Wind and solar power are growing at a steady pace in many parts of the world, since they can now beat the electricity generation cost of conventional fossil fuels. Eight countries including Australia installed more than 1,000 MW of solar power capacity during the year 2017, and five more countries are expected to join the club in 2018. However, since wind speed and solar radiation cannot be controlled, large numbers of energy storage systems are needed to use a larger share of these resources in modern power grids.
Pumped-storage hydroelectricity (PSH) and compressed air energy storage (CAES) are commercially viable energy storage method, but both are very demanding in terms of site conditions: you need an elevated reservoir near a large body of water for a PSH project, and a cavern or unused mine pit for a CAES project. In addition, PSH and CAES are only cost-effective at very large scales – their cost per kilowatt-hour of storage capacity rises dramatically as project scale is reduced. On the other hand, batteries are free from these limitations, adapting to any project site and scale; battery systems range from residential installations having just a few kilowatts of storage capacity, to utility-scale installations like the 129-MWh Hornsdale Power Reserve in South Australia.
There are many types of batteries, each offering advantages and disadvantages. For example, lithium-ion batteries have an extremely fast response and are compact, but system cost increases dramatically when a sustained energy output is required during several hours. On the other hand, flow batteries are better suited for bulk energy storage, but they require much more space than lithium-ion cells while having a slightly slower response.
Proton batteries are a promising concept that is still in the development phase. They have the potential to become a compact and lightweight energy storage system that does not depend on rare minerals, while offering the same benefits as lithium-ion batteries.
A proton battery can be considered a hybrid between conventional batteries and hydrogen fuel cells. Energy is stored just like in a hydrogen fuel cell, using a process called electrolysis to split water into hydrogen and oxygen. However, the hydrogen storage method is very different in a proton battery:
In both cases, when you want to retrieve the stored energy, hydrogen and oxygen react in the fuel cell, combining back into water and producing both electricity and heat. However, a normal hydrogen fuel cell requires a separate hydrogen generation for electrolysis, while a proton battery has a reversible fuel cell that can perform the whole process by itself.
Since conventional fuel cells rely on gas storage while proton batteries rely on solid storage, the size difference between both technologies is extreme. Experimental proton batteries are small enough to be held with one hand, while using the same underlying technology as hydrogen fuel cells.
Proton batteries are more compact and lighter than lithium-ion batteries, making them better suited for small-scale residential applications and electric vehicles. However, they also offer the scale flexibility for larger systems, such as commercial solar arrays and utility-scale generation systems.
Experimental proton batteries are already more compact and lighter than their lithium-ion counterparts, but there is potential to reduce their size and weight even further. One possible enhancement is using a thin-layered form of carbon called graphene, which would allow protons to be stored at a much higher density.
Proton batteries are also based on cheaper and more abundant materials than lithium-ion batteries.
Proton batteries represent an opportunity to use coal in clean power systems, after it has been the most polluting fossil fuel for decades. There are no emissions because there is no coal combustion; it simply serves as a solid medium to store protons.
Although the Snowy Hydro 2.0 project in Australia is massive, with an energy storage capacity of 350 million kWh, it only represents 0.2% of total energy consumption in the country. In order to continue developing the renewable energy potential of Australia, energy storage methods with scale flexibility and a shorter deployment time are required.
Although proton batteries are still an experimental technology, they are expected to reach the commercial market in 5 to 10 years. However, the technology is very promising because it offers the advantages of both hydrogen fuel cells and lithium-ion batteries, plus some extra benefits, while eliminating several limitations of both battery types.
Innovations in energy storage are always good news for commercial solar power, since they translate into a larger market opportunity. There is no way to use solar energy at night and during cloudy days, but this changes if you have a reliable energy storage system: you just have to size the photovoltaic array larger to have surplus production.
Throughout the world, governments and energy companies have tried to develop “clean coal” technologies, achieving only minor results after millionaire investments. There is no need to look further: proton batteries provide a way to use coal in the energy industry without releasing greenhouse gas emissions.