UK Power networks recently completed a 2 year trial of a 6MW/10MWh battery system which was installed as an alternative to adding a 3rd circuit to meet future peak demand of a town. At the end of the trial they produced a projected business case for future deployments of:

Conventional reinforcement (another circuit): £5.1M

Future Net Method Cost (battery): £1.6M

This data is from figure 8 of "SNS Close down report v1.0". This report and other information about the trial can be found at:

http://innovation.ukpowernetworks.co.uk/innovation/en/Projec...