or demo of it, only that it takes account
> of weather forecasts for the next day, and no doubt uses some clever AI.
> But no matter how clever it is, it will still not know all that I know
> e.g. that I am going away for a week so usage will be low, so sell,
> sell, sell, or that we are having a family do tomorrow so the oven will
> be in use a lot.

I find that I can manipulate certain functions to suit my need - more so
since they set mine to be able to export ‘everything’ as they call it.
>
> 8. Does anyone know of any spreadsheets available that will model all
> this based on real data rather than a salesperson’s rosy projections ?

I haven’t tried it but someone has just issued a new app that allows
comparison between the different tariffs.

> I am going to give it a try in my spreadsheet where I already have the
> actual generation/usage data for a whole year, but it will be hard, esp.
> the weather forecasting bit – I can be 100% accurate as I know what
> actually happens the next day but what was the forecast saying the night
> before ??? There’s also the question of how you handle the fact that you
> are still generating between 4 and 7 (and indeed much later with our
> unshaded SW facing array) so would not have to worry about the 3.5kWh
> reserve, at least at the start of the peak rate payback.
>
> I also would need to reconsider our heating strategy – currently we use
> our gas CH set at 19C for a morning warmup and 20C in the evenings,
> supplemented by a fan heater on a smart switch to heat the living room
> (which has been great the last few days), a fire in the woodburner on
> cold afternoons (also the last few days !) or a 30 minute blast from the
> gas CH. If you have free/cheap power in the battery though, you can use
> electric heating in the places and at times you actually need it and
> keep the CH at much lower background levels. I am currently using
> max/min thermometer to measure how warm/cold each room is on the current
> schedule to see what would make sense.
We are all-electric now, no gas - no gas meter!
>
> Although I disagree profoundly with Net Zero on the basis of its
> feasibility (and it seems from today’s news that the Royal Society also
> questions the CCC models) I am not against renewables per se and am
> happy to add a battery to help smooth the load on the grid, but only if
> it makes financial sense for us personally. I know it would add to the
> value of the house, but we’d have to pay for this out of our savings
> which means we’d lose interest on that sum for the rest of our lifetimes
> and of course a battery is not likely to last as long as a solar panel.

On 24/01/2024 15:46, Mike McMillan wrote:
> BrritSki <rtilburyTAKEOUT@gmail.com> wrote:
>> On 22/01/2024 16:11, Mike McMillan wrote:
>>>
>>> https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
>>>
>>> Please excuse the (not my( typos, the Webmaster was using a Merkin spill
>>> chicken which went through my article and nuggered a few worms. They left
>>> me intact and krect!
>>>
> Find a cup / glass of your favourite beverage / tipple, sit back and be
> prepared to lose a few minutes of your valuable life - I hope the loss will
> nevertheless, be of interest and a form of gain into the bargain.;-)))
>
Wow, lots of info to digest there, thanks for taking the trouble to
answer so fully.

I'll read again tomorrow and reply in detail - I've also discovered more
stuff since I wrote that and am close to completing the re-working of my
spreadsheet, so it's good to have the actual import and export rates to
plug in.

Thanks again...

In message <l1d24cFj56oU2@mid.individual.net> at Wed, 24 Jan 2024
18:10:21, BrritSki <rtilburyTAKEOUT@gmail.com> writes
[]
>I'll read again tomorrow and reply in detail - I've also discovered
>more stuff since I wrote that and am close to completing the re-working
>of my spreadsheet, so it's good to have the actual import and export
>rates to plug in.
[]
Just a quickie: I know you get less out of a battery than you put in
(though I don't know what percentage - do you?), but I'm guessing the
varying rates _might_ compensate for that: so, is it possible to make
money by charging from the grid at cheap times, and selling back at
others? Since there's been mention of actually being paid to consume at
times, I presume it is possible, but maybe not enough to be worth the
bother?

Independent of solar, that is.

Oh - does anyone here have their own wind turbine?
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

"Purgamentum init, exit purgamentum." Translation: "Garbage in, garbage out."

