Lead Acid batteries discussion

[Richard Mackay]

There's no doubt that lea acid batteries are a cost effective battery technology and they will be around for a long time yet.

However I don't see much discussion about (and what I reckon is a big disadvantage about lead acid batteries compared to Li-Ion) is their efficiency. As one gets involved with RE systems and trying to get better and better performance out of these systems efficiency plays a part in every department.

See this article from battery University: https://batteryuniversity.com/learn/article/bu_808c_coulombic_and_energy_efficiency_with_the_battery

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7 hours ago, Richard Mackay said:

efficiency

The largest part of it is voltage inefficiency. You discharge the battery at 12.5V or less. You charge it at 14V and above. If you put back the same amount of Amp hours, the efficiency becomes simply 12/14 aka 6/7 (ish), so about one seventh is lost (without having to take the calculator out) or about 14%.

[Richard Mackay]

It's similar to the price you pay for driving an automatic car. From what I remember you lose about the same amount of power. This wasn't ok with me so I always bought a manual car for better efficiency.

The point about Li-Ion battery not using a chemical reaction is evident with their amazing efficiency. I don't think this is fully appreciated. Maybe this isn't an issue when your PV panels are delivering plenty power under the hot African sun but what if you are charging your batteries with a genset?

[phil.g00]

34 minutes ago, Richard Mackay said:

The point about Li-Ion battery not using a chemical reaction is evident with their amazing efficiency. I don't think this is fully appreciated.

In an offgrid scenario, where you are cycling the batteries Lithium is the way to go. Then you are getting what you paid for.

Maybe there is also an argument for grid tied without export.

Grid tie with export is not so clear cut.

It is established that even with Lithiums the grid is always cheaper than using a battery.

So how does it cost out in a scenario (LA vs Lithium) where a user intends to keep his bank fully charged and only deploy it for power cuts?

Just asking... I haven't done the sums, but maybe there is still a place for LA's.

 

[Richard Mackay]

11 hours ago, phil.g00 said:

It is established that even with Lithiums the grid is always cheaper than using a battery.

 

I have suspected as much but not seen a report. Do you have a link to this info?

I would like to see the criteria: SA or other country? etc. questions, questions, questions... 

[phil.g00]

5 hours ago, Richard Mackay said:

I have suspected as much but not seen a report.

There is a spreadsheet on this forum somewhere.

Basically, it goes like this:  the battery cost/ lifetime kWh = X, and X always works out to be bigger than the utility price.

Of course this may not hold true forever, but that is more  because the utility price increases rather than battery prices decreases.

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On 2019/11/23 at 8:08 PM, Richard Mackay said:

It's similar to the price you pay for driving an automatic car. From what I remember you lose about the same amount of power.

Modern boxes have lockup clutches and especially with the latest 6-speed and more boxes they are quite aggressive about locking it up sooner rather than later. As such the efficiency is now on par and sometimes even better (because of the number of gears). But yeah, 4% loss on a manual, 13% on a conventional automatic... but manufacturers are moving away from the manual because computers now shift better than a human... or so they say. If i just watch the shift lights on my manual (it tells you when it thinks you should shift)... I shift pretty much at all the same points anyway.

I drive a manual because I don't like what you might call a lack of control. Off the line, the accelerator is a bit like a "wish" pedal... and you have to wish just the right amount to pull off the line smoothly (and not fly off). So I know I can get used to it... but on a test drive, this just didn't inspire confidence. I'd much rather drive a CVT, thanks.

23 hours ago, phil.g00 said:

It is established that even with Lithiums the grid is always cheaper than using a battery.

Very close to on par. Eg Pylontech battery, around 16k for 2kwh and 6000 cycles. So 16000/(2*6000) = R1.34 per unit. Cape Town charges me R2 on the low end and R2.63 (ish?) on the top end. But that is IF the battery manages to do the 6000 cycles, but even at 4000 cycles we're on par.

[phil.g00]

1 hour ago, plonkster said:

Very close to on par. Eg Pylontech battery, around 16k for 2kwh and 6000 cycles. So 16000/(2*6000) = R1.34 per unit. Cape Town charges me R2 on the low end and R2.63 (ish?) on the top end. But that is IF the battery manages to do the 6000 cycles, but even at 4000 cycles we're on par.

Ah, statistics, gotta love 'em.

Let me have a bash at the numbers, for some fun.

Sure we have an unproven claim about number of cycles, and you've knocked off 1/3 of the claim, fair enough, but we have very hard fixed seven year warranty with a Pylontech if I'm right.

7X365 = 2555  16000/2555 = R6.22 p/day.

