Calculation of energy payback time of PV and its determinants

Transcription

1 Calculation of energy payback time of PV and its determinants Presentation at the Swiss Photonics Workshop Dübendorf, October22 th 2013 Hans-Joerg Althaus PhD LCA expert / scientific coordinator hans-joerg.althaus@quantis-intl.com

2 The principle of Energy payback time calculation EPBT years = Primary energy invested in PV system Primary energy substituted by PV system per year or EPBT years = Electrical energy invested in PV system Electrical energy substituted by PV system per year 3

3 The principle of Energy payback time calculation EPBT years = Primary energy invested in PV system Primary energy substituted by PV system per year 4

4 Definition of primary energy Energy embodied in natural resources prior to undergoing any human-made conversions or transformations. Energy contained in raw fuels, and other forms of energy received as input to a system. Can be non-renewable or renewable. 5

5 What is the primary energy of different sources? Fossil fuels: lower or upper heating value Value choice introduces ambiguity. Differences up to one order of magnitude! Natural Uranium: various methods Substitution: how much primary fossil energy would be needed to produce the same amount of electricity? Average thermal efficiency of nuclear power plant (ca. 32%) Important to choose consistent values for all energy sources! Important to compare only EPBT values from different studies if they are consistent! Energy content in fissile isotope (considering remaining fissile isotopes in nuclear waste or not) Solar: various methods Irradiation Harvested (by PV (cell, module or system) or thermal collector) 6

6 The principle of Energy payback time calculation EPBT years = Primary energy invested in PV system Primary energy substituted by PV system per year 1) 1) For production, use and end of life but without solar irradiation on PV modules during use phase 7

7 How to calculate primary energy invested in PV system? chain of production LCA 8

8 How to do life cycle assessment? Goal definition Life Cycle Model Life Cycle Inventory Resources Materials Energy Disposal Use Production Emissions Product Waste Discussion LCA Life Cycle Impact Assessment (ISO ) Cumulative Life Cycle Inventory Resources System per functional unit Emissions 9

9 Model of the Product system of PV power generation Reference function 10

10 Production of PV cells (thin film Si) Glass Electricity ZnO 11

11 Influence of production location 120% 100% 80% 60% 40% 20% 0% CED Non-renewable Electricity, Switzerland Electricity, Europe Electricity, China 12

12 Product system of PV power generation Central Europe 100% South Europe 170% Reference function 13

13 Ambiguities in LCA (of PV system) System boundaries Cut-off criteria Inclusion of infrastructure Inclusion of R&D Principles for modeling multi-functionality of systems Data sources Choice of background data 14

14 Energy payback time; principle EPBT years = Primary energy invested in PV system Primary energy substituted by PV system per year 1) 1) For production, use and end of life but without solar irradiation on PV modules during use phase 15

15 Share of electricity produced by fuel [%] What energy is substituted by PV electricity? 40 Coal & lignite Nuclear Renewables Natural gas Renewables 0 Oil Source: EEA 16

16 What energy is substituted by PV electricity? CED Non-renewable [kwh/kwh] CED Total [kwh/kwh] Electricity, Switzerland Electricity, Europe Electricity, China Hydro Electricity Wind electricity Nuclear electricity UCTE natural gas electricity UCTE oil electricity UCTE coal electricity 17

17 Examples CED System [MJ/m2] electricity generated [kwh/m2] Central Europe South Europe Crystalline Si Values would be ca. 20% higher for production in China mc-si Ribbon-Si Cd-Te Amorpous Si Exemplary values in reasonable range for PV system produced in Europe. CED of substituted electricity from ecoinvent v2.2 18

18 Examples 6 Energy payback time [years] Differences in electricity generated and substituted. No difference in PV production Values would be ca. 20% higher for production in China 5 4 Value choice introduces ambiguity. 3 2 Differences up to a factor of 2! 1 0 Important to choose reasonable substitute! Crystalline Si mc-si Ribbon-Si Amorpous Si Cd-Te 19

19 A glimpse beyond energy Payback of greenhouse gasses emitted 20

20 Examples GWP System (kg CO2-eq/m2) electricity generated [kwh/m2] Central Europe South Europe Crystalline Si mc-si Ribbon-Si Cd-Te Amorpous Si Exemplary values in reasonable range for PV system produced in Europe. GWP of substituted electricity from ecoinvent v2.2 21

21 Examples Differences in electricity generated and substituted. 60 Value choice 40 introduces ambiguity. 20 Differences up 0 to two orders of magnitude! No difference in PV production CO 2 payback time [years] Important to choose reasonable substitute! Crystalline Si mc-si Ribbon-Si Amorpous Si Cd-Te 22

22 Examples Differences in electricity generated and substituted. No difference in PV production CO 2 payback time [years] Crystalline Si mc-si Ribbon-Si Amorpous Si Cd-Te 23

23 Example: Influence of production location 300% 250% 200% 150% 100% 50% 0% GWP Electricity, Europe Electricity, China Assumption: GWP of PV system produced in China is 1.5 times the GWP of the same system produced in Europe. 24

24 Examples GWP System (kg CO2-eq/m2) electricity generated [kwh/m2] Central Europe South Europe Crystalline Si mc-si Ribbon-Si Cd-Te Amorpous Si Exemplary values in reasonable range for PV system produced in China. GWP of substituted electricity from ecoinvent v2.2 25

25 Examples Differences in electricity generated and substituted. No difference in PV production CO 2 payback time [years] if PV system produced in China Crystalline Si mc-si Ribbon-Si Amorpous Si Cd-Te 26

26 Emissions from scale up of PV What happens if PV electricity generation in Switzerland is scaled from today 0.33 to 11 TWh in 2050? 27

27 Scale-up Worst case Assumptions: - C-Si - Production in CN - Constant properties (efficiency, GHG intensity) t/a 100'000 90'000 80'000 70'000 60'000 50'000 40'000 30'000 20'000 10'000 GHG emitted by expansion of PV to 11 TWh in 2050 in Switzerland GHG emitted / year [t/a] 1 of Swiss emission 2011 GHG emitted per kwh PV electricity kg/kwh

28 Conclusions 29

29 Conclusions EPBT calculation is value based. Care has to be taken when comparing EPBT values of different studies. Influence of (arbitrary) choices can be larger then differences between PV technologies. GHG payback can be much longer then EPBT Influence of value choices on GHG payback is much bigger than on EPBT GHG emissions from transition towards high solar share in electricity generation are comparably small. 30

30 Contact us quantis-intl.com Quantis glatec Überlandstr Dübendorf Tel Quantis Quantis International +Quantis 31

31 Allocation: cut off Bauxite Alu Sheet rolling Door production New scrap to recycling Aluminium sheet Vehicle door Use phase 3 products Deconstruction Old scrap to disposal Old scrap to recycling System boundary Landfill 32

32 Allocation What is right and why? Bauxite Alu Aluminium sheet Sheet rolling Door production Vehicle door Use phase New scrap to recycling 3 products Mass New scrap:10% Car part: 0% Old scrap: 90% Deconstruction Old scrap to recycling Old scrap to disposal Value New scrap:3% Car part: 95% Old scrap: 2% System boundary Landfill 33

33 Aluminium melting Aluminium casting Aluminium Avoided allocation Bauxite Alu Sheet rolling Door production New scrap to recycling Aluminium sheet Vehicle door Use phase 1 product 2 products 3 products Deconstruction Old scrap to recycling Old scrap to disposal Scrap preparation System boundary Landfill 34

34 What energy is substituted by PV electricity? 35