that was great oz. I'll watch the rest of the series for kicks.
So pfitzy, leaving aside cost of the powerwalls, what is the max size powerwall you could realistically charge with your array? I assume you fully charge your battery array atm, ie the amount of charge you get in your batteries is limited (due to cost of the powerwall/s) by battery size rather than charging capacity?
There are a few factors in this, not all of them technical:
1) Some areas of the power network have limits on the size of the grid-connected system you can attach. For example I believe in NSW
less than 10kW is the maximum domestic system allowed (twice the size of mine), and then network distributors have a limit per phase (e.g. 5kW for a single-phase).
2) Physically the Powerwall can only accept a maximum input of 3.3kW peak - and it generally won't sustain that for long in practical terms. Standard flow is 2kW, and if I had multiple Powerwalls chained together, I'd still only be able to push about 2kW through to the whole array because they're in series, not parallel
3) To get around this, I could install a second system that ONLY charges batteries - the way around the limits in Point 1 is to install a system that ONLY pushes DC into the battery. Because that limit only applies to on-grid systems, I could have one whole 5kW array (or bigger) just feeding the batteries all day, without any grid connection, and leave my existing system powering the house and pushing into the grid.
4) That takes away a little from the warranty of the Powerwall (10 years grid, 4 years off-grid) so I would look at another battery to do that. Check out
http://redflow.com/ for the primary manufacturer of Zinc-Bromine power cells. Already heavily used in industry for remote sites, there are pros and cons over lithium. Downside of the zinc-bromine solution is that the liquid needs cycling once the unit is drained, which takes 30-60 minutes I'm told. Also has a service limit between 10-50C (because its fluid) which isn't great in Australia unless you've got decent insulation.
With all that in mind, my dream scenario is this when I win a shitload of cash:
- Build an earth-sheltered house with a room full of Zinc-Bromine batteries in the cellar (accessed by tunnel) to a sleepy 18C
- Stick a massive solar array on top of all that with appropriate inverter technology and enough juice available to power up my Tesla Model S or X
- Water tanks and suitable filters stored in the hill I build into for drinking, cleaning, and fire prevention.
Basically a luxurious bunker with a gorgeous outlook over a valley somewhere, and no real danger of bushfire. The Zinc-Bromine cycling issue is taken care of with multiple batteries in parallel, and with low-use appliances and a crapload of available panel generation, I'm all good.