Sufficient renewable energy storage is the key to a net-zero future.
As energy uncertainty continues to dominate the headlines, the discussion surrounding the implementation of renewables has come increasingly to the forefront. Whilst there should be a focus on installing appropriate levels of generational capacity for renewables, it should not be the sole focus. One of the other major issues is ensuring that citizens can consume the majority of their energy from renewable sources, as the higher the consumption rate is from renewables, the less need there is to rely on high carbon emitters such as traditional fossil fuels. In order to facilitate a high consumption rate, there needs to be an overhaul of the entire transmission and storage capacities of power systems as well as smarter control and energy storage systems.
Another major issue that needs to be tackled to ensure a high percentage rate of total energy use from renewables, is the ‘flexibility’ of renewable sources. From a balancing perspective, the intermittent nature of renewable energy sources is a problem. Renewable energy sources are usually highly dependent on weather conditions, in particular wind and solar energy. Therefore, the storage of generated electricity during peak times is essential to ensure that a balanced grid is maintained at all times. Currently most national grids are maintained by natural gas, however, going forward in a carbon neutral power system, this will need to change.
Therefore, storage is imperative to wide-scale implementation of renewables. The current key form of large renewable energy storage is hydroelectric storage, pumped hydro is by far the most widely used electricity storage system in the world, more than ninety per cent of the world’s energy-storage capacity is in reservoirs. Water is pumped using a motor from a reservoir at a lower level to one at a higher level when there is excess electricity, the flow is then released back down in non-peak times, spinning through a turbine and thus generating electricity. It ensures that the spikes in electricity demand are evened out (but there are losses involved as some energy is wasted pumping etc).
A pumped-hydro installation is like a giant, permanent battery, charged when water is pumped uphill and depleted as it flows down. It is not only a form of storage, but also a way to generate electricity at a low cost. There are several hydroelectric storage facilities in various stages of construction across Europe, the largest currently still in the permitting phase is in Austria. It aims to construct a new hydroelectric facility with a storage capacity of ~152 GWh. Some other countries are expanding their use of pumped hydro, but the construction of new facilities in places such as the United States peaked decades ago. The right geography is hard to find, permits are difficult to obtain, and construction is slow and expensive as well as local opposition to some projects for a variety of community reasons.
Whilst hydro currently dominates in terms of renewables storage options, there has been great advancement in battery technologies in recent years. For example there are new battery technologies such as zinc bromine or vanadium redox flow batteries, that are at a much reduced cost than previous technologies. This means they are much more viable on a larger scale due to their improved economic affordability. Therefore, it is estimated that in 2030 that the role of pumped hydroelectricity storage will still be significant but supplemented by these new and improved battery technologies which may be able to be positioned closed to the point of consumption with less community objections.
Lithium-ion technology has traditionally been the benchmark for batteries since its discovery four decades ago and it continues to be used. However, there is a worldwide shortage of lithium for building battery storage at scale, while cobalt mining – the material that provides a stabilizing effect in lithium-ion batteries – comes at a heavy environmental price due to the amount of water and energy that is required for mining the metals.
Another possibility for storage is hydrogen, which is produced by electrolysis from excess renewable energy generation. It can be converted into electricity through fuel cells or internal combustion engines and can also be used for a range of industrial processes. There are several major hydrogen projects under way in countries such as the UK, but it is hard to directly compare the cost of hydrogen with other large-scale storage technologies given the unknown costs of associated conversion technologies and the diverse range of applications.
Storage is ultimately used to ensure a high consumption of renewables. Another option in ensuring high use and consumption of renewable energy is decentralizing the grid. This can come in the form of prosumer based virtual power plants (VPP), where groups of prosumers come together as micro-generators and share their energy supply, thus, getting greater use and consumption out of the generated supply. This is particularly useful in wind and solar. Solar energy is used by many on a small scale, in the form of rooftop generators.
On a larger scale, there could be a development of an aggregate scheme in which renewable energy is shared between countries, this could work in places such as the EU. This ensures that excess electricity is being put to use on a large scale. Countries with large excesses of generation export to regions in need, then other oversupplying regions could export to said country when they are in need and so on. Europe could be split into a schematic model of seven set regions; the British Isles, Northern Europe, Baltic States, Central Eastern Europe, Central Western Europe, the Iberian Peninsula, the Appenine Peninsula and South Eastern Europe. It could balance the energy supply across Europe and aid in creating high levels of renewable energy consumption across the bloc.
Overall the focus of renewables needs to shift from simply generation, to transmission, storage and smart use. These four elements functioning together are what will ultimately lead to widespread renewables implementation and a drive towards a carbon neutral future.