E-GAS : an innovative solution for intermittent renewable source of energy storage
In order to reach its ambitious Energy Transition‘s objectives, France is developing its renewable energy production. The intermittence of those energy sources like wind and solar power raises the question of the electricity storage, which is more and more necessary in order to optimize our green power generation.
Solar power, wind power, hydropower, biomass or geothermal energy… France is progressively entering a renewable world. First, the European regulatory context which highly recommend this strategy thank to the 3*20 directive : reduce GHG emissions by 20%, increase energy efficiency by 20% and reach a 20% share of renewable generation in the energy mix. Moreover, these green energy sources help to increase the European energy independence, by reducing the fossil sources imports and create jobs that cannot be relocated. France has an important strategy towards those ambitious goals and already plans a stronger renewable energy plan on the long term (2030).
Share of renewable energies in the french raw energy consumption, from 2005 to 2014, and trajectory expected to reach the 2020’s goal, by sector
(Source : « Chiffres clés des énergies renouvelables » – Commissariat Général au Développement Durable – december 2015)
The rising share of renewable energy in the French power consumption and more specifically the increase of intermittent energy sources like solar and wind power, requires a strong development of power storage, in order to face climate (and therefore production) risks and the associated operational difficulties. Whereas conventional power generation is instant and on demand, an intermittent production cannot efficiently meet the energy demand on a flexible way. Over generation and under generation peaks are common. That’s why, when developing those renewable energy sources, it will be necessary to store this intermittent production during overproduction peaks in order to distribute it when the national production isn’t able to meet the demand, or to transfer it in another system, more flexible than the electric network.
A recent electric system modelling showed that, in a strong intermittent capacities penetration scenario (ADEME 2050, 2012), the overproduction surplus could reach around 75 TWh/year by 2050 which counts for 15% of the current French electricity production. In addition, the model enlightens the fact that production surplus will be frequent and on a long period : 80% of the surplus happen on more than 12h periods, which include 26 TWh on 3days to 1 week periods.
Therefore, value this overproduction energy could help to develop a more effective and efficient renewable energy mix.
To date, different power storage solutions exist (batteries, compressed air storage or PHS : Pumped Hydro Storage). Nevertheless, they don’t allow a massive electricity storage capacity on a long term period.
Several solutions do exist and all of them rely on electric power to another form conversion. It is possible to store electricity in a battery and different types of technology are available or in progress. Batteries can be stationary or on board (electric vehicles for example). Indeed, an important electric cars fleet would be an interesting way to store electric production by encouraging the car users to charge their vehicle when power generation exceeds the national demand.
Moreover, it is possible to convert electric power to mechanic power, thanks to compressed air or thanks to a PHS (Pumped Hydro Storage). PHS is a really mature technology but its industrial development is limited by geographical constraints. As for compressed air storage systems, the adiabatic solution with an interesting efficiency is still in development. Despite a wide range of technical solutions, the available storage capacity is low regarding the more and more important overproduction form wind and solar sources, which should increase even more with the European green strategy plan.
The choice between these technologies will be based on the storage capacity and the economic efficiency of the project.
Transformation from green electricity to hydrogen and its injection into the gas network (a low proportion mix with natural gas) turns out to be an interesting solution. Then, hydrogen conversion to methane thanks to a chemical reaction with CO2 could develop an unlimited green power storage capacity.
Power to Gas turns out to be an optimal solution for massive overproduction storage. The surplus of energy produced is converted to hydrogen by electrolyse. To date, hydrogen can be injected into the gas network and mixed in a low proportion to natural gas. If the hydrogen concentration increases, the hydrogen could be combined with CO2 and converted to synthesis methane before the injection into the grid. The chemical characteristics would be much the same. That’s what we call the methanation process, in order to bypass the hydrogen limitation for the gas transported in the grid. The gas resulting from this transformation from electricity is called “e-gas”. The e-gas is a key solution for addressing the issue of intermittent power generation by creating a real bridge from the electric system to the gas network.
Power-to-gas : how to store electricity from renewable sources thanks to electrolyse
(Source : GRTgaz)
Therefore, the « e-gas » answers to the problem raised by the development of the renewable sources of energy thanks to a massive and geographically flexible storage capacity. This transformation of the electric power to gas can be operated everywhere on the national territory where electric and gas networks are connected.
The e-gas is a new innovative solution and widely accepted in Europe.
This technology arouses a strong interest from the European countries. Nevertheless, many technological and economic issues still need to be addressed. The proliferation of several projects and the creation of many task forces like the North Sea Power To gas Platform led by DNV-Kema prove the efforts made in order to develop this sector. Many players are working together in order to promote the E-gas as one of the solution to put in place during our energy transition.
Gas transmission networks have a key role to play in a global energy system, including the renewable energy sources.
