there is also a very very subtle "feature" of the Powerwalls that most people don't realize, and seem to have a hard time wrapping their heads around even when it's explained to them...
99% of residential solar installs are "grid tied" solar - which means you get power from the grid, and provide power to the grid, and the two systems are "interconnected" - but you have "generators" on your roof/ground, and during the day your panels generate power and your home gets it first and any excess goes to "the grid" - great - solar 101 - we all seem to understand that…
however what most people don't realize, is that with "grid tied" solar
if the grid is down - your personal solar is also down! yep , zip, zlinch, nada - you are not producing power today my friend! no grid = no solar power = no kWh's - fire up the generator! cause your panels are doing squat!
whaaaaaaaaaaaaaaaaa? so even on a sunny day with 180,000 solar panels on you roof and you normally generate 457,523,982 kWh/day - _IF_ the grid is DOWN - you generate 0 (zero) kWh's while the grid is down - [insert Homer Simpson 'doh' here]
your solar panels are "inert" while the grid is down - this is the rule, and is a condition set by the power companies and the physics of electricity - that your solar panels will not produce _ANY_ power while there is "NO" grid…ostensibly the most important reason for this is safety - since your home is connected to "the grid" - if you were generating power - your home would be electrifying the grid while workers are trying to work on the lines - and they need/expect there to be no power while they are working on the outage - if your panels and your neighbors panels were generating power, the grid would be "powered" and add complexity and safety issues to restoration issues…
the physics of the issue are - even if your panels were allowed to produce power while the grid was down - it's highly unlikely your panels and your neighbor's panels could meet the demand of the entire neighborhood, so while you would be producing power - the ongoing demand of all your neighbor's power usage would essentially suck your panels "dry" because they simply can't meet demand for an entire neighborhood - think sucking on a straw from an empty container…unless your solar system is big enough to meet the entire neighborhoods demands - the grid would be unstable, and a brownout would occur, and the power quality wouldn't be standard, and cats, and dogs, and the end of the world, and the wrong political party in the White House, and your wife has left you, your dog has died…it just won't work…
so grid tied solar produces zero kWh's when there is _NO_ grid.
however if you can temporarily "disconnect" your home from the grid - you could have your solar generate power while the grid was down - powering your home during the day time - even though there is no grid…
if only there was some device that would monitor 'the grid' - say 1000 times a second - or a millisecond - and when "the grid" goes down - cut over a disconnect switch in less than 10 milliseconds - taking your home off the grid temporarily and then allowing your solar panels to continue to produce power…if only.....
wait that device exists! it's the Powerwall Gateway Module - and that is exactly what it does!
- it monitors the grid
- it connects and disconnects from the grid as necessary
- it coordinates power to/from PW/Solar/Home/Grid
- it "lies" to the Solar panels during an outage and "pretends" to be the grid so that they continue to produce power
my home solar system in summer produces 40-60 kWhs/day - without the PW's you lose that daily production - with the PW's during the day it's very likely your solar system can power the home leaving the batteries untouched...
it's a very very powerful but subtle feature once you understand it - PW's keep your solar producing during a grid outage - without PW's you lose all your potential solar production - which once you understand it is very frustrating…
when PG&E turned off my power last year for 36 hours at my home without Powerwalls - it was quite frustrating to me personally to go a day and a 1/2 with no power, knowing I had 30-40 kWh sitting on my roof "idle"…I ordered PW's the next day - not for whole home backup - but because I was tired of listening to the generator, and dealing with the propane tanks.
Powerwalls keep your solar online while the grid is down - this means you still have access to your normal daily production - and can recharge the PW's during the day - meaning not only do the PW's provide power to the house, they can sit idle saving their power, when your solar can pick up the load - this is a powerful powerful feature - but difficult to wrap your head around until you really understand it....
ohhhhh - you mean I get to power my home with the 30-40 kWh/day I normally produce, only using my batteries at night! Wow that's kinda cool.