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Author Topic: Are batteries worth it, does this calculation work?  (Read 6334 times)
andrewellis
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« on: September 17, 2018, 09:29:12 PM »

I am trying to determine if batteries are worth it.  I should probably wait a year before getting some, but the vat saving could make it worth while doing now.

I am looking at the  ME3000SP range with pylon batteries which seem quite good value for money.  Key points : 6000 cycles, 80% DOD, 94.5% charge efficiency. 94% discharge efficiency.
Assumptions: linear discharge to 70% at 6000 cycles = average of 85% use
Current price of electricity .15.  I'll use that as most of the use is in the early stages
9.6kwh battery
So is this calculation too basic?  

Power per cycle = 9.6 *.8 * .85 *.945 *.94 =5.79kwh
power saved over life time = 6000 * power per cycle
cost  = .15 * 6000 * 5.79 = £5200  This sounds like a god return on investment.

However 6000 cycles is over 16 years assuming 1 per day. I haven’t had a single laptop battery last more than about 4 years before it has no more than 5 minutes charge held.  Does age alone have a big effect on these batteries so I shouldn’t expect more than about 10 years life?  If that is the case I’d not be able to use the 6000 charges before the battery dies and certainly won’t come near paying back.

I’m just curious if anyone has had batteries for a while (>5 years) and what charge the are holding compared to when they bought them. Thanks.
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RIT
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« Reply #1 on: September 17, 2018, 10:57:41 PM »

I am trying to determine if batteries are worth it.  I should probably wait a year before getting some, but the vat saving could make it worth while doing now.

I am looking at the  ME3000SP range with pylon batteries which seem quite good value for money.  Key points : 6000 cycles, 80% DOD, 94.5% charge efficiency. 94% discharge efficiency.
Assumptions: linear discharge to 70% at 6000 cycles = average of 85% use
Current price of electricity .15.  I'll use that as most of the use is in the early stages
9.6kwh battery
So is this calculation too basic?  

Power per cycle = 9.6 *.8 * .85 *.945 *.94 =5.79kwh
power saved over life time = 6000 * power per cycle
cost  = .15 * 6000 * 5.79 = £5200  This sounds like a god return on investment.

However 6000 cycles is over 16 years assuming 1 per day. I haven’t had a single laptop battery last more than about 4 years before it has no more than 5 minutes charge held.  Does age alone have a big effect on these batteries so I shouldn’t expect more than about 10 years life?  If that is the case I’d not be able to use the 6000 charges before the battery dies and certainly won’t come near paying back.

I’m just curious if anyone has had batteries for a while (>5 years) and what charge the are holding compared to when they bought them. Thanks.


The issue regarding battery life is that of the battery management system in place. For laptops and mobiles, there is sod-all to very little, while for large battery packs used for storage and cars there is a lot of focus on the battery management. This is how you can see reports of even the 24kWh Nissan Leaf hitting 100,000 miles when used as a taxi and still usable, with little-reported drop in cell capacity.

When trying to value a battery I start the calculation from a different point. Overall equipment costs are still dropping and this should continue. A case in point is the pylon battery as next year we should see the larger 3.4kWh unit replace the current 2.4kWh unit. So I look at the possible savings from deploying a system for say the next year and then compare it against the likely drop in the cost of the system over the year.

So far the installation of a battery system has never made much sense as the possible value of energy saving for my situation have never been higher than the year on year fall in equipment costs. At the same time, the funds stay doing something else Smiley

In terms of your calculations, you seem to be basing them on the ability of your PV system to fully recharge the batteries every day and that you then gain full value by discharging the batteries every day. You will have to look at your generation and usage in more detail I think. It's more common for the PV to provide excess energy during Spring and Summer, while you do not draw much energy from the batteries. At other times you are likely to draw more but store less.
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« Reply #2 on: September 18, 2018, 02:15:33 AM »

You haven't factored the battery charge efficiency (only the charger/inverter efficiency).
The battery mean charging efficiency (diminishing returns with age).
The simple fact that manufacturer quoted efficiencies are usually contrived and often ≥10% inflated on what you can expect in real world normal operating conditions.
Ambient temperature deratings. Battery self consumption (li-ion smanchy packs often have preheaters to stop them igniting in low ambient temperature conditions)
Installation losses (AKA: installer get home in time for dinner legacy losses)
Power factor considered reduced effective capacity.
Replacement inverter costs (only Studers live longer than 10 years)
Unfounded lifecycle claims.

