Renewable Energy World Conference Expo Europe 2013 –Novel Approach of Thermal Energy Storage Systems in Concentrated Solar Power Plants with Direct Steam Generation

摘要

In order to reach the CO2 reduction goals by 2020 renewable energies play a significant role. Besides wind energy, solar driven energy systems become a major technology to significantly increase the share of renewable energy generation in the energy mix. Solar energy can be converted either direct (PV) or indirect (solar thermal systems) into electricity. It is one of the key challenges in the world wide efforts to face the climate change to convert the fluctuating character of solar generated power to a reliable and dispatchable power source. Dispatchability is a key factor for the success of renewable energies, supporting the system operator in order to secure and increase the system stability. To store the generated energy is obligatory to reach this functionality for solar systems. One big advantage of solar thermal power plants is the ability to store the generated energy in form of thermal energy. In concentrated solar power (CSP) plants, high pressurized steam is generated either indirectly via a heat transfer fluid (HTF) or by direct steam generation (DSG) in the solar boiler itself. DSG systems offer an increase in efficiency compared to current thermal oil systems due to higher temperature ranges and a cost reduction potential compared to existing systems. Energy storage concepts for CSP plants combined with HTF are already commercially available on the market by using 2-tank molten salt storage systems. Storage technologies under current development face the challenge to be applicable for DSG solar thermal power plants considering the phase change in the used water-steam-cycle. The necessity to store as well sensible as latent heat leads to a decrease of the steam parameters between charging and discharging operation. A new approach of a solar boiler used for storage charging is introduced in this paper, allowing higher storage temperatures and an independent HTF mass flow. Additionally, it enables better operation conditions in discharging operation and offers a considerable cost reduction potentia.