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    • Martyn1981
    • By Martyn1981 5th Dec 16, 2:57 PM
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    Martyn1981
    On-grid domestic battery storage
    • #1
    • 5th Dec 16, 2:57 PM
    On-grid domestic battery storage 5th Dec 16 at 2:57 PM
    Hello!

    Right, as discussed elsewhere, battery storage for self generation (typically PV) is interesting (to some), and gathering momentum in the UK. So here's a thread to discuss it, and watch it develop.

    I've called it on-grid, as off-grid is so much more specialised. And domestic as commercial scale storage, or grid scale can be chatted about on the Green & Ethical energy issues thread.

    So, where are, well this article lists about 20 systems that are available or should be available soon:-

    Introducing CleanTechnica’s New Home Battery Overview Page

    Jumping straight in with personal opinions:-

    Economical - Not yet. Prices are falling fast, the range of products is expanding fast, and large numbers are being deployed in some countries, either because the price of leccy is high (Australia & Hawaii) or because subsidy schemes exist (Sweden & Germany).

    Where are we today. My needs are a 4kWh system. That's 4kWh of useable capacity, which would mean about 8kWh of lead acid (LA), or about 5kWh of lithium ion (Li-ion). My research has found batts in the high £2k and up range. I need the price to be nearer to £1.5k.

    The Tesla Powerwall II, installed is approx £6.5k, which works out at about £2.2k for 5kWh, but of course, it doesn't work quite like that, as smaller systems will cost proportionately more.

    Environmental - Tricky one this (to say the least). Until storage is needed, it's not environmental. Renewable energy (RE) generation currently displaces gas generation, which is a demand follower. Once gas generation is pushed down to zero (at times) we need storage, but we aren't there yet.

    However, to push gas generation down to zero, we need more RE, and to ensure it is viable/economic/profitable, we will need storage - chicken and egg situation.

    The advantage of storage to the environment, is to take peaks of RE and timeshift them to peaks in electricity demand. On a domestic level, this works quite well as PV generates during the day into the afternoon (or evening) depending on the month, so any stored leccy is available for the evening peak 5pm to 7pm.

    That's the background, and now here's a thread to discuss options, prices, economics, and watch things unfold. Enjoy.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
Page 24
    • Martyn1981
    • By Martyn1981 3rd Nov 18, 5:06 PM
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    Martyn1981
    Thanks for going through that argument in detail, and I'd be very happy to use a lower rate of price increase if it was justified, but I don't find that data convincing. However good the potential may be for low wholesale prices I see no evidence that retail prices are going up at anything close to just inflation. You also seem to be using quite old data. As I said we took 6.7% from the Commons Briefing Paper from February this year, but the other report I mentioned covers actual data from 2017 and states "The average increase suffered by all those Big 6 dual fuel customers who have been affected stands at 8.4%".

    I've just done a bit more Googling and found the following (from the Independent online "Why are energy bills rising and what can consumers do about it?"):

    The Big Six have made the following changes to bills since the beginning of the year:

    Npower: 5.3 per cent
    SSE: 6.7 per cent
    Scottish Power: 5.5 per cent
    British Gas: 5.5 per cent
    E.ON: 4.8 per cent
    EDF: 6 per cent
    Average: 5.6 per cent


    I can see an argument for going as low as 5.6 per cent, but not below it. Especially as many of these companies now do 2 increases each year.
    Originally posted by TrevorL
    Old data - you mean reality?

    I'm using actual prices for generation and strike prices on contracts issued. Also note that RE auction prices are still falling.

    What you need to convince me off, if you want to use 8.4% compounded, is that wholesale prices can rise to nearly £200/MWh (in todays money) despite contracts being issued at £50-£64/MWh? And that the NAO is wrong in their future estimates which have been reduced massively in line with the dramatic reduction in RE generation costs.

    Regarding your reference to price rises this year, please don't go there. For long term compounded rates you will need to show long term rises, when in reality we see rises and falls, but over a long term the increase has not been enormous.

    The arguments you are trying to use are not new to us. They are near identical to those used by 'guestionable' PV salesmen at the start of this decade, and they are wrong, not an opinion, but fact, they are wrong, prices did not rise by the suggested amounts.

    If future wholesale prices are effectively capped by us now knowing the limit of generation costs, then how can energy prices possibly rise by a factor so, so much greater than 'normal' background inflation? Or to put it another way, can you please tell me what special factors will apply to energy prices, particularly wholesale prices, that will drive them up so dramatically?
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • Martyn1981
    • By Martyn1981 3rd Nov 18, 5:21 PM
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    Martyn1981
    I have seen this argument before and don't find it useful. Certainly our products are warrantied for 10 years, and they have a specification of 6000 cycles, but they are not warrantied for 6000 cycles in 10 years. I think that's just a misunderstanding. 6000 cycles is obviously nearly 20 years of daily use so calculating the cost of a cycle assuming that they will do 6000 cycles in the warranty period and then be unusable is a blind alley.

    By all means if you need a product to payback within its warranty period then you may find a battery doesn't. But most people don't expect require that of other things, like a car. A better approach, in my opinion, is to model the degradation of the battery capacity over its lifetime. Our model does this, assuming 2% degradation per year, and uses that to calculate how much energy you will actually cycle through the system over time. Payback periods we quote to customers take this capacity loss into account.

    Bottom line, given that we know battery paybacks are typically 8 to 14 years or so, requiring them to payback within a 10 year warranty gives them an impossible task. Myself I'm expecting, in broad terms, good capacity for the first 10 years, somewhat lower capacity for the second 10 years, and lower but still usable capacity (perhaps just 40-50%) after that. Anything after payback is a bonus. It's not that dissimilar to solar where we know inverters are typically only warrantied for 10 years but the system won't just die on the first day of the 11th year.

