The UK passed through winter (defined as December to February) without coming close to running out of electricity. The nervousness of autumn 2014 turned out to be unjustified.

At 5.30pm on the chilly evening of January 19th electricity generation hit a peak of 53.3 GW. National Grid had forecast peak generation during a cold spell as likely to hit 55.0 GW. So, as is now increasingly normal, electricity demand was running one or two gigawatts below expected levels. And there was probably another four or so gigawatts of supply available even if demand had reached the figure National Grid had predicted.

How was peak demand actually met in the early evening of January 19th? The tables below give the details. In the first, I’ve written down the amount of generating capacity that the National Grid thought would be operating during the winter, plus its estimate of the percentage that would actually be available at the moment of peak need. (The remainder would be out of action for maintenance and repair).

Table 1

Source: National Grid Winter Outlook

These numbers suggest an expected peak availability of 57.1 GW, plus whatever the wind was providing and also what could be purchased from France and the Netherlands via the interconnector cables. The total - excluding wind - was about 59.6 GW if the estimates of availability were correct and both two international connections were delivering their full capacity. (As it turns out, at the point of peak demand, wind was barely turning the UK’s turbines).

The distribution of supply at the moment of peak need was as follows.

Table 2

Source: National Grid Winter Outlook, BM Reports

Nuclear was slightly over-providing compared to the projected availability of supply. (This was very unusual; most of the winter nuclear has under-performed as a result of minor outages at many of the stations and, on average, nuclear has produced much less than expected). Gas and coal stations were generating about 91% of the National Grid had projected as being available at the moment of peak demand.

The most obvious indicator that peak demand was easy to meet was the low utilisation of open cycle gas turbines (in effect, jet engines used only to provide peak power) and oil-fired power stations (expensive to run so generally also only turned on at moments of maximum demand). Oil-fired capacity was barely being used and there was half a gigawatt of spare capacity at the OCGT plants. Pumped storage might have provided an extra half a gigawatt of supply if it had been necessary.

The position will get tighter in future years as fossil fuel power stations close. Longannet, the UK’s second most polluting electricity generator, is said to be considering shutting within a year as a result of high charges to connect to the National Grid. But the slow fall in electricity demand, and the increased emphasis on ensuring that demand can be reduced at peak times means that the years to 2020 might well be survivable without blackouts.