J. P. Gilliver <G6JPG@255soft.uk> wrote:
> In message <l1d24cFj56oU2@mid.individual.net> at Wed, 24 Jan 2024
> 18:10:21, BrritSki <rtilburyTAKEOUT@gmail.com> writes
> []
>> I'll read again tomorrow and reply in detail - I've also discovered
>> more stuff since I wrote that and am close to completing the re-working
>> of my spreadsheet, so it's good to have the actual import and export
>> rates to plug in.
> []
> Just a quickie: I know you get less out of a battery than you put in
> (though I don't know what percentage - do you?), but I'm guessing the
> varying rates _might_ compensate for that: so, is it possible to make
> money by charging from the grid at cheap times, and selling back at
> others? Since there's been mention of actually being paid to consume at
> times, I presume it is possible, but maybe not enough to be worth the
> bother?
>
> Independent of solar, that is.
>
> Oh - does anyone here have their own wind turbine?

The ‘Round Trip’ for converting the AC in to DC low voltage and then taken
the low voltage from the battery and inverting it to 240 AC to use is
reckoned to be ITRO 10% (maybe a little less, but that is a working
figure). Charging during the lowest rate in the tariff and ‘selling back’
at the highest rate can be a ratio 3:1 and much higher during ‘saving
sessions’ where the rate is likely to exceed £2 per kW/h. Even allowing for
the conversion / storage / re-conversion costs, this can be very
attractive.(i.e., the £232 I was credited with cost me about £4 or 5.) I
also received the normal exported energy rate of 15 p. per kW/h on top of
this. I like saving sessions - and ‘helping the grid out’;-)))

--
Toodle Pip, Mike McMillan

On Wed, 24 Jan 2024 18:53:20 +0000, J. P. Gilliver wrote:

> Oh - does anyone here have their own wind turbine?

Wind turbines have economies of scale - doubling the power output does not
double the cost - so small ones are unlikely to be economical except for
special cases like off-grid living.

Solar panels have a much closer to linear cost-power relationship so small
scale ones are worthwhile.

--
Jim <http://www.jim-easterbrook.me.uk/>
1959/1985? M B+ G+ A L- I- S- P-- CH0(p) Ar++ T+ H0 Q--- Sh0

In message <l1dfnaFc3ipU1@mid.individual.net> at Wed, 24 Jan 2024
22:02:18, Jim Easterbrook <news@jim-easterbrook.me.uk> writes
>On Wed, 24 Jan 2024 18:53:20 +0000, J. P. Gilliver wrote:
>
>> Oh - does anyone here have their own wind turbine?
>
>Wind turbines have economies of scale - doubling the power output does not
>double the cost - so small ones are unlikely to be economical except for
>special cases like off-grid living.
>
>Solar panels have a much closer to linear cost-power relationship so small
>scale ones are worthwhile.
>
I can't help thinking there's a lot of work still to be done in the
small-scale turbine area, though - maybe the vertical-axis ones, for
example. As with - primarily shore-based, so "rectification" can be
implemented - wave power. (And of course tidal.)
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

I'd rather trust the guys in the lab coats who aren't demanding that I get up
early on Sundays to apologize for being human.
-- Captain Splendid (quoted by "The Real Bev" in mozilla.general, 2014-11-16)

J. P. Gilliver wrote:

>I can't help thinking there's a lot of work still to be done in the
>small-scale turbine area, though - maybe the vertical-axis ones, for
>example.

Here is a video on the subject:

<https://www.youtube.com/watch?v=SQKHJm7vd4E>

If you browse his channel you will find lots of energy-related
and interesting stuff.

Chris
--
Chris J Dixon Nottingham
'48/33 M B+ G++ A L(-) I S-- CH0(--)(p) Ar- T+ H0 ?Q
chris@cdixon.me.uk @ChrisJDixon1
Plant amazing Acers.

Chris J Dixon <chris@cdixon.me.uk> wrote:
> J. P. Gilliver wrote:
>
>> I can't help thinking there's a lot of work still to be done in the
>> small-scale turbine area, though - maybe the vertical-axis ones, for
>> example.
>
> Here is a video on the subject:
>
> <https://www.youtube.com/watch?v=SQKHJm7vd4E>
>
> If you browse his channel you will find lots of energy-related
> and interesting stuff.
>
> Chris

I find Matt Ferrell very interesting and he researches his subjects well
too.

