Somer very good points
1) the rand is ****ed, so powerwall doesnt make much financial sense
2) offgrid changes things massively. For a grid tied solution, how many times will you actually cycle your batteries? AGM's are rated to 80% discharge, but i've configured my inverter to only 50% discharge. I have yet to hit that limit and run out of batteries. Most AGM's are rated 500-1000 cycles. lets assume 500 cycles and 50% discharge 2x a week. That gives me 5 years before i need to replace. I'm guessing that in 5 years time, lithium batteries are going to be WAY cheaper than they are now, so in the long run, i'm actually saving money buy not buying lithium now.
3) it doesnt cost "slightly more at offset". It costs a bucket load more at offset. But again, if off grid is your application then your options are very limited
1, 2 (addressing the 5 years down the line pricing)
Yup, the Rand *is* ****ed. Only going to get worse, especially now we've decided on bailing out SAA (*again*, see the just announced news on that vis a vis 17 billion reinjection from business development fund), and Nuclear. Any price decrease in Lithium based solutions is going to be offset by rand depreciation. We'll be lucky if we don't hit junk status by May-June.
Expect 20 to the dollar by end 2016 if we don't make some drastic changes.
In 2-3 years time, who knows where we'll end up. Again, any price drops in Lithium will be offset by that, so
everything imported is going to get far more expensive, rather than cheaper.
LI is rated for 3000 cycles, at 80% DoD, so far cheaper than LA based with 500 @ 50% DoD..
The Tesla is 7KW usable capacity (actual battery capacity is more, in the roughly 9KW range @ 80% DoD), so equivalent to 14KW of LA (assuming 50% DoD) for same *usable* capacity.
Given it also includes the BMS then its not too bad in comparison pricewise.
Upfront costs are higher, but lifetime costs are far lower. You're right, most people are short sighted, or can't fund it upfront.
For those that can though, its a fairly decent deal.
Its more expensive than I can roll my own LFP based storage solution for, but not by that much, and its an out of the box plug in and forget solution.
If I had excess $'s at the moment, I'd probably be buying one. As it is, I'm keeping all my foreign funds the **** away from the rand...
I recognise that different people have different needs. I've always been a proponent of the right tool for the right job.
Not everything is a hammer, and not everything is a screwdriver. The price / lifetime ratio will be in the right spot for a lot of users...
Cape Town is currently R2.86+vat for > 600KW usage.
The Tesla 7KW daily solution can compete with that *already*, and make financial sense.
+-60,000 cost ( ignoring rest of system cost for pure battery calc).
7KWhr usage / day cycling. 365 days a year. 8 year lifetime @ 7KW discharge.
= 20440 KWhrs of output.
20440 x 2.86 = R 58.5K vs R60k +- cost. Pretty close.
You'll still get another 5-10 usable years out of the battery from that point, so lifetime costs are pretty much covered already at *current* costs.
Next year and the year after that when further Eskom / muni increases hit, its going to look a whole lot smarter to mitigate those kinds of costs. The only troubling thing in that equation is where the rand will sit vs the dollar.