Hi all

With Eskom going for another 20% increase, I think it's time to revisit battery economics vs using the grid.

My problem is I can't seem to find all the info required. I use these batteries

https://solaradvice.co.za/product/fusion-4-8kwh-block-lithium-ion-battery/

Let's ignore installation costs for ease of calculation. Let's also assume that you have solar panels that you haven't maximised (e.g. you have excess solar that you cannot or do not want to send back into the grid, and that these batteries will be filled with excess "free" solar that would otherwise not be utilised).

R22,995 for 4.8kW / 80% DOD / 6000 cycles.

When the manufacturer says it can do 6000 cycles at 80% DOD, what do they mean? Do they mean 6000 cycles x 3.84kW = 23,040kwh throughput during its lifetime? Or do I need to take degradation into account - I assume a "cycle" is 3.84kW as advertised? 

Because if I can buy R23,040kwh prepaid for R22,995 in today's rands (R0.998 a kwh), that is an absolute steal. I could calculated with interest and eskom projected increases, but ignoring that for simplicity (likely eskom increases will outpace prime lending rate). It would indicate that anyone buying solar panels should size a battery rack to store as much excess power as possible (even oversizing the batteries just extends their life so not a waste to oversize a little?)

Please correct me!

Thanks,
Richard

 

 

will you be able to utilize the excess battery capacity, i have 4.8 kWh battery storage and don't get to use it down to 20% DoD everyday ( during summer ) and in winter, there are numerous days, when there is not enough pv left over after household use to charge the batteries fully.

Hi Richard

As I understand it, a "cycle" is one "charge and discharge" of the battery.  A cycle does not have to be one event.  Eg, discharging down to 90% and recharging every day will give you one 100% "cycle" in 10 days.  If you never go below 20% remaining in the battery you "should" get the 6000 cycles.

I think this means that you can "buy R23,040kwh prepaid for R22,995 in today's rands" but you pay extra for the charging part of the cycles (unless you do it purely on solar and you ignore the cost of that part of the infrastructure).

 

 

There are two models:

Rainflow cycles - 6000 cycles at 80% means 6000 3.84kWh cycles.

Equivalent full cycles - 6000 cycles at 80% means 7500 3.84kWh cycles.

No battery datasheet I have seen specifies the method they refer to; so my guess is that they use the one that makes the figures look more favorable to them.

 

Another note - R0.998/kWh is the cost of the battery alone (and that assumes you throw it away when it reaches 80% SoH) and does not account for any cost associated with charging it.

Edited December 9, 20213 yr by P1000

This changed over the last two years or so.  When we moved into our house tail end of 2018 I did the sums and at that time batteries would cost more than municipal supply.  With battery prices coming down sharply (for shits and giggles have a look at US$/kWp prices for PV panels from around 2005 to 2012 ... I believe we will see a similar crash in battery prices in the next few years) and electricity rates going the other way it is now most definitely cheaper to run solar-charged batteries. 

Edited December 9, 20213 yr by Scubadude

3 minutes ago, Scubadude said:

This changed over the last two years or so.  When we oved into our house tail end of 2018 I did the sums and at that time batteries would cost more than municipal supply.  With battery prices coming down sharply (for shits and giggles have a look at US$/kWp prices for PV panels from around 2005 to 2012 ... I believe we will see a similar crash in battery prices in the next few years) and electricity rates going the other way it is now most definitely cheaper to run solar-charged batteries. 

I believe battery prices are quite close to the bottom - they won't halve in the next 2-3 years (although I would love to be wrong). The price movement the last couple of years is (AFAIK) mostly due to the LiFePO4 patents expiring.

1 hour ago, RichardZA said:

When the manufacturer says it can do 6000 cycles at 80% DOD, what do they mean?

I don't know about other manufacturers, but the cycle counter in my Pylons (US3000B on firmware 2.8) is based on full original capacity cycles.  They see a cycle as 266400 Coulomb (74Ah) irrespective of the battery's SOH.

