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

ksmithaz1 said:

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.

Click to expand...

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 said:

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

Click to expand...

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.

mciholas said:

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.

Click to expand...

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 ...

PreppenWolf said:

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.

Click to expand...

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.

mciholas said:

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.

Click to expand...

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.

@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

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).

silverstone said:

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

Click to expand...

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.

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

mciholas said:

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.

Click to expand...

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".

G00SE said:

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

Click to expand...

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.

silverstone said:

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.

Click to expand...

My elementary rationale to this is electric dirt bikes
Mototec for example uses 24v for 500w bikes, 36v for 1000w, 48v for 1600w, and their 72v machine has a 5000w motor.
There’s numerous comments saying ev don’t use 48v so I guess my corollary is because of the instant demand makes it less sensical?

G00SE said:

My elementary rationale to this is electric dirt bikes
Mototec for example uses 24v for 500w bikes, 36v for 1000w, 48v for 1600w, and their 72v machine has a 5000w motor.
There’s numerous comments saying ev don’t use 48v so I guess my corollary is because of the instant demand makes it less sensical?

Click to expand...

It also depends how the motor speed vs voltage characteristic is.

It depends if your target is "high torque" i.e. current i.e. dI/dt (i.e. voltage), or "high speed" ( which depends how many "volts" it takes to your motor to achieve a certain "rpm").

Everything can be done. Buck-boost converters, isolated high-frequency soft-switching transformers, etc. But it also takes space, cost, weight, etc.

If it's a mains powered or charged device, your "charger" is actually just a 400 VAC supply typically. With some rectifier / Active Frontend, you are just close enough to the target (battery and DC-link) voltage, without huge voltage transformation ratios (duty cycle). I agree with @mciholas on that side at least.

It's hard to compare EV voltage with stationary voltage and large comercial/industrial voltage. All of these operates at different levels.
EVs don't follow the same rules as the other two.
This comes down to economy of scale. The more you produce the cheaper it is to produce. Will we see higher voltage, maybe but only if someone thinks it's going to make a bazillion $$$!

The main reason for the 48V for home systems is safety and the regulations around it. Anything under 60V is/was considered safe within most legislations, and coming from a lead-acid world, this made sense since you could put 4 batteries in series and not exceed this voltage - thus no special requirements were needed on equipment, installations, etc. Anything over 60V is more problematic, and since these systems started in the DIY and especially the Marine environment (Victron comes from there), it's stuck around.

By the way, the current Low Voltage Directive in the EU for example sets the DC limits from 75VDC to 1500VDC - so anything under 75VDC does not need to worry about complying with the LVD.

upnorthandpersonal said:

By the way, the current Low Voltage Directive in the EU for example sets the DC limits from 75VDC to 1500VDC - so anything under 75VDC does not need to worry about complying with the LVD.

Low Voltage Directive (LVD)

About the directive, implementation and guidance, standardisation, and contact points.

single-market-economy.ec.europa.eu

Click to expand...

Well from an (all-in-one) inverter standpoint I'm not sure it changes a lot. You have anyway 230/400 VAC in there, potentially much more from PV (1000 VDC).

For Battery, BMS, Charge Controller / Battery Charger though I guess it makes the certification easier .

silverstone said:

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).

Click to expand...

With only one motor you have to have a differential of some sort. Mine both have a "reduction gear", though not a shifting gear box. Since electric motors have linear power curves, shifting gears is pointless.

silverstone said:

Well from an (all-in-one) inverter standpoint I'm not sure it changes a lot. You have anyway 230/400 VAC in there, potentially much more from PV (1000 VDC).

Click to expand...

Because back in the day, all-in-one didn't exist, and wiring up the inverter would need an electrician - who very likely was not certified for DC systems, let alone higher voltage ones complying with the LVD. A lot of all-in-ones sold in the EU don't comply with the directive in the first place.

upnorthandpersonal said:

Because back in the day, all-in-one didn't exist, and wiring up the inverter would need an electrician - who very likely was not certified for DC systems, let alone higher voltage ones complying with the LVD. A lot of all-in-ones sold in the EU don't comply with the directive in the first place.

