Executive summary
Great Britain’s electricity demand remains substantially lower overnight than during the rest of the day.
Analysis of every half-hour of National Energy System Operator demand data for 2025 shows that:
- Average demand between 23:30 and 05:30 was 21.69 GW.
- Average demand between 05:30 and 23:30 was 27.65 GW.
- Demand during the longer peak period was therefore 5.96 GW higher on average.
- Average peak-period demand was 27.5% higher than overnight demand.
- Across the year, the daytime and evening period contained approximately 39,162 GWh of demand above the equivalent overnight baseline.
The difference was most pronounced during winter. In January, average peak-period demand was more than 40% higher than overnight demand. Even during the lowest-demand summer months, the difference remained around 15% to 17%.
This demonstrates why a permanent low-cost overnight electricity period can benefit the wider energy system. It can encourage electric vehicles, heat pumps, water heating, batteries and flexible industrial processes to use electricity when the national system is less heavily utilised.
The 2025 demand differential
The table below compares:
- Off-peak: 23:30–05:30
- Peak: 05:30–23:30
Because the peak period lasts 18 hours and the off-peak period lasts six hours, the total energy figures should not be compared directly without adjusting for the different duration.
The percentage difference is therefore based on the average GW demand during each period.
The final column shows the amount of peak-period electricity used above what would have been consumed had average demand remained at the overnight level throughout those 18 hours.
| Month | Off-peak energy | Peak-period energy | Average off-peak demand | Average peak demand | Average difference | Peak demand above off-peak | Additional peak-period demand |
| January | 4,763 GWh | 20,015 GWh | 25.61 GW | 35.87 GW | 10.26 GW | 40.1% | 5,727 GWh |
| February | 4,168 GWh | 17,119 GWh | 24.81 GW | 33.97 GW | 9.16 GW | 36.9% | 4,614 GWh |
| March | 4,319 GWh | 16,081 GWh | 23.35 GW | 28.82 GW | 5.47 GW | 23.4% | 3,124 GWh |
| April | 3,762 GWh | 13,230 GWh | 20.90 GW | 24.50 GW | 3.60 GW | 17.2% | 1,944 GWh |
| May | 3,640 GWh | 12,510 GWh | 19.57 GW | 22.42 GW | 2.85 GW | 14.6% | 1,589 GWh |
| June | 3,520 GWh | 12,210 GWh | 19.56 GW | 22.61 GW | 3.05 GW | 15.6% | 1,649 GWh |
| July | 3,734 GWh | 13,129 GWh | 20.08 GW | 23.53 GW | 3.45 GW | 17.2% | 1,925 GWh |
| August | 3,598 GWh | 12,628 GWh | 19.34 GW | 22.63 GW | 3.29 GW | 17.0% | 1,834 GWh |
| September | 3,537 GWh | 13,476 GWh | 19.65 GW | 24.95 GW | 5.30 GW | 27.0% | 2,863 GWh |
| October | 3,897 GWh | 15,880 GWh | 20.84 GW | 28.46 GW | 7.62 GW | 36.6% | 4,189 GWh |
| November | 4,161 GWh | 17,284 GWh | 23.12 GW | 32.01 GW | 8.89 GW | 38.5% | 4,800 GWh |
| December | 4,396 GWh | 18,088 GWh | 23.63 GW | 32.42 GW | 8.78 GW | 37.2% | 4,901 GWh |
| 2025 total/average | 47,496 GWh | 181,649 GWh | 21.69 GW | 27.65 GW | 5.96 GW | 27.5% | 39,162 GWh |
Figures are calculated from NESO’s half-hourly 2025 National Demand dataset. Totals may differ slightly due to rounding.
What the figures show
Demand is consistently lower overnight
In every month of 2025, average electricity demand was lower between 23:30 and 05:30 than during the rest of the day.
The annual difference was nearly 6 GW.
That is equivalent to the continuous output of several large power stations or millions of household appliances operating simultaneously.
The difference does not mean that the network has 6 GW of completely unrestricted spare capacity everywhere. Local networks can still experience constraints, and generation availability changes from one night to another.
However, at the national level, it shows that electricity demand is materially lower during the proposed overnight tariff period.
The winter gap is particularly large
The strongest differences occurred during colder months:
- January: 40.1%
- November: 38.5%
- December: 37.2%
- February: 36.9%
- October: 36.6%
Winter demand rises sharply during the daytime and evening as homes, businesses, shops, offices and public services use more electricity.
Overnight demand also rises during winter, but not by as much.
This strengthens the case for encouraging technologies such as heat pumps and hot-water systems to pre-heat during the overnight period before the morning demand increase.
The gap remains during summer
The smallest difference occurred in May, when average peak-period demand was still 14.6% higher than overnight demand.
June, July and August recorded differences of approximately 16% to 17%.
Solar generation can make wholesale electricity particularly cheap during some summer afternoons. This should be reflected through optional smart and flexible tariffs.
However, the data still shows that total national demand remains lower overnight on average. A permanent overnight rate therefore continues to provide a useful and predictable demand-management tool throughout the year.
Nearly 40,000 GWh of annual demand sits above the overnight baseline
The 18-hour peak period naturally uses more electricity because it is three times longer than the six-hour overnight period.
To make a fair comparison, the overnight average can be extended across an equivalent 18-hour period.
On that basis, Britain used approximately 39,162 GWh more electricity during the peak period than it would have used if demand had remained at the overnight average.
This does not mean that all 39,162 GWh should be moved into the night. Some electricity use cannot or should not be shifted.