    That doesn't mean you're wrong if you require payback within the warranty period, just that that isn't a requirement for most of our customers.




    Our model uses the inverter manufacturer's specs of Charging efficiency of 94.5% and discharging efficiency 94%, so a round trip efficiency of 89%, but I'd be the first to concede we don't know how well this matches real-life usage.
    Originally posted by TrevorL
    Some general thoughts:

    I'm sorry but you misunderstand my position on cycles, life expectancy and warranty. What I'm saying is that the product is too expensive and new for most of us to rely on value post warranty.

    I'm sure it will last longer, but that doesn't make it a fact. If you are certain it will last longer, then extend the warranty, and by all means apply capacity limitations, but I can't make such a large investment on hope.

    Regarding the 6,000 cycles, I totally agree that it will in reality take longer than 10yrs, but that is irrelevant, 6,000 cycles is 6,000 cycles regardless of the number of years. You can say 10yrs, 20yrs or 30yrs, but even assuming no loss of capacity and 100% DoD, it still comes to 60,000kWh's any way you spin it. So the cost per cycle is still £5k/60,000.

    You can add more years, but then cost of capital is against you (cake and eat it?)

    BTW, you can't suggest an 8-14yr typical payback, then in the very same sentence state that a 10yr payback is impossible.

    Coming from a green angle on this issue, I also feel that "Anything after payback is a bonus." however that is also contradictory as you have been arguing for a solid payback, then switch to a weak argument suggesting a bonus ....... or luck?

    Batt efficiency of 89% (round cycle) sounds perfectly fair, but you just increased the E7 input cost by ~12%.

    Comparing the inverter warranty to a battery warranty doesn't work. Putting aside the fact that my inverters have 20yr warranties, the issue here is that if the inverter(s) fail, you replace them as they only represent a minority of the PV system costs, but if the batts fail (out of warranty) you are looking at replacing a majority part of the system.

    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?
    Last edited by Martyn1981; 03-11-2018 at 5:28 PM. Reason: Added an edit
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • Martyn1981
    • By Martyn1981 4th Nov 18, 7:35 AM
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    Martyn1981
    I have seen this argument before and don't find it useful. Certainly our products are warrantied for 10 years, and they have a specification of 6000 cycles, but they are not warrantied for 6000 cycles in 10 years. I think that's just a misunderstanding. 6000 cycles is obviously nearly 20 years of daily use so calculating the cost of a cycle assuming that they will do 6000 cycles in the warranty period and then be unusable is a blind alley.

    By all means if you need a product to payback within its warranty period then you may find a battery doesn't. But most people don't expect require that of other things, like a car. A better approach, in my opinion, is to model the degradation of the battery capacity over its lifetime. Our model does this, assuming 2% degradation per year, and uses that to calculate how much energy you will actually cycle through the system over time. Payback periods we quote to customers take this capacity loss into account.

    Bottom line, given that we know battery paybacks are typically 8 to 14 years or so, requiring them to payback within a 10 year warranty gives them an impossible task. Myself I'm expecting, in broad terms, good capacity for the first 10 years, somewhat lower capacity for the second 10 years, and lower but still usable capacity (perhaps just 40-50%) after that. Anything after payback is a bonus. It's not that dissimilar to solar where we know inverters are typically only warrantied for 10 years but the system won't just die on the first day of the 11th year.
    Originally posted by TrevorL
    I've been thinking about your comment that you've seen my argument before but not found it useful, plus your statements about cycles, life in years and degradation.

    So, rather than my simple and 'flattering' use of £5k and 6,000 cycles, and a cost of batt use of 8.33p/kWh, I thought I'd try it your way:

    So, a price of £5,027
    A capacity of 9kWh
    A useable capacity of 8.1kWh

    You state that the 6,000 cycles will last more than 10yrs, I agree. I'd suggest approx 300 cycles pa (or less), so using your degradation figures of 2% pa, we get:
    - a capacity of 100% falling to 80% in the first 10yrs (average 90%)
    - a capacity of 80% falling to 60% in the second 10yrs (average 70%)
    - a capacity of 60% falling to 40% in the third 10yrs (average 50%) and corresponding with your statement - "perhaps just 40-50%"

    So, we get:
    0-10yrs - 3,000 cycles @ 90% capacity @ 8.1kWh = 21,870kWh's
    10-20yrs - 3,000 cycles @ 70% capacity @ 8.1kWh = 17,010kWh's
    20-30yrs - 3,000 cycles @ 50% capacity @ 8.1kWh = 12,150kWh's

    So instead of my suggested 8.33p/kWh cost of storage we have

    £5,027 / 51,030kWh's = 9.85p/kWh


    Once again, I'm not against battery use, I believe in it very strongly, and think it will be a major part of supply and demand side leccy use in the future, but the numbers are not good at the moment and I am more than willing (and hopefully capable) to address any misinformation that might get posted.

    Special regard has to be given to over-hyped inflationary figures. As I have hopefully shown, there is no underlying issue anymore* that can support energy inflation being significantly different to 'normal' inflation.

