Rock salt is an abundant mineral typically applied in chemical industry, food industry and road de-icing. Besides extraction from seawater and surface occurrences, subsurface mining is common practice in several European countries (e.g. Netherlands, Germany, UK, Poland, France, Portugal, Denmark) and accounts for ca. 60% of all salt produced. The northern parts of Germany and the Netherlands have favorable conditions for solution mining in salt pillars and domes. On several locations solution-mined salt caverns are deployed for underground storage of natural gas, crude oil, compressed air, nitrogen hydrogen and helium.
In the coming decades Europe’s energy system will change drastically with an expected increase of variable renewable energy production (solar and wind) and introduction of renewable gases including hydrogen. Regular excess peaks in electricity production may become a source for green hydrogen production via electrolysis while the same hydrogen may be used to cover energy demand during prolonged periods without wind and sun as well as periods with peak heat demands (e.g. cold winters). Large-scale storage volumes in salt caverns provide essential solutions for the balancing of hydrogen supply and demand. Future energy scenarios for the Netherlands alone predict a need for several tens of caverns. The development of such amounts introduces several challenges:
- High demand for storage caverns will probably result in overproduction of salt which negatively impacts the salt market and raises the issue brine disposal.
- Storage caverns specifications differ from typical production caverns with smaller volumes and lower revenues for the salt industry.
- Demand for storage caverns does not always coincide with existing salt production sites. Besides that, storage caverns may need to be spread across multiple locations to avoid excessive localized subsidence effects. This may lead to issues of social acceptance among local residents in targeted areas.
- The different interests of the energy and salt industries may trigger competition for the use of subsurface salt formations.
- Storage caverns will eventually be abandoned. With high numbers of locations this raises the issue of potential long term subsidence effects in relation to public safety and acceptance.
The above challenges are a reason for national and regional authorities to review and adapt existing regulations and legislation in order to reassure a responsible development of salt caverns and a well-functioning link between storage and salt market interests. Recent workshops in the Netherlands and Germany concluded that stakeholder participation from national and local authorities, operators, research institutions and local communities is key in this respect.
Serge van Gessel (1), Isis van Wetten (1), Gregor Schneider (2) & Ingrid Kroon (1)
TNO - Geological Survey of the Netherlands, Utrecht, The Netherlands (1); TNO - Geological Survey of the Netherlands, Utrecht, The Netherlands (1); DEEP-KBB GmbH, Hannover, Germany(2)