On-grid domestic battery storage

zeupater

TrevorL wrote: »

... We changed the figure when more up to date data became available. Further, we favour real-world data over projections. That may be something we have to disagree about, but I posted from an example article that outlined why they expect electricity will keep going up above inflation - and that seems to be the reality that our customers come to us about, not the minimal increases that these projections indicate. Based on the data you gave, and our philosophy, I think a figure of 5.6% would be an appropriate annual increase to use and will not skew the results either way.

Hi

Yet the supporting BEIS data is 'real world', not only that, it's the official view of 'real world' and data tables in 2.2.1 provide you with data for long term trend analysis on a (non inflation adjusted) cash terms basis ...

2007-08 +14.9%
2008-09 +2.3%
2009-10 -2.9%
2010-11 +8.2%
2011-12 +5.7%
2012-13 +6.5%
2013-14 +2.6%
2014-15 -1.5%
2015-16 +0.5%
2016-17 +5.6%

Between 2007 & 2017 the total increase in electricity prices has been 49.2%, a compounded 4.1% yearly, whilst for the more recent period between 2012 & 2017 it's been 14.2%, which resolves to a compounded 2.7% ...

This certainly does not support the assertions in ..

(post#459) .. "I'd be very happy to use a lower rate of price increase if it was justified"
(post #468) .. "Energy prices have been high since a 35% spike in 2008, and price rises have barely slowed down since."
(post #468) .. "I am yet to be convinced that we are seeing any evidence of retail prices actually dropping (doing anything other than going up significantly) .."

... as reasoning for lower increases has been described & justified, price rises have been shown to be 14.9% in 2007-08 as opposed to the 35% raised and convincing data has been provided to evidence years of prices both dropping (2009-10 & 2014-15) & not increasing significantly (2008-09, 2009-10, 2015-16) in real cash terms, thus either in line with, or below the averaged CPIH inflation rate for 2005-2018 of 2.5% ...

HTH
Z

zeupater

TrevorL wrote: »

It's terminology - the 90/10 split day/night means what's outside the E7 tariff period vs what's inside it. Our customers have data on their E7 and daytime consumption from their bills, that's all they can give us.

And the 4200 just represents the value in the model when it was last run - though our demographic certainly tends towards bigger energy use (despite your presumption previously that early adopters would be low energy users) - some of their consumption figures are huge. I'd rerun the model for 3100 if it would be of interest.

Got it, my misunderstanding, sorry.

No, remember what I said about our demographic being people who are out while their solar is generating (we wouldn't advise a battery system for the retired, stay at home mums, etc.) so roughly speaking the first 4 kWh goes into the battery and the rest is lost. These are the customers who are getting the best paybacks.

I don't want to put words in your mouths, but perhaps you can see that from my perspective these arguments seem to be along the lines of 'if it can't work for everyone then it can't work for anyone', yet I was very clear about the subset of households we feel get the most benefit from these systems.

Hi

In order ....

- "... day/night means what's outside the E7 tariff period vs what's inside it" ... absolutely irrelevant when talking about charging batteries or battery capacity on a pure solar basis ... as you can't continue to charge from PV when it's dark, then night must be defined as being the period when there's no sunlight, not when an 'overnight' cheap-rate tariff applies ...

- "so roughly speaking the first 4 kWh goes into the battery and the rest is lost" ... no, you're ignoring the year-round baseload daytime appliances such as fridge, freezer, morning/evening kettles, house alarm, clocks, slow cooker, standby items, boiler, pumps/heat-pumps, timed appliance use etc - and, of course, daytime consumption at weekends ... the primary generation goes to maintain these, batteries should be charged only when there's an excess in generation ... the later rounded data provides an assessment of what excess solar PV energy would be available to storage on a averaged daily daylight weighted basis ... for example, in January an average daylight load (including weekends) of around 500W (4280/8.5hrs) would consume all of the PV output before any would be diverted to charge the batteries .... as mentioned, this has been accounted for in my assessment, however your model, as described, would look to charge the batteries in January with 4kWh which simply doesn't exist!

