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Case Studies

Mildenhall Hub

A multi-functional battery energy storage system (BESS) using second life batteries to support services for an award-winning community hub and a local authority’s drive to net zero by 2030. The objectives include grid resilience, solar optimisation and generating revenue through providing grid balancing services.

  • Industry:  Local Authority
  • System no:  1
  • Power:  300kW
  • Capacity:  360kWh
  • Application:  Grid balancing
  • Functionality:  Site decarbonisation, grid load management, revenue generation and community leadership


Mildenhall Hub in West Suffolk is an award-winning initiative that brings public services together on one site to improve health, well-being and education for the community. The new complex features a school, gym, fitness studios and 3G pitch, swimming pools and sports hall, library, health centre, children’s centre, police, Citizens Advice West Suffolk Council, and job centre.

The £40 million project opened in September 2021. It was named project of the year in the Government Property Awards and was a regional winner for best public or community building in the Local Authority Building Control Building Excellence awards.

The Brief

The Hub wanted a battery energy storage system (BESS) to bring in additional revenue to help support services and to optimise the use of solar energy in the building which houses around 600 solar panels.

Collectively, the greenhouse gas emissions savings from the solar array will amount to 200 tonnes in 2021 and 2,300 tonnes over the 20-year lifetime for the plant – the equivalent of taking 820 cars off the road.

West Suffolk Council, which led the project, turned to Connected Energy for advice on a BESS for the Hub and ultimately procured Connected Energy’s E-STOR system. The 360kWh, 300kW BESS with the intelligent management system, is capable of integrating with the grid, on-site renewables, buildings, and EV charging infrastructure.

Mildenhall Hub was looking for an energy storage solution to:

Improve local grid resilience

The BESS is used with the National Grid’s Dynamic Firm Frequency Response (DFFR) market. By storing additional energy on-site, the building aims to improve its local resilience.

Generate revenue for West Suffolk Council

Act as a rapid response resource for the local grid, selling energy back to the grid in microtransactions under the National Grid’s DFFR scheme, the E-STOR’s battery management system manages second-by-second frequency variations, enabling the grid to draw power from the battery to help meet local energy demands.

Revenue generated from DFFR goes to supporting local services, supporting the Hub’s core activities.

Act as a showcase

E-STOR is unique as it uses second-life lithium batteries. Connected Energy repurposes batteries from Renault electric vans when the vehicles reach the end of their life, but the batteries still have 70-80% of their energy storage capabilities.

West Suffolk Council uses this as part of its wider advocacy work to encourage residents to consider switching to renewable energy sources.

Renewable energy was a foundation for this project and using it effectively is a priority. The reuse of second-life batteries increases the overall carbon savings we achieve and managing what we generate efficiently, contributes to the revenue we use to support local services. I’m pleased with the elegance of this solution.

Cllr Jo Rayner, Deputy Leader and Cabinet member for Leisure, Culture and Community Hubs

The Solution

Connected Energy installed our 300kW battery energy storage system and integrated E-STOR with the grid and on-site renewables.

This was quite a complex integration in terms of setting up the BESS to communicate and interact with our solar PV array, the building, and the grid. When there were teething problems due to one of the elements in that equation, Connected Energy was highly responsive to adapt to issues on site. They were also extremely helpful in providing demonstrations of the system so that our team gained a good understanding of how it works.

Luke Simpkin, Environment and Energy Officer, West Suffolk Council

Next Steps

The Hub increased the size of the solar PV array, meaning that the E-STOR can play a bigger role in ensuring the optimised use of on-site renewable energy.

In addition, the unique use of second life EV batteries is providing a real-world example of how EV batteries can be repurposed.

This is helping the local authority with its drive to net zero by 2030, as it underpins advocacy for residents’ take-up of EVs, advocacy for increased renewables, and advocacy for green buildings using BESS.

We chose Connected Energy because its use of second-life batteries fits with our ethos. In terms of community advocacy, it gives us a superb real-life example of how those precious batteries can have a second life application. One of the pushbacks we get about switching to EVs is what happens to the batteries after the vehicle comes to the end of its life. Our BESS is a working example of the answer to that question and is a fantastic message to communicate as part of our wider drive to promote EVs.

Luke Simpkin, Environment and Energy Officer, West Suffolk Council
Battery energy storage system container at Mildenhall hub
Battery energy storage system at the Mildenhall hub
Mildenhall hub in West Suffolk

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