--
Toodle Pip, Mike McMillan

On 25/01/2024 08:43, Chris J Dixon wrote:
> J. P. Gilliver wrote:
>
>> I can't help thinking there's a lot of work still to be done in the
>> small-scale turbine area, though - maybe the vertical-axis ones, for
>> example.
>
> Here is a video on the subject:
>
> <https://www.youtube.com/watch?v=SQKHJm7vd4E>
>
> If you browse his channel you will find lots of energy-related
> and interesting stuff.
>
yes, I follow him and also a entertainingly dotty British inventor who
has done a lot of work on small scale turbines. Forget his name for the
moment - double-barreled, but he's got lots of good stuff.

There's also Kris Harbour who has some excellent videos about hos wind
turbines (home made) as well as his water turbines, including a big one
he's just built for a client in Cumbria I think.

In message <uot8bs$28agj$1@dont-email.me> at Thu, 25 Jan 2024 09:07:08,
Mike McMillan <toodle.pip1@virginmedia.com> writes
>Chris J Dixon <chris@cdixon.me.uk> wrote:
>> J. P. Gilliver wrote:
>>
>>> I can't help thinking there's a lot of work still to be done in the
>>> small-scale turbine area, though - maybe the vertical-axis ones, for
>>> example.
>>
>> Here is a video on the subject:
>>
>> <https://www.youtube.com/watch?v=SQKHJm7vd4E>
>>
>> If you browse his channel you will find lots of energy-related
>> and interesting stuff.
>>
>> Chris
>
>I find Matt Ferrell very interesting and he researches his subjects well
>too.
>
Thanks for the link. I fear it's always something that's nearly ready;
however, unlike cold fusion (which will be along in the next ten years -
and that's been the case for the last fifty!), I think it really _is_
going to move soon. The increasing cost of energy might give the final
push. (Not to mention the silly Net Zero initiatives - not that I think
the _aim_ is wrong, quite the reverse, but the way things are gone about
often is. And as for the abuse of the word carbon ...)

I hope UK planning authorities are forced to keep up, though.
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

"Does Barbie come with Ken?"
"Barbie comes with G.I. Joe. She fakes it with Ken." - anonymous

On 24/01/2024 15:46, Mike McMillan wrote:
> BrritSki <rtilburyTAKEOUT@gmail.com> wrote:
>> On 22/01/2024 16:11, Mike McMillan wrote:
>>>
>>> https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
>>>
> I’ll give you the figures from my Octopus Energy app ...

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 – I am happy doing this myself
(and can see!), but waife wouldn’t although she’d be perfectly capable
(and can also see), and I will probably work up a simple flowchart of
things to check like next day’s 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 wasn’t 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
– probably not, but worth an email.

The COSY rate was close to what I was assuming – 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 – under a fiver for the whole of Aug 21- Jul
22 – 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 there’s 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
today’s 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
under £5. Cost of electricity for overnight topup £77, but last year we
spent about £55 overnight already from using dishwasher when it’s not
sunny and is full. We also spent another £500 on daytime electricity. So
overall we’d save about £500 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 £370 during the 4-7PM peak and another £190 from
spare generation capacity during the day, but that would be offset by
the loss of £150 deemed export FIT payment, so net income would be £410.

The total saving therefore on a very pessimistic basis are over £900, so
a payback period of 9 years which is much more acceptable. The thing I
haven’t 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 – 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 £75 to subtract from the gains, adding another year to the
ROI period. On the upside I haven’t 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 “losing” £640 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 year’s data so I don’t
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 – I am actually surprised at the result which I
think is a good thing !

[1] Do you restrict the max. on your batteries ? I know for battery
longevity it’s 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.
capacity.

[2] Same question for keeping minimum above a certain level – worthwhile
? 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
£100 of income approx..

[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 £2.25 per kWh you
mentioned Mike), but I don’t 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
don’t benefit surely ? 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 ?