- "... from my perspective these arguments seem to be along the lines of 'if it can't work for everyone then it can't work for anyone', yet I was very clear about the subset of households we feel get the most benefit from these systems." ... that shouldn't be the case, however you did supply details for an example household where a 4kWp solar pv system had been paired with a high household consumption of 4200kWh which spurred the reply showing that the mismatch results in a particularly poor return in terms of the best performing element (solar) & therefore would need considerable reliance on the secondary element provided by the purchase of comparatively expensive E7 units with the inherent round-trip efficiency losses ...

The approach I have employed is sound to use as a basic sanity check and what it's effectively saying is that domestic batteries do not provide good value to consumers at current prices ... if you would like me to go further & provide a more detailed analysis, I am willing & able to build a comprehensive model which would have similar complexity & functionality to your own as long as you're able to recompense for the development time expended, however, as we are all aware, the result will be broadly similar to what has already been stated!

When storage prices fall to the levels previously mentioned the position will change, however, at anywhere near current market levels the technology simply isn't a viable option on a purely financial basis ...

HTH
Z

Martyn1981

zeupater wrote: »

Hi

When storage prices fall to the levels previously mentioned the position will change, however, at anywhere near current market levels the technology simply isn't a viable option on a purely financial basis ...

HTH
Z

That is sadly my position too. I like the idea of the technology, but can't support it yet on economic grounds.

I still stand by my earlier comment that I wouldn't include inflation in my personal calculations. I feel it is balanced out by cost of capital (perhaps £50-£100 in year 1), and system degradation. I'm not ignoring inflation, just balancing it out against negatives. I also feel quite strongly that the economics of a battery should stack up in year 1, not rely on the addition of later inflationary boosts.

Regarding E7, that too is a bust at the moment since there is no arbitrage benefit when the cost of storage (about 10p/kWh) is included. But, with a TOU deal similar to one mentioned previously, then it gets better.

I'm also not happy about a lot of claims, such as typical payback being 8-14yrs, when I suspect that there have been no customers yet that have reached payback, so this, like the inflationary uplifts is a projection, and most likely is a projection built on the high inflationary uplift projection.

Also for PV'ers, we simply don't have the high leccy import since the direct PV use moves us from medium consumers to low consumers. Though as I've suggested over the last year or so, my shifting to more ASHP use and hopefully an EV could change this.

With regard to the mention of a 4kWh system, that fits nicely with my old calculations also based on a 4kWh system, and taking into account my summer import capping battery benefits, and my winter lack of generation capping battery use. I would see approx 900kWh of savings, or about £135pa - giving a 24yr payback.

Lastly I notice that there has been some deletion of post(s) at the start of this exchange.

TrevorL

This is turning into a frustrating discussion, not helped by moderators deleting my posts. You guys seem to know what the answers are in advance and don't listen to anything that doesn't match your mindset.

zeupater wrote: »

Between 2007 & 2017 the total increase in electricity prices has been 49.2%, a compounded 4.1% yearly, whilst for the more recent period between 2012 & 2017 it's been 14.2%, which resolves to a compounded 2.7% ...

In your opinion that's relevant. I've said many times that in my opinion the ups and downs of the last decade tell us very little about the next. You're not listening, just repeating the same thing over and over again.

zeupater wrote: »

- "... day/night means what's outside the E7 tariff period vs what's inside it" ... absolutely irrelevant when talking about charging batteries or battery capacity on a pure solar basis ... as you can't continue to charge from PV when it's dark, then night must be defined as being the period when there's no sunlight, not when an 'overnight' cheap-rate tariff applies ...

I didn't say it was on a pure solar basis, I said it considers E7 as our E7 customers are those who benefit most. You're not listening.

zeupater wrote: »

- "so roughly speaking the first 4 kWh goes into the battery and the rest is lost" ... no, you're ignoring the year-round baseload daytime appliances such as fridge, freezer, morning/evening kettles, house alarm, clocks, slow cooker, standby items, boiler, pumps/heat-pumps, timed appliance use etc - and, of course, daytime consumption at weekends ... the primary generation goes to maintain these, batteries should be charged only when there's an excess in generation ... the later rounded data provides an assessment of what excess solar PV energy would be available to storage on a averaged daily daylight weighted basis ... for example, in January an average daylight load (including weekends) of around 500W (4280/8.5hrs) would consume all of the PV output before any would be diverted to charge the batteries .... as mentioned, this has been accounted for in my assessment, however your model, as described, would look to charge the batteries in January with 4kWh which simply doesn't exist!