    *Previously there were fears, now unfounded, that a switch away from FF's would result in a massive rise in prices, but the fall in international gas prices, and the tumbling costs of RE generation have reversed this concern, as can be seen by the reports from the NAO suggesting a 35% reduction in peak price estimations from £85/MWh down to £55/MWh, whereas your suggested inflation rate (after stripping out a 2% nominal/target inflation rate), would when compounded mean a rise of £153/MWh (to £208/MWh) or an increase of 278% on the NAO revised estimates.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • Exiled Tyke
    • By Exiled Tyke 4th Nov 18, 8:02 AM
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    Exiled Tyke
    All trust and respect was lost with the first set of ridiculous assumptions. I'm actually quite surprised that indefensible is continuing to be defended. I've spoken to two very reputable installers recently, both obviously needing business (especially as their PV work is drying up) but both having the decency to back down very promptly and respectfully when I've explained why I don't think the numbers yet add up. I'm sure if there was a way for it to pay off they would have told me, like Martyn I am ready to be convinced.
    Install 28th Nov 15, 3.3kW, (11x300LG), SolarEdge, SW. W Yorks.
    • ASavvyBuyer
    • By ASavvyBuyer 4th Nov 18, 9:05 AM
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    ASavvyBuyer
    All trust and respect was lost with the first set of ridiculous assumptions. I'm actually quite surprised that indefensible is continuing to be defended. I've spoken to two very reputable installers recently, both obviously needing business (especially as their PV work is drying up) but both having the decency to back down very promptly and respectfully when I've explained why I don't think the numbers yet add up. I'm sure if there was a way for it to pay off they would have told me, like Martyn I am ready to be convinced.
    Originally posted by Exiled Tyke

    I found the same with the companies I dealt with that installed our Solar PV system & ASHP. They were both honest and agreed that financially, for home batteries, it was not a good investment at the moment.

    Also, IMHO it is greener (and cheaper) to import electric from a supplier that only uses renewable energy. For example; Octopus Go, which only charges 5p/kWh for 4 hours at night, and about 14p/kWh during the day (So not more expensive than the average of 15p/kWh).

    That also helps them, as a company, being able to invest in more renewable energy.

    When V2H becomes available, at a reasonable cost, it could be worthwhile, as the % use from a EV battery would be very small.
    Last edited by ASavvyBuyer; 04-11-2018 at 9:11 AM. Reason: typo
    Rhondda Cynon Taf, 4kWp, W roof, 30° pitch, 16 x 8.33 Eternity 250w E+10 panels, Solar Edge SE4000-16A Inverter + P300 Optimisers. Inst Aug 2015.
    REUK Diverter, Toshiba RAS-10G2KVP-E Ultra High Efficiency Air Conditioner/Heat Pump, Kia Soul EV & 100% Green Electric Tariff.
    • zeupater
    • By zeupater 4th Nov 18, 12:40 PM
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    zeupater
    I agree generally with the initial statement - but not the conclusion. IMO the more time of use options and tariffs become available, the more benefit you get from a battery.

    As well as the Tide tariff mentioned in another post, a very interesting example is the Octopus Agile tariff with 'Plunge Pricing' where you can actually get paid to take excess electricity off the grid. I think their implementation is a bit ropey, but it is hopefully a portend of more interesting options to come.
    Originally posted by TrevorL
    Hi

    How can you agree with the initial statement but not the conclusion as they're inherently linked?

    I totally understand your argument regarding 'plunge prices' as a currently available option, however any long-term justification based on either this form of supply agreement or E7 as a whole cannot be realistic. To explain why, we need to return to basic economic concepts ...

    Energy prices, just like any product in any sector, are determined by supply & demand ... if the capacity to supply far outstrips demand prices are generally low & where demand approximates to capacity prices are generally high ...

    In terms of energy this would describe why E7 exists. Overnight there's relatively little demand so the competition to bid for energy sales to recover overheads, which is largely driven by high overhead/low incremental generating cost technologies (wind, hydro, nuclear etc) enables the sector to drive prices down & suppliers to offer substantial discounts to encourage consumer overnight purchases ...


    The advent of smart-meters provides the industry a tool to vary prices during the day as demand fluctuates and that tool will be used to encourage a degree of demand shifting so that peak demand doesn't exceed supply .... the error employed by so many when looking into the effect of this is the assumption that demand moved from high unit price periods will be moved to periods where 'off-peak' prices remain at the heavily discounted levels which currently apply, whilst this cannot logically be the case ...

    Think of what happens in straightforward economic terms ... the greater the difference between peak & trough demand levels, the greater the inverse differential in unit pricing, which when charted would approximate to mirrored curves, therefore the justification of a continuation of demand based unit price differentials fully depends on maintaining demand shortfalls ... however, the intent of government & supply industry policy is to encourage energy efficiency, shift parts of current demand, and fill the supply gap with automated appliance control & (/smart) charging wherever practical with the goal being to achieve as close to a fully balanced & smooth demand & supply relationship as possible ...

    So, if the goal is to have no (/little) difference between supply & demand at any time of the day, then the logical implication is that the unit price will remain pretty consistent throughout any 24hour period. Having 'said', it's also relevant to conclude that there's a strong possibility that although tariffs may be consistent on a short-term basis, it's also likely that there will be a seasonal unit price variation which is purely related to energy mix ...

    In summary, any operator has it's fixed & variable costs and those costs are currently recovered by levying a higher price than necessary at the standard daytime unit price rate and a discounted price on E7 .... as the overnight supply/demand gap is filled with developments such as home batteries or EV charging then the most likely outcome in a competitive market would be the combination of an increase in E7 unit pricing and a corresponding reduction in the cost of standard daytime units to a point where they are effectively the same, therefore any battery/storage 'investment' justification cannot be based on future pricing structures or overnight discounts remaining anywhere near what currently applies and therefore caution must be applied wherever this approach is employed ...