BrritSki <rtilburyTAKEOUT@gmail.com> wrote:
> On 24/01/2024 15:46, Mike McMillan wrote:
>> BrritSki <rtilburyTAKEOUT@gmail.com> wrote:
>>> On 22/01/2024 16:11, Mike McMillan wrote:
>>>>
>>>> https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
>>>>
>> I’ll give you the figures from my Octopus Energy app ...
>
> 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 – I am happy doing this myself
> (and can see!), but waife wouldn’t although she’d be perfectly capable
> (and can also see), and I will probably work up a simple flowchart of
> things to check like next day’s weather, state of battery, likely usage

Right, have you your beverage / tipple ready - then let’s begin!
> 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.
Yes, it looks as though OE are going to exploit the capabilities of their
Kraken system and Powerwall app in the near future which may open some new
possibilities - such a fluid world!
>
> I wasn’t 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
> – probably not, but worth an email.

I have managed to stay within the 2 x 3 hour lowest charge bands so far; I
can ‘extract’ or ‘download’ to the Powerwalls at up to 10 kW/s as each
unit can suck in or blow out 5 kW/h to the grid. Usually, my battery will
recharge to 100% in a little over 2 hours as I haven’t run it down below
about 20 - 25 % most days. As a result, during the other 18 hours of higher
rate bands, we are using battery power only. (I have not spotted any
recourse to the grid during the early hours when the heat pump calls for up
to 2 kW for a few minutes. Powerwalls are charged to ‘100%’ which I suspect
is a useable charge level and that that leaves a margin below peak fill-up
if you see what I mean. I normally have mine set to reserve 20% for
eventualities like power outages though we have not had more than a few
minutes at a time as yet and we have been totally unaware of these as we
would have to look outside to notice other have lost power! When we have
had SS’s, I have set the reserve down as low as 5% (approx 1.35 kW/h) so
that the heat pump can continue to use the battery power until the Cosy
cheapest rate comes into use at 04:00 - whereupon, the battery is ready to
charge up to approx 26 kW/h over the 3 hour slot.
>
> The COSY rate was close to what I was assuming – 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 – under a fiver for the whole of Aug 21- Jul
> 22 – 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]

I think that pessimistic is the way to go and then any surprises are likely
to be pleasant ones and less likely to ‘sway’ your judgement if the figures
are in fine balance for and against a choice!
>
> For Export, I have assumed 8p for daytime and 15p for the peak 4-6PM
> hours. Again, very pessimistic I think, so there’s only an upside.

Outgoing Fixed is 15p.at all times.
>
> 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].

Fair enough.
>
> I then did a guesstimate of likely gen the next day (based on a third of
> today’s 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.

A crystal ball is on order - but no delivery date promised as yet!
>
> The results are surprising to say the least. Cost of daytime electricity
> under £5. Cost of electricity for overnight topup £77, but last year we
> spent about £55 overnight already from using dishwasher when it’s not
> sunny and is full. We also spent another £500 on daytime electricity. So
> overall we’d save about £500 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%.
These figure - daily, weekly, monthly or yearly?
>
> Export would earn us £370 during the 4-7PM peak and another £190 from
> spare generation capacity during the day, but that would be offset by
> the loss of £150 deemed export FIT payment, so net income would be £410.

FIT is an unknown world to me.
>
> The total saving therefore on a very pessimistic basis are over £900, so
> a payback period of 9 years which is much more acceptable. The thing I
> haven’t 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 – 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 £75 to subtract from the gains, adding another year to the
> ROI period. On the upside I haven’t considered any additional savings
> from savings sessions (see [3] below) or the rare occasions when you are
> being paid to import power.

All these variable could be put on a database - and as they are still
dependent on so many other variables…. Perhaps gut feelings are still worth
considering? With energy charges so volatile and an election year upon us,
who knows what may happen? I think we just have to take the most
pessimistic figures and see if the gamble is worth risking or not.:-(((
>
> 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 “losing” £640 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.

