On-grid domestic battery storage

zeupater · 6 November 2018 at 8:09PM

TrevorL wrote: »

I proposed 5.6% but you weren't listening.

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.

Hi

- "I proposed 5.6% but you weren't listening." ... and, as highlighted on numerous occasions, the source of your 5.6% relates to a single year whereas official data has been supplied which shows that compounding energy inflation at 5.6%pa would almost certainly be far too high to apply on a 10 to 30 year basis ... I have already provided links & basic historical analysis based on a range of periods from 20years, through 10 years to 5 years and links to officially published information which would lead a 'reasonable person' conclusion that even your revised 5.6% is atypically high ... please review the information previously posted and access the reports & supported data provided in the links ...

- "I don't understand the model you describe ..." .. then you need to sit down & revisit the contents of the posts carefully ... I understand your position regarding E7, however you cannot introduce E7 until there's a grasp of what the solar PV contribution can provide ...

To do this you must first understand the basic concepts contained in (i)-(iv) in the previous post as well as follow how (A) & (B) are derived ... this is essential because it defines a simplified solar+battery solution band of capability based on an assessment of minimum battery configuration & maximum solar array contribution - once we have that then we can look into the effects of real-world intra-day PV generation variability & round trip efficiencies, all this before considering moving forward & looking at E7 in 'top-up' context ....

If you are modelling without considering the contribution of the batteries as a form of accumulated support for the installed solar capacity during daytime hours then you're missing an advantage which has already been highlighted to you by at least two contributors in this thread and likely fully understood by most others with PV installations ... however, if you would like to understand the effect of doing this, it would move the 2.5kWh battery/4kWh daily battery charge/contribution (B) from ...
0 0 2 4 4 4 4 4 4 1 0 0 ... with a total contribution of 825kWh/year to a lower daily pattern of ...
0 0 2 2.5 2.5 2.5 2.5 2.5 2.5 1 0 0 ... therefore the effect of not calculating on a multi-cycle basis when PV generation allows resolves to 550kWh of annual battery benefit, a reduction of 275kWh(825-550) which would logically lead to a corresponding increase in daylight energy imports, which describes a situation which would be relatively disadvantageous ...

At this point I'm going to ask a basic & fundamental technical question ... Does your battery solution have the facility to monitor solar PV generation and household demand & automatically manage daylight support to the PV system generation in order to avoid unnecessary daytime imports ... for example, the PV is generating 1kW and a 3kW kettle is switched on ... does the management system see this and create a demand on the battery system inverter to supply what's required (ie ~2kW) ... if not, then there's probably no-one here with any remaining product interest - and if so, why is this missing in your investment return model as described in "... It assumes one cycle of the battery per day" ??

Anyway, plenty to be getting on with there ... have a look & try to follow what's being conveyed regarding looking at solar on a stand-alone basis before even considering thinking about intra-day generation variability or topping-up with off-peak E7 overnight .. but please refrain from the claims that other's aren't listening, because, believe me, we are ...

HTH
Z

TrevorL · 6 November 2018 at 10:26PM

Martyn1981 wrote: »

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

I have no problem with you agreeing or not, you're entitled to your opinion. I object to not receiving the same courtesy. I explained that in my opinion prices will go up over the next decade and quoted from an online source that said the same, in part because of increased transmission costs. Yet you have to come back to it 10 times because your opinion is better than ours.

Martyn1981 wrote: »

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.

Ready for an open-minded discussion then..

Martyn1981 wrote: »

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?

I've explained that the cycle life is not relevant (it represents about 20 years never mind 10) but you have a bee in your bonnet about it. We model the actual degradation and have shown that payback is still achievable within 10 years for a particular demographic, but not for most people. Nonetheless most of our customers are accepting of a payback of between 10 and 15 years. You want a payback within warranty, fine, but why get so vitriolic because some people don't? Their opinion is different to yours, that's all.

Martyn1981 wrote: »

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.

And repeat, even though cycles are irrelevant. For the ideal demographic it will paid back long before the number of cycles is reached.

Martyn1981 wrote: »

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.

In a nutshell you have shown how different you are to our typical customer, despite your protestations.

zeupater wrote: »

At this point I'm going to ask a basic & fundamental technical question ... Does your battery solution have the facility to monitor solar PV generation and household demand & automatically manage daylight support to the PV system generation in order to avoid unnecessary daytime imports ... for example, the PV is generating 1kW and a 3kW kettle is switched on ... does the management system see this and create a demand on the battery system inverter to supply what's required (ie ~2kW) ... if not, then there's probably no-one here with any remaining product interest -

Sorry, but it does. No more ammunition for you.