    HTH
    Z
    Last edited by zeupater; 05-11-2018 at 9:51 AM. Reason: -f+n
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    • TrevorL
    • By TrevorL 5th Nov 18, 12:03 PM
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    • 2 Thanks
    TrevorL
    Old data - you mean reality?
    Originally posted by Martyn1981
    You were quoting from 2015 and I was using data from 2017 for retail prices, that is all. I am yet to be convinced that we are seeing any evidence of retail prices actually dropping (doing anything other than going up significantly) to match projections of wholesale prices.

    The arguments you are trying to use are not new to us. They are near identical to those used by 'guestionable' PV salesmen at the start of this decade, and they are wrong, not an opinion, but fact, they are wrong, prices did not rise by the suggested amounts.
    Originally posted by Martyn1981
    I thought we were having a useful and informative discussion but I strongly object to your tone and bluster here. I believe that prices will rise significsntly as do many other sources, such as the uk power forecast I mentioned before:

    "The growth of sustainable energy sources has the potential to slow, and even eventually reverse the rise in gas prices, but it looks like nothing can stop a rise in electricity prices.

    This is partly due to the fact that many of the UK’s electricity generation plants have closed down due to the EU’s Large Combustion Plant Directive, a ruling that has since been superseded by the Industrial Emissions Directive (as of January 1, 2016). Coal fire power stations are being targeted to help reduce emissions in energy generation.

    Energy prices have been high since a 35% spike in 2008, and price rises have barely slowed down since. So it looks as though we’re set for steady increases in the cost of energy for the foreseeable future, with increases in demand, transportation costs, wholesale prices, and government legislation all set to keep costs high.

    The cost of transporting gas and electricity is predicted to rise by around 5-6% and 8-15% respectively in the next few years. And consumers will undoubtedly bear the brunt of these increases as energy suppliers will compensate for any additional outgoings by raising their own prices."


    My opinions are my opinions. If you are going to consider your opinions to be facts then we are not going to get far.
    • Martyn1981
    • By Martyn1981 5th Nov 18, 12:22 PM
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    Martyn1981
    You were quoting from 2015 and I was using data from 2017 for retail prices, that is all.
    Originally posted by TrevorL
    The NAO data is actually 2016, and the CfD info is 2018 (I will revise it in April 2019) and valid into the 2060's.

    If you believe that the NAO cost estimates are wrong, then you need to provide a sound argument as to why wholesale prices will rise dramatically, and why a backstop max price of £100/MWh (new nuclear, RE is already cheaper) is wrong.

    You are free to believe that prices will rise significantly, but you also need to provide a reason why. I have provided multiple corresponding reasons as to why prices simply can't rise as far as you claim.

    But, again, I'll point out that the near hyper-inflation rates you are suggesting, in order to support the economics of batteries today, is a tactic used by 'questionable' PV firms at the start of this decade, and the rises did not happen.

    So, I'll repeat the problem/question - putting aside 'normal' inflation that will impact all goods and services and hopefully wages, what reasons do you suggest there are for a far higher inflation rate on UK leccy prices?
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • TrevorL
    • By TrevorL 5th Nov 18, 12:35 PM
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    • 2 Thanks
    TrevorL
    I'm sure it will last longer, but that doesn't make it a fact. If you are certain it will last longer, then extend the warranty, and by all means apply capacity limitations, but I can't make such a large investment on hope.
    Originally posted by Martyn1981
    You are not being fair. You used the word 'fact' not me. It will last longer in my opinion and I'm sure you knew that is what I meant.

    Regarding the 6,000 cycles, I totally agree that it will in reality take longer than 10yrs, but that is irrelevant, 6,000 cycles is 6,000 cycles regardless of the number of years. You can say 10yrs, 20yrs or 30yrs, but even assuming no loss of capacity and 100% DoD, it still comes to 60,000kWh's any way you spin it. So the cost per cycle is still £5k/60,000.
    Originally posted by Martyn1981
    No. In my opinion it will last longer than 6000 cycles. I'm not aware of any physical process that will mean it will stop working at 6001 cycles. I don't think it's a useful metric. I was suggesting that a better metric is to consider a lifetime over which the battery degrades continuously and there is no particular cutoff at 6000 cycles. I explained that that is what our model does.

    BTW, you can't suggest an 8-14yr typical payback, then in the very same sentence state that a 10yr payback is impossible.
    Originally posted by Martyn1981
    I believe you are deliberately misquoting me.

    Batt efficiency of 89% (round cycle) sounds perfectly fair, but you just increased the E7 input cost by ~12%.
    Originally posted by Martyn1981
    I explained that our model assumes a round trip efficiency of 89% when it calculates the payback for a customer. Obviously that takes into account the effective increased cost of E7. I'm not sure what your criticism is.

    Comparing the inverter warranty to a battery warranty doesn't work. Putting aside the fact that my inverters have 20yr warranties, the issue here is that if the inverter(s) fail, you replace them as they only represent a minority of the PV system costs, but if the batts fail (out of warranty) you are looking at replacing a majority part of the system.
    Originally posted by Martyn1981
    I can see we're not going to see eye to eye on this. My point was simply that in £5k system perhaps £500 is installation, £500 is inverter, and the rest is multiple batteries. Having a battery fail outside warranty - depending on the system configuration - may not be a big deal, perhaps as easy as ordering another Pylontech battery and plugging it in yourself (it's just push-fit connectors). It's loads easier than replacing a solar inverter.

    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?
    Originally posted by Martyn1981
    I had been about to say that I was persuaded in part by your arguments and would use a lower increase next time we model for a customer, and also run a test to see how sensitive the results were to differing increase rates. However given the tone of the comments here I feel now that an objective discussion was maybe never on the cards.