Click to expand...

Well they need to comply on the AC and PV side. Or you think it's yet another case of manufacturers thinking "if they don't find out, it's not cheating" ?

silverstone said:

Well they need to comply on the AC and PV side. Or you think it's yet another case of manufacturers thinking "if they don't find out, it's not cheating" ?

Click to expand...

Victron complies, but they only have to worry about the DC side on the charge controllers and the AC side in the inverter. Both are pretty trivial, but it still requires independent testing and verification - can't be self-assessed. I don't think any of the popular all-in-ones like those MPP Solar ones comply.

ksmithaz1 said:

With only one motor you have to have a differential of some sort. Mine both have a "reduction gear", though not a shifting gear box. Since electric motors have linear power curves, shifting gears is pointless.

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Not pointless, just you may be OK with constant torque, constant thrust, same at low speed as at high. That is to say, horsepower linear with speed.
That could work for typical car use.

If you use 100 HP driving into the wind at 100 mph, are you OK only having 10 HP carrying a load uphill at 10 mph?

A 2-speed transmission would let you have much higher pulling power in low gear.
(even some winches are 2-speed.)

Hedges said:

Not pointless, just you may be OK with constant torque, constant thrust, same at low speed as at high. That is to say, horsepower linear with speed.
That could work for typical car use.

If you use 100 HP driving into the wind at 100 mph, are you OK only having 10 HP carrying a load uphill at 10 mph?

A 2-speed transmission would let you have much higher pulling power in low gear.
(even some winches are 2-speed.)

Click to expand...

@ksmithaz1, @Hedges: my point was on high-level. Whether you have 1, 2 or 4 motors it doesn't really matter. Differential (in order to be able to turn) is for sure a thing, but in the grand scheme of things the law I illustrated above holds.

On the mechanical side:
Torque ~ Acceleration
Rotation Speed ~ Driving Speed (assuming no gearbox)
Mechanical Power = Torque x Rotation Speed

And on the electrical side for a 3ph motor:
Torque ~ Current
Rotation Speed ~ Voltage
Electrical Power = 3 x Phase-Neutral Voltage x Phase Current x cos(phi(current,voltage))

(plus plenty of other things, losses due to cooling, R x I^2 and other stuff of course)

Hedges said:

A 2-speed transmission would let you have much higher pulling power in low gear.
(even some winches are 2-speed.)

Click to expand...

Sure, but in the EV world, I'm so glad the Tesla Plaid had prove that single gear ratio work fine.
0-60 mph (0-96 km/h) in 2 seconds and 217 mph (350 km/h) top speed with single speed gearbox

In other words, with a 1000 hp motor and big enough battery, it can be geared for 217 mph top speed and still have phenomenal acceleration from a standing start.

To make that economical let's consider 50 hp and half the top speed. 1/10th the acceleration, 20 seconds zero to 60.
Ok, 100 hp a more acceptable 10 seconds.

But with a 2-speed 3:1 transmission, better towing and low speed hill climbing.

The question is, which costs more:

Second pair of engaged gears and a clutch mechanism, or
More powerful motor and circuitry to support 3x the current.

It may be that a 2-speed motor with switchable windings could be the solution, but I don't think so. Needs stronger magnetic attraction to trade off lower RPM.

The original roadster had 2-speed transmission but kept blowing it up. Seems like either two much power or motor not synchronizing speed when shifting.

Hedges said:

In other words, with a 1000 hp motor and big enough battery, it can be geared for 217 mph top speed and still have phenomenal acceleration from a standing start.

Click to expand...

The thing is peoples want EV with big range who imply big battery.
With big battery, high peak power is almost free.
That why many EV have outrageous peak power number and are the most powerful vehicle in their category. (sedan, pick-up, SUV etc).