I've never known such a hectoring or combative forum as this and I'm feeling that I should have stayed away. But let's have one more go at finding common ground by coming at it from a completely different direction with a couple of thought experiments.

1. Imagine a big solar generating and big consuming user. He pays £6k for a 10 kWh system.

Given you are obsessed with cycles, let's do it in your terms and say he cycles it 6000 times and then it stops dead. Potentially (and we can bring in real-world constraints and inflation/price increases later) I believe this means he could save up to 10 kWh x 6000 x 18p, for a total of £9k.

Can we agree thus far?

2. Now onto the bit you guys can't see, so maybe this is where we diverge. Although physical effects, price changes, etc. are important, the reason most people can't save this much money is because they cannot fill the system with solar during the winter, assuming it is roughly matched to their summer generation. Therefore 6000 cycles of just solar is heading up towards 20+ years.

Our proposal is that they top it up with Eco7 during the winter. Can you see that although it will save them less money (maybe only £7k depending on the numbers chosen) it will reduce the payback time?

Essentially you are trading the opportunity to save 18p/kWh in the years 15-20 for a saving of 9p/kWh in the years 10-15. It absolutely doesn't maximise savings but it does minimise the payback time.

Exiled_Tyke · 6 November 2018 at 11:52PM

'It absolutely doesn't maximise savings' and there we finally have the admission!

Over the years I've come to respect the values and intelligence of the survivors of these boards. They've saved many newbies from over zealous sales techniques and brought clarity and understanding to the economics of Green Energy. Time and time again we've been bombarded with rhetoric and 'not quite right' logic from Renewable haters or those desperate to sell their wares at all costs. I will ever be grateful for those, through the years who have worked hard here to help others with difficult financial decisions and maintain the integrity of the potential for renewables.

zeupater · 7 November 2018 at 1:22AM

TrevorL wrote: »

... Sorry, but it does. No more ammunition for you.

I've never known such a hectoring or combative forum as this and I'm feeling that I should have stayed away. But let's have one more go at finding common ground by coming at it from a completely different direction with a couple of thought experiments.

1. Imagine a big solar generating and big consuming user. He pays £6k for a 10 kWh system.

Given you are obsessed with cycles, let's do it in your terms and say he cycles it 6000 times and then it stops dead. Potentially (and we can bring in real-world constraints and inflation/price increases later) I believe this means he could save up to 10 kWh x 6000 x 18p, for a total of £9k.

Can we agree thus far?

2. Now onto the bit you guys can't see, so maybe this is where we diverge. Although physical effects, price changes, etc. are important, the reason most people can't save this much money is because they cannot fill the system with solar during the winter, assuming it is roughly matched to their summer generation. Therefore 6000 cycles of just solar is heading up towards 20+ years.

Our proposal is that they top it up with Eco7 during the winter. Can you see that although it will save them less money (maybe only £7k depending on the numbers chosen) it will reduce the payback time?

Essentially you are trading the opportunity to save 18p/kWh in the years 15-20 for a saving of 9p/kWh in the years 10-15. It absolutely doesn't maximise savings but it does minimise the payback time.

Hi

In turn ...

- "Sorry, but it does. No more ammunition for you." .. I'm not seeking ammunition, just to clarify why you stated that your model is based on 1 cycle/day when a small capacity (2.5kWh) battery system with a reasonable inverter (say 3kW) could act to accumulate spare low power generation (say 500W) and deliver it to high temporary loads (such as kettles, toasters, irons, lawnmowers etc) for a proportion of the year as this provides a better return ... my original assessment was based on it could before you described your model basis to assume ".. one cycle of the battery per day" ... maybe your model could be improved along these lines, but note that the 1.6cycles during the best 6 months for solar generation would only apply when the battery is relatively small when compared to the solar array ... for example, doubling the battery to 5kWh with the same load pattern would cycle below 1.3x per day during the same 6 months, this being related to the load being diluted by the additional storage capacity and the ability of the array to feed energy into that additional capacity ...

- " ... Imagine a big solar generating and big consuming user. He pays £6k for a 10 kWh system" ... I'm sorry, but you seem to be creating a diversion by changing the criteria ... so for the moment let's stick to options which have been used so far ... I'll explain why ...

