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Measuring and explaining productivity growth of renewable energy producers: An empirical study of Austrian biogas plants

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Abstract

This study explores productivity growth of 65 Austrian biogas plants from 2006 to 2014 using Data Envelopment Analysis. Productivity growth is measured by calculating the Malmquist productivity index, and the contributions of technical change, efficiency change, and scale change to productivity growth are isolated. The results reveal that the average annual productivity growth between 2006 and 2014 is 1.1%. The decomposition of the Malmquist productivity index shows that the annual scale change, technical change, and efficiency change for the average plant is 0.6%, 0.3%, and 0.3%, respectively. These results indicate that the exploitation of returns to scale is a major driver of productivity growth and technical change is rather low. A second-stage regression analysis reveals that rising feedstock prices incentivized efficiency improvements but initial capital subsidies did not have an impact on technical change and productivity growth.

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Notes

  1. One anonymous referee suggested to add some critical remarks on the potential of biogas to supply energy in the future and its potential conflict with food production. Muscat et al. (2020) survey the literature on the competition for biomass across food and bioenergy production. Emmann et al. (2013) examine the validity of several points of criticism regarding biogas production. Further critical remarks on the biogas technology are stated and discussed at https://www.biogas-kanns.de/left/Criticisms-and-answers/445l1/. For the potential of biogas to supply energy in the future we refer to IEA (2020).

  2. OECD-Europe comprises all European members of the OECD (not necessarily EU members). In 2012 these were Austria, Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, the Netherlands, Norway, Poland, Portugal, Slovak Republic, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.

  3. For an overview of the many decompositions of the Malmquist productivity index see e.g. Balk (2001), Lovell (2003), Zofío (2007), and Diewert and Fox (2017).

  4. Lovell (2003) criticizes that (i) technical change is measured relative to a CRS-technology and has no economically meaningful interpretation, and (ii) the scale efficiency change component is not measuring the contribution of scale economies to productivity change. Additionally, Ray and Desli (1997) criticize the internal inconsistency of the decomposition introduced by Färe et al. (1994). They argue that if the technology exhibits CRS technical change is measured correctly but no scale effects exist, and any measure of it is misleading.

  5. Recent comprehensive overviews of concepts and models in DEA are provided e.g. in Bogetoft and Otto (2011) and Zhu (2015).

  6. An anonymous referee pointed out that a balanced sample might be problematic if technological progress is related to plant entry and exit. Unfortunately, we have no information on plant exit. Twelve plants entering operation in 2007 are excluded from the balanced sample. Sensitivity checks indicate that the inclusion of the newly commissioned plants would hardly have any effect on the qualitative results and conclusions of our study.

  7. Note that the average capacity utilization rate in our sample is above the sectoral average indicating that the plants in our sample might perform better than the population average.

  8. Allen (1999) and Dyckhoff and Allen (2001) argue that waste burned in a power plant is an undesirable object. Its destruction is desired and, therefore, waste should be maximized.

  9. The main substrate, silo maize, had a slow start in 2012 due to cold weather in May and June. The rainfall was sufficient, however, the comparatively low temperature level slowed down plant growth. This led to delayed and inadequate formed grain maize. The weather reversed in July 2012. Temperature rose and the rain failed (ZAMG, 2013). The heat wave at the end of August led to a prematurely phasing out of the maize plant (Holzkämpfer and Fuhrer, 2015). This combination led to less developed corn cobs and a drop in the sugar and starch contents at the corn. In return, the early stop in growth leads to lower yields and high crude fibre and lignin contents in the plant (Gruber und Hein, 2007).

  10. Supplementary material provides detailed information (histograms) about the frequency distribution of the Malmquist productivity index and its components.

  11. Estimates for t = 2006–2014, t = 2006–2013 and t = 2006–2012 are available on request. The results obtained are similar to the pooled OLS estimates.

  12. The maximum potential electricity output of a biogas plant is ultimately constrained by the electric capacity of the CHP and is reached if the CHP is running with full load throughout the year (8760 h). Multiplying the installed capacity of the CHP (measured in kWel) by 8760 gives the maximum potential electricity output.

  13. We also estimate models with a dummy variable for investment activities and drop (i) the capacity change variable, as well as the (ii) interaction term between capacity change and size of the plant. The results are available in Appendix B, Table 8. The investment dummy is equal to one if investments were undertaken and zero otherwise. While 66% of the biogas plants in the sample increased their capital stock between 2006 and 2012, 34% do not show any investment activity in that period. We find that there is a statistically significant positive relationship between (i) productivity growth and investment activity, as well as (ii) scale change and investments. Unfortunately, we are not able to distinguish between types of investments (e.g. installed electric capacity, heat grid…).

  14. We also test for the effect of changes in feedstock composition on productivity growth and do not find any evidence that it has an impact.

  15. The standard deviation of the efficiency scores is relatively constant over time. It is 0.15, 0.13, 0.13, and 0.13 for the years 2006, 2012, 2013, and 2014, respectively.

  16. We also exploit the cross-sectional variability in feed-in-tariffs (for details see, e.g., Eder and Mahlberg, 2018) to estimate the effect of production subsidies on productivity growth. The estimated regression models suggest that production subsidies do not impact productivity growth.

  17. The percentage of plants without any heat utilisation in the sample declined from 49% in 2006 to 8% in 2014.

  18. Specialized cogeneration plants, which e.g. focus on the generation of electricity and waste substantial amounts of heat, could increase heat output without using additional amounts of primary fuel.

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Acknowledgements

The authors gratefully acknowledge the valuable comments received from two anonymous referees, Klaus Gugler, Kristiaan Kerstens, Wolfgang Koller, Mikulas Luptacik, members of the Austrian Biogas Network (BiGa-NET), the seminar participants at the Vienna University of Economics and Business as well as the participants at the 9th North American Productivity Workshop (NAPW 2016) in Quebec City, the Annual Conference of the Austrian Economic Association (NOeG 2017) in Linz, the International Association for Energy Economics European Conference 2017 and the 5th IAEE European PhD-Day in Vienna. Special thanks to the Austrian Compost and Biogas Association for providing the data set. The authors would like to thank the Austrian Research Promotion Agency (FFG) for funding the project under project number 845422. The usual disclaimer applies.

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Correspondence to Andreas Eder.

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Appendices

Appendix A

Table 7 Guide values for methane, dry matter and organic dry matter content per t of FM

Appendix B

Table 8 Regression results of pooled OLS-Model, Investment Dummy

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Eder, A., Mahlberg, B. & Stürmer, B. Measuring and explaining productivity growth of renewable energy producers: An empirical study of Austrian biogas plants. Empirica 48, 37–63 (2021). https://doi.org/10.1007/s10663-020-09498-y

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