An innovative thermal energy storage technology is using cooling energy as an alternative to traditional batteries.
The patented Energi Vault system, being developed by O-Hx Ltd, is designed to support the decarbonisation of industrial processes, and commercial and residential buildings using stored ‘coolth’ as a source of energy.
The system is claimed by the manufacturer to reduce energy costs by up to 62 per cent, depending on the application, via a combination of demand shifting, heat recovery, reduction in part-load chiller cycling and
overall efficiency optimisation. The company was recently awarded government funding in the form of a Business Accelerator grant to commercialise the technology.
Cooling energy generated by the system’s refrigeration circuit is stored in a thermal battery
containing a reservoir of phase- change material (PCM). The battery is ‘charged’ by the refrigeration system using off-peak electricity and then drawn-down during high-tariff periods, significantly cutting end-users’ power bills.
Waste heat generated by the refrigeration system is captured by EnergiVault’s heat recovery system and can be used for space heating; hot water for domestic use; or for process heat.
Bob Long, the inventor of EnergiVault said: “Unlike lithium batteries, which can discharge only around 70 per cent of their power, all the energy stored in an EnergiVault can be used without
harming the device or its future storage capacity,”
The unit’s refrigeration system makes use of Bitzer open-drive screw compressors to generate high-efficiency cooling, Mr Long says: “The charging process using ammonia as refrigerant, for example, is highly efficient, due to the inherent efficiency of the refrigerant and Bitzer screw compressors. Any conversion losses are comfortably exceeded by the savings achieved through using off-peak electricity.”
The unit’s refrigeration charging system is rated at 40-60 kW, so with a storage battery containing around to tonnes of PCM, a 1 MW thermal store can be charged over 16 hours and discharged at a cooling rate of 1MW in an hour, or 500 kW over two hours. The EnergiVault can be used standalone or
multiplexed to generate whatever power is required for an application.
One of the keys to the system is
a custom-designed algorithm that ensures that the lowest-cost power source is used at all times, while maintaining maximum battery power back-up.
Mr Long said: “The only potential mechanical risk factor in the process is the battery charger -the refrigeration system. We chose Bitzer compressors as they are supremely efficient and reliable. After four decades’ experience with them in the industry, I am totally confident in the technology.”
Kevin Glass, managing director of Bitzer UK, said: “Energi Vault is an exciting development and demonstrates the potential of refrigeration-based power storage systems as transformational solutions.
“The push for net-zero carbon will require a complete rethinking of our energy infrastructure. With its thermodynamic and efficiency advantages, refrigeration offers the exciting prospect that our industry could be in the vanguard.”