    Dr Trevor Larkum
    Chief Technical Officer, FI
    • Martyn1981
    • By Martyn1981 5th Nov 18, 12:36 PM
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    Martyn1981
    I am yet to be convinced that we are seeing any evidence of retail prices actually dropping (doing anything other than going up significantly) to match projections of wholesale prices.
    Originally posted by TrevorL
    If you could have another look at the NAO wholesale price predictions, you will see that they are not suggesting prices will fall - what they show is that their predictions of price rises have been dramatically reduced.

    As I explained:

    4. But, as you say, you can't take my word for it, so I'd refer you to the NAO who in 2015 revised down their peak price for leccy in 2029 of £85/MWh to a 2027 peak of £70/MWh - please see page 40.

    Then one year later, they further revised the peak down to £55/MWh through the 2020's, before dropping down towards £45/MWh and less in the 2030's - please see page 39.

    If we are generous and stretch to a 1.5p/kWh rise in the wholesale price, then we will see an approximate rise (from 15p/kWh retail) of about 10% over 10yrs, so about 1% pa simple, or 0.95% pa compounded. Again, this is the rise above and beyond normal inflation, but that can simply be put against the lost interest invested in a PV or batt system (cost of capital).
    Originally posted by Martyn1981
    So the NAO are suggesting a price rise (not fall) and I have openly acknowledged this. I even gave the increase (above normal inflation) as approx 1% pa.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • Martyn1981
    • By Martyn1981 5th Nov 18, 12:43 PM
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    Martyn1981
    I will simply respond to this statement to show why I am finding it harder and harder to trust what you are saying:

    I believe you are deliberately misquoting me.
    Originally posted by TrevorL
    Bottom line, given that we know battery paybacks are typically 8 to 14 years or so, requiring them to payback within a 10 year warranty gives them an impossible task. Myself ......
    Originally posted by TrevorL
    I have not misquoted you. I have not deliberately misquoted you. Attempting to claim I have is I believe more revealing of your tactics, than my responses, all fact based.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • zeupater
    • By zeupater 5th Nov 18, 1:23 PM
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    zeupater
    ... I was using data from 2017 for retail prices, that is all. I am yet to be convinced that we are seeing any evidence of retail prices actually dropping (doing anything other than going up significantly) to match projections of wholesale prices ...
    Originally posted by TrevorL
    Hi

    However, medium term projections should be based on extending medium term historical trend analysis as opposed to cherry-picking a figure in a publication which most suits the argument being made ...

    Your source may have been from 2017, but I've already supplied links to two official sources of data (Ofgem/ONS) which would be more suitable and likely be far more agreeable than the percentages you've been using, but if you need official information sources with supporting data which can be used to produce realistic forecasts - try these ....

    This is the latest QEP (Quarterly Energy Prices) report from BEIS dated 27/09/2018 - you'll be particularly interested in section 2 .... https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/743709/QEP_Q2_2018.pdf

    These are the supporting BEIS QEP tables in .xls format which can be used to perform accurate analysis on both domestic electricity & gas bills ... https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/743711/QEP_Tables_Q2_2018.pdf

    ... however, please note - the latest official conclusion (Sept '18) in the report in no way agrees with your selected sources related to historical price increase trends or even the recent round of price uplifts, concluding that ...
    - The price paid for all domestic fuels in real terms has risen by 3.4 per cent in the year to Q2 2018. Between Q2 2017 and Q2 2018, real terms prices including VAT for domestic electricity increased by 4.8 per cent and domestic gas prices rose slightly by 0.3 per cent.

    - The average standard electricity bill in 2017, across all payment types has increased by £33 (5.7 per cent) since 2017, from £586 to £619. However, the average 2017 gas bill across all payment types has decreased by £20 (3.1 per cent), from £650 to £630. These bills are based on standard consumptions of 3,800kWh per year for electricity and 15,000kWh per year for gas
    If you are able to accept the validity of the positions being maintained by various posters in this latest discussion, you may also start to understand the thought processes of your targetted market - we are the group that will form the early uptake customer base for storage, with some already having taken the step ... look at it as being a really cost-effective source of market research, from which the initial finding is that the market preference is for more-realistic returns calculations!

    HTH
    Z
    Last edited by zeupater; 05-11-2018 at 1:26 PM.
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    • TrevorL
    • By TrevorL 5th Nov 18, 2:09 PM
    • 18 Posts
    • 2 Thanks
    TrevorL
    I have not misquoted you.
    Originally posted by Martyn1981
    In my opinion it appears that you did. I wrote:

    Bottom line, given that we know battery paybacks are typically 8 to 14 years or so, requiring them to payback within a 10 year warranty gives them an impossible task.
    Originally posted by TrevorL
    Whereas you wrote:

    BTW, you can't suggest an 8-14yr typical payback, then in the very same sentence state that a 10yr payback is impossible.
    Originally posted by Martyn1981
    I was saying that battery paybacks inhabit a range of timescales, typically in the range of 8 to 14 years depending on circumstances, and therefore it's an impossible task to require them to fit within the warranty period. I never stated that a 10yr payback is impossible.



    ... however, please note - the latest official conclusion (Sept '18) in the report in no way agrees with your selected sources related to historical price increase trends or even the recent round of price uplifts, concluding that ...
    The average standard electricity bill in 2017, across all payment types has increased by £33 (5.7 per cent) since 2017, from £586 to £619.
    Originally posted by zeupater
    Perhaps we are just at cross purposes. I quoted above a source giving Big Six prices increases in detail for 2017 that averaged out to 5.6 per cent. This seems like corroborating data that suggests that a figure of 5.6 or 5.7 per cent represents a real and useful value for electricity cost inflation in the last year.