It does, however, illustrate the scale of the opportunity.
Moving even a modest share of flexible demand could flatten the national demand curve and improve the utilisation of existing generation and network infrastructure.
What could be shifted overnight?
A guaranteed low-cost period from 23:30 to 05:30 would give households and businesses a clear incentive to automate suitable electricity use.
Potential flexible demand includes:
Electric vehicles
Most private cars are parked overnight. Smart chargers can automatically begin charging when the lower rate starts without requiring any action from the driver.
Heat pumps
Homes can be gently pre-heated overnight, particularly during winter, reducing the amount of electricity required during the morning and early-evening peaks.
The objective should not be to overheat homes or switch heating off during the day. It should be to allow heat pumps to make greater use of cheaper overnight electricity while maintaining comfort.
Hot-water cylinders
Electric immersion heaters and heat-pump water systems can heat stored water during the overnight period for use the following day.
Home and community batteries
Batteries can charge overnight and supply homes or local networks when demand rises.
Storage located at substations could also help retain locally generated electricity and reduce unnecessary movement of electricity through the wider network.
Flexible industrial processes
Some refrigeration, pumping, data processing, manufacturing and energy-storage activities can be scheduled for periods of lower national demand.
Why the overnight rate should be predictable
Highly dynamic tariffs can offer extremely cheap electricity when there is excess wind or solar generation. However, prices and available hours can change every day.
That makes them useful for engaged consumers with compatible technology, but unsuitable as the only national demand-management policy.
A fixed overnight window provides certainty.
Consumers know that the rate will apply every night. Manufacturers can configure cars, chargers, heat pumps, cylinders and batteries around the same national schedule. Suppliers can forecast the resulting demand more accurately.
Dynamic tariffs could remain available in addition to the standard overnight rate, allowing consumers to benefit from especially cheap daytime or renewable-heavy periods.
A flatter demand curve benefits the whole system
Moving flexible consumption away from the busiest periods could:
- reduce the need for expensive peak generation;
- reduce stress on parts of the electricity network;
- improve the utilisation of generation that can operate overnight;
- reduce the amount of generation that must rapidly increase or decrease;
- make electric heating and transport more affordable;
- improve supplier demand forecasting;
- support greater use of electricity without requiring every new unit of demand to occur at the busiest time.
The objective is not to make electricity demand identical throughout every hour.
Weather, industry, human behaviour and renewable generation will always create variation.
The objective is to reduce avoidable peaks and make better use of periods when national demand is consistently lower.
Policy proposal
A standard national electricity tariff should include:
- a 15p per kWh standard daytime unit rate;
- a 7.5p per kWh overnight rate between 23:30 and 05:30;
- a regulated network subscription replacing the existing standing charge;
- optional dynamic tariffs for consumers who want to respond to real-time renewable generation and wholesale prices;
- smart controls that allow EVs, heat pumps, water heating and batteries to operate automatically during cheaper periods.
The overnight rate should be available to every household with a compatible smart meter, not only those able to understand or continuously monitor complex wholesale-market signals.
Methodology
This analysis uses NESO’s Historic Demand Data 2025 dataset.
NESO publishes one demand observation for each half-hour settlement period. Settlement period one begins at 00:00 and ends at 00:30. The data follows the UK clock change, so the analysis accounts for the shorter spring clock-change day and the longer autumn clock-change day.
The analysis uses the dataset’s National Demand — ND field.
NESO defines National Demand as Great Britain’s generation requirement based on operational generation metering. It excludes generation required for station load, pumped-storage pumping and electricity exported through interconnectors. The field is measured in megawatts.
Each half-hour MW figure was converted into energy using:
GWh = MW × 0.5 hours ÷ 1,000
Each observation was then allocated to:
- Off-peak: local time from 23:30 to 05:30
- Peak period: local time from 05:30 to 23:30
Monthly average demand was calculated separately for each period.
The percentage difference was calculated as:
(Average peak demand − average off-peak demand) ÷ average off-peak demand × 100
The additional peak-period demand figure compares actual peak-period energy with the energy that would have been used over the same period at the monthly overnight average.
Important limitations
National Demand is not the same as total end-user electricity consumption.
NESO explains that embedded solar and wind generation connected to local distribution networks can suppress the demand visible to the transmission system. Their full output is not directly visible to NESO and is therefore separately estimated.
The figures also describe demand across Great Britain as a whole. They do not prove that every local network has the same amount of available overnight capacity.
A future detailed assessment should therefore combine national demand data with:
- regional distribution-network demand;
- local substation capacity;
- renewable curtailment;
- wholesale electricity prices;
- balancing costs;
- electric-vehicle charging behaviour;
- heat-pump demand profiles.
NESO also warns that the historic dataset can be revised retrospectively and currently carries a general data-quality notice. The figures on this page should therefore be updated periodically using the latest published version.
Conclusion
The 2025 evidence is clear: electricity demand in Great Britain was consistently lower between 23:30 and 05:30 than during the rest of the day.
Average demand during the proposed peak period was 27.5% higher, representing an average difference of almost 6 GW.
The difference reached approximately 40% during the winter and remained at least 14.6% even in the quietest month.
A permanent low-cost overnight tariff would not solve every challenge facing the electricity system. It would, however, provide a simple national mechanism for moving flexible demand into a period when the system is demonstrably less heavily used.
Cheap overnight electricity is therefore not merely a consumer discount. It is a practical tool for creating a flatter, more efficient and more resilient electricity system.