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- Song, Jingjing, 1983-
(författare)
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Restructured district heating price models and their impact on district heating users
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- District heating (DH) is considered to be an efficient, environmentally friendly and cost-effective method for providing heat to buildings, since electricity is usually co-generated in biomass fuelled combined heat and power (CHP) plants. This gives it an important role in the mitigation of climate change. Swedish district heating companies are currently facing multiple challenges, and are in urgent need of new price models to increase transparency and maintain their competitiveness.This thesis describes a survey carried out to understand the structure of the present price models and subsequently proposes and compares two restructured price models with the most commonly used price model. This work also investigates the impact of restructured price models on users who would encounter a significant cost increase if the restructured price models were to be introduced. The district heating costs of different price models are compared with three alternative technical solutions.The results show that price models based on the consumption pattern of users can reflect district heating companies’ cost structure. Meanwhile, adopting a pricing strategy based on users’ consumption patterns increased the incentives to reduce the peak load.Consequently, users with high load factor (flat consecutive load curve) were able to reduce costs whereas users with low load factor (steep consecutive load curve) faced possible cost increases, when the load demand cost was changed to daily or hourly peak demand based methods. Further, the most economically preferable option for the invested district heating user was to combine district heating with direct electrical heating or with a ground source heat pump.
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| 2. |
- Gomes, João, 1979-
(författare)
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Development of Concentrating Photovoltaic-Thermal Solar Collectors
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fossil fuels have greatly improved human living standards and saved countless lives. However, today, their continued use threatens human survival, as CO2 levels rise at an unprecedented pace to levels never seen during human existenceon earth.This thesis aims at gathering knowledge on solar energy in general and photovoltaic thermal (PVT) and concentrating photovoltaic thermal (C-PVT) in particular. This thesis establishes several key research questions for PVTs and C-PVT collectors and attempts to answer them.A comprehensive market study of solar thermal (ST), photovoltaic (PV) and PVT was conducted to obtain prices and performance. Simulations of the energy output around the world were conducted. A ratio between ST and PV annual output was defined to serve as a tool for comparison and plotted on a world map.A key issue for PVT collectors is how to encapsulate the solar cells in a way that, amongst other things, protects the cell from the thermal expansion of the receiver, has a high transparency, and insulates electrically while at the same time conducts the heat to the receiver. In order to be useful, this analysis must also consider the impacts on the production processes. Several prototypes were constructed, a test methodology was created, and the analysis of the results enabled several conclusions on the validity of the different silicon encapsulations methods.This thesis relies heavily on collector testing with 30 different prototypes of C-PVTs being designed and constructed. Most testing was conducted using steady state method but quasi dynamic was also carried out. From this work, several guidelines were created for the design of collectors in terms of reflector geometry, cell size, string configuration, encapsulation method and several other design aspects. These analyses were complemented with thermal simulations (COMSOL & ANSYS), string layout (LT SPICE) and evaluation of existing installations. Two novel design ideas came from this thesis work, which the author will patent in the coming year. Additionally, raytracing work has been conducted and a new reflector geometry more appropriate for C-PVTs has been found to significantly improve the annual performance. Finally, the current and future position of PVTs in the global energy market is discussed.
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