Hydrogen as a storage medium - facilitating increased integration of RES
The share of RES in the European electric power generation mix is expected to reach about 36% by 2020, 45-60% by 2030 and over 80% in 2050. In some scenarios, up to 65% of EU power generation will be covered by solar photovoltaics as well as onshore and offshore wind. Due to the highly variable nature of these renewable energy sources, where production is subject to both seasonal and hourly weather variability, new systems and tools will be required to ensure that this renewable energy is effectively integrated into the power system.
There are four main options for providing the required flexibility to the power system: dispatchable generation, the expansion of transmission and distribution, demand side management, and energy storage. With regards to storage, a number of options are available, from power to power (P2P) solutions such as pumped hydro, compressed and liquid air, Li-ion, flow and lead-acid batteries, and electrolytic hydrogen production and re-electrification. Power can also be converted to heat and stored for final consumption, or it can be converted to hydrogen for use outside the power sector - as fuel for vehicles or in industry.
Currently the only fully-mature technology is pumped hydro, and this accounts for a large share of the energy storage capacity in the EU. However, there are geographic restrictions on this technology, which limit its widespread use. Other large-scale storage options such as batteries, compressed air storage and hydrogen storage are currently at various stages of development. Hydrogen is widely seen as the most versatile means of energy storage: it can be produced and stored in all scales and used as a fuel or as a raw material in the chemical industry. Hydrogen can be produced from a variety of feedstock, including electricity, and stored in many different ways. Hydrogen gas has the largest energy content per unit mass of any fuel, making it a very good vehicle for holding and distributing energy. With the ability to hold 120MJ/kg, a relatively small amount of hydrogen is needed to store significant amounts of energy. Consequently, conversion of electricity to hydrogen and use of this hydrogen in the gas grid (P2G), in the transport sector or in industry can contribute to the decarbonisation of these sectors and help level out the peaks and troughs inherent in the temporal and geographical variability of RES.
The Fuel Cell and Hydrogen Joint Undertaking (FCH JU) supports a number of projects aimed at demonstrating technologies capable of storing hydrogen at a range of scales from small tank storage to large-scale underground storage, and in a variety of forms: gaseous, liquid and solid. The BOR4STORE project focuses on solid-state storage of hydrogen using boron-hydride based materials, while the EDEN project is developing an integrated system for solid-state H2 storage through an optimised fast-reacting magnesium-based hydride. This system will be interlinked to an energy supply system able to match intermittent energy sources with local energy demand (buildings, small dwellings) in stationary applications. The IDEALHY project (see the liquefaction article in this issue) aims to develop an economically viable hydrogen liquefaction capacity in Europe, while the objective of the HyUnder project is to support the deployment of large-scale H2 energy storage in underground caverns.
One of the conclusions reached by the HyUnder project was that, while underground storage of hydrogen in salt caverns is technically feasible for large-scale storage of electricity, hydrogen energy storage as a means to store renewable electricity via electrolysis and underground storage is economically very challenging. Consequently, under the given policy framework, the transport sector is currently the only market expected to allow a hydrogen sales price that may enable the commercial operation of an integrated hydrogen electrolysis and storage plant.
The FP7-financed INGRID project aims to combine recent advances in smart grids and hydrogen-based energy storage with a view to matching energy supply and demand and optimising the integration of electricity generated by intermittent RES. The main innovation of the INGRID project will consist of combining solid-state high-density hydrogen storage systems and electrolysis with advanced ICT technologies for smart distribution grids monitoring and control in a scenario of high penetration of renewable energy sources.
To assess the role and commercial viability of energy storage (both P2P and conversion of power to heat and hydrogen), the FCH JU has supported a study on the Commercialisation of Energy Storage in Europe.1 This study found that very large amounts of energy storage would be required to significantly reduce the required fossil backup even in the case of high RES penetration. Given the scale involved, it is likely that nearly all of the technologies concerned will start running into constraints regarding locations (suitable high-capacity hydrogen storage, elevations for pumped hydro, etc.), and their capex costs will start to rise as they are placed in ever less favourable locations. Of the technologies surveyed, the report found that only chemical storage (notably hydrogen storage) could potentially achieve acceptable economics at this scale.
For this to happen, the necessary regulatory framework will have to be put in place. However, the study also identified some key regulatory obstacles to energy storage, such as a lack of clarity on the rules under which storage can access markets – in particular the inability of transmission system operators (TSOs) and distribution system operators (DSOs) to own and operate storage or purchase transmission and distribution deferral as a service in some countries, or the lack of rules concerning the access of storage to the ancillary services market. Other obstacles include the application of final consumption fees to storage (including P2G), even though storage does not constitute final use of the energy, and payments for curtailment to RES producers, removing an incentive for productive use of the curtailed electricity. That said, the researchers believe that these obstacles can be removed by fair consideration of the role of storage in the electric power value chain.
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