LFP for EV's projected to be less than $56 per kWh within 6 months

[ksmithaz1]

I actually think the ~80s idea is the best. I consider battery tech the most optimal the closer you can get it to the endpoint. Thus having a multiple of 120v would seem to make the most sense. I would roll the battery packs out at a nominal 60v (20s) and bring them in series to 240v, simplifying the conversion to common AC house current. I believe this is how the Eaton UPS I have works, and the entire idea just seems simpler to me.

Higher voltages for a typical residential or small strip-mall style business locations would be somewhat pointless. All bets are off for industrial and higher voltage 3-phase stuff, but you are starting to get a tad esoteric at that point anyway.

 

[Hedges]

I think the ideal battery voltage would be one that doesn't drop below about 340V. That's Vpeak of 240Vrms.
A bit higher for line voltage tolerance.

Inverter is most efficient when input voltage is close to Vpeak. That's when current is highest (if "real" resistive, not reactive load.)
But HV battery inverters (and PV) these days accept a much wider range, buck-boost or something to make them more flexible, probably reduces efficiency. Doesn't seem to be too much, though.

 

[mciholas]

I actually think the ~80s idea is the best.

80s is 256 V nominal, not unreasonable electrically.

When you get to this size, you do end up being constrained on cell sizes. For example, using a 100 AH cell is now a 25.6 KWH pack and will be heavy, like 500 lbs.

If you target around 5 KWH, rack size, you need to find 20 AH cells which doesn't seem too common or fantastic on the 4/KWH scale. Since there are so many, assembly labor is higher and you have more case per AH ratio.

This is the primary downside, the number of cells in the pack.

This is all nice and theoretical, the practical systems you can buy are 50 volts and that's what we have to work with.

Mike C.

 

[Checkthisout]

I think the ideal battery voltage would be one that doesn't drop below about 340V. That's Vpeak of 240Vrms.
A bit higher for line voltage tolerance.

Inverter is most efficient when input voltage is close to Vpeak. That's when current is highest (if "real" resistive, not reactive load.)
But HV battery inverters (and PV) these days accept a much wider range, buck-boost or something to make them more flexible, probably reduces efficiency. Doesn't seem to be too much, though.

340V DC battery bank compressed with scrap plywood and salvaged all-thread.

I pity the fool who drops his Huskey ratchet across the terminals.

Example below of someone hooking up their new EG4 8 billion terrawatt megavolt inverter. Uses 23 gauge wires between the battery and inverter.

 

[Supervstech]

340V DC battery bank compressed with scrap plywood and salvaged all-thread.

I pity the fool who drops his Huskey ratchet across the terminals.

Example below of someone hooking up their new EG4 8 billion terrawatt megavolt inverter. Uses 23 gauge wires between the battery and inverter.

View attachment 199649

Yeah, it is unlikely 300+ volt assemblies will make it to the diy realm anytime soon...
BUT... i can see it being a great home standby option.
Imagine 80+ kWh banks with a small simple set of mossfets and such to create steady stable 240V high amperage output, along with fast DC charging for a few thousand installed in your home garage.

Fabulous...

 

[Supervstech]

Of course, all homes would need "secure locations with authorized qualified personell access..."

 

[Hedges]

340V DC battery bank compressed with scrap plywood and salvaged all-thread.

I pity the fool who drops his Huskey ratchet across the terminals.

Example below of someone hooking up their new EG4 8 billion terrawatt megavolt inverter. Uses 23 gauge wires between the battery and inverter.

View attachment 199649

I've already blazed the trail for you.

I tried out 480VDC (didn't like it).
And found a cheap substitute for insulation. (good for preventing immediate high current faults, and has visible warning of conductive material like that Husky wrench in contact.)

⚡Shock⚡ through the heart,

Speaking of idjit moves...I upgraded a while back from 2 inverters to 3, the main Pos Class-T remained a 300A. while I waited for a bigger fuse to come in. (ie now undersized). Then recently after witnessing the OST (official solar tester) aka the spouse pushing the system near to it's limits I...

diysolarforum.com

Using non-UL insulation

A while back I bragged about creative use of heater hose as tough, large size insulation for electrical terminals: https://diysolarforum.com/threads/fire-never-cover-lifepo4-with-wood.19373/page-12#post-238207 It seemed like a good idea at the time. More recently, I was wiring up...

diysolarforum.com

What I'm working with now is Sunny Boy Storage (HV battery inverter) and LG RESU-10H (and explody chemistry lithium battery, 150V native, with bidirectional boost converter to 450V.) So far I've got it charging to reduce what PV I export at low rates, then discharging when rates are high.
With a $0.20 spread in winter and $0.30 in summer, would make no financial sense at all if I had paid retail, but then I usually don't.