So for a Pylon the internal cycle counter will reach 6000 after 6667 cycles at 90%DOD, or 7500 cycles at 80%DOD.

 

3 hours ago, P1000 said:

I believe battery prices are quite close to the bottom - they won't halve in the next 2-3 years (although I would love to be wrong). The price movement the last couple of years is (AFAIK) mostly due to the LiFePO4 patents expiring.

Maybe you are right ... this chart may suggest the biggest pricedrops are over, with an 88% reduction in the last decade. Of course our ever-weakening Rand dilutes how we perceive costs. I still think it will be like hard drives ... larger and larger units for the same or less money. Would love to buy 10kWh of capacity for R 20 000.

There's talk of $100 per kWh in the next year or so, now with EV's en masse on the horizon etc etc.

some EV designs also allow bidirectional charging, so its basically a big battery in your garage.

current global supply issues are playing a role in pushing prices up atm, the panels I bought for R2400 each not so long ago are now at R3200, but I believe this is a temp hike.

$1000 for 10 kWh is a price I would pay smiling, actually a couple of times.

its gotten to the point where is really is cheaper to go solar, the $100 price point will just push it along even faster.

Edited December 9, 20213 yr by Nitrious

Having built a LiFePO₄ of my own recently and having investigated many different brands, I would recommend Hubble.  Their price per kW/H is very good and they also have a BMS that can communicate externally.  Dumb LiFePO₄ are not worth it.  Those brands will die off at some point they are only around now because people are hasty to buy batteries.

Why I would take the Hubble over Pylon:

1. Pylon is way over priced in my opinion.
2. Pylon is using 15s configuration (maybe they've switched to 16s for newer batteries?), whereas the likes of Hubble use 16s.  So your system voltage with Pylon is lower which just means lower efficiency for the inverter, especially at the bottom of the battery.  15s is really not ideal.

EDIT: Reasons not to buy Hubble

Lastly having done a LOT of investigation, the general consensus is that age is much more of a factor than cycles with LiFePO₄ (at 80% DoD).  You cannot simply use cycles and say, oh so it'll last 15 years.  That is not accurate.  There is very little data on LiFePO₄ life but the data there is (that isn't by a manufacturer who have an agenda) is that LiFePO₄ can realistically last at most 10 years.  Regardless of the number of cycles you have, at 10 years it is likely you cells will start becoming unreliable (ie. some of them will no longer be able to hold charge).  Of course if you drain you battery 100% every day or many, many cycles, age is less important but let's assume you aren't an idiot.

So in terms of life time, there is no solid no manufacturer data yet because the technology is new, so take "life" of the battery guarantees with a pinch of salt, it is almost certainly a lie and they can back up their claim by saying they ran simulated ageing (which is what they do).  But it isn't reliable data.

Lastly LiFePO₄ ages significantly faster in hot conditions. 25 degrees -> 30 degrees is where you ideally want to keep it.  At 40 degrees you are effectively cutting your cell life in half from 30 degrees and it gets pretty hectic up at 60 degrees (like 2 years).

In closing I also want to advise you to be weary of falling into the trap of calculating savings and assuming you will have no additional expenses.  That is unrealistic expectation.  You will very likely have some kind of problems at some point, most people do.  Most people will come back around and call it "school fees".  I call it ignorance.  You are dealing with a complex electrical and complex chemical reaction system, don't expect it to be fire and forget.

Edited December 13, 20213 yr by Gnome

@Gnome, one correction - Hubble is actually 13s but still one of the best value for money and performance at the moment. And I like your points. 
 

 

11 minutes ago, Gnome said:

Having built a LiFePO₄ of my own recently and having investigated many different brands, I would recommend Hubble.  Their price per kW/H is very good and they also have a BMS that can communicate externally.  Dumb LiFePO₄ are not worth it (ie. lithiumbatterysa).  Those brands will die off at some point they are only around now because people are hasty to buy batteries.

