# Solar Battery Storage



## jebatty (Aug 3, 2017)

I came across this review of Solar Storage Batteries. The options are many.


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## jharkin (Aug 3, 2017)

Interesting...

But what I notice is exactly the same thing I noticed the first time we discussed the Tesla Powerwall - most of f these LiIon based solutions are still  more expensive than the proven,  traditional lead acid deep cells that most off grid setups have used for decades...

I have do do some mental math since that site is in AUD, but the average setup there is maybe 30-40 cents (US) per total warranted lifetime KWh   and over $1,000 per KWh of installed usable storage capacity.


So lets look at a traditional off grid storage system using industrial deep cycle lead acid cells from brands like Surette, Concorde, Trojan, Crown:





If you look at a typical large capacity lead cell like this Surette 2v 1284Ah. It costs $399  and has a predicted life of 1280 cycles to 50% DoD. The math on that give me 25 cents per lifetime usable KWh and about $300 per KWh of installed usable capacity.


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## woodgeek (Aug 3, 2017)

Nice roundup.  If you got one, given recent conversations, you could more effectively reduce the carbon footprint of your grid usage.

Have you looked up the carbon intensity of MN grid power during the daytime/summer versus a seasonal average?

For comparison with the table, the current EV arrangement I use to backfeed my house during grid outages is

11 kWh usable storage,
2.0 kW (surge),
1.3 kW (steady),
120 Volt, single phase, sine wave
Chemistry: Lithium Manganese Oxide (LMO),
Mass: 270 kg (battery) 1500 kg (curb weight)
Battery Warranty: 80,000 miles (about 1000 cycles to 95% discharge)

COST: $350 (additional).


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## WoodyIsGoody (Aug 3, 2017)

jharkin said:


> I have do do some mental math since that site is in AUD, but the average setup there is maybe 30-40 cents (US) per total warranted lifetime KWh   and over $1,000 per KWh of installed usable storage capacity.
> 
> 
> So lets look at a traditional off grid storage system using industrial deep cycle lead acid cells from brands like Surette, Concorde, Trojan, Crown:
> ...



You need to compare apples to apples. 

The Lithium Ion systems have a higher percent of useable capacity. If you want your deep cycle lead-acid cells to last more than a few months, you can't cycle them fully. The Lithium ion cells are rated at there warrantied daily discharge (not their full capacity), you can't use all of the lead acid rated capacity. Also, prices are in AU$ and include GST! Also, you pick a cheap lead acid solution to compare with the "average" lithium Ion solution. But many of those prices are old and out-dated. Also, you can't just compare cost per KWh, you need to account for how long they last and how much the storage capacity decreases over time. Total system cost. 

Lithium Ion beats lead acid in so many ways it's not even close.


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## jharkin (Aug 3, 2017)

WoodyIsGoody said:


> You need to compare apples to apples.
> 
> The Lithium Ion systems have a higher percent of useable capacity. If you want your deep cycle lead-acid cells to last more than a few months, you can't cycle them fully. The Lithium ion cells are rated at there warrantied daily discharge (not their full capacity), you can't use all of the lead acid rated capacity. Also, prices are in AU$ and include GST! Also, you pick a cheap lead acid solution to compare with the "average" lithium Ion solution. But many of those prices are old and out-dated. Also, you can't just compare cost per KWh, you need to account for how long they last and how much the storage capacity decreases over time. Total system cost.
> 
> Lithium Ion beats lead acid in so many ways it's not even close.



Read my numbers again.

I *DID* compare on a usable capacity for usable capacity basis.  My calculations for the lead acid where based on a 50% DoD per cycle utilization, and based on expected life at 50% DoD  from the datasheet.

Surette S-1660  $399
2 volts
1284Ah

2v * 1284Ah = 2568 Wh = 2.568 KWh * 50% = 1.284KWh usable

$399/1.284 = *$310 / installed usable KWh*


From the lifespan table 50% DoD = 1,280 cycles
1.284 KWh/cycle * 1,280 cycle = 1,643 lifetime KWh
$399 / 1,643 lifetime KWh=* $0.243 per lifetime KWh*​
The numbers in the article are based on their published usable capacities... which I would assume is no more than 60-70% of the total installed capacity or else there is no way they are achieving lifespans in the multi-thousands of cycles. Lithium degrades when stored both at full and empty so the usual solution is to cutoff the charge at 80-90% full( around 4.0~4.1vpc no load) and then cutoff discharge at 20% full (around 3.7vpc no load)

The lead solution I picked was not cheap at all. Rolls-Surette is the Cadillac of lead acid off grid systems, they are big supplies to the railroads, marine power, etc.  If you want cheap you get china built cells from Universal Battery Group, or surplus forklift, telco, submarine batteries.