Maybe some day I'll DIY a larger battery of safer chemistry (or do V2H), if I figure out what BMS speaks the language.

Sunny Boy Storage 3.8-US / 5.0-US / 6.0-US | SMA America

Discover the flexible Home Energy Solution: The SMA Sunny Boy Storage 3.8-US / 5.0-US / 6.0-US battery inverter! ► Find out more about its benefits!

www.sma-america.com

RESU10H | LG Home Battery

The RESU10H is part of the high voltage RESU range. Using state-of-the-art lithium-ion battery technology, the RESU10H will be there to store energy from your solar panels or the grid during the day. The battery powers your home during the evening, during power outages, when the sun is not...

www.lghomebattery.com.au

 

[nc73]

Must refrain from building another 48v battery...

 

[ksmithaz1]

Of course, all homes would need "secure locations with authorized qualified personell access..."

I dunno, A simple electrical room with a location appropriate door would be fine. You would want appropriately labeled panels and cabinets and no exposed wires. You can do some pretty severe damage wandering around inside a breaker box, not to mention a gas furnace or something, and none of that stuff is generally very secure. I'm in the process of building an out-building to house all my PV cruft, if this becomes prevalent I believe that will become "a thing" like a "well house/ pumphouse" in rural property, you'll just have a small utility room either detached or at the far edge of the structure.

 

[ksmithaz1]

80s is 256 V nominal, not unreasonable electrically.

When you get to this size, you do end up being constrained on cell sizes. For example, using a 100 AH cell is now a 25.6 KWH pack and will be heavy, like 500 lbs.

If you target around 5 KWH, rack size, you need to find 20 AH cells which doesn't seem too common or fantastic on the 4/KWH scale. Since there are so many, assembly labor is higher and you have more case per AH ratio.

This is the primary downside, the number of cells in the pack.

This is all nice and theoretical, the practical systems you can buy are 50 volts and that's what we have to work with.

Mike C.

True, though you've made an assumption of large low voltage cells. You could make a pretty lightweight/simple BMS for smaller strings (20s) of smaller cells, then cascade them. Should be interesting no matter how it plays out.

 

[Supervstech]

I dunno, A simple electrical room with a location appropriate door would be fine. You would want appropriately labeled panels and cabinets and no exposed wires. You can do some pretty severe damage wandering around inside a breaker box, not to mention a gas furnace or something, and none of that stuff is generally very secure. I'm in the process of building an out-building to house all my PV cruft, if this becomes prevalent I believe that will become "a thing" like a "well house/ pumphouse" in rural property, you'll just have a small utility room either detached or at the far edge of the structure.

Idk, NEC has rules in place for equipment rooms with greater than 150V to ground or greater than 250V lead to lead potential.
Usually a locked room with a key accessible only to authorized qualified personel.

 

[mciholas]

High voltage makes things more efficient inside the inverter, too.

This is evident when you look at the inverter efficiency numbers. Using EG4 18KPV:

PV to AC: 97.5%
Battery to AC: 94.0%

The higher voltage of the PV array yields higher efficiency in the inverter.

Mike C.

 

[silverstone]

10 times the voltage rating means 100 times less current losses for any given resistance.

So the 280 to 750 mOhm Rds is actually LESS power loss than the 10 mOhm part when you up the voltage 10 times and reduce the current 10 times.

You also happened to pick a poor MOSFET. Consider:

https://www.digikey.com/en/products/detail/vishay-siliconix/SIHP100N60E-GE3/9695103

600 V, 100 mOhm, 30 A.

That part is 10 times the resistance but that will result in 10 times less heat than the 10 mOhm part delivering the same POWER.

There are a lot of low resistance high voltage MOSFETs these days, lots of work in power systems is in that area.

If we could increase inverter battery voltage to 200 volts, we'd have cheaper more efficient inverters.


No, much less loss as my example above demonstrates.

If your theory was correct, EVs would be low voltage. They are not precisely for the reasons I have stated.

Mike C.