Why I would take the Hubble over Pylon:

1. Pylon is way over priced in my opinion.
2. Pylon is using 15s configuration (maybe they've switched to 16s for newer batteries?), whereas the likes of Hubble use 16s.  So your system voltage with Pylon is lower which just means lower efficiency for the inverter, especially at the bottom of the battery.  15s is really not ideal.

Lastly having done a LOT of investigation, the general consensus is that age is much more of a factor than cycles with LiFePO₄ (at 80% DoD).  You cannot simply use cycles and say, oh so it'll last 15 years.  That is not accurate.  There is very little data on LiFePO₄ life but the data there is (that isn't by a manufacturer who have an agenda) is that LiFePO₄ can realistically last at most 10 years.  Regardless of the number of cycles you have, at 10 years it is likely you cells will start becoming unreliable (ie. some of them will no longer be able to hold charge).  Of course if you drain you battery 100% every day or many, many cycles, age is less important but let's assume you aren't an idiot.

So in terms of life time, there is no solid no manufacturer data yet because the technology is new, so take "life" of the battery guarantees with a pinch of salt, it is almost certainly a lie and they can back up their claim by saying they ran simulated ageing (which is what they do).  But it isn't reliable data.

Lastly LiFePO₄ ages significantly faster in hot conditions. 25 degrees -> 30 degrees is where you ideally want to keep it.  At 40 degrees you are effectively cutting your cell life in half from 30 degrees and it gets pretty hectic up at 60 degrees (like 2 years).

In closing I also want to advise you to be weary of falling into the trap of calculating savings and assuming you will have no additional expenses.  That is unrealistic expectation.  You will very likely have some kind of problems at some point, most people do.  Most people will come back around and call it "school fees".  I call it ignorance.  You are dealing with a complex electrical and complex chemical reaction system, don't expect it to be fire and forget.

@Gnome, why do you say Lithiumbatterysa is dumb, I've done a bit of research and they claim to have a BMS, I'm not 100% sure if that is true, but I suppose if they say so it must be true ! or else in my opinion that would be fraud  

3 minutes ago, Antonio de Sa said:

@Gnome, why do you say Lithiumbatterysa is dumb, I've done a bit of research and they claim to have a BMS, I'm not 100% sure if that is true, but I suppose if they say so it must be true ! or else in my opinion that would be fraud  

Well dumb in the sense that they don't seem to provide mechanism to connect it to your inverter?  Do you even have a way to see what the BMS reports?  Like how do you get the data from their BMS?

EDIT: Ah ok, I see you are right, you can connect it to some inverters! "CAN Bus Comms: Victron,Growatt,Sunsync,DEYE".  There was another thread where someone said they had to set a pre-determined voltage and so on instead of the battery communicating with their Victron, so I assumed it was because it was a dumb unit.

Edited December 9, 20213 yr by Gnome

18 minutes ago, Gnome said:

Why I would take the Hubble over Pylon:

1. Pylon is way over priced in my opinion.
2. Pylon is using 15s configuration (maybe they've switched to 16s for newer batteries?), whereas the likes of Hubble use 16s.  So your system voltage with Pylon is lower which just means lower efficiency for the inverter, especially at the bottom of the battery.  15s is really not ideal.

The hubble is a 13s battery and uses NMC chemistry.

3 minutes ago, Nexuss said:

The hubble is a 13s battery and uses NMC chemistry.

How are they getting 51v nominal with 13s?

3 minutes ago, Gnome said:

How are they getting 51v nominal with 13s?

Not sure .  But here is the inside of an AM2. 

5 minutes ago, Gnome said:

Well dumb in the sense that they don't seem to provide mechanism to connect it to your inverter?  Do you even have a way to see what the BMS reports?  Like how do you get the data from their BMS?

EDIT: Ah ok, I see you are right, you can connect it to some inverters! "CAN Bus Comms: Victron,Growatt,Sunsync,DEYE".  There was another thread where someone said they had to set a pre-determined voltage and so on instead of the battery communicating with their Victron, so I assumed it was because it was a dumb unit.