I work from home and my background load is 2-300W. I've explained multiple times that our customers are out during the day but you're not listening. In that case our background load is 50-100W and I would expect theirs to be too.

zeupater wrote: »

- "... from my perspective these arguments seem to be along the lines of 'if it can't work for everyone then it can't work for anyone', yet I was very clear about the subset of households we feel get the most benefit from these systems." ... that shouldn't be the case, however you did supply details for an example household where a 4kWp solar pv system had been paired with a high household consumption of 4200kWh which spurred the reply showing that the mismatch results in a particularly poor return in terms of the best performing element (solar) & therefore would need considerable reliance on the secondary element provided by the purchase of comparatively expensive E7 units with the inherent round-trip efficiency losses ...

This response is wrong in so many ways:
1. So because our customers don't match you then we have the wrong customers?!
2. It's the use of E7 that gives the best payback. I've said that multiple times. You're not listening.
3. I covered in detail how our model covers round-trip losses. You're not listening.

Martyn1981

TrevorL wrote: »

This is turning into a frustrating discussion, not helped by moderators deleting my posts. You guys seem to know what the answers are in advance and don't listen to anything that doesn't match your mindset.

So the customer is always wrong? Your argument for payback requires external factors - very high inflation, a life expectancy well past the warranty period, charge cycles well past the figure your site suggests:

The batteries have a cycle life of 6000 cycles at 100% depth of discharge (DOD),

So the customer takes all the risk on payback based on claims and assumptions that you make. If you are so certain that the batts will last longer and have more cycles, then warranty them for it, by all means have a descending capacity figure, but back up your claims which are essential for payback. Also back up your high inflation figure (since it's essential to payback) with an independently held insurance guarantee .....

...... or drop all the 'whataboutery' and simply sell based on actual figures, not optimistic ideals.

TrevorL wrote: »

In your opinion that's relevant. I've said many times that in my opinion the ups and downs of the last decade tell us very little about the next. You're not listening, just repeating the same thing over and over again.

But the opposing view to yours is based on facts and events. We've seen the impact on bills from the rollout of low carbon generation via the green levies. So we can learn from the past.

We can also learn from the present by taking account of the rapidly falling costs of RE, and the max wholesale price possible based simply on the HPC nuclear option of £100/MWh (valid through to the 2060's) - taking that worst case price we see an increase in wholesale prices from ~4p to 10p, and a 6p/kWh increase on retail prices (plus 'normal' inflation), so about 40% over a long time period.

I haven't forgotten that all of my info providing support for the lower and slower price increases, supported by repeated NAO reports was dismissed entirely by you as 'out of date' - so you have avoided/failed to provide any argument whatsoever to support an abnormally high inflation rate for energy.

I find it telling that I don't believe payback can be achieved yet based on current economics, and you are pushing so hard for an inflationary increase that is beyond reasonable - it's almost as if you too doubt payback without some sort of 'bonus' external factor? And that's not a bad thing, we'd all then be in agreement and looking forward to the day when the economics stand up on their own.

TrevorL wrote: »

I didn't say it was on a pure solar basis, I said it considers E7 as our E7 customers are those who benefit most. You're not listening.

Pot meet kettle!

At this point in time, with the cycle life your site states as being 6,000, E7 arbitrage is pointless since the cost of cycling the batts adds ~10p/kWh.

If E7 or something like it survives, and batt costs fall, then I do see an important place for this service, but at this point in time it is an invalid argument, and like your other claims is external to the batt deal leaving the customer to take the risk of this being useful, or not.

TrevorL wrote: »

I work from home and my background load is 2-300W. I've explained multiple times that our customers are out during the day but you're not listening. In that case our background load is 50-100W and I would expect theirs to be too.

Actually, over time, you've shifted the dialogue to customers being out, but regardless, on these threads there is about 10yrs worth of advice on how to make the most of a solar system when out. If your customers make no attempt to use the solar during the day, then I'd suggest using E7 at night would be more cost effective at this point in time than a battery storage system.

If your customers are more opened minded, then they should be running the items during the day with the battery reducing the risk of import, but we've already ascertained from you that your customers are not capable of organising leccy use in this way!

