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Comment by PaulDavisThe1st | Hacker News Reader

> The usual cost of a full off-grid system can clear $100k if it's sized to cover HVAC.

Or is essentially absurd... my 6.6kW system generates about 3x more than we need for 8 months of the year, but about 1/3 of what we need for 4 months of the year (the period when our air-source heat pumps, aka minisplits, are in use).

To be able to go off-grid would require either:

    - a systems 3x bigger than we have, generating 9x more power than we need for 8 months of the year

    - a gigantic (10MW?) battery system to store the excess power from the summer

Neither of these make any sense to me, and seem like well-intentioned but fundamentally ill-conceived designs.

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This is a fair observation. Interestingly, what you describe (a system 3x larger than your average load) is essentially what the grid has to have. Looking at the California data, here in Winter, today's peak usage is about 28 Megawatts and the overnight low is about 20MW. However, the peak all time usage for California is over 50MW. Our entire electric grid has to handle that 100% delta in usage; it's not surprising that a personal grid would have to handle at least that much delta. That's just what is required to have 24x7x365 electricity; you can't hide from that reality.

But doesn’t California have rolling blackouts? That makes it seem like the grid needs to be larger than 3x.

Not usually. There are grid shutdowns in wildfire risk areas during high wind events, and there was a brief rolling blackout last year over two nights in a small area, but it's been almost 20 years since the broader blackouts that made national news:

https://www.marketplace.org/2021/07/22/a-california-fix-for-...

It's not about hiding from the reality. It's about how energy storage (and generation) systems scale and can be activated/deactivated.

On the generation side: If I had put in a 21kW system to cover our winter needs, the extra power it generates during the summer would have been unconditionally generated. Do this broadly across the population and the power grid has a substantial management problem. Conversely, utility-run systems are likely to be built so as to be much more modulatable, to match demand.

On the storage side: yes, obviously the total storage required is the same, but for more or less all the technologies I'm aware of today, this would be much more efficiently done with large storage systems than per-household distributed ones.

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