I don't know about other users, I have a Growatt and one LBSA 5.1 KWh 100 AH and I manage to get all the info from it's BMS via Raspberry PI.

What I don't like is the fact that it counts one cycle every time SOC goes bellow 80% 

See Examples.

 

Just now, Nexuss said:

Not sure .  But here is the inside of an AM2. 

Gotcha, shoe I've got a lot of invalid points about brands it seems.  Should have looked at the insides instead of the specs like voltage 😛  Manufacturing quality looks good but you can't really beat good quantity of cells.

I'd say calling it 51v nominal is a bit optimistic (more like 48v nominal).  Maybe LithiumBatterySA isn't so bad then, assuming their BMS can actually work correctly with the inverter.

Guess this goes to show, do your research before buying!

5 minutes ago, Antonio de Sa said:

I don't know about other users, I have a Growatt and one LBSA 5.1 KWh 100 AH and I manage to get all the info from it's BMS via Raspberry PI.

What I don't like is the fact that it counts one cycle every time SOC goes bellow 80%

Yep I think you guys have pointed out, my knowledge of Lithium battery brands is pretty sh!te.  Once I went the DIY route, I didn't care so much.  Still in terms of lithium chemistry, what I said above is what I've found to be pretty much the opinion of engineers who spec these for big sites and locations now.  So I think in terms of life time, etc. it is not bad to keep that in mind.

Lithium is definitely way, way better than lead acid because it needs way less babying.  You can charge discharge essentially as you like and that is a HUGE win.  It is super hard to keep lead acid happy (leave it discharged and you are boned).  But lead acid has really, really good data on how it ages, so you can definitely show that some lead acid cells can survive 15 years assuming it it properly baby'd.  Overall I'd rather replace a battery pack every 8 years and know I can treat it how I want and get 8 years than maybe getting 15 years if I treat it like the golden goose.  Right now tho, the consensus is Lithium will age up to about 10 years but I think we need a couple more years to get some solid data from companies that aren't trying to sell you something.  So age is definitely caveat emptor!

Edited December 9, 20213 yr by Gnome

1 hour ago, Antonio de Sa said:

I don't know about other users, I have a Growatt and one LBSA 5.1 KWh 100 AH and I manage to get all the info from it's BMS via Raspberry PI.

What I don't like is the fact that it counts one cycle every time SOC goes bellow 80% 

See Examples.

 

Yeah the owner of LBSA confirmed that the BMS doesn't calculate cycles properly on one of the threads here.

It would be nice to accurately calculate the cycle count but does it really matter considering warranty is based on years instead of cycle count? I don't know

20 hours ago, Tariq said:

will you be able to utilize the excess battery capacity, i have 4.8 kWh battery storage and don't get to use it down to 20% DoD everyday ( during summer ) and in winter, there are numerous days, when there is not enough pv left over after household use to charge the batteries fully.

In summer, yes will definitely be able to use the extra 4.8kWh as people like cooking at night in the house and some geyser activity.

In winter, I'm not sure, but does this matter? If the batteries can give me 20,000kwH in their life time, perhaps the payback is a bit longer. I'm looking for a realistic "lifetime discharge" that I can use to make ROI calculations. 

 

19 hours ago, jcdup said:

I think this means that you can "buy R23,040kwh prepaid for R22,995 in today's rands" but you pay extra for the charging part of the cycles (unless you do it purely on solar and you ignore the cost of that part of the infrastructure).

 

Yes this is the position I'm in. I have too many solar panels and there are a lot of people on the forum who have oversized solar because it's the cheapest part of their system, so why not (cloudy days, winter etc). But I'm questioning the prevailing logic that you should ONLY size you batteries for load shedding cover, while leaving the rest of your system maximised.

 

13 hours ago, Gnome said:

In closing I also want to advise you to be weary of falling into the trap of calculating savings and assuming you will have no additional expenses.  That is unrealistic expectation.  You will very likely have some kind of problems at some point, most people do.  Most people will come back around and call it "school fees".  I call it ignorance.  You are dealing with a complex electrical and complex chemical reaction system, don't expect it to be fire and forget.

