Storage & Distribution

27 Feb

Dr Jemma Rowlandson, a lecturer in Thermodynamics at University of Bristol, and lead for the GW-SHIFT theme Storage & Distribution explains hydrogen’s unique energy profile and how it could offer a versatile storage solution for renewable energy.

Hydrogen has the potential to revolutionise the energy landscape by reducing carbon emissions and enhancing energy security, aligning with global net zero initiatives.

Hydrogen Has a Unique Energy Profile

One aspect that sets hydrogen apart is its incredible gravimetric energy density – the highest of any chemical fuel known to mankind! However, despite a high energy content by weight one of hydrogen’s biggest hurdles is that by volume it has a very low energy density. This discrepancy poses a significant challenge for the transportation and storage of hydrogen, especially in mobile applications where space and weight are at a premium. The challenge is illustrated in Figure 1 – our conventional fossil fuels have an excellent balance of volumetric and gravimetric energy density, while hydrogen requires additional storage solutions to increase the volumetric energy density and make it viable.

*Figure 1: Hydrogen needs storage interventions to increase its volumetric energy density and make it a viable energy solution (by author).*

A Range of Storage Solutions

To harness the full potential of hydrogen as an energy carrier we need storage solutions. These solutions aim to increase hydrogen's volumetric energy density, making it more practical for a wide range of applications. We can store hydrogen using physical or chemical methods.

Physical Hydrogen Storage:

Widely used in commercial applications, physical hydrogen storage involves compressing hydrogen gas to high pressures (up to 700 bar) or liquifying it at extremely low temperatures (-253 °C). These methods are both very effective ways of storing hydrogen, however they do require a significant energy input and advanced materials to handle these extreme conditions.

Chemical Hydrogen Storage:

An exciting and rapidly growing area is using chemical methods to store hydrogen as a solid. Hydrogen can be stored within a material (such as metal hydrides) or on the surface (such as nanoporous materials). These technologies are promising for storing hydrogen at potentially higher energy densities without the need for extreme temperatures and pressures.

Hydrogen: A Potential Player in Renewable Energy Storage

Beyond its direct use as a fuel, hydrogen could offer a versatile storage solution for intermittent renewable energy. As shown in Figure 2, hydrogen could play a crucial role in the medium to long-term storage of renewable energy, complementing other storage technologies. Applications could include peak shaving, where excess renewable energy can be converted to hydrogen and stored using physical or chemical methods, or even at scale even underground in disused caverns. The stored energy can then be reintegrated into the grid through reaction in fuels cells or combustion. By focusing on innovative storage methods and integrating hydrogen into our renewable network we can move closer to achieving a net-zero future.