I also roughly adjusted the numbers in the link for the 79c to $1AUD current exchange rate as I stated.

LIthium does have advantages (easier to measure charge, lighter/small for the capacity, higher charge rates, more efficient charging), but its still cant beat lead on a cost/capacity basis in stationary power setups.  It probably will eventually, but not yet.  Lead is just plain *cheap*.

Of course, with Lead you have to design your own setup, buy all the components and wiring individually, install, test and maintain. And your basement looks like the battery room of a U-boat.  With something like a Tesla powerwall you get a turn-key, futuristic looking solution and instant green cred with all your McMansion buddies.


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## Redbarn (Aug 6, 2017)

There is a movement starting to use electric car components to make domestic home off-grid systems.

Electric car batteries are available from crashed cars, especially Teslas, and these have immense storage for home use.
By keeping a 400V DC bus, many of the other components are available from EV's too.
Using solar panels to provide 400V + DC power, all that is required from the grid is power to charge the battery when the solar cannot keep up.
The missing parts currently are 400V DC/AC inverters.

A (long winded ) explanation can be found at:
http://evtv.me/2017/07/selfishly-solar/


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## WoodyIsGoody (Aug 6, 2017)

Redbarn said:


> There is a movement starting to use electric car components to make domestic home off-grid systems.
> 
> Electric car batteries are available from crashed cars, especially Teslas, and these have immense storage for home use.
> By keeping a 400V DC bus, many of the other components are available from EV's too.
> ...



Very promising, but not quite ready for prime time up here at latitude 49 north. With our long nights/short days in the winter, we have peak electrical demand right when our solar production is super low. We make it up with our long summer days, however batteries can't be expected to solve seasonal variations. Especially since most winter days are heavily overcast. Eastern Montana, with it's higher percentage of clear winter days would fare somewhat better than (for example) my ski cabin in the North Cascades. Not only are there tall trees and endless weeks of heavy cloud cover and rain, but also steep mountains on all sides limiting morning and evening light.


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## Redbarn (Aug 6, 2017)

I agree that the EV battery method is not ready for Prime Time at the moment. 
Some of the hardware required doesn't exist yet in any real quantity. 
What appeals to me is the elegant simplicity of the concept. 
It bypasses the current bottleneck of 48V to 240V inverters with readily available and  potentially rugged components.


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## woodgeek (Aug 6, 2017)

I'd have to agree.  The problem is price and performance.  A lot of wealthy customers can afford a whole house, automatic genny that just runs everything, basically forever.  Even a 100 kWh Tesla (at $100k) will not run all the large appliances in a large house over a worst-case, multi-day outage.  Folks spending several $k to get a high power 240V inverter will not be pleased when the lights go out on day three, and their Model S is dead to boot.

I see my $350 inverter setup (which taps the 12V 150A DC-DC converter on the LEAF) as a nice improvement over my $100 HarborFright genny,  It will run all my 120V appliances for 30 hours, which should cover most of my outages....but I still have to keep my HF genny around for longer contingencies.

In time, using EVs for backup will take off....but the market needs to grow and prices need to fall.


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## Redbarn (Aug 6, 2017)

The EV battery solar concept does not use a live EV. 
It relies on getting a wrecked or scrap EV, removing the battery system and using it as a home energy sink.
If you have a large house, get 2 batteries

The EV batteries are rugged, have working BMS and battery heating/cooling systems and can provide 800 amps at 350 V DC with ease.
All the associated compnents are available from EVs and are proven & rugged.
Essentially, this concept is like a Tesla PowerWall but larger and cheaper for equivalent energy storage.

The weakness is that no commercially available 400V DC to 240V AC inverters currently so you cannot actually build a system.
The concept relies on abundant solar panels to provide energy and using the grid to top up on cloudy days.
No attempt is made to feed power back to the grid.
The grid is only used to charge the battery when the solar doesn't provide enough energy.

Tesla current build systems like this on a much larger scale for the island of Kauai and South Australia.
So the concept is proven, just that a home system using EV components is not ready for Prime Time yet.


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## woodgeek (Aug 6, 2017)

Sure.  I was thinking of the 'backup' version of the powerwall that seems to have been a dud (now you can only get the solar version) and the V2G systems discussed for similar backup applications.....which I also expect to be a dud.  Its hard to compete with a genny for backup.

AS for 400 VDC, I have read about folks rigging suitable inverters from commercial UPS systems....that use a high voltage AGM battery bank.

