Harmony Energy’s UK Battery Storage Portfolio 

Project title: Harmony Energy’s UK Battery Storage Portfolio   

Project location: UK

Client: Harmony Energy Income Trust (HEIT) 

Project Summary:

OWC, and the wider ABL Group, was contracted as independent technical expert (ITE) to validate the Harmony Energy Income Trust (HEIT) portfolio of battery energy storage system (BESS) projects, to be installed in England and Scotland. 

The ITE services were provided as part of the rules set out by the National Grid Electricity System Operator (NGESO), with the objective largely to confirm the achievement of various milestones for Harmony Energy’s HEIT portfolio. 

The portfolio has a combined total capacity of 214.9 MW / 429.8 MWh, using Tesla’s 2-hour Megapack system. 

Our scope of work

OWC was engaged to create ITE reports on energy storage revenue streams for HEIT’s 430 MWh UK portfolio. 

Start date: 2022 


BESS acts to support the grid by balancing green energy supply with variable demand, providing complex services to maintain overall system stability and security in what are currently unprecedented times. 

  • Complicated for developers to securing planning permission and near-term connections to the electricity grid network – highly regulated 
  • BESS operators are required to obtain independent technical certification of systems. 
  • Costs are increasing in line with inflation, interest rates and supply chain delays 


  • ITE reports to confirm compliance with National Grid ESO technical performance requirements for Dynamic Containment (DC), Dynamic Moderation (DM), Dynamic Regulation (DR) and Firm Frequency Response (FFR)​.
  • Additional ITE reports to confirm the requirements for capacity market milestone achievements have been met including proof of spend and substantial completion. 


  • Dedicated BESS / Energy Storage team in-house 
  • Strong track record of energy storage projects in both Owner’s Engineering and Technical Due Diligence 
  • 5GW Energy storage projects supported
  • Expert local knowledge of government regulations and legislation 

Founded in 2010, Harmony Energy is one of the UK’s leading developers, owners and operators of utility-scale battery energy storage, as well as other renewable energy technologies. 

“It is a pleasure to work with such an established developer in energy storage, among other renewable technologies. Furthermore, we are really happy to have the opportunity to apply our skills to one of the strongest BESS project pipelines in the UK.” 

Aimee Besant, ABL’s Energy Storage Lead 
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