Posted: 19 June 2017

Winter Review published

Review, Consultation, winter, electricity, gas, supply, demand, generation, interconnectors, UKCS, Norway, security, storage, National Grid

The Winter Review and Consultation is one in a suite of documents from the System Operator exploring the future of energy.


The Winter Review and Consultation 2016/17 sets out National Grid’s analysis of supply and demand for electricity and gas during winter 2016/17.  So, what are the main findings and what do they tell us about the changing shape of Great Britain’s energy sector?

While winter 2016/17 was colder than the previous two winters, it was average in terms of temperature. The GB electricity and gas networks continued to deliver reliable supplies of energy to consumers and National Grid did not need to call on extra reserve services over the course of the winter.

The picture for electricity

As anticipated in the Winter Outlook Report, there was enough generation and interconnector imports in place to meet demand across the winter.

Weather-corrected transmission system demand was 50.9GW, 1.1GW lower at peak than forecast in the report. Transmission system demand was consistently lower throughout the winter compared with winter 2015/16. This was mainly caused by a drop in weather-corrected demand and an increase in non-weather related embedded generation.

Generation availability was in line with forecasts. The unplanned outage and loss of half the capacity of the IFA interconnector to France in November led to lower actual output during that period. Demand management peaked at 2GW last winter, similar to winter 2015/16. The estimated number of days when demand management was used rose from 36 to 48.

Rise in proportion of gas-fired generation

Gas-fired generation, as a proportion of total generation, increased significantly. It accounted for almost half of GB electricity output compared with around a third in winter 2015/16.

The main reason for this was changes in fuel prices, with gas being cheaper to run than coal, plus a reduction in available coal generation. Coal-fired generation provided 12% of total supply, as against 20% during winter 2015/16. Wind provided 10% of total generation – a similar figure to the previous winter.

Interconnector flows were lower than winter 2015/16, with unexpected outages on both the IFA interconnector to France and the EWIC interconnector with the Republic of Ireland. High prices in continental Europe were also a factor.

Ahead of winter 2016/17 National Grid procured 3.5GW of Contingency Balancing Reserve (CBR) to support system balancing. With margins not as tight as forecast, and lower demand combined with reliable generation, no CBR plant was required.

Analysis of gas

There was sufficient gas available from a variety of sources to meet demand across winter 2016/17. The total weather-corrected gas demand over the period was 50.3bcm, which was higher than forecast in the Winter Outlook Report.

The reason for this was increased gas demand to generate electricity, due to lower gas prices. This demand increased to 13.8bcm, which was 30% higher than winter 2015/16. The highest gas demand was 372.2mcm on 26 January.

There was also increased cycling of storage injection and withdrawal.  A consequence of restrictions at Rough, the long range storage facility, and shippers responding to short term changes in market demand.  Storage injection increased by 50%, from 1.2bcm in winter 2015/16, to 1.8bcm a year later.

Gas supplies from the UK Continental Shelf (UKCS) and Norway were within forecast ranges, although higher than the previous two years. There was a sharp decline in LNG supplies from the start of October following price increases on the East Asian market. Deliveries remained low until the beginning of March.

Diversity of supply and the effect on network operation

Diversity of gas supply continues to benefit GB security of supply. However, the variation in sources can make flows around the network less predictable and increase the challenges of operating the system.

For winter 2016/17, there was an increase in changes to ‘within day’ demand profiles alongside a continuous high supply from UKCS and Norway. Combined with the drop in LNG supplies this caused numerous operational challenges, particularly relating to the amount of gas held in the National Transmission System. This is known as linepack.

Some of the linepack swings were magnified by other connected loads – for example, the volume and variability of gas demand from Combined Cycle Gas Turbine (CCGT) generators was much higher than for winter 2015/16.

Where gas entered the system

There were also changes to the volume of gas entering the system at each terminal.  High supplies dominated three terminals in the north and east of GB. Collectively they accounted for 82% of total gas throughput during winter 2016/17. This meant a greater need to move stock to balance regional supply and demand requirements. National Grid will continue to work with industry to understand its need for flexibility.

Find out more

The Winter Review and Consultation is one in a suite of documents from the System Operator exploring the future of energy. The responses from stakeholders to the Winter Consultation provide valuable insight and will help to inform development of the next Winter Outlook Report which is due to be published in October.

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"Gas-fired generation, as a proportion of total generation, increased significantly"

National Grid Winter Review and Consultation.