Your 6000cycle example has nothing to do with what I've been trying to convey regarding the understanding of the solar generation element and it's relationship with the available storage capacity ... it's also clear that a flawed argument is also developing based on the assessment that the PV "... cannot fill the system with solar during the winter, assuming it is roughly matched to their summer generation. Therefore 6000 cycles of just solar is heading up towards 20+ years." because of the daily generation variability element that we have yet to discuss ...

Let me make it clear without going into detail prematurely ... a typical 4kWp system will not be guaranteed to fill a 10kWh battery system as often as you may believe, even in the best 6 months. You must understand that the PVGIS daily generation estimates you referenced are simply averages - the high summer daily PVGIS estimate of 16kWh over ~15Hrs could be met over two consecutive days by returning 25kWh & 7kWh, subtract the household load over the generating hours (say 5kWh) and you're looking at charging the battery with the full 10kWh and exporting 10kWh one day, followed by only having enough spare energy to provide a 2kWh charge the next which seriously impacts on the cycle count ... I have analysed hundreds of thousands of lines of historical PV generation data in the past to understand energy storage relative to various forms of generation/collection and have been storing various forms of energy for decades, so believe me, you need to follow and understand what myself & others are trying to convey through the use of simple models & concepts before introducing additional complexity, so let's just keep it simple for now ...

Don't think or worry that E7 is being ignored ... many contributors on these boards understand the capabilities of solar, the basic capabilities of typical battery offerings and that E7 can be used as an option to leverage the value of the battery capacity, however, step 1 is to help you address the basics of solar and how this impacts your overall investment/returns model ... please review the previous posts regarding this & try to understand, it's not complex yet, but it will be when we really get going, so just look to take the small steps at the moment, one at a time ...

HTH
Z

Zarch · 7 November 2018 at 9:42AM

I'm enjoying this and learning a lot from it.

I applaud TrevorL for continuing to fight his own corner in the face of stringent questioning from Martyn and Z.

Its never good having just a one sided opinions.

pile-o-stone · 7 November 2018 at 10:23AM

Can you guys please just agree to disagree on whether there is currently a ROI on batteries?

We've had a couple of pages now and no change of positions in the discussion. At this point if we were sat in a pub we would give up and move the discussion along.

Let's draw a line under all this because we will end up with the board moderators telling us off and changing the title of this thread to "On-grid domestic storage with ROI calculations valid only within the last 2 weeks"

Joking aside, there is also the worry that it drives people away from the board and we end up in a diminished echo chamber with everyone too scared to express an opinion that isn't part of the mainstream.

This happened with that pro-nuclear chap who's contributions made me think again about my anti-nuclear stance. He left a few weeks back, never to be seen again.

Martyn1981 · 7 November 2018 at 2:11PM

TrevorL wrote: »

I have no problem with you agreeing or not, you're entitled to your opinion. I object to not receiving the same courtesy. I explained that in my opinion prices will go up over the next decade and quoted from an online source that said the same, in part because of increased transmission costs. Yet you have to come back to it 10 times because your opinion is better than ours.

Ready for an open-minded discussion then..

I've explained that the cycle life is not relevant (it represents about 20 years never mind 10) but you have a bee in your bonnet about it. We model the actual degradation and have shown that payback is still achievable within 10 years for a particular demographic, but not for most people. Nonetheless most of our customers are accepting of a payback of between 10 and 15 years. You want a payback within warranty, fine, but why get so vitriolic because some people don't? Their opinion is different to yours, that's all.

And repeat, even though cycles are irrelevant. For the ideal demographic it will paid back long before the number of cycles is reached.

In a nutshell you have shown how different you are to our typical customer, despite your protestations.

Sorry, but it does. No more ammunition for you.

I've never known such a hectoring or combative forum as this and I'm feeling that I should have stayed away. But let's have one more go at finding common ground by coming at it from a completely different direction with a couple of thought experiments.

1. Imagine a big solar generating and big consuming user. He pays £6k for a 10 kWh system.

Given you are obsessed with cycles, let's do it in your terms and say he cycles it 6000 times and then it stops dead. Potentially (and we can bring in real-world constraints and inflation/price increases later) I believe this means he could save up to 10 kWh x 6000 x 18p, for a total of £9k.

Can we agree thus far?

2. Now onto the bit you guys can't see, so maybe this is where we diverge. Although physical effects, price changes, etc. are important, the reason most people can't save this much money is because they cannot fill the system with solar during the winter, assuming it is roughly matched to their summer generation. Therefore 6000 cycles of just solar is heading up towards 20+ years.

Our proposal is that they top it up with Eco7 during the winter. Can you see that although it will save them less money (maybe only £7k depending on the numbers chosen) it will reduce the payback time?

