New Storage Technology For "green" Electricity

A reliable, economical and environmentally compatible energy supply that focuses on climate protection is one of the greatest tasks of the 21st century. Renewable energies are of particular importance here, but storing them economically is still a challenge. This is exactly where the research project "Dess 2020+" - "District Energy Storage and Supply System 2020+" - comes in: The main goal is to no longer transport the "green" electricity over long distances in the future. To this end, decentralized storage options for renewable energy are to be developed. In the project funded by the Federal Ministry for Economic Affairs and Energy (BMWi), Robert Bosch GmbH works as a coordinator with the Fraunhofer Institute for Solar Energy Systems ISE.

Focus on storage

In its energy concept from 2010, the federal government envisages a far-reaching restructuring of energy supply in Germany by 2050. The main goals are to reduce primary energy consumption by 50% and to increase the share of renewable energies to 80% of electricity consumption and to 60% of gross final energy consumption - i.e. the consumption of all energy sources including heat and fuels. A particular challenge is the storage of renewable energies from the sun or wind, the amount of which fluctuates greatly depending on the weather.

“We are investigating a largely closed system for residential quarters in which electricity is generated regeneratively, stored on site and also used there. This should not only work in the connected households, but also in hydrogen-powered vehicles,”says Annika Utz. The engineer heads the Dess 2020+ project at the Bosch research campus in Renningen. The researchers are relying on a system consisting of three core components: a proton exchange membrane electrolyzer (PEM electrolyzer), a solid oxide fuel cell (SOFC) and several hydrogen storage tanks. This combination is intended to solve the problem of storage and thus security of supply when using renewable energies.

Hydrogen as an energy source

The researchers assume a residential area with around 100 households, in which electricity is generated, for example, via a photovoltaic system. A PEM electrolyser uses this electricity to split water into hydrogen and oxygen. The hydrogen is stored in tanks and used to operate the fuel cell regardless of when it was generated. This supplies electricity and energy for water heating and space heating of the connected buildings as required.

“The solid oxide fuel cell is particularly suitable because it runs on both hydrogen and natural gas, making it ideal for the transition from fossil to renewable energy supplies. This is a crucial criterion for security of supply. If there is actually not enough hydrogen available, you can switch to natural gas at short notice,”explains Utz. The advantage of this storage system: In the case of battery storage systems that have been customary to date, larger capacities always go hand in hand with considerably higher costs. Hydrogen, on the other hand, can be stored comparatively cheaply and therefore more economically even in large quantities.

Fuel for vehicles too

In addition to supplying energy to households, the system should also contribute to environmentally friendly mobility. For example, a hydrogen fuel pump could be installed in the district, which fueled fuel cell vehicles in a matter of minutes. To do this, however, the hydrogen pressure must be increased to around 800 bar - a pressure of 50 bar is sufficient for the energy supply to buildings. To increase compression, Bosch and Fraunhofer ISE are investigating the potential of a low-maintenance, highly efficient electrochemical compressor for the transport sector.

The research project Dess 2020+ was set to run for three years - until October 2018. It is part of the sixth energy research program "Research for an environmentally friendly, reliable and affordable energy supply" of the Federal Ministry for Economic Affairs and Energy. (kj)