Thoughts on modular home battery? (like Tesla Powerwall)

If you were looking at making a Tesla Powerwall competitor how would you configure it? I'm looking at the following configurations:

18650/CALB/other format?

Per-cell BMS?

Hot swappable cells less than 50 pounds each with a slide connector similar to those you would see on a cordless drill.

Wall mounted horizontal module rack with integrated charge controller and inverter

sleek just like the powerwall, no sharp cornered boxes sitting on the floor

up-gradable expandable individually serviceable modules with a life readout and service required notification.

1) .. i would not design it for wall mounting..it just complicates the unit design, structure, and limits the potential locations ( wall strength)
2) casing design/shape would be last the consideration after practicality and functionality of design. most units are likely to be located in a utility room etc.
3) cell type and chemistry will depend on the intended use..off grid Solar storage/smoothing, emergency back up, etc.
for static installs ( & floor mounted) energy density ( weight/size) is not a priority, so large format Lifepo4 becomes an option.

Something with a genuine 10+ year service life.

Hillhater,
1: wall mount like the tesla for easy access to all the controls and to keep it out of harms way on a garage/utility floor where water/road salt could be an issue
2: design shape is a large portion of making an easily marketable product. Too many green products are ugly for the sake of being ugly. Exhibit: Nissan Leaf
3: cell type is ambiguous with the following constraints: good KWh/lb, KWh/cuft. It must be customer removable and shippable using normal shipping services.

Punx0r,
I can't think of a single mainstream battery tech that has a servicable life of 10 years at 1 discharge per day. That is why I'd design something with battery health readouts, a low health battery could be removed and shipped for refurbishment as needed. New or refurbished batteries with original or upgraded chemistry would be available to keep the system modern.

I have a drobo networked hard drive rack at home and as I needed more storage capacity I simply slipped in a new hard drive, the old small and dying hard drives could be replaced with modern higher capacity hard drives as needed. The architecture remains the same, capacity increases and its health is maintained.

If it's to be 10+kWhr, you are dealing with ~100kg. That will need a strengthened wall to hang on......or it could be floor mounted but in a raised position.
I see this as a utility device like a furnace , central vac, or chest freezer, etc , ..out of sight in a utility space, rather than a artwork for display to visitors.
If you are thinking of a unit only doing one cycle daily , I assume this is aimed at solar storage, ?
If so then it will need to be much more than 10kWhr ,..and weight / size factors become more prominent.
...Replaceable battery " modules" are certainly possible, but would add to the complexity and costs.

Home storage unless the power goes out all the time is too expensive right now.

Spending your hard earned on an electric car / bike is much more fun.

10 years is not enough life!

EG simple 60AH 12V GBS lifepo4 pack $450 + BMS (cell level balancers +$55) + GST makes it a $550 proposition.

1500 cycles to 80% DOD http://ev-power.com.au/webstore/index.php/12v-lifepo4-batteries/gbs-12v-lifepo4-batteries-1/12v-4-cell-060ah-lfp-battery-module.html

Gives 12x60x0.8 = 576Whrs per cycle 1500 cycles $550 = 37c/ cycle turn that into kWh rate and you're at 64c/kWH = TOTALLY NOT VIABLE!

TESLA powewall will cost $3500 USD + ALOT for it to actually work (Fronius SYMO HYBRID $3K AUD SolarEdge box $2k + existing solaredge inverter)
+ freight to AU (Dangerous goods cargo top load only container or DHL DG air etc etc)
+ conversion to AUD, installation, etc

will cost ~$7-8K which is ~$1200 / kWH IMHO which......funnily enough is about what my GBS example above works out at but without a shiny box.

either way math doesnt stack up *****UNLESS***** Cycles double making 32c/kWh then double again (ie 6000cycles +) down to 16c/kWh

Fronius BAttery is good for 8000 cycles..... stacking up at ~16c/kWh storage for its cost.
Enphase have a smaller system, they spent $100Million USD to develop theirs and fronius spent $100million Euros to develop the SYMO Hybrid and battery.
SMA spent $60million Euros on their close coupled battery system (SMA smart energy) and i'm guessing ABB / BYD etc have all spent cubic bucks as well.

they end up with nice products that you and I simply cannot replicate cost effectively.

Start Salvaging 18650's will need ~20kWH for 50% usable to get several thousand cycles (EG charge to ~4V instead limit discharge to 3.6V)
Assume 2AH and 3.6Volts per cell nominal you're going to need
wait for it............2777 of them or 14S 198P.....
i'd make modules of 14S10P x 20 of them

I'm aware this wouldn't be able to compete with grid energy but the higher cost would be more acceptable in a grid down or off grid situation.

