Abstract

This paper presents an analysis of how the design of a photovoltaic (PV) system influences the greenhouse gas emission balance in a net zero emission building (nZEB). In a zero emission building, the emissions associated both with the energy required in the operation of the building (operational emissions) and the energy used to produce the building materials (embodied emissions) are offset by renewable energy generated on-site (avoided emissions). The analysis is applied to a nZEB concept for a single-family building, developed by the Norwegian Research Centre on Zero Emission Buildings. Previous analyses have shown that the installation of a PV system accounts for a significant share of the embodied emissions of a nZEB. The objective of this paper is to assess how the PV system design choices influence the embodied and avoided emissions, in order to determine how the environmental impact can be minimised. Four different PV technologies (Si-mono, poly-Si and CIS, and high-efficiency Si-mono) in four different system designs for flat roofs are evaluated using two different grid emission factors. The installations are compared by means of net avoided emissions, greenhouse gas payback time (GPBT), greenhouse gas return on investment (GROI), and finally the net emission balance of the building. The results show that the system with the largest area of high-efficiency Si-mono modules achieves the best lifetime emission balance, but that the greenhouse gas return on investment is highest for the optimally oriented CIS modules.

Abstract

Greenhouse gas (GHG) emissions from the combustion of fossil energy need to be reduced to combat global climate change. For zero energy and Zero Emission Buildings (ZEB), photovoltaic solar energy systems are often installed. When the goal is to build a life cycle Zero Emission Building, all emissions come under scrutiny. Emissions from photovoltaic (PV) energy systems in Zero Emission Buildings have been shown to have a relative large share of material emissions. In this paper, we compare GHG emissions per kW h of electricity and greenhouse gas emission payback times (GPBT) for three residential PV systems in Zero Emission Pilot Buildings in Norway. All the buildings have roof mounted PV systems with different design solutions. The objective is to analyse the emission loads and GPBT of these three systems to facilitate for more informed choices of energy systems for Zero Emission Buildings. The results show that the total embodied emissions allocated per square meter of module area are around 150–350 kg CO2 eq/m2 for the three different systems. Emissions from the mounting systems vary from 10 to 25 kg CO2 eq/m2 depending on the material types and quantities used. When modules replace other roofing materials, such as roof tiles, mounting emissions were reduced by approximately 60%. GHG emissions per kW h electricity produced were in the range of 30–120 g CO2 eq/kW h for the different systems. The system with the lowest emissions was the largest system, which had a simple mounting structure and modules with reused cells. It was found that the GPBT was strongly dependent on the scenario used for electricity grid emissions. By applying a dynamic emission payback scenario with an optimistic reduction of emissions from the European electricity grid, the GPBT was 3–8 years for the different systems. When comparing the emissions with current Norwegian hydropower emissions, of around 20 g CO2 eq/kW h, it was found that all of the PV system’s emissions were higher. When compared to a mainly fossil fuel based grid, all the PV system’s emissions are low. This study highlights the importance of reliable emission documentation for PV modules and their mounting structures on the market.

Abstract

In a net zero energy building (nZEB), the energy demand from the operation of the building is met by renewable energy generated on site. Buildings require energy both in the form of heat and electricity, and solar energy utilization is important in order to reach a net zero energy balance. In projects with ambitious energy targets or limited available areas for local energy generation, solar thermal and photovoltaic (PV) installations will eventually compete for space on roofs and facades. Hybrid photovoltaic–thermal (PV/T) modules, in which heat and electricity is generated simultaneously, are therefore an interesting technology for building applications, which can potentially lead to a higher total efficiency and lower use of space. This paper describes a comparative simulation study of different solar energy solutions for a Norwegian residential building concept aiming for a net zero energy balance. Separate PV and solar thermal systems are compared to PV/T systems, and the resulting energy balances analyzed. The results show that the building with only high-efficiency PV modules comes closest to reaching a zero energy balance, but that the results depend greatly on the nZEB definition, the boundary conditions and the design of the building’s energy system.

Abstract

The net-zero emissions building (nZEB) performance is investigated for building operation and embodied emissions in materials for Norway’s cold climate. An nZEB concept for new residential buildings was developed in order to understand the balance and implications between operational and embodied emissions over the building’s life. The main drivers for the CO2 equivalent (CO2eq) emissions were revealed for the building concept through a detailed emissions calculation.
Previous investigations showed that the criterion for zero emissions in operation is easily reached by the nZEB concept (independent of the CO2eq factor considered). Nevertheless, embodied emissions from materials appeared significant compared to operational emissions. It was found that an overall emissions balance, including both operational and embodied energy, is difficult to reach and would be unobtainable in a scenario of low carbon electricity from the grid i.e. low CO2eq factor for electricity. In order to make these conclusions robust, a sensitivity analysis was performed on the dominant sources of CO2eq emissions, as well as, on how it impacts the emission balance during the building lifetime. In the baseline work, embodied emissions were evaluated using the EcoInvent database in order to get a consistent life cycle assessment (LCA) method for all the building materials. The first step of this sensitivity analysis is therefore performed to compare embodied emissions when specific Norwegian Environmental Product Declarations (EPD) were used instead of generic data from EcoInvent thus making data more representative for the Norwegian context. In addition, the photovoltaic (PV) system, which supplies renewable electricity to the building, also contributes significantly to the embodied emissions. The second step of the analysis evaluates different PV system design options in order to find the one with highest net emissions reduction. Finally, since the building concept was based on a highly-insulated building envelope, the dominant source of emissions during building operation turned out to be electric appliances. The third step of the analysis thus discusses the energy consumption of electric appliances and how it could be reduced through more efficient products, especially the so-called hot-fed machines (i.e. washing machines, tumble dryer and dishwasher).

Abstract

This paper presents a review of projects where hybrid photovoltaic-thermal (PV/T) systems are used in buildings. PV/T systems convert solar radiation to electricity and heat simultaneously, in one module. The output of both electricity and heat suggests that the technology can be suited for use in buildings, especially when the available area for installation is limited. The market and research activities related to PV/T technology has increased in recent years. This article adds to existing reviews on PV/T technology by focusing on the building perspective. Different strategies for the use of PV/T in buildings are discussed, and examples of building projects are presented. An attempt is also made to assess to suitability of different PV/T technologies for use in buildings. Finally, the regional variations in market and applications are discussed.

Abstract

The paper presents a case study of an office building with a façade integrated PV system in Norway. Due to the urban surrounding the PV system is subject to significant overshadowing. The aim is to optimize the solar energy potential of the building in order to propose improved alternatives to the current system applying a multi-level simulation approach. The first level is performed to calculate the maximum solar potential on the building envelope in an unobstructed scenario. The second level examines the shading effect on the building in its urban context. The analyses allow localizing the areas of the building with the highest solar potential. In the third level, the energy output of different solar technologies (solar thermal and PV) is evaluated. The results demonstrate that the solar potential analysis in the early stage is important for choosing the most performing system.