Hybrid Renewable-Fossil Fuel Energy Systems

Dear Colleagues,

Penetration of renewable energy is a key goal for the future, in order to reduce pollutant emissions and fossil fuel dependency. The increasing number of renewable sources is posing challenging issues to grids and/or power plant operators in several countries, where the responses in terms of reinforcement of transmission lines and ancillary services are not adequately fast and/or effective. This is because the potential of nonprogrammable (wind and solar) sources is huge, but it is adversely impacted by: (i) variability, (ii) lack of correlation with load demand, and (iii) rapid change in generation over relatively short time periods. As a consequence, large penetration of nonprogrammable energy sources causes an increasing need for regulating power, i.e., an increase in the spinning reserves.

Renewable generator power output fluctuations force conventional fossil-fuel-based power units to provide compensating power in order to maintain the overall system balance. At present, wind or solar fluctuations are mostly mitigated by the large-scale distribution of conventional generators or by quick ramping storage systems, such as hydropower units. Thus, quick ramping generators (such as gas turbines) are forced to deviate, most of the time, far from their maximum efficiency condition (i.e., minimum operating cost). Storage technologies could handle the unsteadiness of renewable sources with smaller fossil fuel plant capacity while still providing a fast response.

All these issues are the main limitations to increasing renewables penetration in the actual mix of primary energy sources for electrical and thermal energy production.

With this Special Issue, we would like to encourage original contributions regarding recent developments in the field of the integration between renewable generators and fossil-fuel-based energy systems, with the aim to promote the increase in energy conversion efficiency and renewable source exploitation and to encourage the reduction of greenhouse gas emissions. The goal of this Special Issue is to cover all the aspects related to these aspects, focusing on technologies, optimized off-design operational and/or management strategies or applications.

Potential topics include but are not limited to:

• Management of gas turbines to stabilize the renewable generators fluctuations;
• Strategies for combined cycle power plants and/or steam power plants regulation;
• Integration between renewable generators and storage technologies;
• Integrated renewable–natural gas energy conversion systems;
• Integration between small-scale renewable thermal generators and district heating networks;
• Power to gas;
• Power to liquid;
• Power to heat;
• Power to cold.

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• Renewable and fossil fuel hybrid power plant
• Electrical, thermal or cooling energy storage
• Strategies/policies for optimal penetration of nonprogrammable renewables
• Power to gas
• Power to liquid
• Power to fuel