Operability of highly renewable electricity systems

Status:Final report complete.  Published:

Analysis of the solutions available to address the challenge of maintaining security of supply.

Executive summary

Managing the electricity system is becoming more complex. The increasing diversity of sources, and the potential for growing demand for electricity, creates new challenges to maintaining a stable system. But these challenges can be addressed. Current evidence provides confidence that a highly renewable electricity system, for example one with over 70 per cent generation from renewables, can maintain secure and reliable electricity without adding significantly to the costs of generating electricity.

The Commission has recommended that government should ensure that the electricity system is running with at least 65 per cent per cent renewable generation by 2030. This will ensure maximum advantage is taken of recent cost reductions in renewable generation and put the country on the pathway to a highly renewable electricity system. Continuing with rapid deployment of renewables now is the best way to deliver the net zero consistent electricity system the country needs whilst keeping costs low for consumers.

The GB electricity system was designed to operate with the types of generation that have traditionally been connected like coal, gas, or nuclear. Renewables operate differently from these traditional forms of generation which is introducing new operability challenges that need to be addressed. Often these challenges are not accounted for in electricity system modelling which has led to concerns being raised that deploying lots of renewables will make a highly renewable system either unviable or that such a system would be prohibitively expensive to manage. To maintain stability on the system will require services to be purchased that were previously provided by traditional forms of generation.  These requirements are already being met, through actions taken by the Electricity System Operator (ESO) and can continue to be met using approaches that will not significantly add to the cost of managing the electricity system.

There are existing technologies that can provide the system with what it needs to maintain secure and reliable supply. Some of these technologies, such as synchronous condensers, have been deployed on electricity networks for decades. Others, such as virtual synchronous machines, have not yet been developed for at scale deployment, but offer scope for a lower cost solution. So, while it is not clear at present what mix of technologies will best deliver the critical operability needs for the system, the evidence is clear that they can be met.

Therefore, the engineering constraints, whilst real, should not undermine the deliverability of the Commission’s recommendation to move towards a highly renewable electricity system.

Overview of the electricity system

The electricity system has four primary components: generation of electricity from plants and technologies; storage of some of the electricity produced; transportation of electricity along a network of overhead and underground cables; and households and businesses that use the electricity. The cost of the system is around £30 billion per year, paid for through consumers’ electricity bills. This covers the cost of operating and maintaining system assets and also less visible costs such as policy support for deployment of new generation plant and financing the investment in assets on the system.

Over time this system has evolved. Great Britain has moved from a reliance on coal to gas to running a system with a growing proportion of renewable technologies in the mix. It is essential that electricity supply is always able to meet demand, which fluctuates on a second by second basis. It is the ESO’s role to keep the system in balance.

Key challenges of operating the electricity system

The electricity networks are a complex engineering system. Alongside matching supply with demand there are engineering needs the electricity system must meet to ensure reliable flows of power. There are four key system needs that must be provided: inertia, short circuit level, voltage control and system restoration.

The ESO takes actions to ensure the safe and efficient movement of power across the network. The system services delivered to meet these needs have largely, to date, been met by synchronous generators, namely coal, gas, and nuclear plants. Increasing levels of variable renewables, and therefore a reduction in synchronous generation on the system, is resulting in additional actions being needed.

The changing nature of operability

Over the past decade the proportion of electricity from variable renewables has risen dramatically. In 2019 variable renewable generation provided 38 per cent of the electricity generated in the UK. This increase in variable renewables output, and resulting reduction in synchronous generation, has led to a reduction in the system needs naturally met by the plants connected to the electricity system. Further actions have, and will continue, to be needed to ensure system needs are met.

Connecting more variable renewables changes the electricity system in other ways too. Renewables will be sited in different locations than traditional generation and the pattern of generation will be less predictable as it is linked to weather patterns.

Alongside increasing deployment of renewables there are other trends in the energy sector that will impact the operability challenges on the system, such as the potential for increased reliance on fewer but larger generators and changing patterns of electricity demand as the heat and transport sectors increasingly rely on electricity and our climate warms resulting in increased summer demand for air conditioning.

How these challenges can be met

A highly renewable system may exacerbate the challenge of meeting the key system needs, but these challenges can be addressed through deploying a range of available technologies and developing new ones. Uncertainty exists on what level of services will be required in the future and what the best mix of solutions will be. However, evidence provides confidence that the additional cost will be small.

Government and the ESO can take actions to ensure that costs of operating a secure and reliable system remain reasonable by continuing to support market approaches to deploying viable technological solutions, removing any barriers to deploying the necessary technologies and developing novel solutions.

The UK is not alone in its journey towards a highly renewable electricity system. This provides an opportunity to learn from the experiences of others and to impart its own knowledge on the development of electricity systems globally.

Final Report

Operability of highly renewable electricity systems

The increasing diversity of sources and the potential for growing demand for electricity creates new challenges to maintaining a stable system. This paper shows that current evidence provides confidence that a highly renewable electricity system can maintain a stable supply without adding significantly to the costs of generation.

Download the report

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