TrevorL wrote: »

This response is wrong in so many ways:
1. So because our customers don't match you then we have the wrong customers?!
2. It's the use of E7 that gives the best payback. I've said that multiple times. You're not listening.
3. I covered in detail how our model covers round-trip losses. You're not listening.

How do you know what your customers do or don't do, since it's clear you don't listen to potential customers. There's a whole pack of us keen to get storage (when economical), but said pack is also well aware of high inflationary uplift miss selling.

E7 at this point in time does not give a good payback, or best payback, how does buying leccy at ~7p/KWh work out better than using PV at 0p/kWh? And on that issue do you warn your customers that PV leccy will cost them a little over 5p/kWh if export is metered (something that posters on here have experienced depending on supply company and smart meter installation)?

zeupater

TrevorL wrote: »

This is turning into a frustrating discussion, not helped by moderators deleting my posts. You guys seem to know what the answers are in advance and don't listen to anything that doesn't match your mindset.

You're not listening. I didn't say it was on a pure solar basis, I said it considers E7 as our E7 customers are those who benefit most.


I work from home and my background load is 2-300W. I've explained multiple times that our customers are out during the day but you're not listening. In that case our background load is 50-100W and I would expect theirs to be too.

This response is wrong in so many ways:
1. So because our customers don't match you then we have the wrong customers?!
2. It's the use of E7 that gives the best payback.
3. I covered in detail how our model covers round-trip losses. You're not listening.

Hi

I'm sorry you feel frustrated, that's not my intent ... I'm attempting to take you on a step-by-step journey of the logic that should be applied to ensure that your modelling provides a view which would be accurate enough for consumers to make their decisions ...

Observations have to be made on the following points related to the examples you have given ...

- Prediction of future energy price inflation
- Solar contribution
- E7 contribution

Firstly, the inflationary assumptions should not be used to enhance the future savings & therefore shorten the potential 'payback' timescales ... information has been provided to suggest what would be considered to be more realistic than simply chasing & referencing the highest available published figure or grabbing a figure from the previous year ... you wouldn't have wanted to apply a long-term deflationary percentage of -1.5% if we were having this discussion in 2016 (BEIS 2014-15 data) because it doesn't represent a medium term average and would therefore be unfair and that's effectively what we've been discussing ... is/was it fair to apply an average 8.4% over a term of maybe 10 to 30 years? ... Agree? ...

Secondly, we've been discussing battery system installations to enhance & support solar PV installations and the potential payback period when winter period generation shortfall is supported by 'off peak' discounted tariffs such as E7 .. Agree? ... if so, it's no use even looking at the E7 element until we get a handle on the shortfall pattern that would likely exist that E7 could fill ... Agree? ... therefore the logical step is to initially concentrate on the solar PV element ....

If there's agreement to this point (and there should be!), then we need to establish the storage/PV foundation facts that ...

(i) - If power demand is greater than power generation, the battery cannot be charged.

(ii) - The rate of battery charge is a function of (Generation-Demand) and limited to the battery system maximum charge rate according to a charge curve algorithm ... for example if there's 20kWp PV system but the battery charge is limited to (say) 3kW, then the maximum rate of charge will be 3kW, typically tailing off as the battery passes a threshold of around 80% ...

(iii) - The maximum charge is limited to both the battery capacity and the ability of a suitable sized PV array to support that capacity. There is the potential for cycling capacity during daylight hours to meet demand, but this would require there to be PV generation available to replace what's been used.

(iv) - Solar generation over a month does not conform to a model where PVGIS daily data can be applied evenly - this has not been raised in detail yet, but must be recognised as the effects will be raised further down the path, if you're interested!

Okay, so to the data used in the previous 4200kWh annual demand with 4kWp solar PV +xkWh battery example ... for simplicity we'll leave power charge rate constrictions aside for the moment & simply concentrate on energy ...

- Your monthly solar PVGIS generation data pattern ...4.28, 6.53, 10.90, 13.80, 14.70, 15.10, 14.60, 12.60, 11.50, 8.22, 5.49, 3.85
... suggests that it's a 4kWp system & an analysis of the data resolves to 3703kWh to be the expected annual generation. If there was absolutely no daylight household power demand and all daily generation was even, then that sets the maximum upper limit for daily cycles as 1460kWh(4*365) ... in the real world, supplementing daytime power shortfalls from the battery would increase the number of daily cycles, but conversely also reduce the level of generation available to divert to the batteries for evening/overnight consumption, particularly during months with short daylight hours & on dull days throughout the year ...

