On Mon, 30 Jul 2018 18:47:14 +0100, Ahem A Rivet's Shot wrote:

> At domestic scale they make the householder immune to brown out and
> outages short enough not to drain them, proven repeatedly by everyone
> who has domestic power storage

er, AIUI the vast majority of domestic solar PV systems shut down
when the mains goes. They do *not* provide any autonomy.

> So for off-grid winter usage you need a system that produces enough
> energy for your needs at 20% of rated capacity,

So for 20 kWHr/day you need at *least* a 100kW rated system.

> The usual estimate for off-grid usage is at least five days storage.

1 kW @ 48 V = 20 A (ish). Total battery capacity 20 * (5 * 24) =
2,400 AHr.

>>> A few hours storage (say ten to twenty kilowatt hours) and a few
>>> kilowatts peak of panel (just enough that the total collected
annually
>>> is close to the total used annually)

"a few kilowatts peak"?  Do the maths ... see above ... 20 kWHr/day
at 20% means a 100kW peak array.

--
Cheers
Dave.

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