EDIT: yes, the equivalent for "same losses" would have been 10 mOhm vs 10 x (10)^2 mOhms = 1000 mOhms. At least for conduction losses in BMS. For switching losses is more complicated than that (in Inverter), as theoretically it's a linear relationship, but in practice higher voltage MOSFETs are slower (except SiC) and have higher Qrr (reverse diode recovery), plus Gate Capacitances and the whole drive circuit also.

However, you are a bit comparing apples to oranges here.

If you want to TRANSFER the same amount of power at 10x higher voltage, you will have 10x more current.
If you want the SAME POWER DISSIPATION at 1/10x of the current, you will need 100x higher resistance, agreed.

Can you get a MOSFET with lower resistance ? Of course. Just pick one where the MOSFET channel width is larger, or parallel several of them. For a BMS that doesn't really matter, but for an inverter that will significantly increase switching losses. Again, everything it's a compromise. Of course you can do ZVS (Zero Voltage Switching) or ZCS (Zero Current Switching) i.e. Soft Switching to reduce Losses, but that requires extra components (capacitors, inductors), more complex control topology, measurements, etc.

But the FET you linked is 5 $ / PIECE vs 0.5 $ / PIECE of the 2 comparable that I linked (at small quantities, similar discussion can be had at higher quantities). And for the battery-side of the inverter in the best case you'll need 2 (without isolation transformer, without paralleling) or 4 (full bridge, with isolation transformer, without paralleling). Then if you start paralleling (due to steady-state current, loss reduction, cooling more compact, etc), you might end up having to use 8, 16, 32, 64 etc of those ... The cost adds up.

About your efficiency claim for 200V ... Well, the current would get reduced, that's for sure. Then it's a SYSTEM analysis that needs to be performed in order to find out really what's best. Is your now say 300V capacitor and inductor more cost-effective ? You are going to need a 600V ("standardized" voltage class) MOSFET instead of a 120-150 V MOSFET, with the implications I outlined before.

Can it technically be done ? Sure, I agree with you on that.
Can it get more efficient ? Absolutely.
But again, nothing is free, either in terms of cost, losses/cooling, control, measurement, etc.

I was also "all-in" at the start of my power electronics career to improve efficiency of Power Semiconductors etc when designing a Power Converter. But at the end of the day, is it really worth for say a 1000$ converter, to improve efficiency from 98.0% to 98.5%, if the Converter ends up costing 2000$ after your change ? You won't be able to sell it. You will have lower quantities ordered from your Semiconductors, Reactors, Capacitors suppliers, thus higher prices. Etc.

Look at the marketplace today.
Low-Voltage (48VDC) inverters are quite expensive relatively speaking, but batteries are super cheap.
Higher-Voltage (200-600VDC) inverters are quite chea, but batteries are very expensive.

Why is that ? Because in a way it's always a matter of push "the problem" to the other side. Higher voltage (200-600VDC) inverters aren't really very complex per se. But again, Breaker/Isolator wise (if you want something that you can trust !), Fuse, BMS, ... aren't trivial at higher voltage.

Can it be done ? Yes again. But you are comparing (supplier-for-supplier, apples-to-apples) a breaker that might cost 100$ at 48VDC-96VDC with something like 1000$+ at 600VDC.

At the end of the day, you have to factor in your total SYSTEM cost. I had a friend buying a Higher Voltage Inverter because it was on offer super cheap. I clearly told him "BEWARE: batteries are much more expensive". Now he's realizing he would have liked 60+ kWh of battery storage. Good luck price-wise with a Higher voltage battery, which is 2x-3x more expensive for the same energy ...

 

[silverstone]

As others have pointed out our solar arrays are already will into the danger category. My array is 35A @ 450V under max sun.

It's a lot easier to wire up 35A @450V than 350A @ 45V.

Sure. And cheaper. I don't disagree with you there . Copper is very expensive after all.

I do NOT advise wiring 350A hard parallel modules either. You'd also string fuses to be able to clear a fault with that many solar panels in parallel, otherwise for your (N) panel array you'd have up to (N-1) panels feeding into the faulty panel. Your wiring (and panel) is going to catch fire unless you isolate the fault. And of course fuses (or breakers) have their own problem (space in a combiner box, cost, additional losses, selectivity/clearing time, ...).

But on SYSTEM level, other things becomes a bit more expensive. Think 800VDC-1000VDC breaker or isolator.

And 1200V or 1700V class MOSFET/IGBTs have their own set of problems at higher voltage.

Yes, SiC is also a thing especially in automotive (but still relatively $), but that comes with their own set of problems. EMC/EMI, need VERY low-inductance Board Design and low ESL Capacitors to keep voltage overshoot under control, etc.