With the earlier analysis two 4kWp monthly data sets were extracted directly from your data based on an averaged 5.8kW of total daylight demand, which when sub-analysed & apportioned by available daylight hours in each day in each month were presented as ...
A - 0 0 4 7 8 9 8 7 5 2 0 0
B - 0 0 2 4 4 4 4 4 4 1 0 0

Data set A represents the total amount of energy which would be available to an unlimited storage capacity if the PVGIS data is used and 'real world' daily variability is disregarded at the moment ... this resolves to an estimated upper limit from 4kWp of solar PV which can be available to storage of 1529kWh/year.

Data set B sets a low range position based on a 2.5kWh single battery pack (your entry point solution) ... note, allowance has been made for multiple cycles on days where the PVGIS data suggests that solar generation is sufficient to allow the process ... ie for 6 months of the year the 2.5kWh battery is cycling at an an equivalent of 1.6(4/2.5) times per day ... this resolves to an estimated upper limit for 4kWp of solar PV which can be available to a limited 2.5kWh of storage of 825kWh/year.

This analysis is based on your own generating figures and should approximate to the solar PV contribution in your own model if it doesn't allow for daily generation variability, which does affect the figures, but when we've agreed this step in the basic methodology, we can address the effect of that later .... consequentially, that's also before addressing the E7!

I fully understand the issue, and as can be deduced, I certainly am listening! ...

---

Regarding .. "I work from home and my background load is 2-300W. I've explained multiple times that our customers are out during the day but you're not listening. In that case our background load is 50-100W and I would expect theirs to be too." ... I'm at home at the moment, and our current load is 260W, that's 130W to baseload+50"TV+Laptop & the rest providing ~750W of background heating ... we're generating 191W (14:44 that's 1.64kWh so far today) and therefore would be drawing 170W from storage if it were available ... that's described a position where we're not likely to have too much to divert to storage today, regardless of what our PVGIS target may be ... so, back to the 4200kWh/year customer .... lets apply a basic sanity check ... 8-16 out, 16-24 home&awake & 24-8 home&asleep ... with 16Hrs effectively being at a "background load is 50-100W" (assume 100W), that accounts for 1.6kWh of a daily demand of 11.5kWh(4200/365), describing an average load over the remaining 8 hours of around 1.2kW((11.5-1.6)/8) ... weighing this against your own 2-300W average daytime load tends towards describing how irrelevant the comparison is ... now, apportioning parts of that 11.5kWh to weekends, light evenings & timed devices would reduce the 1.2kW 8Hr load, by how much, well that's for the data to explain away, but it's relevant to convey that for much of the year the home is actually occupied even when it's still light, therefore the average 1.2kW load actually applies ... obviously, there's also another consideration, in consuming 11.5kWh over 8 hours of occupancy, if this is due to high parallel loads (select from - cooker+hob+kettle+washing machine+tumble drier+toaster etc) then when the battery power delivery capability to deliver is surpassed, the household will revert to consuming energy at daytime tariff rates ...

HTH
Z

TrevorL

You're still not listening so this is likely pointless.

Martyn1981 wrote: »

So the customer is always wrong?

I've said a bunch of times you are not our customer. Each time you keep saying that it doesn't work for you. Frustrating doesn't cover it.

Martyn1981 wrote: »

Your argument for payback requires external factors - very high inflation, a life expectancy well past the warranty period, charge cycles well past the figure your site suggests:

6000 cycles is at 100% DOD, our system uses 90% DOD as it says on the same page. But whatever. I've already explained in detail why I don't consider cycle life to be a useful metric. But you're not listening, just repeating.

Martyn1981 wrote: »

At this point in time, with the cycle life your site states as being 6,000, E7 arbitrage is pointless since the cost of cycling the batts adds ~10p/kWh.

And repeat.

Martyn1981 wrote: »

If your customers make no attempt to use the solar during the day, then I'd suggest using E7 at night would be more cost effective at this point in time than a battery storage system.

If your customers are more opened minded, then they should be running the items during the day with the battery reducing the risk of import, but we've already ascertained from you that your customers are not capable of organising leccy use in this way!

