Energy payback time and carbon footprint of commercial photovoltaic systems

doi:10.1016/j.solmat.2013.08.037

Solar Energy Materials and Solar Cells

Volume 119, December 2013, Pages 296-305

https://doi.org/10.1016/j.solmat.2013.08.037 Get rights and content

Highlights

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Energy payback times and carbon footprints range 0.68–1.96 years and 15.8–38.1 g CO₂-eq/kWh (hydropower/UCTE electricity, 1700 kWh/m² year).
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Assuming production in China results in similar energy payback times but increases the carbon footprint by a factor 1.3–2.1.
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New data are used for production of monocrystalline-, multicrystalline, amorphous silicon-, micromorphous silicon-, cadmium telluride- and CIGS-PV modules.
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The analysis is performed for roof-top photovoltaic systems excluding installation, operation and maintenance and end-of-life phase.

Abstract

Energy payback time and carbon footprint of commercial roof-top photovoltaic systems are calculated based on new 2011 manufacturers' data; and on 2013 equipment manufacturers' estimates of “micromorph” silicon photovoltaic modules. The energy payback times and carbon footprints are 1.96, 1.24, 1.39, 0.92, 0.68, and 1.02 years and 38.1, 27.2, 34.8, 22.8, 15.8, and 21.4 g CO₂-eq/kWh for monocrystalline silicon, multicrystalline silicon, amorphous silicon, “micromorph” silicon, cadmium telluride and CIGS roof-top photovoltaic systems, respectively, assuming a poly-silicon production with hydropower; ingot-, wafer-, solar cell and module production with UCTE electricity; an irradiation on an optimized-angle of 1700 kWh/(m²×year); excluding installation, operation and maintenance and end-of-life phase. Shifting production of poly-silicon, ingots, wafers, cells and modules to China results in similar energy payback times but increases the carbon footprint by a factor 1.3–2.1, depending on the electricity intensity of manufacturing.

Introduction

The increase in scale of production of PV modules goes hand in hand with economies of scale of manufacturing and optimized designs. This work shows the latest results for energy payback time and carbon footprint based on new data for commercial scale manufacturing of PV modules and updates of several data sets of ecoinvent 2.2+ [1].

Life Cycle Assessment (LCA) methodology was used to calculate the cumulative energy demand and global warming potential of PV modules and Balance-of-System components. Energy payback time and carbon footprint were calculated using the IEA PVPS task 12 guidelines [2]. The ecoinvent 2.2 database was used for background data, and calculations were performed with Simapro 7.3.3 software.

Data for PV systems and its components are described in [3] and are based on: (1) manufacturers' data collected by SmartGreenScans, (2) International Technology Roadmap for Photovoltaics (ITRPV) [4], (3) crystalline silicon solar cell data in [5], (3) market surveys of equipment in Photon International, and (4) Estimated data of “micromorph” silicon PV module with Oerlikon Solar THINFAB 120 MWp [6].

The roof-top balance-of-system amounts of a PV system with crystalline silicon modules on a typical Dutch house is described in [7]. The cable diameter for modules with lower module efficiency is smaller but no data are available so far, for thin film modules; therefore the same cabling is assumed here as for crystalline silicon. Inverter sizing values are taken from Stetz [8].

The IEA PVPS task 12 guidelines [2] recommend assuming a performance ratio of 0.75 for roof-top systems. In this study we used a performance ratio of 0.77 which is the average of Belgian and French residential PV systems investigated by Leloux in 2010 [9].

The IEA PVPS task 12 guidelines [2] recommend taking into account a linear power degradation of 20% after 30 years (0.67%/year) for all module technologies. A typical power guarantee on nominal module power is 80% after 25 years [10]. In this study we used system power degradation values of PV systems installed after the year 2000 from a recent literature review by Jordon [11].

To be able to compare the LCA results, the electricity mix to produce solar grade poly-silicon is taken to be hydropower, whereas for the ingots, wafers, cells and modules UCTE electricity mix is assumed. The efficiency of the UCTE electricity grid is 11.4 MJ/kWh (ecoinvent 2.2). The system analyzed is a roof-top PV system with PV modules with optimized-angle. Excluded are installation, operation, maintenance and end-of-life phase. Key parameters are shown in Table 1. High module efficiencies are important to reduce area-related impacts. Historical and roadmap average total area module efficiencies are shown in Fig. 1.

Section snippets

Results

Key results are shown in Table 1. Energy payback times and carbon footprints are shown in Fig. 2, Fig. 3, Fig. 4, Fig. 5.

Conclusions

For commercial PV roof-top PV systems, with the poly-silicon, ingots, wafers, cells and modules produced with Chinese electricity mix and installed at an irradiation of 1700 kWh/m² year:

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The energy payback time is significantly shorter than the expected lifetime of 30 years.
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The carbon footprint of PV electricity (20–81 g CO₂-eq/kWh) is favorable compared to the carbon footprint of electricity from fossil fuel based electricity. Electricity from coal, lignite, oil, natural gas has carbon footprints

Acknowledgments

Applied Materials, Avancis, First Solar, Oerlikon Solar, Pillar, PV-Silicon, Solar Frontier, T-Solar, Upsolar, Yingli Solar for discussions and providing data.

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Short communicationEnergy payback time and carbon footprint of commercial photovoltaic systems