    Note, I am specifically not considering gas or 'average energy' cost increases, as I only think electricity increases are relevant in this instance. However if a customer's intention was to replace their gas usage with a solar diverter, or a heat pump, then I can see projected gas pricing would be relevant, and would likely reduce the argument for going solar+battery in those circumstances.
    • Martyn1981
    • By Martyn1981 5th Nov 18, 3:41 PM
    • 8,495 Posts
    • 13,460 Thanks
    Martyn1981
    An item on domestic battery storage from this weeks Carbon Commentary newsletter:

    1, Domestic batteries for grid services. It doesn’t make financial sense in most markets for domestic customers to install batteries at home. However some utilities are encouraging the growth of storage by paying for the right to use batteries for grid management purposes. EdF in the UK now offers a discount of £1,500 ($2,000) to purchasers of a 4 kWh Powervault battery in return for the right to remotely instruct the battery to charge or discharge at moments of grid instability. I’m not sure that even this discount is enough to give the owner an adequate return but we’ll see a continuing stream of arrangements like this around the world.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • zeupater
    • By zeupater 5th Nov 18, 3:55 PM
    • 4,718 Posts
    • 6,359 Thanks
    zeupater
    ... I had been about to say that I was persuaded in part by your arguments and would use a lower increase next time we model for a customer, and also run a test to see how sensitive the results were to differing increase rates. However given the tone of the comments here I feel now that an objective discussion was maybe never on the cards ...
    Originally posted by TrevorL
    Hi

    I'm all for an objective discussion, so I've run the 'simplistic' model offered up in a previous example to provide some slightly less 'rough-cut' but still 'simple' analysis ...
    .. Let's return to your figure of £0.13 with a more typical battery size, a SX45-2 with 9kWh for £5k. Potential first savings are 9 x £0.13 x 365 = £427. At 8.4% price inflation that's £463 in the second year, then £502 in the 3rd year, etc. Payback is about 9 years. So not bad ...
    ... firstly, agreeing the calculated saving of £427 at a compounded 8.4% pays off sometime before the end of year 9, we'll look at a range of energy inflation rates .... starting with the 8.4% you were preciously using then moving down through a range of other alternatives recently raised ...

    8.4% - 9 Years (Your source)
    6.7% - 10 Years (Your HoCEPBPaper - 5year SC only!)
    4.8% - 10 Years (BEIS Q217-Q218)
    3.8% - 11 Years (HoCEPBPaper - 5year all supply)
    3.0% - 11 Years (Ofgem 7year High)
    2.5% - 11 Years (ONS CPIH inflation 2005-2018)
    2.0% - 11 Years (Ofgem 7year Low)

    ... so as can be seen, on the simplistic model where all battery charge is supplied by solar at no cost there's little difference so historical term CPIH might as well be used ...

    Where the difference comes in is when realistic usage patterns come into play ... I haven't researched an annualised battery effectiveness for a 9kWh battery, but for total simplicity, let's assume that the average battery contribution would from solar would be 6kWh for 6 months of the year and 3kWh for the rest, with an additional 5kWh of E7 tariff shifting benefit at 85% return efficiency over that period with E7 rates being 6p/kWh overnight and 4p more expensive during the day .... we get an initial first year annual battery cost benefit (to which inflation must be added) of ~£222/year((182*6*13p)+(182*3*(13-4p)+(182*5*(13-4-5p)*0.85)).... note this is still on the ambitious side for a low energy user in representing a household currently importing 1274kWh/year moving to no imports at the E7 daytime rate ... for information, our 12month rolling import is 1219.4kWh.

    Applying the same set of annual energy inflation assumptions we resolve to a different range of 'payback' timelines ...

    8.4% - 14 Years (Your source)
    6.7% - 15 Years (Your HoCEPBPaper - 5year SC only!)
    4.8% - 16 Years (BEIS Q217-Q218)
    3.8% - 17 Years (HoCEPBPaper - 5year all supply)
    3.0% - 18 Years (Ofgem 7year High)
    2.5% - 19 Years (ONS CPIH inflation 2005-2018)
    2.0% - 19 Years (Ofgem 7year Low)

    .... note this is still on the ambitious side for a low energy user (the normal early adopter target market) in representing a household currently importing 1274kWh/year moving to no imports at the E7 daytime rate & would not include any change in tariff standing charges resulting from the move to E7, any ongoing (/ through life) costs, equipment financing or any lost opportunity from having the £5k held as an investment - as stated, it's still relatively 'simple', but should be in line with the results from introducing any model complexity ...

    HTH
    Z
    Last edited by zeupater; 05-11-2018 at 4:33 PM. Reason: formatting / grammar
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    • zeupater
    • By zeupater 5th Nov 18, 4:13 PM
    • 4,718 Posts
    • 6,359 Thanks
    zeupater
    ... Perhaps we are just at cross purposes. I quoted above a source giving Big Six prices increases in detail for 2017 that averaged out to 5.6 per cent. This seems like corroborating data that suggests that a figure of 5.6 or 5.7 per cent represents a real and useful value for electricity cost inflation in the last year ...
    Originally posted by TrevorL
    Hi

    Yet you used replaced an analysis basis of 6.7% with 8.4%! ....

    Anyway, please read the posts carefully, they provide a view that a medium-term projection cannot be based on price movements in a single year ... if you disagree we will remain at 'cross purposes', however, the consensus of any group of (decent) economists, statisticians, accountants or engineers would reasonably consider trend analysis as being the more reasonable assessment methodology ...

    Please look at the charts in the BEIS document referenced as well as the supporting spreadsheet data ... there is no reasonable argument to not base an assessment of future energy price increases on these figures unless there's an (yet unknown) externality which seriously changes the trend projection.