Age does not have a big effect on batteries the potential for neglect and abuse over lifetime is the more pertinent issue.

Are batteries worth it?
I think so. I don't pay a lot for them though and none of mine are proprietary.

Ain't no data like empirical data.
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splyn
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« Reply #3 on: September 18, 2018, 03:03:11 AM »


I am looking at the  ME3000SP range with pylon batteries which seem quite good value for money.  Key points : 6000 cycles, 80% DOD, 94.5% charge efficiency. 94% discharge efficiency.

Its easy to claim xxx thousand cycles but LiFePo4 batteries haven't been round long enough for any reliable data on lifespan to have become available. Accelerated life testing in relatively ideal conditions in a manufacturer's test environment is one thing - whereas data from customers using them in real world, variable, conditions over long periods is almost none existent (unless anyone here knows different).

Personally I'd be very wary of any claims beyond 2000 cycles which used to be typical specs for LFP cells until one manufacturer (Winston?) starting claiming 7000 cycles. That claim, along with Pylon's 6000 cycles may well be legitimate but it will take a long time before it is verified by independant parties.

Quote
Assumptions: linear discharge to 70% at 6000 cycles = average of 85% use
Current price of electricity .15.  I'll use that as most of the use is in the early stages
9.6kwh battery
So is this calculation too basic?  

Power per cycle = 9.6 *.8 * .85 *.945 *.94 =5.79kwh
power saved over life time = 6000 * power per cycle
cost  = .15 * 6000 * 5.79 = £5200  This sounds like a god return on investment.

I assume your electricity is coming from PV. As RIT said, to be able to generate, and use 5.79kWh in excess of your usage during the generation period, daily throughout the year seems to be surprising if not impossible - in winter a 6kW PV system might produce that much, on average, and given the average 10kWh/fday UK household consumption would likely be easily consumed. But in summer it would be producing far more - from perhaps 8am to 8pm or later - so would you be likely to consume nearly 6kWh after 8pm?

And averages, being what they are, means there will be many periods of a few days when you get very little generation and many when you get far more than you can use. I'd be surprised if you could use this much stored capacity every day which would have a big impact on the economics if you don't

Quote
However 6000 cycles is over 16 years assuming 1 per day. I haven’t had a single laptop battery last more than about 4 years before it has no more than 5 minutes charge held.  Does age alone have a big effect on these batteries so I shouldn’t expect more than about 10 years life?  If that is the case I’d not be able to use the 6000 charges before the battery dies and certainly won’t come near paying back.

I think you are right to be wary. In the Pylon datasheet I looked at it stated 'Design life 10 years'. I have no idea what that means precisely, but to hope for 16 years life in addition to 6000 80% cycles seems to be a truely heroic assumption.

I suggest you have a look at this site (especially the 6 month reports) which is an Australian company testing several home storage systems:

http://batterytestcentre.com.au/

They are testing a variety of battery types including Li-ion, LFP, Lead acid etc. They produce reports every 6 months and so far it's not very encouraging - they have had a lot of 'issues', including BMS faults, faulty cells and a manufacturer going bankrupt. It is important to note that the tests are being conducted in Australian temperature conditions which are quite high in summer compared to UK conditions which will  adversely impact lifespan. Also the Tesla Powerwall 1 system, which is performing badly, is being driven harder than the other systems so is not directly comparable. They are testing the Pylontech US2000B as part of their second tranche and although it is rather early, it looks to be performing well wrt. capacity fade (see the 4th report) - so perhaps it will meet the manufacturesers claims.

Despite the caveats, the thing I would takeaway from this study is that these systems are still in their infancy and I personally wouldn't put much trust in any of the specifications at this stage. The warranties may look good but some of the smaller companies might not be around in 5 or ten years time; claiming on the warranties may be almost impossible, except in cases of relatively clear cut early failures, given the typically very long list of conditions in the warranty small print - most of which will be virtualy impossible to prove either way.

