Energy and its ubiquitous supply are taken for granted in our lives today. A spontaneous loss of power at grid level, instigated by manmade or natural disaster, would cause failures and chaos on a massive scale. We propose the establishment of a revitalized energy infrastructure predicated on a robust network of distributed energy storage devices that can provide the necessary backup and instantaneous readiness to fill any void in grid supply.
The energy storage devices we propose must be both in front of the meter as part of the existing transmission and distribution grid, as well as behind the meter as part of every major industrial complex. Not only does this approach support grid security and resiliency, but it has the added benefit of enhancing the use of renewable energy generation, and so creates a more environmentally friendly electric grid and reduces our dependence on fossil fuels.
A broad spectrum of existing technologies can play a role in energy storage; each has its own strengths and none of these can meet all of the diverse needs of a robust energy storage infrastructure. On one end of the spectrum are large infrastructure programs such as the long-used pumped hydropower and the more experimental compressed air systems. These can provide tremendous amounts of energy storage (think Hoover Dam) but are limited by scale and geography. On the other end of the spectrum are technologies like supercapacitors, which have excellent response times but have energy storage limitations.
In the middle of this spectrum are the class of technologies that are typically called batteries – which includes the zinc-carbon cells that go in your flashlight, the lead-acid batteries that go in your car, and the lithium ion batteries that power your computer and (nowadays) perhaps your car, too. Each of these technologies comes close to that sweet spot that combines rechargeability, energy storage, and response time essential for a distributed grid energy storage system. However, none has yet been demonstrated sufficient or cost effective.
We want to highlight another battery technology, still in the early stages of development, which has much promise: flow batteries.
A flow battery, also known as a redox flow battery (a shortening of reduction–oxidation, which is chemistry-speak for the transfer of electrons), is a type of rechargeable battery wherein rechargeability is provided by two chemical components dissolved in liquids contained within the system and separated by a membrane. A flow battery is rechargeable like a Li-ion battery yet without the flammability, runaway issues, and exhaustion well-known in Li-ion systems. Flow batteries have an advantage of separating power and energy. The energy is stored in the electrolyte volume while the power is based on the size of the stacks of cells. This characteristic makes flow batteries easily scalable and adaptable to their application because the discharge time scales only with the size of the external electrolyte reservoirs and not the number of batteries cells. Furthermore, the energy-normalized cost of a redox flow battery system is projected to be two-thirds to one-half of other battery systems.
In the traditional power grid, electricity must be produced continuously and used simultaneously yet the demand is not always in line with the supply. Hence, for example, in 2006, a total of 1,638 billion kWh of energy was lost on the U.S. power grid, with 655 billion kWh lost in the distribution system alone. By creating a robust network of distributed devices to store and deliver grid energy storage on a large scale, we will achieve a means of balancing the demand and supply cycles. In this way, utility customers draw upon stored energy during periods of peak demand and thereby help utilities manage their power loads. As a result, the asset utilization of existing infrastructure is improved, investment required for new power plants is reduced and, most significantly, infrastructure upgrades to increase transmission and distribution limits are minimized. The outcome would be to see lower costs of energy distribution transferred to the end-user/consumer, as well as to provide improved power quality, increased resilience, and more robust security for the grid as a whole.
For these reasons and others, we conclude that flow batteries are poised to be one of the most economical and scalable form of distributed energy storage available in the near future. They provide the energy capacity, response time, operational robustness, and low cost necessary for a practical distributed energy storage system. The time is now to start further investment in such technologies designed to support an efficient distributed energy storage infrastructure and to enable successful technology transfer for commercialization and deployment.
Barbur is senior vice president and chief technical officer at Concurrent Technologies Corporation (CTC), and Pugh is the principal at Prospect Ridge Consulting.