Essentially you are trading the opportunity to save 18p/kWh in the years 15-20 for a saving of 9p/kWh in the years 10-15. It absolutely doesn't maximise savings but it does minimise the payback time.

I am being courteous to you despite your response each time being that I'm not listening, despite my referring to your claims. What you call combative, or lack of open mindedness is simply folk not agreeing with your chosen data. This is very important as your claims of payback rely on your claims of inflation. It also relies on factors external to your warranty, such as a larger number of cycles and life expectancy - now that's fine, but as I've said a number of times this is a risk borne by your customers not you as for payback to happen the product has to exceed your warranted expectations.

Yet again what I find most interesting is your avoidance to own the future price of 34p/KWh in 10yrs that you suggested, not me, you suggested:

TrevorL wrote: »

When we run our financial model we assume 2% capacity degradation per year and an annual price rise of 8.4%.

I've always found that folk speaking the truth and commonsense have no problem sticking to their story, but those with questionable claims get into trouble rapidly (after about 20 posts) because their own claims are counter intuitive.

The fact that you won't support your own claim is interesting.

Now let's take it to your end date:

TrevorL wrote: »

I don't understand the model you describe. Ours considers each month through the year ........ // ....... 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.

So, 8.4% on 15p/kWh for 20yrs gives us 'your' predicted unit price of 75.3p/kWh. That's what your financial model is based on, right?

Regarding the benefits of E7 based on your 10kWh £6k price (I can't find one, the closest I get is 8.1kWh useable for £5k) we see a unit cost of 10p/kWh (£6k / (10kWh x 6,000 cycles). [Note, this is ignoring your own 2%pa capacity degradation.]

Next we need a price differential, so again to avoid arguments I will use yours:

TrevorL wrote: »

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.

So your price differential is 7.5p with a target to beat of 15p.

So we buy the leccy at 7.5p, which after system losses gives us an input of approx 1.12kWh for 1kWh out, so 7.5p x 1.12 = 8.4p.

Next we add the cost of storage, which was 10p/kWh (out), so we get a cost of 18.4p/kWh v's buying it from your supplier at 15p/KWh.

This loss of 3.4p/KWh is described by you as:

TrevorL wrote: »

Our proposal is that they top it up with Eco7 during the winter. Can you see that although it will save them less money (maybe only £7k depending on the numbers chosen) it will reduce the payback time?

No it won't, it will lengthen the payback time whilst consuming cycles and reducing capacity.

And before you attack me yet again, please be reminded that I'm using your claims and statements.

BTW, how many customers do you have that achieved a payback after 8-14yrs? Or is that simply a projection based on your chosen data set?

Martyn1981 · 7 November 2018 at 2:19PM

pile-o-stone wrote: »

Can you guys please just agree to disagree on whether there is currently a ROI on batteries?

We've had a couple of pages now and no change of positions in the discussion. At this point if we were sat in a pub we would give up and move the discussion along.

Let's draw a line under all this because we will end up with the board moderators telling us off and changing the title of this thread to "On-grid domestic storage with ROI calculations valid only within the last 2 weeks"

Joking aside, there is also the worry that it drives people away from the board and we end up in a diminished echo chamber with everyone too scared to express an opinion that isn't part of the mainstream.

This happened with that pro-nuclear chap who's contributions made me think again about my anti-nuclear stance. He left a few weeks back, never to be seen again.

I'm sorry but there is simply too much money involved to sit idly by and accept/tolerate claims of ROI on overly high inflationary uplifts.

Strip that out and accept that the technology is hopefully within a few years of being a good investment (from falling prices) and all's sweet.

zeupater · 7 November 2018 at 2:47PM

TrevorL wrote: »

1. Imagine a big solar generating and big consuming user. He pays £6k for a 10 kWh system.

... I believe this means he could save up to 10 kWh x 6000 x 18p, for a total of £9k.

.... Essentially you are trading the opportunity to save 18p/kWh in the years 15-20 for a saving of 9p/kWh in the years 10-15. It absolutely doesn't maximise savings but it does minimise the payback time.

Hi

I was going to add this last night, but decided that at well past midnight I'd rather turn in! ... so, as an addendum to the previous post ...

The error you're introducing here is in the relative value of energy. This was planned to be well down the line as logic dictates that the process would be to establish - solar, storage, E7, value, forecast - in that order ... however, to put a flag on the energy assumptions made, I'll just highlight the issue for now ...

A1) - This is the same error that's made by companies & suppliers looking to cost justify PV to DHW proportional diversion products.