Batteries are essential for off-gridders but my opinion is they are a mug's game for anyone else who isn't in it principally to enjoy the challenge and experimentation. Those who are trying to game the system by taking our FIT money for generating power and getting paid for deemed exports that they aren't delivering, deserve everything they get... IMHO.
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djs63
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« Reply #4 on: September 18, 2018, 09:13:20 AM »

Good detailed topic, thank you to the contributors, it is helping me considerably.

Some one on here called the grid “a battery’ and at the moment, that is how I treat it.  As an extremely simplified example, if I use 5 KWh per day from the grid it costs around 75 pence (UK) and if I’m lucky I can take 3 pence per KWh off that for fITs export.  Thus 365 days at 75 pence, call it £280 per year for the use of a battery, ie the grid.

In 10 years equals still only £2800 though the price of electricity and of battery packs will be different, much less than a big battery pack currently.

But is diesn’t help the planet as much as not using the grid at all.

Do Li based batteries require “looking after”? Should you regulate the environment temperature, clean the terminals...?
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« Reply #5 on: September 18, 2018, 09:46:42 AM »

I assume your electricity is coming from PV. As RIT said, to be able to generate, and use 5.79kWh in excess of your usage during the generation period, daily throughout the year seems to be surprising if not impossible
Another factor is charge rate, i.e. the maximum rate at which the batteries can accept charge (sorry if it's already been mentioned & I didn't spot it). Even if you have 5.79kWh of excess you can't necessarily store it all if at times the excess PV is being generated at a rate that is greater than the batteries can accept; in that situation some of your 'excess' will still be exported.
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Regards
David
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andrewellis
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« Reply #6 on: September 18, 2018, 10:25:29 AM »

Thanks chaps for the detailed replies. It makes very interesting reading and has certainly helped with my decision making.

RIT - thanks, I didn’t realise the importance of the BMS. I didn't realise laptop batteries had no management.  With regard the calculations, I was thinking hypothetically if I was able to make use of all 6000 cycles independent of the time taken.  That’s where the concern about age comes in.  Will I achieve 6000 cycles at a rate of say 180 a year?  I am on economy 10 already so could time shift but the return on that wouldn’t cover the cost of the batteries.  So it doesn't seem to make sense to waste charge cycles on that.

Scruff -  So it is even more pessimistic for the electricity round trip than I realised.  I am running a GSHP so the power factor would be an issue.  I am curious, do you build your own battery packs? I would love to go down the line of retrieving the battery from my Leaf at EOL but knowing what a clumsy fella I am I don’t think I would survive long enough to tell you about it afterwards.


Splyn - We do have a very high usage which would easily allow for a cycle or two a day during the summer months.  We have 40kwh most days during the summer so we have the ability to absorb the solar pv usage. If I could ultimately use all 6000 cycles it might be worth it.  I remember there was a lot of fear about the life span of electric cars.  A well managed car battery seems to do quite well these days. I hadn't noticed the site you linked to. Thanks for the link. I feel that on some level, taking on renewables as a small invididual whilst noble is a bit of a gamble.  Reading those reports seems to back this up.  The testing site got decent backup support with battery issues as the companies involved want to show the product in the best light.  What happens to the general public who don't monitor every stat on the batteries. As an aside, wind turbines when working are fantastic, but get a turbine which is misbalanced out of the factory can lead to large repeat repair bills.  They seem to be suffering from the same problem of companies disappearing rapidly leaving a lot of farmers locally with very expensive stationary decorations.  Without a field of turbines averaging out the problems you are playing a 1 in 1000’s lottery of sending your cash down the toilet.  

The whole FIT argument / gaming the system is an interesting one which is probably for a different thread.  The government wanted to encourage the uptake of all these technologies which seem to come with a reasonable risk of equipment failure.  Without direct support for replacement of the equipment, the FIT gives some cover for the failures.  Without it, from a monetary point of view there is no point in installing the renewables at small scale.  On another hand if it is such an inefficient process of funding renewables why did we bother doing it.