I've said repeatedly our typical customer is already on E7, but you're not listening. And no they don't want to be running their dishwasher in the middle of the night, they just want a battery so they don't have to think about it.

Martyn1981 wrote: »

How do you know what your customers do or don't do, since it's clear you don't listen to potential customers. There's a whole pack of us keen to get storage

And again, you are not our current customer.

Martyn1981 wrote: »

E7 at this point in time does not give a good payback, or best payback, how does buying leccy at ~7p/KWh work out better than using PV at 0p/kWh?

And again - who said 7p is better than 0p? You're making facetious arguments. The bulk of the benefit comes from solar in summer but needs to be supplemented with E7 in the winter to optimise payback, but I said that 10 times and you're not listening.

TrevorL

zeupater wrote: »

is/was it fair to apply an average 8.4% over a term of maybe 10 to 30 years? ... Agree? ...

I proposed 5.6% but you weren't listening.

zeupater wrote: »

Secondly, we've been discussing battery system installations to enhance & support solar PV installations and the potential payback period when winter period generation shortfall is supported by 'off peak' discounted tariffs such as E7 .. Agree? ... if so, it's no use even looking at the E7 element until we get a handle on the shortfall pattern that would likely exist that E7 could fill ... Agree? ... therefore the logical step is to initially concentrate on the solar PV element ....

I don't understand the model you describe. Ours considers each month through the year, dividing the monthly expected generation by the number of days in the month. It assumes one cycle of the battery per day, with the day's solar generation going into the battery considering the round trip efficiency, the battery capacity, the 24hr/E7 night/day and standing charges, and the annual degradation. Where there isn't enough solar to fill the battery it calculates how much E7 to use to optimise savings for the month. It sums the months across the year and then projects forward savings over the next 20 years considering the decreasing battery capacity and increasing price. Then it cycles through potential battery sizes to produce a table of savings, ROI and paybacks for each battery size for 24 hr tariff plus battery / 24hr moving to Eco7 plus battery / Eco7 plus battery.

Martyn1981

TrevorL wrote: »

You're still not listening so this is likely pointless.

Oh, I'm listening, the real problem you have is that 'I'm not agreeing'.

TrevorL wrote: »

I've said a bunch of times you are not our customer. Each time you keep saying that it doesn't work for you. Frustrating doesn't cover it.

But I/we are your customers, we are PV'ers with a very strong interest in storage, and willing to jump in when it doesn't make great financial sense too.

I assume that 'I'm not your customer' because I can see the real economics, and because I object as strongly as it is possible to the miss selling of a product via the use of a hysterical level of inflationary uplift.

TrevorL wrote: »

6000 cycles is at 100% DOD, our system uses 90% DOD as it says on the same page. But whatever. I've already explained in detail why I don't consider cycle life to be a useful metric. But you're not listening, just repeating.

Then support the longer life claim with some actual numbers and a warranty or performance guarantee - but don't state a cycle number that ensures your product is un-economical today, whilst simultaneously arguing economic viability by assuming a longer life cycle period. Cake and eat it?

TrevorL wrote: »

And repeat.

Yes, and repeat, at the stated number of cycles the cost of each kWh drawn from the batteries is (cost of input x 112%) + 10p.

If you don't like the calculations then revise your site and support a greater number of cycles, but beware, the longer the payback term the worse the cost of capital (lost interest) gets.

TrevorL wrote: »

I've said repeatedly our typical customer is already on E7, but you're not listening. And no they don't want to be running their dishwasher in the middle of the night, they just want a battery so they don't have to think about it.

If they don't want to run the dishwasher at night, then the daytime seems a logical alternative, but this works against your earlier claims that they don't consume anything more than baseload during the daytime, whereas a sensible PV'er would run the dishwasher (via a timer) around midday (if southerly orientation for example) and if really on the ball, at a time having referenced the weather forecast. The problem with this though is that it again undermines your economic argument as it both reduces available excess during the day for storage, and reduces demand for the battery to meet.

You may enjoy playing these games, but they aren't new, and they aren't difficult to see through.

TrevorL wrote: »

And again, you are not our current customer.

Please see earlier response addressing this excuse of yours.

TrevorL wrote: »

And again - who said 7p is better than 0p? You're making facetious arguments. The bulk of the benefit comes from solar in summer but needs to be supplemented with E7 in the winter to optimise payback, but I said that 10 times and you're not listening.

