Tesla PW2

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T1 Terry
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Re: Tesla PW2

Post by T1 Terry » Sun, 01 Sep 2019, 10:53

francisco.shi wrote:
Sat, 31 Aug 2019, 18:40
I have been thinking about how to do this. As you said most solar panel strings would be able to feed the car battery directly. And most solar inverters I assume would have a 400 or so volt bus. So it may be as simple as just connecting the car battery to the internal bus and reprogramming the inverter.
This could potentially fix the duck curve produced by solar without having to spend money in storage. As we get more electric cars they can be used as domestic energy storage.
Until you want to use the EV of course. The partner who is the designated house slave could use their EV as long as they understood just how to plug/unplug before and after the vehicle was used. The house slave is the one most likely to be home when the higher draw appliances were being used and that is when the EV battery could supply the current required even if it was raining. It would require some sort of control so the grid tie inverter didn't try to drain the EV battery so it could export to the grid at its max capacity but rather just supply enough to cover the house loads.

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Re: Tesla PW2

Post by francisco.shi » Sun, 01 Sep 2019, 11:51

I was thinking more of an off grid system and use the car battery as backup for when it is cloudy for a few days.
You would still need a small storage battery.

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Re: Tesla PW2

Post by T1 Terry » Mon, 02 Sep 2019, 09:20

So a house battery the same voltage as the EV battery? Voltage regulation and cell high/low voltage protection would still be required for both batteries along with a method of switching off the charging to each battery bank as well as the discharging to each battery bank. So 2 BMS units dedicated to the solar only? Getting complicated, the EV being charged via 240vac generated by the grid tie inverter (if you were still on grid) sounds a lot simpler and a simple Anderson plug from the EV battery and a cable that ran up to the solar feed in for the grid tie inverter. A lock out switch that cut the 240vac charging when the EV battery was powering the grid tie inverter to stop the spiral to death occurring and to keep the Anderson plug on the EV disconnected from the EV battery. Simple Schottky diodes to stop the solar returning down the cable that plugged into the EV so that cable remained safe and no risk of the solar overcharging the EV battery if there was a power outage.

Probably better to use the PIP-5048MG inverters so you have grid independent house supply that also powers the EV 240vac charger. The solar or EV battery can still power the PIP inverter, the lock out blocks the spiral of death, it just needs a cell level LVC to the Anderson plug to protect the EV battery, that could be the same system that protects the battery while driving.

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Re: Tesla PW2

Post by brunohill » Mon, 02 Sep 2019, 22:59

Should be able to make a direct solar DC to Chademo charger (or DC fast charger into a DC slow charger) that just delivers what ever current is available from the solar panels. I can program my current solar inverter to regulate output to maintain a AC voltage, therefore in will regulate generation to suit demand. A BMS to disconnect the 400 volt car battery from the AC solar inverter at a preset voltage limit etc (probably already in the battery pack). Sounds like a great project (but perhaps not me at the moment).

Maybe I could just bolt an old Nissan LEAF battery (with a few internal mods) against the wall.

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Re: Tesla PW2

Post by francisco.shi » Wed, 04 Sep 2019, 03:58

The car connects to the house via the dc charging port. As far as I understand when charging the car connects the battery to the port and the external charger does all the work. As long as the car does not disconnect the battery when it sees power being taken out. You do not need a BMS for the car because the car already has one. All you need to do is program the charger/inverter to keep the battery within specified range.
The second battery is a small battery which is there so when you drive both cars you still have power in the house.
That battery can be a standard storage battery of any voltage which could run thru a normal inverter.

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Re: Tesla PW2

Post by Rusdy » Wed, 04 Sep 2019, 10:11

francisco.shi wrote:
Wed, 04 Sep 2019, 03:58
...All you need to do is program the charger/inverter to keep the battery within specified range...
This was my original plan, i.e. learn how ChaDeMo protocol works (need to buy the standards, legally, of course :geek: ), then design and built my own HV charger that is directly connected to solar PV (saves DC/AC/DC conversion). The charger obviously needs comms to the solar PV inverter (to get power data) and incoming grid CT. The custom charger will vary the power delivered to the car's battery to get net-zero export to the grid. Since the PV inverter has its own MPPT, loading the solar PV with my cowboy-HV-charger just before the inverter should work.

Sounds all too cowboy and illegal? Why, yes, of course! :lol:

Then came PW2... 8-)

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Re: Tesla PW2

Post by francisco.shi » Thu, 12 Sep 2019, 08:31

I have been giving this idea some extra serious though.
Does anyone know much about how the solar inverters work ?
What is the bus voltage to where the solar panels feed to?
Does anyone have a circuit diagram of the power electronics of a solar inverter?
Do all inverters use the same topology?

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Re: Tesla PW2

Post by coulomb » Thu, 12 Sep 2019, 08:58

francisco.shi wrote:
Thu, 12 Sep 2019, 08:31
What is the bus voltage to where the solar panels feed to?
I'm only familiar with the Voltronic Power inverter-chargers.

