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Electricity Networks – Coping with Lockdown

At a time when public focus is rightly on the work of the NHS, supported by private health companies and an army of care workers, we should also spare a thought for the people who must keep the lights on.

24th April 2020

With UK demand significantly reduced due to the number of businesses that are closed, you might think that it is easy to supply the country’s needs. However, the current demand profiles are producing a number of challenges, particularly for the National Grid ESO.

Since 18th March, the National Grid has been holding weekly webinars to brief stakeholders on their Coronavirus Preparedness and this has revealed some interesting facts and figures about the current demands on the transmission system and the issues that these create.

Changes in Demand

Unsurprisingly, domestic electricity consumption is currently higher than normal whilst commercial and Industrial demands are much lower than we normally see at this time of year.  However, there is also a change in the demand profiles;

Compared with previous years there is a slight delay in electricity demand increasing in the morning as many erstwhile commuters can enjoy a sleep-in before travelling to the spare room to start work and morning demand for the national grid is currently around 17% lower than normal. However, the reduction in demand falls below 15% by the afternoon and is around 10% lower in the evening and for the daily peak period.  At weekends the peak demands are only a few percent lower than normal.

Impact of Renewables

The last few weeks have seen both windy and sunny weather and these have both contributed to reductions in transmission network demand due to increasing levels of embedded generation within the distribution networks.

In the early hours of Easter Monday (13th April), the shutdown of Industry (exacerbated by the Easter Holiday period) coincided with windy weather and the demand on the grid fell to 15.2GW, which is the lowest value ever recorded.

On the following Monday (20th April) the UK was bathed in sunshine and the National Grid calculated that embedded solar PV produced a record 9.68MW of generation in the early afternoon, which is the highest ever recorded in the UK. At 3pm the demand on the National Grid was only 16.7GW, which is extremely low for a working day.

Maximum solar intensity normally occurs in late June, so further good weather may mean that some of these records will continue to be beaten.

Managing Low Inertia

A key function of the National Grid ESO is to ensure that frequency is always controlled to 50Hz and this is achieved by several means, but primarily by fossil-fired power stations along with some pumped storage facilities. These plants can regulate their power export indirect responses to grid frequency; If frequency falls then these plants increase load almost instantaneously and if the frequency gets too high, they will reduce their output. Such control is carried out automatically by governors on the generation units – humans wouldn’t be able to react fast enough!

These generators have large masses of spinning metal and part of the ability to regulate frequency is due to the large rotational inertia of such power units.

By comparison, wind turbines have smaller lightweight components with small amounts of inertia and cannot increase load if grid frequency falls since their output is controlled by wind speed. Solar PV is worse, it has no ability to control frequency and has no rotational inertia.

Now the challenges for the National Grid become clearer; if there is low demand on the grid then renewables will form a much higher proportion of the generation, so there will be less conventional generation operating and therefore less inertia and less control over frequency.

If frequency falls too quickly due to the tripping of large generators then the back-up method of saving the grid from collapse is to load-shed, which involves disconnecting consumers at pre-selected primary substations.  The bigger the frequency drop the more consumers are affected. If you want to know what this looks like, then go back to your news archives and remind yourself of the events of 9th August 2019 when two power stations tripped at the same time and load shedding was initiated resulting in around 5% of consumers being disconnected.

To cope with periods of low demand and high renewable output the grid must manage the conventional generators by running additional generators but operating them at lower loads to increase inertia and frequency response. This incurs costs that will form part of your BSUoS charges in your next bills.

Clap for Carers

An interesting analysis of demand data shows the impact of the ‘Clap for Carers’ event that now takes place at 8pm every Thursday. Between 8.01pm and 8.05pm the grid is seeing a sudden increase in demand of around 1GW.

So, what do people do when they finish clapping? – They obviously go and switch the kettle on!

And Finally,

Inenco would like to thank the employees of the Energy and water industries for their continuing work in ensuring that the UK continues to be supplied safely and reliably.

It’s hard to imagine being in lockdown without gas, water and electricity!