Interesting graph and story over at Tallblokes place:
This post is concerned with the two main forms of UK Weather Dependent Renewable Energy in the UK, Wind Power, (Onshore and Offshore), and on grid Photovoltaic Solar Power. In the UK these amount to ~75% of all installed Weather Dependent Renewable Energy. The other Renewable energy inputs are traditional Hydro power ~8% and the remainder are other sources such as biomass, waste and landfill gas amounting to ~17%.
The capacity percentage, or load factor, of any power generating installation is calculated as the actual electrical output achieved annually divided by the nominal maximum Nameplate output. This article uses the real measures of capacity reported in up to date time series data of UK Renewable installations. It thus provides reasonably correct comparisons of the efficacy of Weather Dependent Renewables as is reported annually by the Renewable Energy Foundation in the UK.
When announcements are made about Weather Dependent Renewable Energy installations, they are reported as the full Name Plate capacity usually in Megawatts and also often disingenuously as the number of homes that could be supplied at their full level of power output. So such announcements are always over optimistic because the question of Capacity Percentages / Load Factors are not fully explained. So Renewable Energy announcements usually assume erroneously that the wind blows all the time at a productive speed and that the sun shines overhead 24 hours /day.
But because Weather Dependent Renewable Energy output is crucially dependent on the vagaries of the weather, (for wind), and the weather in combination with the season and the time of day, (for solar), the useful electrical output achieved by Weather Dependent Renewables is inevitably substantially less that the maximal Name Plate capacity of the installation. Accordingly in 2017 Weather Dependent Renewable Energy in the UK was operating at about one fifth of nominal name plate capacity overall.
Lots more in the story. Hit the link…
It is interesting how 1/5 keeps showing up. At about 20%, or 1/5, of your grid power coming from “Unreliables”, the grid starts to destabilize in uncontrollable ways. Now this says you get about 1/5 of nameplate power out of the systems. Put those together it says you need to install about 100% of exiting nameplate power as Unreliables to get just 1/5 of your needed power, but at that time you also will have an entirely unstable power distribution grid.
Why become apparent when you think a moment…
On a good day, at high noon with wind blowing: 100% of your power comes from solar and wind as nameplate Unreliables make it all.
At any moment the wind can stop or cloud blow in (or just guaranteed the sun will set) and you can get 0% from Unreliables.
Unfortunately, power plants that are really really good at making cheap baseload power (coal and nuclear) can have start-up times measured in a day or two. Not really suited to rapid “load following” (or in this case “lack of power from Unreliables following”)
So you get rapid swings of production that can’t be made up by the best baseload production capacity. Even gas turbines need a bit of time to warm up and spin up, so even with a 100% replacement of all coal and nuclear with gas turbines (and you WILL need a 100% backup to the Unreliables nameplate capacity because the wind WILL stop at night some times) there will still be grid instability as the wind can stop faster than cold turbines can start.