Who said it, well, you said it:

TrevorL wrote: »

2. It's the use of E7 that gives the best payback. I've said that multiple times. You're not listening.

Take the cost of E7, multiply it by about 112% for system losses, then add on approx 10p/kWh for battery costs, and not only will it not be the best payback, but it is more likely to result in a loss.


But now for the interesting bit, what you didn't answer, again!

Martyn1981 wrote: »

But the opposing view to yours is based on facts and events. We've seen the impact on bills from the rollout of low carbon generation via the green levies. So we can learn from the past.

We can also learn from the present by taking account of the rapidly falling costs of RE, and the max wholesale price possible based simply on the HPC nuclear option of £100/MWh (valid through to the 2060's) - taking that worst case price we see an increase in wholesale prices from ~4p to 10p, and a 6p/kWh increase on retail prices (plus 'normal' inflation), so about 40% over a long time period.

I haven't forgotten that all of my info providing support for the lower and slower price increases, supported by repeated NAO reports was dismissed entirely by you as 'out of date' - so you have avoided/failed to provide any argument whatsoever to support an abnormally high inflation rate for energy.

I find it telling that I don't believe payback can be achieved yet based on current economics, and you are pushing so hard for an inflationary increase that is beyond reasonable - it's almost as if you too doubt payback without some sort of 'bonus' external factor? And that's not a bad thing, we'd all then be in agreement and looking forward to the day when the economics stand up on their own.

So you don't seem able to provide an underlying reason for the large increase in energy prices, nor an explanation as to why the NAO are wrong in predicting a far lower price peak in wholesale costs than previously expected.

And you also seem to be avoiding the simple question I asked you based on your (not mine) chosen inflationary uplift percentage:

Martyn1981 wrote: »

Edit- for simplicity, and based on your 8.4% inflation claim, are you happy to state that in 10yrs time you predict a leccy unit price of approx 34p/kWh?

This isn't a trick, all I've done is present your inflationary choice in the form of a monetary value. No cheating, no spinning. So if you stand by your inflationary choice, then you should, without obfuscation, stand by the 34p/kWh price, so do you?

Martyn1981

TrevorL wrote: »

I don't understand the model you describe. Ours considers each month through the year, dividing the monthly expected generation by the number of days in the month. It assumes one cycle of the battery per day, with the day's solar generation going into the battery considering the round trip efficiency, the battery capacity, the 24hr/E7 night/day and standing charges, and the annual degradation. Where there isn't enough solar to fill the battery it calculates how much E7 to use to optimise savings for the month. It sums the months across the year and then projects forward savings over the next 20 years considering the decreasing battery capacity and increasing price. Then it cycles through potential battery sizes to produce a table of savings, ROI and paybacks for each battery size for 24 hr tariff plus battery / 24hr moving to Eco7 plus battery / Eco7 plus battery.

That paragraph contains a shocking number of significant errors.

1. Dividing monthly generation by number of days will falsely flatter the economics. In reality you will have many plus days, where generation will exceed battery capacity, and many days of poor generation. This is fine if you have a battery capacity large enough for several days use, something the off-gridders will have, but not something worth our while.

2. You can't assume solar generation will go into the battery. Some will be consumed directly, and some will go as export either due to the battery being full, or generation exceeding the charge rate of the battery.

3. Use of E7, at today's storage costs will simply burn through cycles for little to no benefit, and could even cost.

4. 20 years is I believe a reasonable time span, but as I said way back, for such an expensive item that is currently unproven then you have the same issue I've raised before, your reliance on out of warranty years to justify the expense/risk borne by your customers.

5. These products (battery storage) appear to have a similar cost trajectory to that of PV and Swanson's Law, with a roughly 20% reduction in cost for every doubling of production volume. Therefore, there's a good chance that any savings in the early years will be less than the price reduction in the product.

However, I appreciate that early adopters are needed, in order to achieve production doubling, but I've already covered this earlier on when I pointed out that the automotive side is driving up battery production and technology, regardless of the smaller domestic storage market. But it would be remiss of me not to acknowledge that in the case of the Tesla PWII prices have actually gone up recently due to both high demand for their product and the squeeze on availability of batteries due to said automotive ramp up.