Photovoltaic-thermal systems for zero emission residential buildings
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This thesis concerns the use of solar energy in energy efficient buildings. More precisely, the topic is photovoltaic-thermal (PV/T) solar energy systems, and how these can be used to provide renewable energy in zero emission buildings. PV/T modules are a hybrid between photovoltaic (PV) modules and solar thermal collectors, and therefore generate electricity and thermal energy simultaneously. The objective of the thesis was to investigate the potential of PV/T systems to minimize the life cycle greenhouse gas emissions of a residential building. The main research method in this thesis has been simulation of solar energy systems in buildings. Using simulations, PV/T systems have been compared to other solar energy systems with separate PV modules and solar thermal collectors. The simulation studies were performed in the simulation programs Polysun and PVsyst, and were based on commercial solar energy products available on the current market. The use of heat pumps, air-source and ground-source, in combination with solar energy systems was also studied. Two case buildings, the ZEB residential concept and the Living Lab, have been used in the simulation studies. The buildings are two of the pilot buildings of the Norwegian Research Centre for Zero Emission Buildings (the ZEB Centre). Both buildings are single family residential buildings located in Central or Southern Norway, and are designed to meet the Norwegian passive house requirements. The embodied emissions of the solar energy systems were determined using elements of life cycle assessments (LCA). A review of previous research found few studies of the environmental impact of PV/T modules, especially using industrially produced modules. The embodied emissions of such a PV/T module was therefore determined in this thesis, based on a combination of data from databases and information from module producers. The embodied emissions of the case buildings and the other solar energy systems studied were determined using a combination of databases and previously published research in the ZEB Centre. The results show that PV/T systems can be a good renewable energy solution for energy efficient buildings, but that their performance is highly dependent on how the system is designed and what control strategies are used. The simulations showed that the systems with PV/T modules typically had higher primary output per unit area than the systems with separate PV modules and solar energy collectors, but that this also depended on how the solar energy systems were designed. However, due to a higher use of electricity to run e.g. circulation pumps, the energy balance of the whole building was not improved compared to systems with separate solar technologies. The thermal output of PV/T systems are typically of a lower temperature than that of solar thermal collectors, and the technology should therefore be used in energy systems where low temperature heat is valuable. The combination of PV/T modules and ground source heat pumps showed potential to increase the efficiency of a building’s energy system compared to other solar energy technologies, especially when PV/T modules were installed on the source side of the heat pump. However, the studies also showed that it is a complex task to design such as system, and the energy demand required to operate it can easily be higher than the gains. No clear benefit from cooling of PV/T modules were found in the simulations in this thesis. In terms of emissions, no benefit of PV/T modules was found in the case studies. The generic PV/T module which was modelled had around 30% higher embodied emissions than a comparable PV module, and the increase in energy output from the PV/T module was not high enough to allow for this. It was in general found to be quite difficult to reach a net zero emission balance for a building, at least if embodied emissions of materials were included. A large solar energy installation was necessary to reach a balance, which sometimes resulted in non-optimal system designs. Nearly zero emission buildings, or zero emission neighbourhoods, might be a more feasible goal for new buildings. Even though all of the studied solar energy systems were found to be the source of a high share of the total embodied emissions of a building, they also contributed to a large reduction in greenhouse gas emissions over their lifetime. That is, solar energy installations, PV/T systems included, contribute to reduced emissions also in a Scandinavian climate.
Has partsPaper 1: Good, Clara Stina; Chen, Jinfeng; Dai, Yanjun; Hestnes, Anne Grete. Hybrid photovoltaic-thermal systems in buildings – a review. Energy Procedia 2015 ;Volum 70. s. 683-690 http://dx.doi.org/10.1016/j.egypro.2015.02.176 This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Paper 2: Good, Clara Stina; Andresen, Inger; Hestnes, Anne Grete. Solar energy for net zero energy buildings - A comparison between solar thermal, PV and photovoltaic-thermal (PV/T) systems. Solar Energy 2015 ;Volum 122. s. 986-996 http://dx.doi.org/10.1016/j.solener.2015.10.013 This article is reprinted with kind permission from Elsevier, sciencedirect.com
Paper 3: Good, Clara Stina. Influence of system lifetime on environmental impact assessments of photovoltaic systems in buildings. Presented at CESB13
Paper 4: Good, Clara Stina. Environmental impact assessments of hybrid photovoltaic-thermal (PV/T) systems - a review. Renewable & Sustainable Energy Reviews 2016 ;Volum 55. s. 234-239 http://dx.doi.org/10.1016/j.rser.2015.10.156 This article is reprinted with kind permission from Elsevier, sciencedirect.com
Paper 5: Good, Clara Stina; Kristjansdottir, Torhildur; Houlihan Wiberg, Aoife Anne Marie; Georges, Laurent; Hestnes, Anne Grete. Influence of PV technology and system design on the emission balance of a net zero emission building concept.. Solar Energy 2016 ;Volum 130. s. 89-100 http://dx.doi.org/10.1016/j.solener.2016.01.038 This article is reprinted with kind permission from Elsevier, sciencedirect.com
Paper 6: Good, Clara Stina; Kristjansdottir, Torhildur; Houlihan Wiberg, Aoife Anne Marie; Georges, Laurent; Hestnes, Anne Grete. Influence of PV technology and system design on the emission balance of a net zero emission building concept.. Solar Energy 2016 ;Volum 130. s. 89-100 http://dx.doi.org/10.1016/j.solener.2016.03.063 This article is reprinted with kind permission from Elsevier, sciencedirect.com