    HTH
    Z
    Last edited by zeupater; 05-11-2018 at 4:25 PM.
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    • Martyn1981
    • By Martyn1981 5th Nov 18, 4:19 PM
    • 8,495 Posts
    • 13,460 Thanks
    Martyn1981
    In my opinion it appears that you did. I wrote:



    Whereas you wrote:



    I was saying that battery paybacks inhabit a range of timescales, typically in the range of 8 to 14 years depending on circumstances, and therefore it's an impossible task to require them to fit within the warranty period. I never stated that a 10yr payback is impossible.
    Originally posted by TrevorL
    If a payback is possible within 8yrs, and you went further than just saying possible, but stated that 8-14yrs was typical, then not only is a 10yr payback possible today, but could become normal going forward.

    So perhaps I have more faith in the storage industry than you do, but it certainly seems like a payback would be possible (not impossible) with a 10yr warranty.

    However, you've missed my positive comments, which was that if the warranty (cycles and years) can be extended, perhaps to 10,000 cycles and 15yrs, or 20yrs, then that massively improves the economics (by reducing the batt cost per cycle) without even reducing the battery price.


    It seems you have decided that I am 'the enemy', you could not be more wrong. I'm one of the silly people who is willing to invest a substantial amount of money, perhaps £5k, on the basis of there being a reasonable chance of getting my money back over a 10-20yr period. Or to put it another way, risk £5k for absolutely no financial benefit whatsoever, since risking zero pounds on zero battery systems would place me in the same economic position.

    Now, is that sensible, of course not. After 20yrs I'll be back where I started if my gamble pays off. This is not something that most people will be willing to do, and I would caution them strongly against it ...... despite my being willing to do so. This is a money saving site and if I suggested others copied me, I'd be wrong.

    Yes, this is a green and ethical board, but I'm also not convinced about the green side of batts today (tomorrow yes) since we do not as a nation need storage today as RE generation is not in excess, so batts will actually 'waste' green generation through system losses. I'm also not entirely convinced on the need to promote/subsidise batts today, despite arguing the exact opposite for PV at the start of this decade - my reasoning is that batts don't need an artificial boost since they will receive a massive ramp up from the automotive side. I'm just being honest and pointing out the negatives.

    So, as I said at the start, I like the site, I like the clear pricing. I'd go further and say the pricing is good, but that's compared to other products, whilst it is bad compared to where the pricing needs to be.

    Is this your fault, no. Is it my fault, no. Is it the industry's fault, no. It is simply where we are today whilst we impatiently wait for prices to fall, production to ramp up, to bring prices down, to increase demand, to ramp up production, to bring down prices ..... you see where I'm going with this - to a point that it is economical.

    BUT - will I let my passion for RE, PV and storage blind me to reality and sit by idly when I see marketing tactics like this:

    When we run our financial model we assume 2% capacity degradation per year and an annual price rise of 8.4%.
    Originally posted by TrevorL
    NO, no I won't.

    It might seem strange that I (and others on here) should take such um-bridge at such a short sentence, but you've inadvertently set off every alarm bell possible, and as another poster said:

    "All trust and respect was lost with the first set of ridiculous assumptions. I'm actually quite surprised that indefensible is continuing to be defended."

    We are your market, but I personally wouldn't go within bargepole range of a company using, or misusing inflation rates to justify the economics of a product. Perhaps, unknown to you, we are simply too jaded to this argument on MSE.


    Lastly I need to address this previous issue as it has played on my mind:

    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?
    I had been about to say that I was persuaded in part by your arguments and would use a lower increase next time we model for a customer, and also run a test to see how sensitive the results were to differing increase rates. However given the tone of the comments here I feel now that an objective discussion was maybe never on the cards.
    Originally posted by TrevorL
    Firstly, let me give you the benefit of the doubt, and assume you thought I was 'spinning'. I hate spin doctors.

    I was not trying to spin, not trying to be clever, not trying to look big, not using games & tricks. All I did was take your statement, apply 10yrs to it (we are talking about a 10-20yr product after all), and then ask you if you still stood by it.

    Sometimes folk say something numerically without thinking how it would actually turn out, and it can sometimes surprise all. This may have been the case with you.

    So you can take offence at my question, you can be outraged at my question, but the data upon which it's based is yours, not mine. You set the path, all I did was go down it, and if it leads somewhere uncomfortable for you, then that's your cross to bear, not mine.

    I do hope you can be persuaded to step back from this inflationary cliff edge you are standing on, as I really meant my original post that having some industry input would be so helpful and interesting. I know next to nothing about batts, but like many others on here, I can hold my own in a discussion on maths and economics.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • TrevorL
    • By TrevorL 5th Nov 18, 4:45 PM
    • 18 Posts
    • 2 Thanks
    TrevorL
    let's assume that the average battery contribution would from solar would be 6kWh for 6 months of the year and 3kWh for the rest, with an additional 5kWh of E7 tariff shifting benefit at 85% return efficiency over that period with E7 rates being 6p/kWh overnight and 4p more expensive during the day
    Originally posted by zeupater
    I think we're close to agreeing on the method, and maybe our differences are largely in the detail into which we go and the choice of values to use. For solar generation we use figures from the PV GIS database (you should be able to find details of the process we use if you Google for 'fuel included blog "how much solar power could my roof generate"'). For a default case we use a south facing array in the Midlands which will generate as follows (daily kWh Jan to Dec):

    4.28 6.53 10.90 13.80 14.70 15.10 14.60 12.60 11.50 8.22 5.49 3.85

    Running the model optimises payback as it will consider the full range of available battery capacities from 2 to 20kWh. In this case we would expect to fill a 4 kWh battery most days just from solar, with a top up from Eco7 in the winter. Ordinarily, though, we would expect a bigger differential than you suggest between Eco7 and the daytime rate - my own is something like 7.5p and 15p, and we generally use the British Gas standard rates of 8.61 and 19.4p unless the customer can give us their specific rates.