Ok but guys let's get back to the original question. Does anyone have a better calculation than I just provided to work out how many watts I can get out of a LifeP04 battery during its lifetime, in optimal conditions (a lifetime kwH). Even if it's not R0.99 per kwH and it turns out to be R2 per kwH, it's still cheaper for me to get more batteries whereas the prevailing attitude on this forum is that batteries are "expensive" and don't provide investment return and should be undersized in a hybrid environment.

Batteries are expensive as a cash layout, although the ROI is good as per your calculations. Getting the pricing down further would just enhance it. Has anyone looked at say Nissan leaf 2nd life batteries for home use, I know in the states it's happening. Something like that would be my ideal goto. 

Edit: so I found these guys https://www.secondlife-evbatteries.com/, they sell used ev batteries. its then just to check pricing, put together a bms if it doesnt already have one, and you get a really big battery at hopefully scrap prices. sure it may be at 70& of original, but thats also 70% of a really big battery. ROI ?, likely to be very impressive.

The pricing above doesnt seem to be that great, so a bit of digging later I found this, which is more in line with the kind of pricing that would make the effort worth it I think. - 

Edit  : it turns out the unit below wasnt specified correctly, my apologies, so the math doesnt work out as below. I still think a good idea though overall, but may need a bit of work to finetune.

NISSAN LEAF ZE0 Electric 80kw Battery Pack 295B0-3NA0A 2011

£3,000.00

£37 per kw

Now 80kw is a lot for any household, soo... lets say a group buy, everyone gets a 20kw system out for £750 plus incidentals and maybe a bms.

now thats good investment, and great roi.

pls note I'm not pitching for a group buy here, but am simply using it as an example.

Another interesting tech are panels that provide power at night, not much mind you 50w or so, and they're yet to hit market, but an ideal design would be say 500w day, 50w night

in closing, I'd say like anything, batteries can be expensive or cheap, depending on approach taken. I think the approach I've suggested shows that batteries can be incredibly cheap, from a cash layout point of view, and of course roi.

Edited December 10, 20213 yr by Nitrious

Battery technology and research is driven by the EV manufacturers. These people do not have limited resources and they each want to sell millions of their vehicles per year.

The household inverter + batteries industry is not coming to the party currently.

Expect big changes in the future.

12 hours ago, phidz said:

Yeah the owner of LBSA confirmed that the BMS doesn't calculate cycles properly on one of the threads here.

It would be nice to accurately calculate the cycle count but does it really matter considering warranty is based on years instead of cycle count? I don't know

@phidz Regarding the issue with the cycle count, yes, I did phone they technical department and they did confirm to me that the warranty is based on years and not on the number of cycles, yet, as you say, it would be nice to have an accurate count.

1 hour ago, RichardZA said:

I'm looking for a realistic "lifetime discharge" that I can use to make ROI calculations. 

So in my calc I considered a few things:

Yes your batteries can go down to 20% SOC but what are you actually comfortable taking them down to daily? My Pylontechs can go to 5% SOC per the warranty but i also want a little left for safety and surprise loadshedding. So in my ROI calc I used a 20% SOC in my daily cycle and not 5%. This is up to you but realistically you dont want the battery to shut down daily.

Secondly as someone else alluded to, how often will you use the stored capacity? My personal experience is that i cycle my batteries 24 times in a 30 day period (80% of the time). Now this may seem like I'm using the full daily discharge from point 1, but the reality is that there are cloudy patches and so there is some dynamic use of the batteries during the day as well, not just overnight usage.

Finally for my own calc, my usage would get a useful life of nearly 21 years! (6000cycles/24 cycles per month/12months). I hope this will be true but it isnt realistic in my eyes. So I took the shorter of the cycles and the warranty and used 10 years. so 10 years x 24 cycles per month x 12months = 2880 cycles.

Maybe I'm too conservative so take or leave what you need