A2) - Where a household uses their GCH to heat DHW their cost is based on gas tariffs. Through diverting excess PV energy to DHW, the household (if on a deemed export FiT agreement) can effectively displace the cost of gas with 'free' energy, thus making a saving which would eventually cover the capital cost of the diversion equipment ...

A3) - Many manufacturers & suppliers look at the capability of their system to divert excess self-generated electrical energy to DHW and then, whether intentionally or unintentionally, value the unit cost differential on an electricity tariff basis, using this to establish an enhanced payback period ...

A4) - Before installing proportional diversion the energy cost to the consumer was £GasTariff*TotalUnits, the true diversion saving is £GasTariff*TotalDivertedUnits as opposed to £ElecTariff*TotalDivertedUnits ...

We've had this discussion many times and you'll find that there's a very high degree of consensus on both this part of the forum and the one dedicated to energy supply. Taking this into consideration we'll look at the above PV/DHW proportional generation points as applied to battery diversion ...

B1) - From the justification logic posted last night (as referenced above), you seem to be making the same error in diverting to battery storage as highlighted in (A1) ...

B2) - Where a household has PV but no battery storage and no justifiable requirement to use E7, then their imported electricity cost is based on single rate electricity tariffs. Through diverting excess PV energy to battery, the household (if on a deemed export FiT agreement) can effectively displace a proportion of the cost of electricity with a combination comprising 'free' energy from the PV and a top-up element leveraging E7's 'cheap rate' overnight tariffs, thus making a saving which would eventually cover the capital cost of the battery system ...

B3) - Battery manufacturers & suppliers have the same potential to look at the capability of their system to divert excess self-generated electrical energy to their storage solutions and then, whether intentionally or unintentionally, value the unit cost differential between the 'free' self generation element and the daytime E7 tariff for storage supplied by PV, with the tariff differential between the E7 daytime & 'cheap-rate' being used to value the E7 contribution, again using this to establish an enhanced payback period ...

B4) - Before installing a battery system the imported energy cost to the consumer was £ElecTariff*TotalImportUnits, the realistic battery diversion position being ...

(a) - Remaining Daytime Rate Imports - (£OriginalElecTariff-£E7DayTariff)*Import
(b) - E7 Cheap Rate Imports - (£OriginalElecTariff-£E7CheapTariff)*Import
(c) - PV Diverted to storage - £OriginalElecTariff*Diverted
(d) - E7 Cheap Rate Import to storage - ((£OriginalElecTariff-(£E7CheapTariff)*Diverted)+((£E7CheapTariff)*(Diverted*0.15)))

... Note that the logic used in your quoted example doesn't recognise the following -
(a) represents a higher unit cost to the consumer
(b) reduces the E7 contribution for energy directly consumed in the 7 cheap rate hours
(c) values the PV saving correctly, but reduces the value of the calculated savings (although the round trip efficiency impact on total PV energy availability has been intentionally excluded for simplicity!)
(d) values the E7 storage contribution correctly if the storage round-trip efficiency is 85% & reduces the value of the calculated potential savings ...

In addition to the capacity errors highlighted in last night's post which would result in overestimating the energy based returns, the unit price saving assumptions would also overestimate the valuation of the potential, thus compounding the two errors, whether intentionally or unintentionally, having the effect of delivering unrealistic expectations which feed though to unrealistic investment justifications ....

This is why we need to compartmentalise the issues & look at the basics first ...

HTH
Z

zeupater · 7 November 2018 at 3:29PM

Martyn1981 wrote: »

I'm sorry but there is simply too much money involved to sit idly by and except/tolerate claims of ROI on overly high inflationary uplifts.

Strip that out and accept that the technology is hopefully within a few years of being a good investment (from falling prices) and all's sweet.

Hi

Agree, I know a couple of people (and am aware of a number more from various sources!), who have been disappointed by their battery performance relative to supplier claims and have eventually been able to return their product for a full refund (took some time, but they have done it!), which supports a conclusion that many justification models are seriously flawed ...

I would rather expend my effort helping both suppliers & consumers understand the issues involved in employing erroneous logic at this early stage, than see seriously negative newspaper headlines concerning home storage in a few years time ...

In reality, I'd rather that the relevant industry associations, Ofgem, FCA etc sat down and agreed to commission a standardised assessment process & basic algorithm to be employed by all suppliers in correspondence with potential customers, particularly so at quotation stage, but that would either need to be driven by the industry now, or imposed by regulation later !

HTH
Z

On-grid domestic battery storage

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