18 May 2017

O.2.6.1 BIG Solar Graz: Results of a techno-economic feasibility study

Current heat generation for district heating (DH) in Graz, Austria is primarily from waste heat of fossil-fired combined heat and power (CHP) plants. Due to low prices on the European electricity market, the operation of CHP plants is not economic sound anymore and may lead to problems for cities, that are highly dependent on the heat of such plants. The operator of the CHP plants in Graz recently announced their closure in 2020. Almost 80% of the overall heat production has to be replaced.
The research focus of this paper is to analyze the technical and economic potential of integrating a centralized large-scale solar thermal system including seasonal pit storage and absorption heat pumps for DH. Therefore, the purpose of the research is to determine the techno-economic optimum size of such a solar system, that can be integrated into the district heating system of Graz. The study includes the design of a technical concept using dynamic simulation, an investigation of appropriate land for collectors and the storage and an economic cost evaluation of its realization.
First results indicate a techno-economic optimum of the system of 450,000 m² providing 20% solar fraction of the overall heat demand. Especially, the use of a series of absorption heat pumps with a total capacity of 100MW is a key element in the system in order to accelerate the cooling down process of the seasonal pit storage and enables a higher solar fraction.
There is a high potential of integrating such a large-scale solar system in the DH net of Graz. Considering the framework conditions such as grid temperatures and waste heat potentials the BIG Solar Graz concept is applicable to other cities with DH and may ultimately lead to a more sustainable heat supply for domestic hot water and space heating in the European Union.