Comment by Corentin Jankowiak, Systems Engineer (Networks & Energy Storage), and Rosie Madge, Analyst (Networks & Energy Storage), at Energy Systems Catapult.

As the UK transitions to Net Zero, intermittent renewable energy generation and electrification of demand will increase. This will require a change in the type and scale of energy system flexibility to ensure our energy demands and supply are balanced. These types of flexibility will sit at different locations within the energy system and will have different requirements.

This blog is based on work we carried out on local flexibility on behalf of the Department for Energy Security and Net Zero. In this work, we looked at the requirements for flexibility at different parts of the network (represented by network levels including behind-the-meter) and the technologies capable of providing this flexibility from a UK-wide perspective. This provides a different perspective to other flexibility projects that focus on individual local areas, such as specific postcodes.

Method

We identified different flexibility technical requirements (services), network levels and flexibility technologies. We specified fourteen services across five network levels (transmission, distribution and three types of behind-the-meter connection). These services fit into three broad service categories (operational, resilience and utilisation).

We then selected 23 technologies for review that were able to provide different flexibility services at their connected network level. For each, we assessed their key parameters, such as technology readiness level, response time and storage duration. For this work, we defined flexibility services as the electricity network’s technical requirements for flexibility (e.g. frequency regulation) rather than commercial services, as these can evolve based on policy or political decisions.

We reviewed and analysed the energy system within the context of a plausible 2035 world (an increase in flexibility challenges). Given the short timeframe and the difficulty of predicting major changes, we assumed no disruptive technological breakthroughs, only incremental advancements of existing technologies.

After mapping the compatibilities between different network levels, flexibility technologies, and flexibility requirements (Figure 1), we created a flexibility matrix to represent them. The ability of a technology to provide a service at a given network level was based solely on technical parameters, not on variables like policy support and available markets, as these can often change. By focusing on technical factors, we can identify where policy and market support is needed to deliver flexibility services.

The flexibility matrix

In the flexibility matrix (Figure two), each cell indicates the level of compatibility between a flexibility service (row) and a technology (column). The change in compatibility between different network levels can be observed by switching between them using the navigation menu. Each matrix shows the compatibility between the different flexibility requirements and technologies at that network level. The score (-1 to 3) indicates the level of compatibility between the three components: the higher the score, the higher the compatibility. A score of -1 indicates that there is at least one major incompatibility between the components. This means the technology cannot be used for that service whilst connected at that specific network level although this does not mean that the technology will be unable to provide services at other network levels.

Note that the matrix shows the level of compatibility for a flexibility technology to provide a service when connected to a given network level, not necessarily to provide the flexibility service to that network level, although it is normally the same thing. This is most relevant for Demand Side Response (DSR) technologies which, in our matrices, appear incompatible with the Transmission and Distribution network levels: this reflects the working assumption that DSR is connected from behind-the-meter, although it may be providing a service to the transmission or distribution network.

It is also worth noting that some of the interactions between the different flexibility services cannot be fully captured by the matrix. For example, if there is more short-term flexibility then it is possible that less medium to long-term flexibility will be needed, although of course they are not complete replacements for each other.

The matrices show that:

• Whilst most flexibility services can be met to some degree at all network levels, there are some exceptions, such as uninterruptable power supplies, whole system restoration, self-consumption and seasonal storage, which can only be met at specific network levels.
• Very few technologies can provide UPS (Uninterruptible Power Supply) and seasonal storage because these services require very specific technological requirements.
• Batteries are versatile and capable for a range of services across the different network levels. However, although they are capable, this work does not measure whether they are the most suitable technology for a given application (e.g. there has been no comparison between technologies of a given compatibility score).
• Different technologies excel in different flexibility services and at different network levels. This highlights the need for a diverse portfolio of different technologies to meet all flexibility requirements.
• Behind-the-meter – Small (equivalent to a domestic scale behind-the-meter connection) has the largest number of incompatibilities, this is mainly due to several of the technologies having incompatible sizes and power ratings at this network level.

Figure two: Interactive flexibility matrix

Barriers for technologies

We identified common barriers found for the technologies at specific network levels or for specific services:

• For operational services with a very short response time, some technologies cannot start up within this timeframe. This issue is mainly found for mechanical technologies.
• Technology units connected at the small or medium behind-the-meter levels are small scale. Therefore, aggregation (grouping several units together) will be needed to provide a flexibility service at a larger scale. Further developments are needed to make this aggregation possible.
• The discharge time of some technologies is limited and therefore this prevents them from contributing to some flexibility services. Innovation to increase storage durations or the development of larger storage units will help to overcome this issue.

Summary

We developed a matrix-based framework to evaluate how well flexibility technologies provide services across network levels, including behind-the-meter connections. Markets should focus on required outcomes rather than specific technologies to avoid favouring less-suitable mature solutions and to encourage innovation.

While flexibility spans all network levels, some services, like seasonal storage, are unsuitable for smaller scales. Flexibility technologies are typically aligned with specific network levels due to technical and economic factors, which determine where services can be effectively delivered.

Finally, innovation, such as extending discharge times or enabling larger storage units, could expand the ability of certain technologies to deliver services across more network levels.

Flexibility developers, network operators and policymakers should be aware of the advantages and disadvantages of using specific technologies to meet specific services at given network levels. They should consider the interaction between these services and technologies and plan accordingly.

Interested in learning more about energy flexibility?

The Enabling Distributed Flexibility for Net Zero report emphasises the importance of enhancing distributed energy flexibility to support the UK’s Net Zero targets. The focus is on integrating behind-the-meter assets like residential and small non-domestic systems into a flexible, low-cost energy grid, reducing dependency on fossil fuels, and accommodating intermittent renewable energy sources.