Having some trouble understanding how PW3 makes sense when more than 2 are needed/wanted for longer backup.
Some background....got my detailed plan and plan set from Tesla yesterday. This is for 58 panels at 23.49kW with 4 Powerwalls. Good thing is that they actually got me from original design which was 97% offset to 100% offset with less panels by shifting more panels onto the rear (southern facing) of the home's roof since their survey showed it was larger. They were able to remove 2 panels overall as part of this change. This was a win.
However, I was shocked to see they spec'd my PW system for 2 Powerwall+ and 2 Powerwall 2s with 2x 7.6kW AC from PW+inverters and 1x extra 5.7AC inverter for total AC output of 20.9kW.
This is contrary to what I was told a week ago the day of the site assessment where my project advisor and the site assessor both said at least 2 of my PW would be 3s and the remaining 2 would be either 3s or 2s. I asked at the time if PW3s and PW2s are compatible and project advisor said yes. The reason they gave at the time for it possibly being 2 PW3 and 2 PW2 was that some utilities do not allow the additional AC output of the disabled inverters of the 3rd and 4th PW3 to be removed from the total AC output consideration (even though they aren't used) and they have strict output limits for total AC output.
Based on our convo and design they came up with, It seems to me that PW3 are not actually compatible with PW2 or PW2+. I asked if my specific utility would not allow 4x PW3 and that's why they made them all 2s? He said no, that isn't the case with my utility and this decision right now is more-so because Tesla may not want to provide PW3s where inverters are not used for financial reasons. This makes no sense to me. Why would they allow config with 4x PW3 then since its very unlikely non VPP setups will need 46AC output (4x PW3 AC inverter).
The advisor also told me (incorrectly) that the only difference between PW3 and PW2 is that PW2 does not have same starting power for AC units etc. as PW3 but everything else is the same. Said it's not an issue for me since I will be having 4 PW2 (which is true) and they will have more than enough power to start the AC unit and any other item with high initial peak V needed. I explained that this was not the only difference (and not even the largest or even relevant in my case since I have 4 PW). The biggest difference for me is continuous kW output per PW where it is 5kwH for the PW2 and 11.5kWh for PW3. I explained this is a huge difference in terms of supply to my home! Just my 2 Model Ys would use 22+ kWh if they are both charging at full speed. Not sure if the advisor did not know this, or was ignorant to the facts, but considering the more than double continuous output per PW is a huge selling point of the PW3, its hard to believe he wouldn't know.
electrek.co