We were fortunate in having funds we had saved and at the time of our
plunge interest rates were so low - there was little need to give it more
than a little thought - we did consider - but it wasn’t a difficult
decision to make.
>
> I should really do this exercise again using last year’s data so I don’t
> 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

Oh! You mean like to very frequent way that the Cost of Living Index is
manipulated so that comparison year to year is difficult and open to abuse!
(Me -cynical?!)
>
> 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 – I am actually surprised at the result which I
> think is a good thing !
>
> [1] Do you restrict the max. on your batteries ? I know for battery
> longevity it’s 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.
> capacity.
I am using the Tesla Powerwall app settings and I suspect the ‘100%’ allows
for this (as mentioned above) as these are their settings rather than mine.
Now I have the Powerwalls set by Tesla Customer Services EU. (Or some
such), I am able to Export ‘Everything’ rather than just Solar, and I can
export at any time I choose and this is how I help the grid out during
SS’s. I did not have my Powerwall set until early December so could not
export much at chosen times or my refund would have been higher. (Including
last week’s session, I have now had £267.95 over 9 SS’s. This might have
reached about £400 had I had ‘everything’ set by Tesla earlier.
>
> [2] Same question for keeping minimum above a certain level – worthwhile
> ? 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
> £100 of income approx..
>
> [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 £2.25 per kWh you
> mentioned Mike), but I don’t 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
> don’t benefit surely ? 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 ?

On 25-Jan-24 11:32, J. P. Gilliver wrote:

> Thanks for the link. I fear it's always something that's nearly ready;
> however, unlike cold fusion (which will be along in the next ten years -
> and that's been the case for the last fifty!), I think it really _is_
> going to move soon. The increasing cost of energy might give the final
> push. (Not to mention the silly Net Zero initiatives - not that I think
> the _aim_ is wrong, quite the reverse, but the way things are gone about
> often is. And as for the abuse of the word carbon ...)

I remember when the greatest misuse of "carbon", was when referring to
what should be called "Carbon Paper".

Harrumph and Pshaw!

--
Sam Plusnet

On 26-Jan-24 18:16, Mike McMillan wrote:

There will come a day when individuals who act to support the Nation's
power network (taking no power when it is scarce, but supplying power
when available) will be recognised as public benefactors.
There might be an OBE in it for you Mike.

--
Sam Plusnet

Sam Plusnet <not@home.com> wrote:
> On 26-Jan-24 18:16, Mike McMillan wrote:
>
> There will come a day when individuals who act to support the Nation's
> power network (taking no power when it is scarce, but supplying power
> when available) will be recognised as public benefactors.
> There might be an OBE in it for you Mike.
>

Did I???!!!

--
Toodle Pip, Mike McMillan

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:
>>>>
>>>> https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
>>>>
>> I’ll give you the figures from my Octopus Energy app ...
>
> 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 – I am happy doing this myself
> (and can see!), but waife wouldn’t although she’d be perfectly capable
> (and can also see), and I will probably work up a simple flowchart of
> things to check like next day’s 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 wasn’t 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
> – probably not, but worth an email.
>
> The COSY rate was close to what I was assuming – 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 – under a fiver for the whole of Aug 21- Jul
> 22 – 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 there’s 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
> today’s 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 £5. Cost of electricity for overnight topup £77, but last year we
> spent about £55 overnight already from using dishwasher when it’s not
> sunny and is full. We also spent another £500 on daytime electricity. So
> overall we’d save about £500 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 £370 during the 4-7PM peak and another £190 from
> spare generation capacity during the day, but that would be offset by
> the loss of £150 deemed export FIT payment, so net income would be £410.
>
> The total saving therefore on a very pessimistic basis are over £900, so
> a payback period of 9 years which is much more acceptable. The thing I
> haven’t 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 – 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 £75 to subtract from the gains, adding another year to the
> ROI period. On the upside I haven’t 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 “losing” £640 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 year’s data so I don’t
> 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 – I am actually surprised at the result which I
> think is a good thing !
>
> [1] Do you restrict the max. on your batteries ?  I know for battery
> longevity it’s 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.
> capacity.
>
> [2] Same question for keeping minimum above a certain level – worthwhile
> ?  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
> £100 of income approx..
>
> [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 £2.25 per kWh you
> mentioned Mike), but I don’t 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
> don’t benefit surely ?  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 ?
>
>