I built an excel calculator to quickly determine the best pack configurations but I don't have readily available battery information regarding typical bulk costs.

Based on an 18650 LiFePO4 1200 MAh battery at $2.80ea and 55 BMS per pack I'm getting:

14S21P for a 50.4V module storing a nice round 1.01KWh, $878+ manufacturing/case costs, say $1756 per module/KWh retail. DOD of 80%, maybe 5000 cycles that's $.35/KWh, I agree seems pretty high. 294 cells per module, ~35 pounds per module.

Enphase does have one of the nicest looking solutions (besides powerwall). I found additional inf on the enphase: http://www.myelifenow.com/2014/11/enphase-ac-battery-technical-details.html

doing a little more research,

LiFePO4 prismatic 3.2V 20AH cell http://www.batteryspace.com/lifepo4-prismatic-module-3-2v-20-ah-10c-rate-64-wh-6-0---un38-3-passed-dgr.aspx

15s1p/module
.768 KWh
24.74 Lbs
48V
$659 includes BMS, would need case/framework.

I could go with larger/cheaper $/KWh cells but then they wouldn't be portable modules anymore.

If I were building my own permanent installation I'd use the largest prismatic cells available.

Modular...For me that means standardizing all of my pack to one voltage. Then the modular portion is that all of my EVs are plugged in parallel to the home based pack. The stationary pack would have 1 extra series cell, but the same top of charge voltage, so the pack is run even more conservatively than those on the ebikes. Charging the EVs would mean simply plugging to the home pack, which is solar and wind charged, with several options in the resistance to control charge rate.

For the home pack what matters is cost per wh of storage capacity over the long-term with of course only safe cells considered. Run conservatively even 500 cycle rated cells can last many times longer. Price, price, price, both in cost and retail. 5-10 years from now batteries will be far cheaper and far better, so get them onboard now using price as the attraction. It's not like the pack would be dead at the end...just diminished capacity, so it would still be usefu.

+1 I worked on 2000mAH 18650 s for my calcs. I can buy them new un-used at AUD $1.2 a pop - pulled out of god knows what 2 years on the shelf.

I hadn't thought of +1 cell but all my DC-DC converters are step up hence charged house ++ over flat bike....
hence i went for 7S house and 14S bike (my solar controller happy with 7S too!)

Thus..... assuming the following 3.6V nominal and 2000mAh = 7.2Whrs per cell

DC/DC converter lucky to make 85% efficincy

charge to 80% at 4Vpc discharge to 20% remaining or better at <1C

gives 7.2*.8 =5.76Whs

20% remaining = 5.76*.8 = 4.6Whrs per cell

after the DC-DC conversion gives 3.91Whrs (not very good but hey i want it to last)

battery in bike typically for my ride uses less than 9AH at 55V (14S) thus 495Whrs

hence 495/3.91 = 126 cells required for a LONG life (i ordered 60 for 7S 8P, 2 x 7S BMS units 30A max discharge)

now assuming (not counting my labour to assemble)...... and at $160 o less for the components and a 100% charge/discharge being good for 14S 10P x 2AH = 1008Wh for ~$200...... I'm in the game

Karl

My friend in Michigan has these.

http://www.schultzengineering.us/battery.htm

they are ~twice the money of currently available 10C rated LifeP04 stuff.
www.evpower.com.au
hence fizzer

Why not just buy powerwalls? Price is quite low.

For home storage, Lead Acid makes lots of sense. While a car battery may not be the way to go, the type of Lead Acid battery used by the Telecom industry are a long lived beast. The last switching office I was in had a bank of old glass rebuildable batteries, still in service. If one went bad, they would drain it, swap out the plates, refill it with new acid, and send the old lead and acid off to be recycled. A NOC I used to work in had a bank of ancient submarine batteries as backup power. Many decades old, but rebuildable, and still in spec.

Lead is dead..... as far as transportation is concerned. However, we already have an infrastructure in place to easily recycle them, there is very little waste in the process, and they can be maintained for decades.

John in CR said:

Modular...For me that means standardizing all of my pack to one voltage. Then the modular portion is that all of my EVs are plugged in parallel to the home based pack.

Click to expand...

Right now, it seems that means dropping down to 48V and 'bulk charging' from the inverter/controller. Any suggestions on >72vdc packs and inverter/charge controllers?