Power plants could cut one-third of their emissions with solar

The COMBO-CFB project, led by the VTT Technical Research Centre of Finland, has developed a new innovative concept to increase solar energy production. According to the research, the concept can reduce fuel consumption and emissions stressing the climate by more than 33%.

The project examined how various types of hybrid plant solutions can produce power flexibly according to demand, without the need for energy storage. It found that if part of the fuel used by a power plant is replaced with solar energy, power plant emissions will be reduced.

The most efficient solution was based on the combination of concentrated solar power (CSP) technology and a traditional power plant process into a hybrid plant which produces electricity on the basis of consumption. Steam generated by a solar field was fed directly into the power plant’s high-pressure turbine, bringing a reduction in emissions and fuel consumption which at best exceeded 33%.

Furthermore, a reasonable dimensioning of the hybrid plant and process optimisation can bring efficiency benefits as compared to the use of separate power production methods. In the aforementioned case, the plant’s net efficiency improved by 0.8%. In addition to positive climate effects, good hybrid plant planning can also bring financial benefits since part of the power plant components are shared by two power production methods.

The dynamic nature of a hybrid process poses challenges to production system design and operation, particularly when the share of solar energy in power production is high. The COMBO-CFB project examined these challenges by using Apros software designed for dynamic modelling, as well as through combustion tests conducted by using VTT’s pilot equipment in Jyväskylä, Finland. This dynamic assessment at the plant design stage proved important since it enables designers to take account of factors such as those affecting the lifetime of components.

The concept in which part of the feedwater preheating is substituted with solar steam can be implemented in the present power plants, but compared to the aforementioned high-pressure turbine concept, the benefits are considerably smaller due to the smaller share of solar energy. The functioning of a hybrid process can be generally improved by attaching to it an advanced predictive control system and a short-term solar irradiance forecast. In the COMBO-CFB project, Vaisala developed a cloud camera which identifies cloud movements in the sky in order to increase the accuracy of the solar irradiance forecast for the area.

The production concepts developed through this project will expand the application possibilities of the CSP technology. The implementation of such technology in power production is reasonable in areas with an abundance of sunlight; in the case of Europe, this refers to countries bordering the Mediterranean. However, the technology can also be implemented in areas with less sunlight by using hybrid power plants in which solar power is supported by another form of energy.

Image caption: The project accumulated knowledge about the CSP technology by visiting internationally renowned commercial and test plants, as well as through a research exchange with the German Aerospace Center (DLR).