Skip to main content
This project ended in April 2018 and is now closed.Dismiss

Solar Storage

Funding mechanismNetwork Innovation Allowance (NIA)
DurationApril 2015 - April 2018
Project expenditure1.75 million
Research areaEnergy Storage and Demand Response
  • South West


The objectives of this project are to:

  1. Quantify the potential value to network operators and others of integrating storage with DG;
  2. Use real-world operation of integrated utility scale storage: generation system to provide data to regulators and potential investors; and
  3. Demonstrate safe, reliable operation of the system under operational conditions.



While battery storage costs are falling, the case for investment is often difficult to make based on providing services to National Grid alone.  This project looks at the additional services that could be provided to DNOs or to a solar site co-located with the battery.  This project investigates how effectively such services can be delivered and the commercial frameworks needed to make battery storage economically viable. 

Problems that can be addressed with battery storage:

  1. Generation that exceeds the connection capacity at midday – stored for later export;
  2. High voltages overnight on the DNO network in areas of embedded generation –reduced by overnight battery charging;
  3. Voltage fluctuations due to rapidly changing generation output – smoothed using the battery;
  4. Constrained customers on nearby networks - constraints reduced by operating the battery;
  5. Voltage excursions – managed with reactive power from the battery inverters;
  6. Overloaded network assets – managed by exporting from the battery at peak times; and
  7. Reducing the variation of output from DG to make voltage profiles more stable and power flows more predictable. 



A battery and control system will be integrated with a 1.3MW PV array connected to WPD South West’s 11kV network. Analysis of the detailed data set created by carrying out a set of well-defined use cases will form the technical core of the project. The use cases will demonstrate:

  1. Sale of energy stored in the battery for a higher price;
  2. Better matching of generation profiles to demand profiles;
  3. Use of storage to peak lop PV generation above a (dynamic) power threshold;
  4. Import electricity from the grid at times of low demand;
  5. Absorption and supply of reactive power to help manage the network voltage;
  6. Reduced connection capacity requirement per MWp generation capacity;
  7. More predictable PV output through smoothing PV's steep ramp rates;
  8. Raise or lower the export power threshold depending on thermal or voltage constraints;
  9. Show the control system allows smart co-ordination of multiple storage systems;

Analysis of the data will quantify the potential value of each use case.

The project team will work with stakeholders and project participants to propose potential changes to regulations, grid code, balancing mechanisms etc. to allow reward for investment in storage.

  • Complete Design of Battery Electrical Storage System;

    1. Procure equipment, install and commission;
    2. Run trials and write report; and
    3. Identify regulatory obstacles, such as those relating to the Balancing Mechanism and recommend changes.
  • The success criteria of the project is defined through successful delivery of the following:

    1. Phases 1 to 4 above completed safely, on time and on budget;
    2. All use cases are investigated and a comprehensive analysis of all data collected undertaken;
    3. Useful and applicable conclusions generated from the data analysis;
    4. Effective communication of the project’s results and conclusions to the UK renewable energy and power distribution community; and
    5. Successful engagement with stakeholders, influencing the development of relevant governing mechanisms such as the grid code or balancing mechanism (BM).
  • A manual for the business case for future solar energy storage systems will be produced covering:

    1. A control system for this application that only imports electricity when intended;
    2. The size of battery and clipping probability required for a given level of peak lopping;
    3. The fraction of the battery used and the typical duty cycles, informing design requirements; and
    4. Best operation strategy and optimum revenue streams.
  • August 2018

    A report for the battery sale and removal process is in draft and photographs of the removal process are due to be released externally.
    The final project report is also in draft.

    July 2018

    Following the conclusion of the testing at the solar farm, the battery from the project has been sold and relocated so that it can be given a new lease of life.  A drone was used to capture footage of the removal process. 

    June 2018

    Battery sale agreed.   We have now selected a winning bid for the battery and are in the process of finalising the contract of sale and planning for the battery removal.  We will be capturing the learning from the sale and removal process as additional learning for the project. 

    April 2018

    The results are in!  The final tests on the battery have shown that the battery is still operating at high levels of round trip efficiency, in fact some values have improved since the battery was commissioned.   The improvements are likely to reflect the installation of a more efficient air conditioning unit during the project, and less demanding weather conditions.  The battery capacity has reduce by 7.5% to 677kWh.

    March 2018

    Testing is complete!  We have now completed the testing of the battery for Solar Storage and the final tests to establish the battery capacity and round trip efficiency.   We are now looking for potential new owners for the battery.

    February 2018

    We have agreed the final test schedule for the battery.  These final tests will be similar to those that were carried out when the battery was first commissioned and will allow us to see how the overall capacity of the battery has been affected by its operating regime during the project.   

    December 2017

    The second dataset has been completed. BRE have published their review of BSR’s testing.

    November 2017

    The second dataset is nearing completion. Solar Storage presentation delivered at LCNI 2017.

    October 2017

    The first dataset has been delivered for validation. 
    The process review by British Research Establishment has begun. 

    February 2017

    Having replaced a faulty current transformer, investigations by the battery supplier are continuing as to why batteries four strings are not remaining equally charged when the battery is operated. Early results from our testing of arbitrage are in agreement with the techno-economic modelling carried out earlier in the project. This suggests that there is usually not a high enough spread in prices between night and morning peak to generate significant profits for the battery owner, once cycle efficiency has been taken into account.

    January 2017

    The project welcomes Christie Sims as the new project manager for British Solar Renewables Ltd.  Christie will take over from James Parrot in mid-February. The battery technology and software has been demonstrated to staff from Innogy, however, battery operation continues to be hampered by operational issues.

    December 2016

    Battery testing continues. Some unexpected battery operation has been experienced that was not seen in the commissioning tests, suggesting that battery operators should negotiate guarantees and not rely on commissioning tests alone.

    November 2016

    Testing continues.

    October 2016

    Project testing has begun. the battery has started the year long programme of testing where it will demonstrate the nine use cases. 

    September 2016

    The battery has passed a series of site acceptance tests over the course of three days. We were able to see the battery export power at various different levels and power factors. We saw that the battery produced round trip efficiency values at different charging speeds that were all comfortably above the specification requirements.  Lastly, we were able to observe the RESolve control system to schedule the battery operation and to use different control modes, reflecting the different use cases being trialled in the project.

    July 2016

    A report by Utilities Insight into the impact of the existing regulatory framework on the adoption of storage is now available to download.

    June 2016

    The battery has now passed the factory acceptance test and is now in transit due for arrival next week. It has cleared customs and has been inspected by Trading Standards.