And if we talk big power (say 1MW-10MW), when you scale up SiC, the gains in efficiency is not really linear. I had seen a presentation recently from an university study. Cannot remember if it was the conduction losses or the switching losses that didn't go up linearly with the number of parallel modules, but it becomes trickier. And you need some sharing reactor inductance, special turn on sequencing algorithm, board traces layout impedance match, etc.

 

[silverstone]

This is evident when you look at the inverter efficiency numbers. Using EG4 18KPV:

PV to AC: 97.5%
Battery to AC: 94.0%

The higher voltage of the PV array yields higher efficiency in the inverter.

Mike C.

It has their own advantage, yes.

But I also believe it's more of a commercial tradeoff than something that cannot be solved technically.

If the PV voltage is "high enough", you don't need to boost, it just goes straight to the DC-link, probably using a MOSFET as "synchronous rectification" (to avoid the ~ 0.7-1.2V of a Diode). Then after that you have your inverter, with MOSFET switching, NO transformer, and a space efficient LCL filter most likely.

For the battery part you are talking at least a H-bridge of MOSFETs and a medium-high frequency transformer. So yeah, the transformation chain is less direct there, I agree on that. And besides the magnetics, you have an additional semiconductor bridge SWITCHING. Not sure if they have a resonant (soft-switching) transfomer though.

For efficiency figures I'm always a bit skeptical though. I'd like to see the full chart (e.g. efficiency vs load in %, both for PV-AC, PV-BAT, and BAT-AC), but of course manufacturers don't typically share that.

Don't forget the "safety" discharge resistors, depending on the capacitance value used in DC-link and filter, they can also add up to quite a bit of power.

For my 3 x 12kW Deye (48VDC) setup, at zero-low load, I thought the losses were approx. 400W. Now it seems more like 800W. I'll need to check more carefully with a comparable Energy Meter once I setup Home Assistant and InfluxDB a bit more.

 

[silverstone]

@mciholas I like to engage in discussions .

Let's take it from another angle. Why then, in your opinion, are 48VDC batteries more widespread than higher voltage ones ? Why are they cheaper ?

I do NOT believe the reason is due to Inverter Manufacturers and Battery Manufacturers targeting DIY enthusiasts.

And I also do NOT believe it's a conspiracy.

So what is the reason in your opinion ? As I see it, the main advantage in 48VDC systems is the Isolator/Breaker Cost part, which can get VERY expensive at higher voltages, as I tried to illustrate previously. The BMS I think it's (or at least was) much easier at 48VDC.

EDIT

If I have a look at NKON for instance for Prismatic batteries

Prismatic - LiFePO4 - Rechargeable batteries | NKON

NKON is a webshop, specialised in batteries, chargers en LED-flashlight. We ship worldwide!

eu.nkon.nl

Price vs Capacity
Eve LF22K B-grade - 22 EUR / 22Ah = 1 EUR / Ah
Eve LF32 B-grade - 25 EUR / 32 Ah = 0.78 EUR / Ah
Eve LF105 A-grade - 37 EUR / 105 Ah = 0.35 EUR / Ah
CALB L148F88A B-grade - 39 EUR / 88Ah = 0.44 EUR / Ah
Eve LF50K A-grade - 50 EUR / 50 Ah = 1.00 EUR / Ah
CALB L173F125A B-grade - 50 EUR / 125 Ah = 0.4 EUR / Ah
CALB L194F130A B-grade - 51.5 EUR / 130 Ah = 0.4 EUR / Ah
BYD C13 FP44147272P B-grade - 67 EUR / 125Ah = 0.54 EUR / Ah
CATL LF173 B-grade - 70 EUR / 173 Ah = 0.4 EUR / Ah
CALB L300F187 B-grade = 73 EUR / 187 Ah = 0.39 EUR / Ah
Envision ESS 4LH3L7 B-grade - 73 EUR / 280 Ah = 0.26 EUR / Ah
Eve LF230 B-grade - 75 EUR / 230 Ah = 0.33 EUR / Ah
Envision ESS 72173207 B-grade - 78 EUR / 305 Ah = 0.26 EUR / Ah
Eve LF280K A-grade - 86 EUR / 280 Ah = 0.31 EUR / Ah
Eve LF304A-grade - 90 EUR / 304 Ah = 0.30 EUR / Ah
CALB L173F230 B-grade - 95 EUR / 230 Ah = 0.41 EUR / Ah
Eve LF280K A-grade - 100 EUR / 280 Ah = 0.36 EUR / Ah
Eve LF304 A-grade - 108 EUR / 304 Ah = 0.36 EUR / Ah
Lishen LP71173207 B-grade - 119 EUR / 280 Ah = 0.43 EUR/Ah
Catl CB310 B-grade - 120 EUR / 280 Ah = 0.43 EUR / Ah
Eve LF280K A-grade - 123 EUR / 280 Ah = 0.44 EUR / Ah
Catl Prismatic 302Ah B-grade - 145 EUR / 302 Ah = 0.48 EUR / Ah