Then there is the assumption, behind your logic that a 2kWh battery will save you 2 kWh/day. That is an absolute optimum situation, when your night time consumption perfectly matches your battery storage.  If you get a day that your batteries don't charge or if you have extra stored power in the morning that has not been used at night, you are sub-optimum for the same R6.22/day.

Then we have to factor in that the choice to store power in a battery is at the expense of foregoing the export tarriff. ( which I have no idea what it is, so lets say its a fictious R0.50, for the sake of the sums).

So using a kWh at night from your battery, which you chose not to export during the day, isn't saving R2, it is saving you R2 minus the export tarriff foregone = R1.50.

Saving the full 2kWh from the Pylontech, everyday and fully utilizing at night ( absolute best case scenario) will save you R3.00.

But,  that 2kWh battery costs you R6.22 p/day...........

 

Edited November 24, 2019 by phil.g00

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12 minutes ago, phil.g00 said:

But,  that 2kWh battery costs you R6.22 p/day...........

There is also opportunity cost, if I had rather invested the 16k into some interest bearing vehicle.

So what I said sounds confusing, I know. I said it is close to on par, and then I positively proved that it's already cheaper... but that is simply because I didn't bring in all the factors. Cause you know... even this short message was interrupted twice by my kids who wanted something...

[phil.g00]

1 minute ago, plonkster said:

There is also opportunity cost, if I had rather invested the 16k into some interest bearing vehicle.

That too.

[Fuenkli]

11 hours ago, phil.g00 said:

but we have very hard fixed seven year warranty with a Pylontech if I'm right

if they can afford to give you a 7 year warranty then the average battery out there will live much longer than that. Also interesting is to look at the Australian battery test center result which indicate a very high probability of achieving 6000 cycles.  

[phil.g00]

2 hours ago, Fuenkli said:

if they can afford to give you a 7 year warranty then the average battery out there will live much longer than that.

You are drawing an unsafe conclusion from their warranty offer, but you are drawing the conclusion that the marketing department hoped you would.

Business models like, Ponsi schemes ( and I am not saying this is one at all), actually rely on credibility and getting mass buy in, only evaporate when the chickens come home to roost.

Because people have different opinions, people make different investment decisions.  Although marketing claims are ubiquitous, not all are true.

2 hours ago, Fuenkli said:

Also interesting is to look at the Australian battery test center result which indicate a very high probability of achieving 6000 cycles.  

Let's consider the Australian battery test center study. People often misquote the source material as told to them by others.

The study is incomplete and characterized by bi-annual performance reports, since 2016. It onto it's 3 phase, with Pylontech entering since the second phase. 

Lets put some further context and detail to the Australian battery test center's reports.

The report specifically states on several occasions that linear degradation of lithiums may not the correct model and therefore extrapolating may not be valid.

But, the latest report does go on to extrapolate the batteries and here I have to correct you, they indicate that Pylontech will achieve 60 % at 4460 cycles.

Other Lithiums in the same study (that have made similar claims) seem to be floundering and indeed some have failed, well short of the claims.

To me, and as stated in the report, there actually appears to be a clear non-linearity to the degradation of the more cycled Lithiums, and some batteries ( with more cycles than Pylontech complete to date) seem to be heading for sub-2000 cycles by 60% performance level. (The report's extrapolations).

My opinion of the study shows me that your odds of backing the correct Lithium horse in a race, are about the same as backing real horses.

And we are not in the home straight yet with any of them.

Your bet on a Lithium horse is only mitigated by an honored warranty period. That is why I base my ROI calculations on this period.

I contend that basing your considerable investment on the mis-reading of the (self-doubting) extrapolations of an incomplete study or on  biased marketing blurb is an unsafe basis.

 

Edited November 25, 2019 by phil.g00

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Warranties are marketing tools. A family member who works for a chemical company (they make paint) explained this to me.

What the company cares about is that the claims are low enough, usually below some acceptable number (1% or so, maybe). If you operate in a market with low claim rates, you can actually inflate your warranty claims and still remain within the acceptable claims limit.

Paint for example. If you read the small print, there are all sorts of things in there about using a qualified professional to apply it and sending in documentation afterwards.

How many people actually bother sending the paperwork to Plascon/Dulux? How many will bother with a claim if they decide to repaint after 6.5 years into a so-called 7-year warranty?

The pain company knows this, and hence they can claim a 7 year (Dulux) or 10 year (Plascon) warranty without too much stress.

Of course this doesn't mean the paint won't last that long. Usually it does. But that is for house paint...

