THE public are generally aware that the key sources of renewable energy including wind and solar are variable and intermittent which results in their needing back-up when supply cannot meet demand or indeed when renewables output frequently collapses and such back-up includes the running of quick-responding gas turbine generation and hydro power including pumped storage.
Superficially this seems simple. However, there is considerable background serious and complex power systems science behind ensuring security of supply.
As we close down major coal, nuclear and older gas-powered generating stations and replace them with wind and solar we have progressively less rotational inertia, which is stored energy, within the Grid to support our electrical frequency during system disturbances and Scotland, in particular, will be acutely challenged when Torness closes in a few years followed later by the Peterhead gas turbine station, which is seriously elderly and cannot run indefinitely. Loss of system inertia results in frequency changing much more quickly when faults occur, increasing the risk of supplies being tripped, including domestic to prevent danger at home.
A second major challenge is to generate sufficient reactive power (wattless Megavars) around the country to support voltage as it does not travel well and is not source produced by renewables. Also without reactive power we cannot create magnetic fields which transform electrical energy into mechanical energy and run equipment.
Hydro annual output in 2021/22 in Scotland was 10.7% of demand but in 22/23 was down to 8.7%. This will be partly due to Scotland’s total generation output having grown via start-up of new renewables with no new hydro capacity being available but, I suspect, the measured hydro active power output of 10.7% likely also reduced over the year because quick-responding hydro stations like Foyers were periodically being run to only output reactive Megavars and not active Megawatts in order to keep the north of Scotland voltage afloat. Insufficient reactive power will cause the grid voltage to collapse in a very few seconds.
Rarely aired is the dirty secret regarding the variable amounts of methane produced by hydro, including pumped storage, from organics in the reservoir water when they are generating as it bubbles out of solution. Methane, of course is around 85 times more potent as a greenhouse gas than CO2 over 20 years. The UK, whilst more temperate than warmer countries, is now not regarded as immune from this problem now being seriously studied across the globe.
So electrical power systems are immensely more complex than simply installing
Megawatts of renewables generation to match Megawatts of load demand and the UK is having to introduce huge and expensive catch-up changes to protect the grid system as a result of our un-coordinated rush to renewables, all of whose huge costs are over and above the oft-quoted Contracts for Difference strike prices for renewables generation and will be largely if not totally met via our bills.
DB Watson, Cumbernauld.
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