I am a bit skeptical of the *DIY* potential for second life EV battery solutions for off grid. The high voltages and high currents are more dangerous than the low voltage high current systems used today.  The BMS systems of Li-ion are a lot more complicated than balancing lead acid.  Etc.

I suspect that we will see EV-tech cells in home off-grid systems when the price falls far enough.  Whether these are first life cells or rebuilt packs from used EVs comes down to price and warranty....probably we'll see both.


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## jebatty (Aug 7, 2017)

Redbarn said:


> The weakness is that no commercially available 400V DC to 240V AC inverters currently so you cannot actually build a system.


 I am out of my pay grade on this one, but grid tie 400+VDC string inverters are available, Fronius IG 5100 for example. Is it practical/possible to modify one of these to use an EV battery pack as the energy source?


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## Redbarn (Aug 7, 2017)

jebatty said:


> I am out of my pay grade on this one, but grid tie 400+VDC string inverters are available, Fronius IG 5100 for example. Is it practical/possible to modify one of these to use an EV battery pack as the energy source?



This is beyond my range of knowledge too.
The current EV tinkerers are like the "hot rodders" of yore.
Very creative people who can make things like this happen but for the rest of us it is a stretch at the moment.

I'd been playing with the idea of getting a first generation Leaf (available for under $10K or so) and repurposing the battery system as a solar energy store. However, I rapidly realised the limitations of my knowledge and so will wait on this.
There seems to be a larger group of people repurposing Tesla hardware and I follow this with interest.


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## ken morgan (Oct 16, 2017)

get a custom wound dc transformer.....they are not that expensive.  drop your 400 VDC down to 100 VDC  and run two 48 volt inverters in series from the batteries, but parallel there output for more available wattage.  the transformer should not cost much more than a medium sized 3 phase motor as it all boils down to the windings and the cost of copper.  toss another hundred on for a cooling system to make it so that the transformer can run 24-7 and you are in business the 48 VDC sine wave inverters from say magnum run on anywhere form 36~64 VDC so its not a stretch or even difficult.  the issue is how to charge the batteries, thats where I am stuck at currently.  I assume (dangerous I know) that there should be a way to take the entire charging system from a prius as it charges form multiple sources, reverse engineer the program and adjust it to accept whatever voltage you have your PV array set up for... been thinking about this for a while as lately the payback for our solar array is not as good as what we get charged to use electricity in the non producing hours.  I would keep mains only for emergency purposes and run off of  a couple of prius batteries if i could figure out the last of the angles here.


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## begreen (Oct 16, 2017)

Ken, I thought that DC can not be transformed with a wire-wound transformer. It must be converted to a form of AC first, then dropped and then converted back to DC. This process is somewhat lossy. 

https://van.physics.illinois.edu/qa/listing.php?id=2354


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## ken morgan (Oct 16, 2017)

begreen said:


> Ken, I thought that DC can not be transformed with a wire-wound transformer. It must be converted to a form of AC first, then dropped and then converted back to DC. This process is somewhat lossy.
> 
> https://van.physics.illinois.edu/qa/listing.php?id=2354


you are correct, Twas a bit in the cups last night.  brain was swimming in ideas myself.  the other that popped into my grape was a dc motor to ac generator.  I have seen ac motor to ac generators used in rural areas where 3 phase was not available, but the loss is there of course.   maybe you could stack multiple 48 volt inverters in series to achieve your 400 volt input and run a distributed inverter grid instead? you would need either 6 or 8 and the things are not cheap, but it could be done.   almost better to have a company in china build a 400VDC inverter.


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## jebatty (Oct 17, 2017)

As an electricity inventor kid, my friends and I stepped up DC all the time to make shock machines. Used a 1-1/2V battery powering a little DC motor in series with the secondary-output side of a speaker (step-down) transformer, and then wired the primary to our shocking device, which provided a good jolt. We didn't care whether the output was DC or AC. As I know now, the stepped up DC was not AC, but choppy, very dirty DC.


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## WoodyIsGoody (Oct 17, 2017)

jebatty said:


> As an electricity inventor kid, my friends and I stepped up DC all the time to make shock machines. Used a 1-1/2V battery powering a little DC motor in series with the secondary-output side of a speaker (step-down) transformer, and then wired the primary to our shocking device, which provided a good jolt. We didn't care whether the output was DC or AC. As I know now, the stepped up DC was not AC, but choppy, very dirty DC.



Very clever! When I was a small kid, we didn't need to muck about with motors and transformers, when we wanted a thrill we could just dare each other to touch an electric fence (first with a piece of grass, when that lost it's thrill, with our hands). We never got enough courage (or full on stupidity) to risk the family jewels by peeing directly on it). 