(Price per kWh divide above by 3.2V and multiply by 1000)

So .. surprise surprise ... most cost-effective options per capacity are LF280K and LF304, i.e. "big" cells.

Granted OEM get much better deals, quantity discounts etc than these prices, but anyway they do NOT pass the savings onto you .

So now, if you want to build a battery pack:
- 16s "big": 16 x 90 EUR (LF304) = 1440 EUR for 16 * 3.2V * 304A = 15.6 kWh
- 80s "big": 80 x 90 EUR (LF304) = 7200 EUR for 80 * 3.2V * 304A = 77.8 kWh

80s "small" apples-for-apples with 1p16s would be (304Ah*16/80=61 Ah). Closest is EVE LF50K at 50EUR for 50Ah:
- 80s "small" apples-for-apples (size, capacity) with 1p16s would be approx. 50Ah cells: 80 x 50 EUR = 4000 EUR for 80 * 3.2V * 50A = 12.8 kWh

So if you later want to expand, 48V is cheaper. You start and get up and running with 1p16s for just 1440 EUR plus box, BMS, fuse/breaker, cables etc. Want to expand ? You just add another 16 cells. You do not need to set aside 5x the amount of money all at once.

80s of course can be done provided my comments about breakers, BMS, MOSFETs, etc are kept into account . But either you sacrifice capacity and get up & running sooner, or you need a bank loan / set aside much more money "just" to get started (at much greater capacity of course).

 

[mciholas]

At the end of the day, you have to factor in your total SYSTEM cost.

Higher voltage is less cost, less size, less weight, less losses. Some components will get more expensive, but the savings in other parts of the design make up for that and more.

This is why you won't find any EVs operating at 50 volts.

If lower voltage was better, they would be using it, and they aren't. And their wires are so short the copper penalty is relatively small, so it is mostly about the inverter design that drives them to higher voltages.

If lower voltage was better for PV to AC, we'd be using it, and we aren't.

All things are tradeoffs, but that doesn't mean it is a zero sum game, some design choices are clear winners and higher DC voltages is one of those when dealing with powerful AC inverters.

Mike C.

 

[G00SE]

Higher voltage in vehicles is used for high power output no? Home based systems don’t need the equivalent of 300hp to start their appliances.
I apologize if this is not within the spirit of this topic, my brain seems to think it’s relevant

 

[silverstone]

Higher voltage is less cost, less size, less weight, less losses. Some components will get more expensive, but the savings in other parts of the design make up for that and more.

This is why you won't find any EVs operating at 50 volts.

If lower voltage was better, they would be using it, and they aren't. And their wires are so short the copper penalty is relatively small, so it is mostly about the inverter design that drives them to higher voltages.

If lower voltage was better for PV to AC, we'd be using it, and we aren't.

All things are tradeoffs, but that doesn't mean it is a zero sum game, some design choices are clear winners and higher DC voltages is one of those when dealing with powerful AC inverters.

Mike C.

If your target capacity is the EV range of say 70 kWh, you can use high capacity cells which are cost-effective.

And your battery voltage being "close" to the inverter DC-link, grid charger and motors, makes it also more attractive. I agree with you there.

But you'll then need to build in ~ 70-90 kWh increments (see my calculation example above) if you want the best "bang for your buck".

 

[silverstone]

Higher voltage in vehicles is used for high power output no? Home based systems don’t need the equivalent of 300hp to start their appliances.
I apologize if this is not within the spirit of this topic, my brain seems to think it’s relevant

Power = Torque x RPM

So ... it depends. Also if you use a gearbox or not (typically for hybrids you might have one, for pure EV ... I don't think it makes sense).

Not every EV is crazy Torque like Tesla eh. Less torque = typically less current. And less insurance premium.

I think the Hyundai Ioniq 5 and/or Volkswagen ID 3-4 were that case at least.