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Cumulus Energy Storage (CES) has de-risked and shortened its battery development, using technology based on existing proven chemistries and architectures used daily in the metal-refining industry. These industrial Copper and Zinc electrowinning plants operate at ~100MWh equivalent scale, over lifetimes of 10-30 years. Consequently our battery configuration is already at grid-scale.


The first battery in modern times was invented by Alessandro Volta in 1799, using discs of Copper and Zinc as the electrodes, cardboard to keep the discs apart and brine as the electrolyte. The ‘Voltaic Pile’ Copper/Zinc battery was later developed into the Daniell cell, which was used extensively by the telegraph industry. These cells were primary (single-discharge) cells, which could not be recharged electrically: the cells had to be recharged physically with fresh chemicals.

In 2014, Cumulus Energy Storage Ltd’s Michael Hurwitz and Darron Brackenbury developed a patented system for making Copper/Zinc rechargeable, using an ionically permeable separator, which was the significant missing component from Volta’s original battery.

The link with electrowinning is that every time the battery is charged, the Copper electrode releases Copper ions into the electrolyte and Zinc ions electro-win onto the Zinc electrode. On discharge the reverse happens. Providing the Zinc and Copper ions are prevented from migrating to the opposite electrode, the battery can be electrically charged and discharged for thousands of cycles.

Key Benefits

The Copper/Zinc battery offers several benefits, including:

  • Scalability – its bipolar design means individual cells can be added in series to meet the desired voltage requirement
  • Low cost – the target LCOE is $180/MWh, making it suitable for distributed energy storage applications
  • Low stress, low energy density, low voltage couple – low energy density is a desirable property for grid-scale energy storage because the cells will not be put under stress and will be inherently reliable
  • Long life, low maintenance – the target lifecycle for the battery is 30 years
  • Operational at all voltages – high voltages - 320kV and potentially up to 800kV as well as low voltages - 800-1,000V
  • Reliable – Cu/Zn chemistry is well understood and electrowinning plants have operated at ~100MWh scale for years
  • Available – the very reliable battery chemistry and ease of maintenance provides 98% availability
  • Efficient – with an anticipated round trip efficiency of greater than 80%
  • Abundant materials – Copper and Zinc are the 25th and 26th most abundant materials in the earth’s crust.
  • Sustainable – the electrolyte is easily replenished if necessary and each cell can be refreshed by draining and filtering. There is no electrolyte consumption or waste.


The key measure for time-shift energy storage is the levelised cost of energy (LCOE) in $/MWh, which is the cost of energy delivered over the lifetime of the installation. Cumulus Energy Storage is positioned at $180/MWh which is in the middle of the pumped hydro range $150-$210/MWh. See the white rectangle labelled Copper/Zinc for our positioning as the lowest cost grid-level energy storage battery in the figure below.

The Cumulus Energy Storage Copper/Zinc battery is ideally suited for stationary bulk energy storage applications with a 4-6 hour charge and 4-6 hour discharge cycle where energy density is not an issue. Applications include commercial renewable electricity generation time-shifting, infrastructure security of supply (including off-grid) and energy intensive industry energy management.

Intellectual Property Rights

The rechargeable Copper/Zinc battery is UK patent granted with international patents pending, with a thicket of other international patent applications pending, which mean Cumulus Energy Storage is the only company in the world that can make and sell a bipolar rechargeable Copper/Zinc battery.

What Can I Do Next…

UK Enquiries
For more information please contact Nick Kitchin, Chief Executive Officer.

T: +44 (0) 1142 541240
M: + 44 (0) 7870 455995

US Enquiries
For more information please contact Darron Brackenbury, Chief Operating Officer.

T: + 1 (510) 374 4593
D: + 1 (510) 374 4581