May 3, 2022

Técnicas Reunidas participates in the Undergy Project for the development of seasonal storage technologies for renewable energy with green hydrogen integrated in a smart grid.

Technologies for the development of seasonal renewable energy storage with green hydrogen integrated into a smart grid

The commitments acquired by Spain in energy matters entail a wide deployment of renewable generation with clearly defined objectives in the PNIEC for 2030 and a 100% renewable horizon in 2050. The current energy context, in which the UNDERGY Project is framed, considers the need to have a mass storage system to manage surplus electricity from renewable sources , and provide security of supply to the energy system. Only by having sufficient energy storage capacity will we be able to manage the seasonal fluctuations of renewable energy.

The UNDERGY (UNDERground enerGY) project will investigate the technological bases to improve the competitiveness of stationary storage of renewable energy through green hydrogen.

UNDERGY proposes the use of renewable energy, integrating renewable generation and high-capacity seasonal energy storage into a smart grid, through two levers:

  • underground storage of renewable energy, using green H2.
  • creating an efficient energy management system.


The project promotes the use of current national gas and electricity infrastructure networks towards the necessary transformation into a 100% renewable distribution network. The penetration of hydrogen as a renewable energy vector and its storage in the subsoil are still in an incipient stage, giving the project a strong innovative character.

The UNDERGY Project is a consortium project led by Petroleum Oil & Gas España (a subsidiary of Naturgy) and 5 other companies: Gas Natural Comercializadora (Naturgy Group), Ayterra, Gessal, H2B2 and Técnicas Reunidas. The expected duration is 39 months, until the end of 2024.

In addition, also 6 reference research organizations collaborate: the National H2 Center, the Geological and Mining Institute of Spain, the Polytechnic University of Madrid, the University of Salamanca, the University of Loyola and Tecnalia, which have a complementary technological capacity to carry out all the activities of research proposals throughout the project.

The UNDERGY project has a total budget of €5,599,227.00 and a grant of €3,490,674.75. It has been subsidized by the Center for Industrial Technological Development (CDTI), within the framework of the 2021 call for the SCIENCE AND INNOVATION MISSIONS Program (Recovery, Transformation and Resilience Plan), and has the support of the Ministry of Science and Innovation. The aid granted to the project is financed by the European Union through the Next Generation EU Fund.

6 complementary research activities

UNDERGY Project Structure

Petroleum Oil & Gas España will lead the entire project, with the Naturgy Group also leading two specific activities: Activity 2, through Petroleum Oil & Gas España, and Activity 6, through Gas Natural Comercializadora. For this, we will have the support of the National H2 Center, the Geological and Mining Institute of Spain, the Polytechnic University of Madrid and the University of Salamanca.

Within the subsurface area, the project will focus on validating the conversion of our Palancares gas field as underground green hydrogen storage. To this end, various laboratory studies will be carried out on samples from the warehouse that may be extended to other warehouses with similar characteristics in the future.

Activity 1. Seasonal storage capacity of green H2 in Spain

The objective of this activity, led by the company Gessal, is to investigate and determine the storage capacity of green hydrogen in the peninsular subsoil, enabling a tool that allows the study of the potential of suitable geological sites and structures (resource, feasibility, potentiality).

Activity 2. Green H2 storage pilot structure

Petroleum Oil & Gas Spain will address the feasibility of storing green H 2 on a pilot structure. A depleted natural gas field located in Aljarafe (Seville) will be used on a laboratory scale to investigate the reactions of gas mixtures (H 2 -CO 2 -CH 4) and containing rocks. In addition to the feasibility of storing H 2, the potential methanation that could occur in the subsoil due to the joint injection of green H 2 and captured CO2 will be investigatedFinally, a 4D modeling of the pilot storage will be carried out.

On the other hand, the possibility of scaling the results obtained in this activity to other depleted deposits with similar characteristics will be assessed.

Activity 3. Electrolysis

Led by the company H2B2, the objective of the activity is to analyze the main technologies of the electrolytic process to produce H 2 from the integration of different sources of renewable electricity generation and water qualities. The activity aims at the conceptual design of a new 20 MW electrolyser suitable for operating on large energy storages (geological type) and designed ad hoc to work under the operating parameters of renewable energy.

Activity 4. Facilities investigation

Técnicas Reunidas will be responsible for leading the feasibility study and the necessary modifications to the surface facilities, and for investigating the use and total reconversion of the existing gas facilities (surface facilities and gas pipeline distribution networks) to distribute green H2 and the potentially resulting gas mixture (H2-CH4-CO2), addressing the study for storage of H2/CH4 mixtures and a final scenario of pure H2 storage (100%). Likewise, the feasibility of using surface facilities for CO2 transfer, injection and extraction will be investigated, as well as the management and treatment of effluents in the different study scenarios. In addition, the integration of hydrogen production by electrolysis in the existing facilities and the analysis of risks related to the transfer of gases in the surface facilities will be carried out.

With this project, TR reaffirms its commitment to the energy transition and the decarbonization of processes, positioning itself at the forefront of the hydrogen production and management sector for the promotion of a more sustainable energy.

Activity 5. Risk and CO2 analysis

The objective of this activity, led by the company Ayterra, will consist of evaluating the potential risks related to the storage of green hydrogen in the subsoil. Environmental, hydrogeological, geotechnical and geomorphological aspects will be addressed, including seismic danger, taking into account the processes of electrolysis and transfer of gases in surface installations (H 2 -CO 2 -CH 4). It will include the design of an environmental monitoring network for a future operational phase.

Considering the in situ methanation potential determined in the laboratory, the supply of CO 2 will be evaluated, the emission reduction capacity associated with pilot storage and the possible use of existing infrastructure.

Activity 6. Integrated efficient energy management system

The objective of this activity, led by Gas Natural Comercializadora, will consist of proposing an efficient integrated energy management system, combining renewable generation and seasonal storage of green H2. To this end, various technical-economic studies will be carried out against different scenarios of the energy system, pursuing the avoidance of discharges and the optimal use of the renewable resource, in which the degree of penetration of the renewable generation of the Integrated National Plan will be taken as a reference of Energy and Climate (PNIEC).

Additionally, a Geographic Information System will be developed that will collect the seasonal storage capacity in the subsoil, as well as various relevant information on the energy system such as data on generation, demand, renewable resources, networks, etc.

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