There are two different Solar Charge Controllers (SCCs) that come with these.
  • In the PIP-5048MS and similar, there is a buck converter that takes the 60-130 V panel voltage and bucks it down to battery voltage, directly connecting to the battery. With these machines, PV power gets to the AC load through three power stages, the PV buck stage, a 50-400 V DC-DC stage, and the DC-AC inverter stage.
  • In the PIP-5048-GK and similar, there is a boost converter that takes the 120 V - 430 V panel voltage and boosts it up to the "bus" voltage, which is somewhere between 400 and 500 VDC. They use 500 VDC rated capacitors. With these machines, PV power gets to the AC load in two stages, the PV boost stage and the inverter proper. The battery is not involved in this process, and so in these models it is possible to operate without the battery at all.
In both of the above types, there is a 400-500 VDC "bus" that feeds the inverter proper. Pretty much all inverters would require a DC bus of at least 350 VDC (since the peak of a 240 V sine wave is some 340 VDC). The IGBTs have a 2-2.5 VDC drop across them, and when conducting there are two in series, plus you need some headroom, so the 350 V would be a pretty strict minimum (perhaps 335 V if you only ever want to generate 230 VAC). Grid interactive models have to cater for AC mains up to say 265 VAC, so that would requirea minimum of some 385 VDC on the DC bus.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

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Re: Tesla PW2

Post by francisco.shi » Thu, 12 Sep 2019, 17:35

I am thinking more about straight solar inverters with no battery hardware.
So I assume when the solar panels are not generating any electricity would the bus drop until the mains start feeding back in?

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Re: Tesla PW2

Post by coulomb » Thu, 12 Sep 2019, 20:27

francisco.shi wrote:
Thu, 12 Sep 2019, 17:35
So I assume when the solar panels are not generating any electricity would the bus drop until the mains start feeding back in?
If nothing else happened other than the PV power ramping to zero, the bus voltage would slowly bleed down, and when it got to about a volt higher than the peak of the Ac mains, the free-wheeling diodes in the IGBTs (occasionally these are separate, but usually are built-in) would start conducting at the mains peaks and charge the bus back up. This would be like a low power factor rectifier, like a diode bridge, so this is not desirable behaviour. My understanding is that therefore the controller would detect this situation before it happened, and would use a relay to disconnect the mains from the inverter output before the feed-in power dropped below a certain threshold. The other reason to do this is that if the PV power goes to near or actual zero, the power for the control electronics is in danger of disappearing, so it has to have made a clean disconnect before that happens.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

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Re: Tesla PW2

Post by adam lippiatt » Wed, 04 Dec 2019, 06:42

I have had the Powerwall installed. Been fiddling with the settings. Works as advertised. I see the last software with notes update added Western Australian 3-Phase support (something I heard about through my discussions). Latest update seems to add "grid services". On set-up you were asked whether you wanted to sell services to the grid. I said no for now (I suspect it is a future offer anyway).
Powerwall.jpeg
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Re: Tesla PW2

Post by jonescg » Wed, 04 Dec 2019, 12:59

Interesting to hear about the WP 3-phase requirements.

Also, is there any indication of which cells are in the PW2? I have heard they might be using the new 20-70 cells same as in the Model 3. But as always with Tesla, lots of secrets.
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Re: Tesla PW2

Post by T1 Terry » Wed, 04 Dec 2019, 13:59

Big bugga, how much real useable capacity in there? Can the 5kW inverter actually pull a continuous 5kW out of the battery until it is fully discharged?

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Re: Tesla PW2

Post by Rusdy » Wed, 04 Dec 2019, 14:22

T1 Terry wrote:
Wed, 04 Dec 2019, 13:59
Big bugga, how much real useable capacity in there? Can the 5kW inverter actually pull a continuous 5kW out of the battery until it is fully discharged?

T1 Terry
Hi Terry, the battery testing centre latest report (click here) provides really good objective data. Yes, they can pull 5kW constantly for (almost) the whole SoC band, and yes, it's as advertised (pretty damn close) of 13.5kWh usable capacity (fading shown in the report too).

You need to go to the live data to see the full 5kW charge discharge cycle. The report does explain the current unreliable 5kW full power discharge due to over-voltage issue at the centre.

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Re: Tesla PW2

Post by adam lippiatt » Wed, 04 Dec 2019, 21:00

I hear they are model 3 cells.

5kW continuous draw I don’t know. It is supposed to, peak 7.2 for 10 seconds. I try to do my energy intensive work during the day when solar inverter augments.

I have it set as though peak charges are from 7am-9pm. This is true if I consider anything above my 13c Synergy tariff peak (which I do). If you ask it to cost save it will actually draw from the grid between 9pm - 7am.

97% solar powered today but it considers a day finishes at midnight.

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