Solar photovoltaic and district heating: Paradigm shift

Abstract

Consulta en la Biblioteca ETSI Industriales (Riunet)

[EN] This thesis has investigated the possibility of using photovoltaics together with heat pumps to generate heat in Danish district heating plants. An economic study has been carried out in order to assess the feasibility of replacing some current solar heating plants by the plants using PV panels and heat pumps. For that, a literature review has been done rst, where optimistic arguments in favor of the new technology have been found but large-scale projects using the proposed technology have not been discovered. A state of the art chapter has been dedicated to give an overview of the European and Danish heating sector, solar heating technology and technologies to be used in the new PV-HP system. Heat storage has been demonstrated to be a crucial technology when using solar energy to produce heat. Three solar heating plants have been selected due to their representative solar fraction: S by (7%), Gr asten (28%) and Dronninlund (50%). In order to replace them, three new PV-HP plants have been designed. Ammonia heat pumps operate with an assumed constant COP of 4 powered by the PV panels. The PV subsystem has been designed using the software PVsyst. Afterwards, heat demand and heat production pro les have been calculated for each plant and used as input in an Excel model that has been built to control the storage situation throughout the year. With this model, it has been possible to identify overproduction in the solar heating system or electricity surplus in the PVHP system. This electricity surplus from the PV-HP system will be sold to the electricity market. Dronninglund and Gr asten have presented overproduction in the solar thermal system and also electricity surplus in the PV-HP system. Contrarily, S by has not presented neither overproduction in the solar collectors nor electricity surplus in the PV-HP system. The last chapter has economically compared the current solar heating systems and the newly designed PV-HP systems. An introduction to the theory behind the economic analysis and the studied economic parameters is followed by the creation of the economic Excel model. The results have been presented, showing that Dronninglund and S by have obtained pro tability for both the solar thermal system and the PV-HP system. Moreover, S by has been the most pro table solar heating plant due to the lack of overproduction. Regarding the PV-HP system, Dronninglund has had slightly better results than the other plants, just having a higher LCOE than S by, which happens again due to the overproduction. However, Gr asten has just obtained pro tability in the solar heating system, since the PV-HP project has resulted unfeasible. The main reason is the low heat price in Gr asten, which is around 30% lower than the heat price in Dronninglund or S by. Note that for the three studied cases, economic results have been better for the solar heating plant. Finally, a sensitivity analysis on the economic results (NPV) of Gr asten's PV-HP system has been carried out, varying several key inputs of the economic model. The parameters a ecting the most the economic results have been: the COP of the heat pumps during operation, the discount rate, the investment costs and the heat price. Nevertheless, when considering the changes of these parameters also in the solar heating plant, the COP and investment costs become the main way for the PV-HP plant to become competitive. This is because an increase in the heat price or the discount rate would a ect the feasibility of both the solar heating plant and the PV-HP plant at a similar level. In conclusion the PV-HP system is not competitive against solar heating in Danish district heating plants, since the latest is the cheapest option to generate heat. Some changes would be needed for PV-HP to reach the same pro tability as solar collectors' plants. Changes in the aforementioned parameters, as well as other possibilities such as subsidies for heat pumps would enhance the competitiveness of the PV-HP system in the future.