Even that's not necessarily true; your run-of-the-mill lead-acid car battery works fine for this at small scales, and a collection of them can be good enough for household-wide use. Not the most environmentally-friendly option, but such batteries are cheap and abundant.
You're right that at large scales (neighborhood-wide, city-wide, nation-wide, etc.) we don't really have the battery infrastructure in place quite yet. I'd guess that said lack of infrastructure could be resolved well before 2025, though.
Modelling energy densities and costs tends to suggest that's not a viable option.
Flywheel energy storage is useful as a substitute for spinning reserve (that is, the inertial mass of extand thermal generation turbines), but other than serving to dampen grid fluctuations, it's not good for more than a few minutes', perhaps at the outside a few hours', storage.
There's so much lithium in the earth's oceans that if you manufactured batteries out of it would be enough to store 50 years worth of the world's electricity consumption.
>it just has to charge a battery (or some other means of energy storage) which is reliable.
That's not true. Let's say you build your system with enough solar panels to fully charge batteries that lasts 3 days. And lets say sun doesn't shine for 4 days, which is not uncommon. Where is your reliability? Lets say you are designing a system to have reliable power. How many days worth of power backup would you design it to support?
>Also worth mentioning (at the risk of being very pedantic) that solar is technically nuclear power.
Yeah, and fossil fuels is solar. I don't see how it's worth mentioning.
Also worth mentioning (at the risk of being very pedantic) that solar is technically nuclear power.