Second example. Sinoteq televisions. At one point they had a 5-year warranty. Does anyone really believe they are that good? Nope... they are cheap enough that they can afford a slightly higher claim rate.

Even stuff like medical aid vs gap cover. Medical aid is a mutual fund and has high claim rates, hence the cost is high. Gap cover is an insurance product with much lower claim rates, and therefore the cost is low.

[Richard Mackay]

And then at the smaller end of battery suppliers (SLA) they have this clause: REGRETFULLY NO RETURNS ON BATTERY ORDERS

Does this mean that there's no warranty whatsoever or is it to try and let unhappy customers know that they shouldn't try? 

Despite this clause I will take a faulty battery back to the supplier and stand my ground!

[phil.g00]

It is a long time since I was at school.

Does anybody know the NPV versus FV comparison calculation to work out a battery budget to go off- grid.

I pay X /month standing line charge.

I can expect this standing charge to go up year-on-year by Y1%.

I could invest the money alternatively at Y2%

The payback period is: Z months ( the battery life)

What will my battery budget be to break even.

Who can still remember the equations?

 

 

[DeepBass9]

Just work out the yearly cost in excel and use the npv function if you want to do it that way.  It is easier though to just use current costs rather than inflate into the future and then discount back to an NPV.

Edited November 25, 2019 by DeepBass9

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12 hours ago, phil.g00 said:

Who can still remember the equations?

I assume you're talking about the equation for compound interest? Starts out with a series of (1+i)^n factors (cause each month you have the original money plus interest i), and then you do some magic and end up with

A = P(1+r)^t

Which I totally googled because I too cannot remember it. About two decades ago I wrote a tool for a customer called the "medical aid prefunder", which used this formula a number of times to work out that if the medical aid rates grow at rate X and I can save money at rate Y, how much money must I save to afford my medical aid after retirement. This sounds the same

Edited November 26, 2019 by plonkster

[phil.g00]

6 minutes ago, plonkster said:

Which I totally googled because I too cannot remember it.

I'm guilty too. Electrics are in my DNA, that stuff I'd have to get my head around again. Surely someone has finances in their DNA here.

Edited November 26, 2019 by phil.g00

[phil.g00]

OK. I cobbled some numbers together:

Based on a fixed my line rental of R3.215K/m, say increasing by 10% annually, and an annual rate of inflation of 5% (discounted monthly).

With a battery life of seven years for ROI. ( 84 months)

I will spend pay a total of 366K, which discounted for inflation in today's money would be worth 302K.

So you'd think 302K would be the budget, but:

If I took that 302K  lump and invested it for seven years at anything above the inflation rate it would be worth more than 302K in today's money.

So none the wiser.

 

 

 

[DeepBass9]

Look at it this way. The batteries replace your line cost, which is R300k over the life of the batteries. If you batteries are cheaper than that then you win. A R100k battery pack is pretty substancial, a R10k generator for emergencies and the solar panels are paid for by your kwh rate. 

When I went off grid the all in cost for usage was about R5/kwh (line cost plus all the other charges and usage). With a high fixed cost, the less power we used, the higher the effective kwh cost became, so even 5 years ago it was easy to make a case for off grid at that cost. Now it should be even easier.

[phil.g00]

1 hour ago, DeepBass9 said:

If you batteries are cheaper than that then you win. A R100k battery pack is pretty substancial, a R10k generator for emergencies and the solar panels are paid for by your kwh rate. 

I am happy that the solar panels will beat the kWh rate, and without (relatively) much more capital outlay, I could make enough energy to cover my full daily usage.

Storing what I make during the day to use at night is the expensive bit.

A 300K battery would be too small. I'd get about 50kWh of Lithium storage for R300K,  and I'd want about 75kWh to cover average usage.

If a generator is part of the mix as well. Then running costs enter the equation again.

From what I see on the web, I should work on 0.5l/kWh for a diesel generator.

Which, if I am correct, at ZAR prices is R8.20/kWh, my grid price/kWh is R1.50ish/kWh, so about 5.5 times cheaper.

But there are times when the maximum demand, can be 4 times the average demand, so a generator has its place for occasional use.

 

[DeepBass9]

You use 75kWh over night? With such high usage the fixed line cost then becomes a small part of the total cost.

Generator diesel cost is about R5 or R6/ kwh.

Edited November 27, 2019 by DeepBass9

[phil.g00]

59 minutes ago, DeepBass9 said:

You use 75kWh over night? With such high usage the fixed line cost then becomes a small part of the total cost.

Yeah, you haven't lived 'til you've had a 15K 'lecky bill.

Edited November 27, 2019 by phil.g00