I am approaching this from many sides;the geek side of things, slightly altruistic, financial gains (effectively locking in to current electricity rates).  However 4.8Kw of solar panels only produce about a 5th of what I use in the year.  Batteries would allow me to time shift the solar production during the summer months in to my GSHP, car charging, dishwasher etc.  However I suspect from replies you have solidified my view in that it probably isn't worth it financially this year.  I have quite a high base load of 900w so I'll be better off spending a few £100 on the solar edge car charger and diverting straight into the car when it is parked on the drive. I shall give it a year and reassess based on my usage rather than diving headlong into purchasing a battery set up now.


« Last Edit: September 18, 2018, 02:18:24 PM by andrewellis » Logged

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Scruff
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« Reply #7 on: September 18, 2018, 11:22:44 AM »

I build my own batteries. I get the terminals of one battery/cell usually it's about 20kg thereabouts per, I find this easier and more reliable than 90 bazillion teeny ones. I attach it to one beside it lather rinse repeat until I have the desired capacity. I put a master fuse on it and I tail it to a bus bar.

I don't have any li-ion BMS problems because I use lead acid. I've never found them lacking.
I notice most of the proponents of li-ion rather read marketing than data.

I agree with Splyn, batteries as a financial investment for grid-tied is a mug's game.
Mechanical grid-level storage is a no-brainer.

PS. I think you are confusing pessimism with pragmatism.

A lottov people like to call me cynical too. I'm not. I simply benchmark products against their own claims (with certified or traceable calibrated independent test gear) and more often than not find them lacking. Studer and MorningStar are the only manufacturers in this business I have found that live up to self-assured expectations. I could give you a much longer list of those that don't and it'd be fact not defamatory but life's too short.

« Last Edit: September 18, 2018, 12:46:25 PM by Scruff » Logged
andrewellis
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« Reply #8 on: September 18, 2018, 01:26:39 PM »

Crikey, 20kg.  Where do you get them from?  I was looking at the fork lift based ones earlier.

I am on the cautious side in life, would I be right in saying that I should build a small shed to house them with lots of holes in the roof?  I remember, in the Navy, the battery charging bay was usually above deck in its own shed.
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biff
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« Reply #9 on: September 18, 2018, 02:06:40 PM »

This is indeed an interesting thread,
                         "Is it worth it"
     The Answer is both YES and NO!  or depending where you live,,either in the town or the country, Or again, how much you value your independence.
                    Biff
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« Reply #10 on: September 18, 2018, 03:39:39 PM »

As someone who is a "soft-gridder" - as in I have solar PV and a grid-connected battery - for almost 2 years now, I can say that the question of whether it's worth is depends on what you consider the priority.

Firstly - this a clean energy/renewables forum, so you would hope a major priority for anyone here is reducing/ eliminating their reliance on fossil-fuel power.   Therefore on that basis alone, if you have some spare cash and want to spend it on reducing your import of grid power, then that's definitely "worth it."  There's a mantra on here which is "insulate insulate insulate" as far as reducing your heating energy consumption is concerned - but rarely does anyone go "oh don't bother with spending money on insulation you'll never make a return on your spend".   It's also a different equation if you're fully off-gridding as you are doing it by necessity, but each to their own. We can't all do that, but we can all try and make a difference.

Secondly - what else would you do with the money if you didn't spend it on a battery system? Is it just burning a hole in your trousers, do you need it for a "rainy day", or are you happy to splash some cash on what is basically an experiment in early adoption, but one in which you get to learn, and reduce your grid import at the same time?

Thirdly - how prepared are you to tinker?  If renewables/ batteries/ lowering your electricity/carbon consumption is something you're basically rather interested in and want to get involved with, then buying/building a battery is a good way to learn something - for your own benefit, but ultimately for others' benefit too.  But it does take up time!

Now on the actual finance-side...
To get the 15% VAT saving for a grid-tied battery, you're supposed to have to install it at the same time as some Solar PV.
To maximise the battery efficacy, get yourself on an Economy 7 tariff as well, so that in the dark months, you can get some charge in it overnight at the lower rate and get some useful work out of it as a result.
If you can build it yourself it'll be cheaper, but you won't have the warranty support. 
Some battery manufacturers and also some DNOs/ utility suppliers are experimenting with supporting batteries via a remote control tariff as well - ie they pay you to use your battery capacity as a local voltage control unit.  See if they are available in your area.