    Anyway, if we run the model for that user, assuming annual consumption of 4200 kWh and a 90/10 split day/night, 2% annual degradation, 2.4kWh batteries, and 5.6% inflation we get the following paybacks for the given number of batteries:
    1: > 20, >20, 15
    2: 16, >20, 11
    3: 15, >20, 9.9
    4: 14.9, >20, 9.5
    5: 15, 16.5, 9
    6: 14.5, 14.5, 9
    7: 15.5, 14.5, 10
    8: 16.5, 16, 11

    Where the results, as described previously, are for staying on 24hr and adding a battery, moving to Eco7 and adding a battery, and staying on Eco7 and adding a battery.

    Here my recommendation would be that it's only viable if they are an Eco7/EV user, as mentioned before, and they should start with 3 batteries (7.2 kWh) and upgrade to more once it has proved itself.

    For the case of 3 batteries the model suggests the following figures for the battery charge level from Eco7 to maximise savings:
    January: 26%
    November: 5%
    December: 33%
    Last edited by TrevorL; 05-11-2018 at 6:10 PM.
    • TrevorL
    • By TrevorL 5th Nov 18, 5:34 PM
    • 18 Posts
    • 2 Thanks
    TrevorL
    Our posts seem to be crossing over each other, I'm not sure why.

    Yet you used replaced an analysis basis of 6.7% with 8.4%! ....

    Anyway, please read the posts carefully, they provide a view that a medium-term projection cannot be based on price movements in a single year ... if you disagree we will remain at 'cross purposes', however, the consensus of any group of (decent) economists, statisticians, accountants or engineers would reasonably consider trend analysis as being the more reasonable assessment methodology ...
    Originally posted by zeupater
    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.
    • zeupater
    • By zeupater 5th Nov 18, 7:39 PM
    • 4,718 Posts
    • 6,359 Thanks
    zeupater
    ... Running the model optimises payback as it will consider the full range of available battery capacities from 2 to 20kWh. In this case we would expect to fill a 4 kWh battery most days just from solar, with a top up from Eco7 in the winter. Ordinarily, though, we would expect a bigger differential than you suggest between Eco7 and the daytime right - my own is something like 7.5p and 15p, and we generally use the British Gas standard rates of 8.61 and 19.4p unless the customer can give us their specific rates.

    Anyway, if we run the model for that user, assuming annual consumption of 4200 kWh and a 90/10 split day/night, 2% annual degradation, 2.4kWh batteries, and 5.6% inflation we get the following paybacks for the given number of batteries ..
    Originally posted by TrevorL
    Hi

    I really don't want to get into a detailed argument to agree a methodology at the moment when there are a number of basic assumptions which need to be addressed.

    Firstly, as the average UK electricity consumption is closer to 3100kWh than 4200, that night has nothing to do with E7 tariff rates but logically starts at sundown and ends at sunrise, the typical household consumes more energy when occupied than when simply running baseload and, on average, it's darker when occupied (say 5pm - 8am) than when the PV is generating, then the assumption that "annual consumption of 4200 kWh and a 90/10 split day/night" must be questionable as a typical model from the outset, if at all! ...

    Secondly, on the E7 differential ... that was based on a 13p/kWh single rate electricity tariff moving to 17p(13+4) daytime and a discounted 7 hour overnight tariff of 6p/kWh, a day/night differential of 11p(17-6), which is fully in line with your BG differential of 10.79p (19.4-18.61) ... as my provided calculations we purely based on differential logic, I think that the difference (0.21p/1.9%) is typical of an acceptable rounding tolerance ...

    Regarding ... "In this case we would expect to fill a 4kWh battery most days just from solar" ... that cannot be the logical assumption as the priority for the solar generation would be to meet household demand ... if the total demand (as per your figures) is 4200kWh, the simplistic sanity check is to say that average daily daylight consumption would be ~5.8kW(4200/365/2), therefore in simplified terms the average generation available to be committed to storage from your PVGIS dataset ...

    4.28, 6.53, 10.90, 13.80, 14.70, 15.10, 14.60, 12.60, 11.50, 8.22, 5.49, 3.85

    ... would likely look more like the following as realistic daily generation available to commit to storage ... 0 0 4 7 8 9 8 7 5 2 0 0 ... which when exploded to an annualised basis approximates to 1529 kWh from a ~4kWp system, no matter what size the battery, whereas capping storage to a single 2.5kWh battery pack would, after round trip efficiencies, result in a deliverable daily energy pattern something similar to ... 0 0 2 4 4 4 4 4 4 1 0 0 ... so around 825kWh/year ....

    This sets the benefit for using a battery pack/solar combination with the model assumptions provided as ranging from £107(825*13) to £199(1529*13p) before resorting to reliance on E7 ... all this because of the mismatch between the example annual consumption and the size of the example PV array ...

    Now, if the array was bigger or the demand was lower things would be different and a more advantageous saving could be described, it's all a matter of keeping things in balance! ... I certainly wouldn't have chosen such an example!

    ... and yes, almost everyone in this discussion would be fully familiar with PVGIS & understand that the annualised ~3703kWh that the monthly data resolves to would be typical for a 4kWp system! ..

    HTH
    Z
    Last edited by zeupater; 05-11-2018 at 7:48 PM. Reason: formatting
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
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