Lerwick Power Station on Shetland is an ageing power station using a number of large diesel generators. Eventually it will be replaced with more modern technology and the purpose of the energy storage system is to reduce the peak demand on the power station and level out the loads. This should allow downsizing of the new power station, potentially using more efficient and more modern technologies and integrating renewable energies into the grid.
This 1 MWh battery is a pilot project to better understand the potential and impact of grid connected energy storage devices, to determine suitable control mechanisms and to gather long term experience with battery technologies for such applications. Originally a Sodium Sulpher (NAS) battery technology was chosen to be installed in a purposely designed building next to the Power Station. However after the innovative NAS battery had been installed it was decided not to operate it due to the news of a fire in another large NAS battery installation in Japan. It was then decided to replace the NAS battery with a more established valve regulated lead acid technology.
The installed battery is a 6.3MWh energy storage (usable 3MWh), weighing 200 tonnes, operating at approx 20deg C and capable of producing 1.3MW electric power. The battery supplier YUASA claims a life time of 5 years or 1500 cycles for their 1000Ah cells. Lead acid batteries offer very good recyclability and this particular cell type used is suitable for deep cycle operation, however even though lead acid batteries are well established this is still a very new application and achieving claimed life requires sophisticated control protection and management of that battery.
REAP has developed and supplied a custom battery monitoring and management system and assisted YUASA with the commissioning and installation. The battery consists of 12 parallel battery strings and the REAP management system monitors all string currents and voltages, calculates state of charge, communicates with the inverter to limit charge and discharge limits, manages essential equalisation for the lead acid battery, logs data and allows YUASA to remotely access information about usage and battery behaviour. The later point is important for YUASA in order to provide the claimed life time and detect any problems early, understand the usage and the behaviour on this application which in turn will allow them to continuously improve the battery technology and the settings in the BMS.
To specify and implement algorithms that would satisfy both minimal restrictions on operation (max performance) and on the other hand maximise the battery life. Maximising life of such a large lead acid battery is a very challenging task and required us to understand lead acid battery technology and its key operational requirements, whilst appreciating that the end user may wish to use the battery without any restrictions. Other challenges were high accuracy current measurement in order to calculate state of charge and managing a number of parallel strings. Also system testing and validation is challenging because such a large system cannot be rebuild the laboratory for testing. Testing and commissioning on site requires a number of stakeholders to be involved.
Project update June 2017
Now that the official trial period of this project has been completed Scottish & Southern (SSEN) has released a report on the project outcomes and the findings are overwhelmingly positive:
Highlights from the SSEN report:
- The project “demonstrated that an islanded electricity distribution system can operate securely with a high penetration of local renewable generation.”
- The project allowed connection of “more than 8.545MW of new renewable energy…which represents a trebling of renewable energy capacity on Shetland.”
- The project made possible “Shetland is already reaching 30% of energy requirements” from renewable energy.
- The “1MW battery at Lerwick Power Station was used to help to provide a stable electricity network and to reduce demand peaks.”
- “The battery stored the renewable generation at times of low demand so it could be used at a time when it was needed” The project “has directly resulted in the reduction of diesel used at the station by about 10%.”
- "This project has enabled the Association to meet the Scottish Governments Energy Efficiency Standards for Social Housing (EESSH) well in advance of the compliance year of 2020” Stewart Reid, Head of Asset Management and Innovation at SSEN said: "We would like to thank all our project partners and the customers that participated in the NINES project. With their help and support we were able to successfully deliver the project, which will benefit the Shetland Isles and the wider UK electricity network system." I know that this project has faced some challenges. However, I think you should all be commended. Your work on this project has demonstrated a clear benefit to the people of the Shetland Isles, the wider UK and the global environment.