Results in brief


Hybrid plant offers energy system flexibility all year long

Researchers unveiled an innovative process that offers a flexible energy supply – electricity, fuel for vehicles and heating. The process provides a viable route to integrating renewables into buildings and transport, without having to dump any excess energy from sunny summer days.

The share of variable renewable energy sources in the energy mix is rapidly increasing over time. According to the latest renewable energy market forecast of the International Energy Agency, their capacity could expand by 50 % between 2019 and 2024. While the growth of renewables helps reduce carbon emissions and tackle climate change, balancing their availability with varying levels of electricity demand is quite challenging. For example, solar and wind energy technologies only produce energy during sunny and windy days, respectively.

Sustainable biofuels: what holds them back

Reliable energy storage is the target technology to unlock the vast potential of renewable energy. The use of hydrogen for energy storage is also relevant for combined heat and power (CHP) technologies commonly found in district heating systems of cities and central heating systems of larger buildings. “State-of-the-art CHP technologies have been under severe financial stress in the changing European electricity market. There is a clear need for new, flexible district heating and CHP solutions that can maintain economic feasibility under the increasing penetration of variable energy supplies,” notes Esa Kurkela, coordinator of the EU-funded FLEXCHX project. Trigeneration of power, heat and an intermediate product that can be refined to a transport fuel is an affordable way to address the challenge of the poor match between solar energy availability and the demand for electricity and heating. “Advanced biofuels are a key part of low-carbon transport development since early 2000, but industrial deployment has been held back. A fundamental reason for this is the attempt to reach satisfactory economics by exploiting economies of scale. This leads to extremely large-scale plant constructs (powers exceeding 300 MW) that are eventually deemed too risky by investors,” adds Kurkela. “Finding consumers who could effectively exploit such large amounts of heat supply provided by large-scale plants is also rare.”

The FLEXCHX process

Researchers working on the FLEXCHX project have successfully unveiled an innovative power plant that prompts a rethinking of how CHP is combined with variable renewables. “We have developed a flexible and integrated process that combines electrolysis of water with biomass gasification and catalytic liquefaction. This process produces heat, power and an intermediate energy carrier – Fischer-Tropsch wax – that can be processed to a transport fuel using existing oil refining equipment,” explains Kurkela. FLEXCHX plants can be integrated with various CHP systems, both industrial and district. “During summer, renewable fuels are produced from biomass and hydrogen; the hydrogen is produced from water electrolysis that is driven by low-cost excess electricity from the power grid. In the dark winter days, the plant runs on biomass, maximising the production of heat, electricity and Fischer-Tropsch wax. Most plant components are used throughout the entire year - only the electrolysis unit is operated seasonally,” adds Kurkela. Operating the same plant flexibly, either with biomass or combining it with renewable electricity, is radical. State-of-the-art biomass-fired district heating plants are usually operated only during cold days, approximately 5 000 h/year. By contrast, the annual operation time of conventional power-to-fuel units that exploit solar energy is limited to approximately 3 000 h. The main advantage of the FLEXCHX process is that it constantly produces electricity, fuel and heat all year long.


FLEXCHX, biomass, CHP, district heating, transport fuel, Fischer-Tropsch wax, combined heat and power


Grant agreement ID: 763919
Closed project
Start date1 March 2018
End date30 April 2021
Funded under
• H2020-EU.3.3.
• H2020-EU.3.3.2.
Overall budget € 4 489 545
EU contribution € 4 489 545