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:
>>>>>
>>>>> https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
>>>>>
>>> I’ll give you the figures from my Octopus Energy app ...
>>
>> 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 – I am happy doing this myself
>> (and can see!), but waife wouldn’t although she’d be perfectly capable
>> (and can also see), and I will probably work up a simple flowchart of
>> things to check like next day’s 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 wasn’t 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
>> – probably not, but worth an email.
>>
>> The COSY rate was close to what I was assuming – 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 – under a fiver for the whole of Aug 21- Jul
>> 22 – 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 there’s 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
>> today’s 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 £5. Cost of electricity for overnight topup £77, but last year we
>> spent about £55 overnight already from using dishwasher when it’s not
>> sunny and is full. We also spent another £500 on daytime electricity. So
>> overall we’d save about £500 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 £370 during the 4-7PM peak and another £190 from
>> spare generation capacity during the day, but that would be offset by
>> the loss of £150 deemed export FIT payment, so net income would be £410.
>>
>> The total saving therefore on a very pessimistic basis are over £900, so
>> a payback period of 9 years which is much more acceptable. The thing I
>> haven’t 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 – 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 £75 to subtract from the gains, adding another year to the
>> ROI period. On the upside I haven’t 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 “losing” £640 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 year’s data so I don’t
>> 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 – I am actually surprised at the result which I
>> think is a good thing !
>>
>> [1] Do you restrict the max. on your batteries ?  I know for battery
>> longevity it’s 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 don’t know, they certainly
supply the full 13.5 kW/h from full charge anyway. It seems that there is
no “warning’ or zone at 80%.
>> capacity.
>>
>> [2] Same question for keeping minimum above a certain level – worthwhile
>> ?  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
>> £100 of income approx..
>>
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.

>> [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 £2.25 per kWh you
>> mentioned Mike), but I don’t 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
>> don’t benefit surely ?  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 ?
>>
>>
>
>
I have only had full control over ‘everything’ as Tesla call it since early
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 SS’s at this time of
year!

On 31/01/2024 15:46, Mike McMillan wrote:
> As I replied before, Tesla allow a charge up to 100%
....
Ooops, I seem to have missed this reply before. Thanks again.

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:
>>>>>>
>>>>>> https://renewableheatinghub.co.uk/green-transformation-my-journey-to-a-sustainable-and-energy-efficient-home
>>>>>>
>>>> I’ll give you the figures from my Octopus Energy app ...
>>>
>>> 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 – I am happy doing this myself
>>> (and can see!), but waife wouldn’t although she’d be perfectly capable
>>> (and can also see), and I will probably work up a simple flowchart of
>>> things to check like next day’s 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 wasn’t 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
>>> – probably not, but worth an email.
>>>
>>> The COSY rate was close to what I was assuming – 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 – under a fiver for the whole of Aug 21- Jul
>>> 22 – 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 there’s 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
>>> today’s 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 £5. Cost of electricity for overnight topup £77, but last year we
>>> spent about £55 overnight already from using dishwasher when it’s not
>>> sunny and is full. We also spent another £500 on daytime electricity. So
>>> overall we’d save about £500 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 £370 during the 4-7PM peak and another £190 from
>>> spare generation capacity during the day, but that would be offset by
>>> the loss of £150 deemed export FIT payment, so net income would be £410.
>>>
>>> The total saving therefore on a very pessimistic basis are over £900, so
>>> a payback period of 9 years which is much more acceptable. The thing I
>>> haven’t 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 – 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 £75 to subtract from the gains, adding another year to the
>>> ROI period. On the upside I haven’t 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 “losing” £640 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 year’s data so I don’t
>>> 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 – I am actually surprised at the result which I
>>> think is a good thing !
>>>
>>> [1] Do you restrict the max. on your batteries ?  I know for battery
>>> longevity it’s 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 don’t know, they certainly
> supply the full 13.5 kW/h from full charge anyway. It seems that there is
> no “warning’ or zone at 80%.
>>> capacity.
>>>
>>> [2] Same question for keeping minimum above a certain level – worthwhile
>>> ?  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
>>> £100 of income approx..
>>>
> 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.
>
>>> [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 £2.25 per kWh you
>>> mentioned Mike), but I don’t 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
>>> don’t benefit surely ?  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 ?
>>>
>>>
>>
>>
> I have only had full control over ‘everything’ as Tesla call it since early
> 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 SS’s at this time of
> year!
>
>