Yeah, two PW3 each with incoming solar (from what sounds like a single plane of panels)
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Discussion: Powerwall 3 [Speculation / Discussion etc]
- Thread starter n.one.one
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Which of those columns refers to MPPT port (if any)?
I notice you have some 2 module strings. Also putting together a PW3 string design and have one string with two PV panels/modules also. Only issue I'm seeing is the 150V minimum voltage per MPPT on the PW3 where two modules will be less than that:
Am I interpreting this correctly and what's the solution to a two panel string? I can't merge strings as these two panels have their own shade and orientation profile and want to avoid optimisers.
Example panel specs I'm looking at:
Good question. Once a module drops below the MPPT voltage range, the efficiency drops but the inverter will still fire up and produce power.
So to produce the rated efficiency you need to stay in the MPPT voltage range. Also dropping to low DC voltages will have higher line losses.
Nerding out here:
That's more tied to the installation itself than MPPT though, right?
Even with MPPT, the line loss will only be slightly better due to 1 Amp difference between Imp and Isc for those panels. So max of ~14% more dissipation in the wires.
The DC loss is effectively spread across the number of panels in the string:
Net panel output = gross_panel_output - lineLoss/number_of_panels_on_string
Gross panel production would be higher with MPPT so better total efficiency of the system.
Correct, it is just another reason why those panels will produce less, both out of MPPT range and also around 60 volts operating voltage.
For instance, a 12 AWG wire at 60 VDC and 11A with a run of 100 ft long one way will have a Vdrop of about 6.2% so you actually need just about 64VDC calculated from the modules irradiance to see the 60 VDC at the inverter.
So I take from this that if I only connect two panels to one MPPT it would still contribute to overall power production, is this a certainty with PW3 given it's outside of specs? If the above solar design was from Tesla and I'm correct in interpreting there were a couple of two panel strings going into one MPPT alone, would suggest this is a done thing.
I need these two panels as have constrained roof space and need all the panels I can fit on roof.
Any estimate as to what power reduction would be produced on let's say 440W panels? Those panels will be mounted very close to the PW3 (3-4m away).
That system diagram shows the two panel string has a max power point voltage of 75V. Those are higher voltage panels than your example ones which could likely be less than 60V at the PW3. Question is how much tolerance the panels and MPPT input have...
Taking a closer look at PW3 spec sheet:
My understanding of these specs is if two panel string has an output of > 60V (which they should on a higher wattage panel), MPPT will still be functional at this voltage but less efficient as outside the MPPT range?
Looking at a different higher wattage panels which may be required anyway to meet PW3's lower current requirements, here's a candidate:
Any guesstimate as to what efficiency loss I'd have with two of these panels on their own string/MPPT? If above say 80% would still be feasible to proceed with this string.
My understanding of these specs is if two panel string has an output of > 60V (which they should on a higher wattage panel), MPPT will still be functional at this voltage but less efficient as outside the MPPT range?
Looking at a different higher wattage panels which may be required anyway to meet PW3's lower current requirements, here's a candidate:
Any guesstimate as to what efficiency loss I'd have with two of these panels on their own string/MPPT? If above say 80% would still be feasible to proceed with this string.
Attachments
PW3 - What's Max Solar Charge Rate?
Separately, I've misread the PW3 spec sheet when it states "Maximum Continuous Charge Power 5 kW AC". Originally thought this meant you could only charge the batteries from solar at max 5kW (which would suck for a multi-PW arrangement), but I missed the reference to "AC" here which appears to be related to charging the batteries from the grid, not from solar.
Can the batteries can be charged to whatever your solar is producing up to 20kW? Anyone with a single PW3 charging from solar at greater than 5kw?
Anyone care to guess if getting a PW3 now and adding a second PW3 battery expansion module (not including inverter) when they come out, what max solar charging capacity total would be?
For context looking to put 13+kW of solar modules/panels on roof and don't want to be constrained by 5kW solar battery charging on high yielding days.
Separately, I've misread the PW3 spec sheet when it states "Maximum Continuous Charge Power 5 kW AC". Originally thought this meant you could only charge the batteries from solar at max 5kW (which would suck for a multi-PW arrangement), but I missed the reference to "AC" here which appears to be related to charging the batteries from the grid, not from solar.
Can the batteries can be charged to whatever your solar is producing up to 20kW? Anyone with a single PW3 charging from solar at greater than 5kw?
Anyone care to guess if getting a PW3 now and adding a second PW3 battery expansion module (not including inverter) when they come out, what max solar charging capacity total would be?
For context looking to put 13+kW of solar modules/panels on roof and don't want to be constrained by 5kW solar battery charging on high yielding days.
I expect the 5kW limit on the grid side remains even with additional battery modules, but the charge level from solar would increase (assuming it is limited now).
My guess on internals:
Solar DC -> Internal DC
Batteries <-> Internal DC
Grid inverter <-> Internal DC
Where the batteries may have their own DC-DC stage for charge control.
ACarneiro
Active Member
That seems plausible.
5kW charge from grid still seems fairly unimpressive, especially for larger systems with 3 or 4 PWs
Each full PW3 would pull up to 5kW.
Each add on battery PW3 would take an additional 3 hours to recharge.
Could PW3 be AC coupled internally (support for which will be announced later in roadmap), which might account for the poor 89% round trip effiency (double conversion)?
Video link is broken, but isn't that referring to external AC coupling?
I mean it could, but that seems like a waste of electronics since the PFC front end of the battery unit/inverter would be the same sort of HV rail you would get from a solar MPPT converter.
The 90% round trip efficiency has tracked all PW so far. 95% each way is pretty good considering electrochemical processes and the 97.5% solar to grid efficiency.
The two sections of PW+ are AC coupled.
Yeah...
That's for compatibility with existing solar inverters, right?
I thought @xrg458 was talking about PW3's internal solar-battery link. If it were AC internally, then it wouldn't need to be added in the future?
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