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

The ambition level for the zero emission neighbourhood Aadland is that the area will be self supplied with both thermal and electric energy. This paper presents how emissions from operation of the 500 dwellings are offset by on-site renewable energy production. The paper also describes a procedure for how to deal with embodied emissions from materials in an early stage design phase. The study verifies that it is possible to reach a zero emission balance for the neighbourhood. Zero emission from operation is achievable as an average for the neighbourhood. For individual zero emission buildings this also includes embodied emissions from materials and construction in a lifecycle perspective. Qualitative requirements for emissions from materials are defined for all buildings in the neighbourhood.

Abstract

The net-zero emissions building (nZEB) performance is investigated for building operation (EO) and embodied emissions in materials (EE) for Norway's cold climate. nZEB concepts for new residential and office buildings are conceived 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 (CO_2e) emissions are revealed for both building concepts through a detailed emissions calculation. The influence of the CO_2e factor for electricity is emphasized and it is shown to have significant impact on the temporal evolution of the overall CO_2e emissions balance. The results show that the criterion for zero emissions in operation is easily reached for both nZEB concepts (independent of the CO_2e factor considered). Embodied emissions are 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. In this particular scenario, the net balance of emissions alone is nonetheless not a sufficient performance indicator for nZEB.

This report deals with how to define what a Zero Emission Building (ZEB) is with explanation and analysis of different parameters related to embodied emissions of CO₂ equivalents. The report can be used as a guidance tool on how to assess embodied emissions, and also on what parameters should be evaluated in such an assessment.

Different ambition levels for ZEBs may include life stages, operation, material, construction and end-of-life and can be documented according to EN 15978. Calculation procedures should include system boundaries, embodied emissions from materials, transport, the construction process and waste handling according to the ambition level. CO_{2 eq} emissions factors, service life estimates and payback scenarios for CO₂ emissions need to be considered.

The report does not contain one single clearly defined method, but rather a state-of-the-art summary on the different issues and refers to other relevant national and international work in the field of ZEB definitions. The issues presented here are in early stages of development and will need to be verified and further developed.