There seems to be a basic error in the engineering of zero carbon electricity. All distribution is based on 50 Hz AC transmission which is the only practical system for long range (over500 metres) electricity Distribution. This 50 Hz frequency is set by large turbo alternators running at 3000 rpm (for 6 pole machines).
Alll the "green" alternatives (Except Nuclear) generate DC power. This has to be Inverted to 50 Hz AC by synchronous systems. It has been calculated (By greater minds than mine) that the the minimun level of synchronous power for a stable system is 40% so we can not have more than 60% renewable energy even assuming that it would be available in low wind, low light conditions.
Eur Ing Roger Pendleton DipEE.CEng. MIET
Tidal and pump storage are renewable energy but are unlikely to be part of that 60/40 limitation.
There is a lot of work on-going for the conversion of such short term renewable energy (e.g. wind & cloudy solar) into stored energy.
My main point was to always be cautious of these grand 'facts' and 'limitations' and to discern the hidden assumptions.
Do we have too many people wanting too comfy a life that is dependent on the carbon cycle (plant absorption (CO2 -> O2, and combustion C+ O2 -> CO2)