COMBO-CFB Project Develops Innovative Concept to Increase Solar Energy Production

The project accumulated knowledge about the CSP technology by visiting internationally renowned commercial and test plants, as well as through research exchange with the German Aerospace Center (DLR). Photo: The Puerto Errado plant in Calasparra, Spain.

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

The concept combines a conventional power plant process and concentrated solar power (CSP) technology into a hybrid plant to produce electricity on the basis of consumption.

If solar energy replaces part of the fuel used by a power plant, then the power plant’s emissions could be reduced. This is also necessary to meet the emission reduction targets. The COMBO-CFB project (Combination of concentrated solar power (CSP) with circulating fluidized bed (CFB) power plants) explores how different types of hybrid plant solutions can produce power as per demand without the requirement for energy storage. The project examined and compared various hybrid plant concepts.

The concept in which steam produced by a solar field was supplied directly into the power plant’s high-pressure turbine caused a reduction in emissions and fuel consumption which exceeded 33%. In addition, a moderate dimensioning of the hybrid plant and process optimization can bring efficiency benefits when compared to separate power production methods. In the previously mentioned case, the net efficiency of the plant improved by 0.8%. In addition to positive climate outcomes, good hybrid plant planning can also bring financial benefits, as part of the power plant components commonly are shared by two power production methods.

The COMBO-CFB project used the Finnish project partners’ advanced expertise in boiler technology. Solar energy production, which varies with weather condition, is balanced by using a steam boiler in a hybrid power plant. The production concepts developed through the COMBO-CFB project will increase the application possibilities of the CSP technology.

A hybrid process’ dynamic nature can pose challenges to the design and operation of the production system, particularly when the amount of solar energy in power production is really high. The COMBO-CFB project explored these challenges with the use of the Apros software developed for dynamic modeling, and through combustion tests carried out by using the pilot equipment of VTT in Jyväskylä, Finland. This dynamic evaluation at the plant design stage proved very important since it allows designers to consider factors that affect the lifetime of components.

The concept wherein part of the feedwater preheating is replaced with solar steam can be applied in the current power plant, however, compared to the previously mentioned high-pressure turbine concept, the benefits are significantly smaller due to the smaller share of solar energy. The performance of a hybrid process can be generally enhanced by attaching a short-term solar irradiance forecast and an advanced predictive control system to it. In the COMBO-CFB project, Vaisala created a cloud camera that can identify cloud movements in the sky to improve the accuracy of the solar irradiance forecast for the region.

In regions with an abundance of sunlight, the execution of the CSP technology in power production is reasonable. In Europe, this means, for instance, the countries bordering the Mediterranean. However, the CSP technology can also be employed in regions with less sunlight by using hybrid power plants wherein solar power is supported by another form of energy. For the present, Finland is not implanting this technology, while Denmark is already using a CSP-bio hybrid plant to generate district heating.

Finland has unique, globally competitive expertise that it can offer to the hybrid power plant export markets. The partner network of the COMBO-CFB project can support the commercialization of such hybrid plants. The areas of expertise for the Finnish project partners include process modeling, weather measurement and forecasting, and boiler and control technology.

Research partners

VTT Technical Research Centre of Finland, Vaisala, Telog, Pöyry, Amec Foster Wheeler, Finnish Energy, the Federation of Finnish Technology Industries and the University of Oulu.

Concentrated solar power (CSP) technology

Concentrated solar power is a renewable energy technology. It can be used to generate both heat and electricity. Other applications include, for instance, desalination. The CSP technology concentrates the sun’s energy through mirrors. This energy is then converted into heat that runs the turbine, similarly to conventional power plants. However, unlike in conventional power plants, the power production differs depending on the irradiance level.

Currently, the CSP technology can be used to generate electricity in accordance with consumption by separating solar heat collection from power production by using a heat storage unit. However, these storage units continue to be expensive, and technically, there is still no reasonable storage solution for all CSP technologies. So, for this reason, hybrid plants are a significant development step to flexibly adjustable renewable energy production.

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