The Riehen heating network has been supplying households in Riehen with geothermal energy for 26 years. The heart of the heat network is the geothermal plant, which has been in operation since 1994 and pumps 67-degree warm water from a depth of over 1,500m. This is used in the 38km district heating network and today covers the heating requirements of around 8,500 people with the demand continuing to rise.
Riehen is one of the most suitable locations in Switzerland for the use of geothermal energy. The amount of energy obtained from geothermal energy has more than doubled in the past 10 years from 10GWh to 23.3GWh in 2018. This corresponds to approximately 2,200t, or approximately 2.6 million litres of crude oil per year.
In order to meet increasing demand and increase the share of CO2-free energy, a second geo2riehen plant is to be built and long-term financing to be arranged. According to current planning, the new system is to supply around 4,000 additional people within a few years within the supply perimeter.
Riehen was the first municipality in Europe to receive the European Energy Award Gold in 2004 and continues to pursue the goal of remaining in this area thanks to forward-looking projects.
A feasibility study in 2018 showed that the chances of operating a second geothermal plant are good thanks to favourable geological conditions. The next step is to confirm this with trial drilling. Before this, the course of the underground rock strata is modelled in a so-called measurement campaign in order to be able to define a drilling target. With existing bores on the Bachtelenweg and in the Stettenfeld, a favourable water supply was proven. Based on this experience, the probability of success is relatively high.
Before the project can continue and test drillings can be carried out, the cooperation between the shareholders must be organized.
A grant was requested from the Federal Office of Energy (SFOE) in December 2018 and the project was examined by a BFE expert group. After the examination was completed, a subsidy contract of CHF1.2 million (US$1.24 million) was signed for the measurement campaign in January 2020. A further subsidy is requested for the drilling and until then the project will continue to be accompanied by the BFE expert group.
In Riehen, as with the previous drilling, the naturally broken, permeable and water-bearing subsoil is used. No new fractures are generated, so that no noticeable tremors can be expected. All project risks are continuously monitored and, depending on the project development, measures are taken to further minimise risk and communicated about it.
In order to achieve the ambitious goals of the geo2riehen project, Wärmeverbund Riehen AG faces major technical and financial challenges. In addition to the investment for geo2riehen, further investments in the existing production facilities and in the networks will be necessary in the next few years. This against the background that the new BS energy plan requires a CO2 reduction (decarbonization) of the heating system. As a result, both WVR AG and the IWB face major challenges that need to be solved in partnership. Replacement and new investments for production facilities and the expansion of the district heating network are pending in Riehen. Because the district heating in Riehen and Basel district heating are already technically connected, it is very important that the interests are brought into line.
Depending on the demand scenario, the investment requirement in the coming years is estimated at CHF42 to 49 million, with geo2riehen accounting for around CHF14 million after deducting the possible subsidy contributions. In order to be able to meet these challenges, the two shareholders (the municipality of Riehen and the IWB) have reviewed their partnership.
In the future, the shares will be 50 per cent instead of the current 72.9 per cent (Riehen municipality) and 27.1 per cent (IWB). With regard to energy supply, the IWB is not only the most important player in the canton of Basel-Stadt, but also an indispensable partner of the community in the Riehen heating network and have extensive technical and operational know-how.
With the shift in the equity component, the IWB also assume more financial responsibility and risk.