> You can check Brazil in recent history to check the effects of droughts in the power grid. In the end there is a need of conventional power plants always ready to backup the grid when the renewable energy is not available.
Disclaimer: I'm Brazilian
Sure, you need some conventional powerplants as backup system. However, that's much better than having them run all the time. Don't forget that conventional plants should also have their backups.
The hydroelectric dams do the heavy lifting really. We also have a nationwide energy grid, so we can reallocate resources as necessary. What we actually need is more renewables. The northeast is (almost!) always sunny. If there's not enough sun, it's usually because of rain(increasing reservoir levels) and there's wind (boosting wind power).
The north (near the Amazon forest) has an abundance of rain. The south and southeast are hit and miss, the weather is far less reliable.
With a nationwide power grid, surplus can be reallocated. In case that's insufficient, then the thermoelectric power plants can be started, hopefully running on natural gas or biodiesel. We do have a nuclear power plant, wish we had more.
> The majority of losses of the power distribution network are on the last mile
Which is why microgeneration should be encouraged. Having enough local generation to offset the losses alone would be a win.
> Since we are talking of the environment, rare earth metals have a very pollutant and energy intensive extraction process which in most cases is not accounted in the environmental cost of solar panels.
Sure. But what about the resources to build conventional power plants? It is not like their extraction, transportation, processing and assembly is free.
Thermoelectric power plants also release harmful gases into the atmosphere for as long as they are operating. Solar panels, wind turbines and hydroelectric dams don't do that (for hydro, I guess they'll release a bunch of methane and other chemicals for quite a while after they are constructed, due to the dead life when the artificial lake is formed).
Fusion is always 10 years away. I wouldn't hold my breath. Nuclear power plants will also require a lot of energy (and pollution!) in order to be constructed. The newest designs are a win in my book, but we can't pretend they don't do environmental damage.
Oh, almost forgot. If you are concerned about rare earth mining, then let us build more solar concentrators. They only require mirrors, no rare earths. The heat exchange medium can also be molten salts, which will retain a lot of thermal energy for the night, without using batteries. They require direct sunlight however, while solar panels will work (at reduced efficiency) even in overcast skies.