Engineering news
The government needs to place an urgent technological focus on how energy storage could be used for more efficient distribution of heat to homes and business, a report by the Institution of Mechanical Engineers has said.
Most thinking around decarbonisation of energy systems and security of supply has been focused on generating electricity capacity to 'keep the lights on'. But with heat accounting for a higher percentage of energy use, the IMechE has called for greater research efforts into technologies such as latent and thermochemical heat storage.
Dr Tim Fox, head of energy and environment at the IMechE, said: “The need for energy storage is not just for electricity generation, which only makes up around 26% of UK energy demand. We also require storage for the bigger demands for heat, and transport, as they transition to renewable sources.”
Fox called on the government to work with the engineering community to develop innovative energy storage systems to cope with the intermittency and seasonality challenges that renewable sources present.
Around 40% of UK energy consumption is in the form of heat, largely associated with domestic and commercial heating of buildings, as well as the heating requirements for a wide range of industrial processes. Despite this substantial demand, relatively little attention has been paid by government to the development of heat management and storage strategies.
The report identifies three primary ways that heat energy can be stored:
* Hot water systems (Sensible Heat Storage) where thermal energy is stored as a result of a change in a material’s temperature. The most widely-used material is water, but other materials such as rock, sand, ceramics and clay can also be used.
* Phase-changing materials (Latent Heat Storage) where thermal energy is stored and released as a result of a change in a material’s physical state (eg liquid-to-solid). Materials used to store latent heat are termed ‘phase-change materials’.
* Chemical reaction systems (Thermochemical Heat Storage) where heat is applied to certain materials that, on heating, undergo a reversible chemical reaction with an enthalpy change as a result of the breaking and forming of chemical bonds. Examples include the dehydration or thermal decomposition of metal salts, or dehydration of framework materials such as zeolites.
Each approach has its drawbacks though. Hot water systems have a low energy density and hence large volumes/masses required, while efficiency is low due to heat losses and costs being high for small-scale storage.
Phase-changing materials are not suitable for long-term storage owing to inevitable heat losses to surroundings. Reproducible performance over multiple heating/cooling cycles can be compromised by effects such as incongruent melting of salt hydrates. And salt hydrates can cause corrosion of components, while organic-based phase-changing materials may be flammable.
In terms of chemical reaction systems, meanwhile, energy densities are compromised by space required by ancillary components. There are potential corrosion issues associated with use of salt hydrates, and it is a relatively immature technology.
The IMechE report called on the government to work with industry to overcome technology challenges and produce a roadmap for energy storage commercialisation.