If it helps, I got a 4kWh PowerVault fitted in Dec 2016. In the first year it discharged 864kWh - so that's power I generated and avoided importing.
This year, I added E7 charging and have so far in the first 9 months discharged  1150kWh - which obviously includes E7 tariff import, but again shows the battery is working and saving me from buying electricity from the grid at the full rate.   I've probably "saved" £200 now in avoided import/tariff shifting, so it's not a total game-changing amount, but my dual fuel bill is now below £60/month for a household of 4 people.

Shop around and see what you can find.
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« Reply #11 on: September 18, 2018, 05:29:50 PM »

Very good post Dan b,
                        And very true,
 You put it a lot better than i could. I wrote a load of drivel about being off grid and even if i was on grid, i would have a large bank and a 5kw UPS between me and the CU.
  However, I scrapped it because not everyone wants to "Tinker" and "Tweak" like me. Not everybody wants complete control over their electricity generating like me.
 Having a battery like in your situation is obviously the way forward for everyone and will also lessen the need for heavier infrastructure , lines ,transformers, etc.
 The Aussies lead the way in this respect with whole communities connected through their home Batteries , kept topped up by PV. It,s a worker. A giant step in the right direction.
                                               Biff
                         
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« Reply #12 on: September 18, 2018, 07:21:44 PM »

Like others I have been thinking about this issue and concluded that stand alone batts do not work financially, but when the advent of TOU (Time of use) tariffs are imposed and then we have EVs and V2G tech. i wonder if there may not be a better way. Most of the PVs have diverters for the DHW but now we can have them for the EV and i believe that these two items and may be other demand controlled items can absorb  more than stand alone batts but in the case of the EV i feel i am saving expensive polluting FF.  I know for some people this may entail more than one EV ie an expensive one and a cheap one say £5K  but the cheap one will be cheaper than a powerwall etc and have twice the capacity.  Anyway just my thoughts.

Ken
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« Reply #13 on: September 18, 2018, 08:29:34 PM »

Crikey, 20kg.  Where do you get them from?  I was looking at the fork lift based ones earlier.

Flooded golf carts for light duty. Flooded OPzS if yer serious. Flooded forklifts if you want cost effective. AGM if they're half price or less compared to flooded. Winston cells if you need lightweight high energy density. 18650s for charging yer phone.
If your charger can't charge to specific gravity 1.28 per cell bin it and get a new one. (sigh...I sound like a broken record....and yet Victron is a major player  Roll Eyes)
 
Holes in the roof? WhaaaaT?
Nah! Hydrocaps!

There's no such thing as a game changer that's a marketing buzz word.
What's the sense in buying a battery so other people can use it?  facepalm
Energy in costs more than energy out..you're signing up to be short-changed.

State storage is not domestic storage.
« Last Edit: September 18, 2018, 08:31:23 PM by Scruff » Logged
offthegridandy
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« Reply #14 on: September 18, 2018, 08:53:27 PM »

Actually it may be if you stick to tried and tested lead acid batteries the equation is not so bad. Off grid experience (years of) so no subsidies etc.

We have 4.5 Kw of PV panels in power production.
This year since February no fully operational WT.
Red diesel cost 2018 to date £285.00
Expected red diesel cost this year £500.
1000Amp 24V FLA battery cost £1600 (2 years ago) give it a 5 year life( will be more like 12 years) so annual cost is £320
£320 + £500 =£820

So our annualised electric cost 4 bed house fully civilised with fridges and freezers UFH etc is £820. And we run a business from here.

I'd  have thought thats' got to be around break even point compared with utility supplied. And depends on life style, if you not trying to run a swimming pool or summat.

I accept I'm  ignoring the cost of the inverters and PV panels but the OP presumably all ready has these and will also be harvesting some grant money. I also ignore the cost of maintaining a Lister generator due to it's potentially near infinite life expectancy.

Depending on orientation and exact set up, for at  least 6  months of the year any surplus over battery charging and house loads could go to charging an EV for free.

One thing to think on though is, how much more you consider energy expenditure if you are directly responsible for the generation.  Eg in mid winter at night I wont use the coffee machine and electric kettle at the same time.  I'll do one then the other and thus avoid tripping the genny on, battery energy expended the same but no diesel burned in genny.


Andy
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