Electricity balancing challenges
Future summers will see times of low transmission demands due to the increasing amounts of generation embedded within the distribution networks, solar photovoltaic (PV) in particular. Without action these increases will create balancing challenges for the system operator. This case study considers these challenges for a typical summer Sunday in 2020, using the Consumer Power scenario from our 2015 Future Energy Scenarios.
Managing periods of low electricity demand in the summer is just as important as managing the high demands we see in the winter.
We have undertaken analysis to look at future demand on a typical summer Sunday with low demand using the Consumer Power scenario (due to its large volumes of intermittent distributed and micro generation).
- Minimum demand falls to 16.7 GW in July 2020 in the Consumer Power scenario
- Under high solar outputs, demand remains flat across the day
- Operability and balancing challenges impact all scenarios at different points in the future.
Innovative solutions are likely to be required to address these challenges. For example, greater flexibility from existing sources of generation and demand, greater use of interconnection, more demand side response or the development of energy storage and new balancing products. National Grid’s System Operability Framework (which is published in autumn each year) will be the process where we work with the industry to explore operability challenges and identify potential solutions.
As system operator, we must match demand for electricity with supply on a second-by-second basis. Historically, balancing the system has been maintained mostly by directing thermal power plants to increase or reduce output in line with changes in demand. Storage and interconnectors have also played a part, but a much smaller one. As the volume of intermittent generation on the system grows, we will balance the system by utilising both supply and demand resources.
Distributed and micro generation impact on summer transmission demand
There is a direct correlation between the volumes of distributed and micro generation and low transmission demand. Historically, summer minimum demand was at 06:00hrs. This was reflected within the base demand value (which excludes distributed and micro generation) shown in the graph below. However, as the amount of distributed and micro output increases on the system, this minimum demand shifts to 07:00hrs. The demand profile is also flattened as distributed and micro generation offsets the transmission demand.
Impacts of solar PV
The technology that has the single most significant impact on transmission demand is distributed and micro solar PV which is illustrated by the red line in the graph above.
Transmission demand is supressed to 15 GW by 07:00hrs. This level of demand is maintained to 14:00hrs as increasing solar output offsets transmission demand. Between 14:00hrs and 20:00hrs transmission demand climbs as output from distributed and micro solar PV reduces.
Solar capacity has already had a rapid rise from 0.9 GW in 2011 to 5.2 GW in 2014. This rate is expected to increase to reach an installed capacity of 18 GW in 2020.
We have considered three load factor sensitivities for solar output at 14:00hrs: high (84%), average (63%) and low (26%). The difference in transmission demand between high and low output could be a swing of up to 10 GW. Focusing only on average solar conditions during July, demand is supressed to a minimum of 16.7 GW (at 07:00hrs).
Is this just an issue for Consumer Power?
Whilst the case study focuses on Consumer Power (due to its high distributed and micro generation capacity levels) we have analysed the opposite scenario Slow Progression. We explored the summer demand profiles for Slow Progression in five year intervals to discover when this scenario would face the same challenges as Consumer Power.
Slow Progression has slow economic growth and high emphasis on sustainability; the opposite environment of Consumer Power.
Analysis shows that by 2035 afternoon minimum demands are at similar levels to Consumer Power in 2020. This highlights that across all four scenarios we will experience balancing and operability challenges at some point from 2020 onwards.
In continuation we explored Consumer Power over the same period. In the graph below we can see that by 2035 the pattern of transmission demand has significantly changed.
There is no longer any increase in transmission demand in the first half of the day as it falls continually from midnight until 14:00. This produces a steeper ramp rate in evening demand which is very pronounced by 2035 under Consumer Power; producing a 16 GW rise in 6 hours.
The graph below shows the demands under both high (HS) and low solar (LS) output conditions for 2035 for Consumer Power, showing that transmission demand could swing by 17 GW within-day solely due to a change in cloud cover.
Balancing and cash-out
Balancing the system during low transmission demand periods is a challenge.
At all times there must be sufficient generation plant operating to allow output to decrease without any generator going below its minimum output level and disconnecting from the system in case of demand forecast error or loss of demand on the system; this is known as foot room.
At the same time, there must be sufficient generation part loaded, ready to pick up for a generation loss; known as headroom.
Low transmission demand can also have an effect on cash-out pricing. On Monday 11 August 2014 minimum transmission demand was 19 GW and led to 13 consecutive ½ hour periods of negative generation prices (settlement periods 01:00 to 07:30), as we constrained excess wind generation off the system.
Historically in low demand periods we have constrained generation and interconnector imports to maintain system security. With a growing proportion of summer generation coming from distributed and micro generation, especially from uncontrolled intermittent sources such as solar and wind, the balancing challenges are likely to increase.
The way forward
To address the balancing challenge we need to undertake further analysis and work alongside the industry to develop solutions. These solutions may include the provision of greater flexibility from existing sources of generation and demand. This could be achieved if such resources had the capabilities to start and stop multiple times per day and start up with short notice from a zero or low electricity operating level.
Although in its infancy, demand side response is already a reality. The ability for businesses and consumers to increase, decrease or shift their pattern of electricity consumption allows them to opportunity to save on energy costs, reduce their carbon footprint and help address these balancing challenges. Power Responsive is an ongoing framework to facilitate demand side response.
Greater use of interconnection may also play a part, mindful of the fact that the ability to export power depends on the needs of neighbouring countries. The development of energy storage, new balancing products and services, greater visibility and/or control of all generation or even a more fundamental reform could also form part of the solution.
Some of these issues are already being considered via various projects within the industry and we will use this information to develop our analysis. National Grid’s System Operability Framework addresses the operability issues in detail.
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