Nowdays you can buy a game called Lightening Reaction for your kicks. It runs on 3 x AAA batteries but provides quite a jolt:

https://www.amazon.com/dp/B0006B2Q50/?tag=hearthamazon-20


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## TonyVideo (Jan 20, 2018)

WoodyIsGoody said:


> Very clever! When I was a small kid, we didn't need to muck about with motors and transformers, when we wanted a thrill we could just dare each other to touch an electric fence (first with a piece of grass, when that lost it's thrill, with our hands). We never got enough courage (or full on stupidity) to risk the family jewels by peeing directly on it).
> 
> Nowdays you can buy a game called Lightening Reaction for your kicks. It runs on 3 x AAA batteries but provides quite a jolt:
> 
> https://www.amazon.com/dp/B0006B2Q50/?tag=hearthamazon-20


Now buying a device takes all the fun out if it.

Sent from my SM-G930V using Tapatalk


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## woodgeek (Jan 21, 2018)

I recently upgraded by Li-ion home backup battery for a larger one, made by LG Chem in Korea.  It came with a new Chevy attached. 

28 kWh usable output,
2.5 kW (0.5s surge),
1.4 kW (few minute surge)
1.1 kW (continuous),
120 Volt, single phase, sine wave
Chemistry: Lithium ion NMC111 (Nickel:Manganese:Cobalt 1:1:1 mole ratio doped Cathode),
Mass: 436 kg (battery) 1600 kg (curb weight)
Battery Warranty: <40% capacity loss before 100,000 miles/8 years (about 450 cycles to 95% discharge)

COST: $0 (additional, after buying the Chevy).

GM bought the batteries from LG Chem, and leaked the price... *$145/kWh* for the cells alone.  The entire pack module (with BMS) is supposed to cost $12.5k, or *$208/kWh.*

Nice technical info on Bolt EV and battery: http://www.advantagelithium.com/_resources/pdf/UBS-Article.pdf



woodgeek said:


> Nice roundup.  If you got one, given recent conversations, you could more effectively reduce the carbon footprint of your grid usage.
> 
> Have you looked up the carbon intensity of MN grid power during the daytime/summer versus a seasonal average?
> 
> ...


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## peakbagger (Jan 21, 2018)

The storage market still is on an accelerating development curve. I lived through the PC era and remember the years where replacing computers on  a yearly basis was pretty well required due to how rapidly things were changing. It could be that lithium technology get replaced with some other technology. Whatever you buy, dont buy it for the long term as the capacity will double and price will drop a year or two out . It may not be Moore's law but its pretty darn close. 

I just dont see the value for new Lithium Ion Chemistry batteries for home use, it makes perfect sense for autos where weight to output make sense and the partially worn out cells most likely will at one point be good for home use to get more use before they get scrapped but it doesnt make sense to put new cells in a house where a low power density less costly battery will work. 

I thought the Aquion's were a better solution for home and now that they are going back in production maybe they will have a chance.


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## RFarm (Jan 24, 2018)

Good to hear the Aquions are coming back-hopefully the new owners will be more customer focused.  I tried getting information on a bank of 4 prior to the bankruptcy and it was the most frustrating experience of my life.  I am probably going to have to replace my 48V Rolls setup this summer and the Iron Edisons are at the top of my list.  Going back into lead acid just seems so 2010!


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## peakbagger (Jan 25, 2018)

I think Aquion suffered from IPO/VC pressure to get product on the street and get the cash flow going. They really didnt match the product characteristics to the demand. The discharge curves just didnt line up with lead acid technology and expect that a lot of folks who bought them were tying up their tech support folks. Iron Edison seems to have learned lessons on how to sell nickel iron batteries, the business model of the prior firm, Be Utility Free just didn't work for most folks where the customer took much of the responsibility for getting the batteries shipped from China and picked up at a port.

In theory there is a lot to be said for the Aquion chemistry as it doesn't require the frequent care and feeding of Nickel Iron chemistry and to lesser extent Lead Acid. I am not sure but I dont think the Aquions require equalization (but I could be wrong).


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## RFarm (Jan 25, 2018)

From what I recall they required a very low bulk/absorb charge rate of 57 - 58 volts for 4 hours then a float setting of 54-56 volts for up to 20 hours, no need for equalization.  Folks that had them seemed to like them and reported using the generator more frequently, but for less time overall.  I am looking forward to seeing them back on the market and possibly at an even lower price point than the $1,100.00 for a 50ah battery.


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