The problem with renewables lies in unpredictability of wind power and photovoltaics, and in transmission infrastructure designed for predictable (and controllable) power sources.

We don't have good storage for electricity at the scale that is needed, not within few orders of magnitude, so at all times energy produced must be equal to energy used (the available storage is insignificant globaly, it is very expansive and is limited by geography - basicaly we can pump water upstream and let it flow back through turbines - this is only possible when you have a lot of water and some place much lower, where it can safely go, and it's still not cheap).

Additionaly each transmission line has maximum capacity and it will destruct itself if you try to send more.

With old-style energy sources we had baseload produced by water dams, coal, gas and nuclear plants, and peak load produced by plants that can be quickly (in less than 30 minutes) switched to produce more or less energy depending on demand - these are usually gas or coal powerplants. So with average demand for X, and peak deamd of Y you need X of stable powerplants and (Y-X) of controllable powerplants. Network is designed around that Y, using assumptions that power is divided into smaller and smaller lines from source to destination.

Only thanks to that, and to accurate predicting of demand by each level of power distribution hierarchy (I know about details of Polish system, but I guess it's similar everywhere) - the system works.

If you just swap 1000 MW of coal/gas/nuclear baseload plants with on-average 1000 MW of photovoltaics or wind turbines - you will literaly destroy your energy network. Half of the time it will produce too much energy (which results in blackouts and costly repairs), the rest of the time you will have blackouts because of not enough energy produced. You need to prepare infrastructure for that.

You need to adjust the whole network to bigger load, and to change the network topology from "connected stars" to peer-to-peer (or at least orders of magnitude more stars, connected orders of mganitude more intimately), and you need to expand the transmission lines a lot, because the only way to provide baseload with renewables is to average out production from a lot of places with different weather.

Right now electric networks aren't designed for that, and upgrading the whole infrastracture is going to be very expansive.

Germany is trying to do that - props to them, but in the meantime they are kinda problematic to their neighbors, because when they cannot deal with excess energy produced by renewables - they dump in on Polish, Czech,etc networks. Germany needs to pay for that (too much power is exactly as bad as not enough power - Polish and Czech controllable powerplants need to adjust production because of that and it costs both ways, also routing the power through the lines need to change because some lines may exceed capacity with that additional energy, and that cascades through the whole network. Energy distribution is organised in such a way, that when somebody predicted demand or production wrong - they pay for the rebalancing of network caused by that.

Sorry for wall of text...