Environmental impact comparison of a ventilated and a non-ventilated building-integrated photovoltaic rooftop design in the Netherlands: Electricity output, energy payback time, and land claim

Highlights

• Design of a ventilated and non-ventilated BIPV rooftop installation.

• Energy output simulated and environmental impact assessed in different tools.

• Non-ventilated BIPV shows a lower calculated electricity output.

• Non-ventilated BIPV shows a lower calculated environmental impact.

Abstract

Building Integrated PV (BIPV) is considered as a key development for successful deployment of PV in the built environment. However, the effect of PV integration on environmental impact is not fully understood. In this study a single indicator for environmental impact assessment of BIPV is investigated in the Netherlands. A BIPV rooftop with 24 multi-crystalline 60-cell modules has been designed with and without backside ventilation, and the environmental impact of these configurations has been assessed in the current situation and three future scenarios. The results are expressed in terms of electricity output difference (Δ_Eout), Energy PayBack Time (EPBT), and the single indicator Land Claim (LC); the calculated claim in land-time on the carrying capacity to realize the BIPV rooftop. The EPBT calculations are based on two different datasets, SimaPro and the Inventory of Carbon and Energy (ICE), and the LC calculations are based on two different models, SimaPro and MAXergy. Calculations indicate that the ventilated BIPV rooftop design generates 2.6% more electricity than the non-ventilated BIPV rooftop design on a yearly basis. Calculations indicate that the EPBT of the ventilated BIPV rooftop design (3.56 and 4.59 years, based on SimaPro and ICE, respectively) is 9 and 6% longer than the EPBT of the non-ventilated BIPV rooftop design (3.25 and 4.32 years, based on SimaPro and ICE, respectively). Calculations indicate that the LC of a m² ventilated BIPV rooftop design (24.4 and 19.4 m² a, based on SimaPro and MAXergy, respectively) is 18 and 10% higher than the LC of a m² non-ventilated BIPV rooftop design (20.0 and 17.4 m² a, based on SimaPro and MAXergy, respectively). In the optimal future scenario EPBT might decrease to 2.06 years and LC might decrease to 10.6 m² a. This study indicates that the non-ventilated BIPV design shows a lower environmental impact in spite of a lower electric performance and that environmental impact can significantly be reduced in future scenarios.

Introduction

To reach lower fossil fuel dependency and to decrease CO₂ emissions in the European Union (EU), it has been agreed to increase the share of renewable energy sources in the Final Energy Consumption (FEC) to 20% by the end of 2020 (European Commission, 2010). Photovoltaics (PV) can be a major contributor to this target. In 2011, electricity consumption was 3500 TWh in the EU of which 117 TWh in the Netherlands (European Commission, 2013). The amount of PV surface needed to cover this electricity consumption would result in a total of 7100 km² PV modules for the EU and 1300 km² for the Netherlands, placed in the optimum orientation and inclination (Šúri, 2007). This area calculation is not taking into account improved efficiency of PV systems, degradation of PV systems, grid/storage interaction and increasing electricity demand. The potential roof and façade surface for building integrated PV is a total of 4979 km² in the EU and 210 km² in the Netherlands (Defaix, 2012). Theoretically, 70% of the electricity demand in the EU and 16% of the electricity demand in the Netherlands could be fulfilled by BIPV, not taking into account lower efficiencies due to less optimal inclination and orientation, degradation over time, PV efficiency improvement, grid/storage aspects, and other installation and operational aspects.

PV can easily be applied to buildings because PV installations are easily connected to the electricity system of a building and are not based on either potentially dangerous processes or use potentially dangerous resources, as opposed to for example gas based heating systems. The 60-cell multi-crystalline PV modules under investigation in this study can be added to the building envelope (Building Added PV - BAPV) or can be integrated in the building envelope (Building Integrated PV – BIPV), as illustrated in Fig. 1A and B.

In the case of BAPV, a construction is added to the building envelope to carry the PV modules, with in general an air gap between rooftop and PV. In the case of BIPV the modules are directly placed on the rooftop construction, possibly replacing roofing materials resulting in a smaller or no air gap.

The acronym BIPV is generally used when the PV installation is both technically and aesthetically contributing to the functionality of the building (Sinapsis and Donker, 2013). Four key factors are considered essential for the success of PV: cost reduction, efficiency increase, electricity storage, and its integration in the building, i.e. BIPV (Raugei and Frankl, 2009). One of the barriers on the track towards more BIPV is the possible negative side effect of physical integration on the performance and durability of the PV installation due to increased operating temperatures and increased relative humidity (Ritzen et al., 2014a, Ritzen et al., 2014b, Ritzen et al., 2014c, Mei, 2009, Norton, 2011, Ritzen et al., 2017), caused by a lack of backside ventilation. For this reason, the relation between PV output and backside ventilation is an important topic of ongoing research (Ritzen et al., 2014a, Ritzen et al., 2014b, Ritzen et al., 2014c). PV application has an environmental impact, in the form of energy necessary to produce the PV installation (embodied energy – EE) and in the form of resource extraction and processing, which might increase due to a shorter lifespan of PV installations. This creates a possible imbalance between energy generation on the one hand and embodied energy and material consumption on the other hand.

The availability of resources, in combination with the renewable energy potential, to deliver the necessary operational energy and embodied energy, determines the carrying capacity¹ of a system.² Overexploiting the material resources or energy resources within a system will result in either the collapse of that system or import from other systems, as described by Diamond (2005). The impact on the carrying capacity can be determined by calculating the amount of land and time needed for the extraction of raw materials, the growth of materials, the generation of power, and is expressed in Land Claim (LC) in m²⋅a, and is further described by Rovers, 2010, Rovers, 2011a, Rovers, 2011b, Rovers et al., 2011 and Ritzen et al., 2013a, Ritzen et al., 2013b, Ritzen et al., 2014a, Ritzen et al., 2014b, Ritzen et al., 2014c, Ritzen, 2016. Due to the increase of material consumption with 30% between 1995 and 2005 (Bruckner, 2012), an increasing amount of land is needed for the extraction of these materials and for the generation of energy to process these materials.

Insight in the offset between energy performance and material consumption of BIPV, expressed in a single indicator related to the carrying capacity, contributes to evaluate the possible imbalance between energy performance and material consumption, which is not fully covered in current Life Cycle Assessment (LCA) methods (Keoleian and Lewis, 2003). The aim of this study is to investigate LC as a single indicator of environmental impact assessment of BIPV rooftop design in the Netherlands in the current situation and three future scenarios described in Frischknecht et al. (2015).

In this study, a BIPV rooftop installation has been designed in a ventilated and non-ventilated configuration. Three aspects related to the performance have been calculated; electricity output difference (Δ_Eout), Energy PayBack Time (EPBT), and Land Claim (LC). The EPBT calculations are based on two databases, SimaPro and ICE, and the LC calculations are made in two models, SimaPro and MAXergy, to indicate the effect of different datasets on outcome.

This paper is structured as follows. In Section 2, the different methods, used to calculate electricity output and environmental impact of the designs, are presented. In Section 3, the ventilated and non-ventilated BIPV rooftop designs are described. In Section 4, the calculated results are presented of the different designs and the different scenarios. Finally, Sections 5 Discussion, 6 Conclusions consist of the discussion and conclusions.