You need inverters to run them, and you can't just put more battery on one inverter. The price is about 1:1 now for battery and inverter costs when I looked into it last.

You absolutely can put multiple batteries on one inverter. The limiting factor is the DC bus bar and breakers, not the inverter, which just needs to be sized to consumption.

Yes there's nothing stopping you, but economically a given kW battery installation stores about 4 hours of power.

There's 4 to 6 hours of peak renewable energy per day.

If you add more batteries, you increase power and energy at the same time and ratio: so for any practical home battery system you're cycling the cells daily, which means you your power for charging must match.

If you put more batteries on one inverter, then you're scaling a lot of other costs (BMS, bus bars and space) but you'll never actually be able to utilize that capacity - it'll sit idle most of the time because you can't get it in and out of the cells fast enough.

Are your figures, notably 4-6 hours of generation, overlooking the potential for home battery owners to buy power in during off-peak (cheaper) periods, for either their own usage, or for selling back to the grid, at other times?

I've costed it and it doesn't work out. But you can realize why without doing the calculations: unlike solar, batteries aren't surface area limited. So better capitalized producer can achieve better economies of scale and just build warehouses of the things to do exactly that. Which is what they do - and thus off peak power trends towards a tiny margin over the warranted kWh cost of a battery.

Okay, I think you're in a different part of the world to me, then - I can generate about 85kWh in a day here, mid-summer, about 34 degrees south, and that's throttled by my 10kW inverter.

I could go higher with a better inverter, but energy providers in Australia, or at least my part of it, basically drop all pretence once you go over 10kW feed-in, and the already pitiful rates they'll offer as standard asymptote towards zero.

Time of usage tariffs vary quite wildly here, but it's not uncommon to have close to 70c at peak hours, and 20c at off-peak. These fees are complicated by the daily connection charge, which is around $1.00 but varies on your location, provider, and your ToU and other schemes.

Some 'pretend to be a wholesaler' options exist here, but our wholesale pricing is bid and sold in 10m blocks, not 15m, as per your other note.

Also, we have ~6 hours a day where peak pricing is generally applied, and maybe ~9 hours where we're at off-peak pricing - so the math tends to be more compelling.

Well, I suppose our perspectives differ. My own solar installation is off-grid, so the battery pack is sized to last for 4-7 days. I don't have the luxury of tapping the grid if they tap out, and running the generator's quite expensive.

6.2kW 48V -> 230AC inverter is $300

And if you run the numbers, the battery which can deliver 6.2kW is only about 1.5kwH in capacity. This matters because while discharging slowly is fine, to gain any economic benefit you need to be able to charge at essentially full power.

If you have 100kwh of batteries and only 6kw of AC connection then it would take 3 days of typical solar charging to get them to full capacity. And any kwh sitting there that you don't charge/discharge is costing you money for grid batteries - the economics still depend on being grid interactive.

The best demand signal in my local grid for example is exactly 1 hour wide. Which means s you get 4 15 minute intervals to basically try and dump power for the best price.