Unlikely that you need more than 10kwh. You just want to cover morning and evening electricity consumption. During the day you recharge and consume directly.

Absolutely agree - I think people fall into a major fallacy with sizing their battery systems. Their power consumption probability* distribution is skewed, and they think their battery needs to be sized for 99% or 100% of their daily consumptions. This gives a drastically oversized battery.

Instead, a simple approach is to download the daily power consumption for a year and size the battery for about your 80th-90th percentile consumption. You tend to find the sizing is not that sensitive to whether you go for 80th or 90th percentile, and in any case the batteries come in standard sizes.

If you've sized your battery system economically, it should be empty a good proportion of the time, but that just doesn't "feel right" to consumers.

* Yes I mean frequency not probability but I didn't want to cause confusion with electrical frequency

Maintaining reliable access to off grid electricity and going net zero are very different applications requiring very different expenditures. Both are valid choices, but going net zero relies on a great deal of grid infrastructure investment and maintenance, and the understanding is that utilities in high home solar areas will rapidly de-emphasize per-kwh pricing in favor of per-month access pricing.

It depends on how many cloudy/winter days you want to be proof for right? There needs to be some backup capacity for when you won't be able to fully recharge for weeks on end.

Although I suppose it is cheaper to oversize solar and not the battery, but that's usually already maxed out and limited by roof space. Maybe a small wind turbine to compensate for stormy days...

> There needs to be some backup capacity

I think they're talking about the situation where you're still connected to the grid, in which case you don't need to handle the backup capacity.

> Hmm yes super cheap, might impulse buy later.

It's part of a house. Of course it's not an impulse buy. That's not a useful basis for comparison.