Many of these problems don't seem scientific at all, but rather a problem of political will.
As you said, Solar power is incredibly economical. There are plenty of ideas around putting them over farms, or parking lots en-masse to provide cleaner energy.
Access to clean drinking water, while certainly scientific in some situations, is also a problem of political will and money.
Restore and Improve Urban Infrastructure - It's infrastructure week!
"Solar PV with storage = solar PV installation paired with four-hour duration battery storage, scaled to 20% of the output capacity of the solar PV."
Sometime the sun goes away for more than 4hrs.
That may be OK for closed-ended systems (turn off the science at night and during storms), but not for open-ended systems with diverse user demand.
4hour batteries are competitive with gas peakers to match high demand during and after sunny times, but solar needs gas peakers or similar to over for non-sunny times.
everywhere? all at once? The grid is distributed, this is a solved problem. Most of what is needed now is to build the systems, storage, and transmission lines.
Not sure what you’re talking about here. We can’t replace all energy needs with solar but it’s clearly one of the cheapest energy sources and with the added benefit of low capital expense to get started so you can set it up in distributed grids without the massive expenditure to support nuclear installations.
If it is profitable without subsidies from government then everyone would do it as there is money to be made. You do not need peer review studies to prove something is profitable.
But also, solar power is already economical.