Energy Storage for Backup Power - Redox Flow Batteries and Metal Combustion as Energy Storage for Bumker Applications

Authors:

  • Hanna Ellis
  • Wilhelm Sahlén
  • Markus Pastuhoff
  • Martin Skarstind

Publish date: 2022-01-28

Report number: FOI-R--5259--SE

Pages: 49

Written in: Swedish

Keywords:

  • redox flow batteris
  • metall combustion
  • back-up power
  • bunkers
  • energy storage

Abstract

The Swedish Defence Research Agency (FOI) has studied two different energy storage and energy generation systems for the Swedish Fortification Agency. The two systems are the redox flow battery and metal combustion. The demands for both systems are that they can deliver 100 kW for 24 h, FOI should also evaluate robustness, redundancy, up-start time, calculate cost and maintenance etc. After having performed a survey of available chemistries and types of systems of redox flow batteries the conclusion is that the Vanadium based redox flow battery is the most adaptable for the application. A survey of commercially available producers was also performed. Within the study, calculations for design of system and maintenance costs were performed. The cost of buying a commercially available system would be approximately 1.2 million Euro. If FOI would design, construct and operate a system, the cost would be approximately 0.93 million Euro. For a redox flow battery the volume of the electrolyte define the capacity while the area of the cells define the power. From calculations based on the Danish redox flow producer Visblue's set-up, a system of 2×1000 dm3 electrolyte provides 50 kWh i.e. 25 Wh/dm3. In order to obtain 2400 kWh, 48 times more electrolyte is required. The total volume for a 2400 kWh system equals 2×48 000 dm3. Depending on how the system is designed, volume of electrolytecontainers and placement of these can be varied, and space-savings are possible. Redox flow batteries have a short start-up time, within the millisecond frame. One can design the system to be able to start off-grid, without external power source. FOI do consider the Vanadium redox flow battery to be relatively safe and robust. The electrolyte is water based and hence non-ignitable. The system is relatively easy to maintain and FOI asses that for maintenance specialist competence is not required. Metal combustion is a technology where commercial systems are still not available. Researchers and engineers at Eindhoven University of Technology and the company Metalot are considered to be at the forefront of metal combustion research. They have put together a pilot plant for commercial use. In discussion with representatives from Eindhoven University of Technology and Metalot, the metal combustion process was compared with the coal power process. The most prominent differences are that metal burns at a higher temperature than coal and that the gas flow carries particles throughout the combustion process. However, the efficiencies can be assumed to be similar to each other, the efficiency of a modern coal-fired power plant is around 45 %. The metals that are investigated in more detail for the process in this report are iron and aluminium. To satisfy the requirement of 2400 kWh, a metal powder storage with either 319 dm3 (2222 kg) of iron or 227 dm3 (620 kg) of aluminium is required. The electricity can be produced in different ways, the two most attractive ways are either by using a Stirling engine or by using steam production with a Rankine cycle. FOI concluded that a project where FOI would buy components and build a 100 kW pilot plant would cost around 0.8-1.2 million ?. The storage for metal powder is considered to be maintenance-free, cheap and robust.