Page 405 - A Comprehensive Guide to Solar Energy Systems

414 A COmpREHENSIvE GUIDE TO SOLAR ENERGy SySTEmS

21.2.3.1 Confusion in PV EROI Results Caused by Inconsistencies in Objectives and
Energy Input Accounting
Given that the concept of EROI analysis is relatively young; covers a broad range of disci­
plines; and attempts to answer very large questions of social importance, it is no surprise
that there are some disagreements on EROI terminology. As EROI analysis has only recently
become more popular, especially in Europe, communication and standardizations are
more important than ever. Issues of compatibility and broad conclusions are often argued
among an interdisciplinary body of analysts interested in the subject of particular fuels.
Specifically, issues tend to relate to poor or evolving definitions, and boundaries of analy­
ses and how that relates to their compatibility.
more explicit terms are necessary to move the field of EROI analysis into more complex
analysis. King [24] argues this point and introduces some explicit terminology. The first
distinction King makes is between “EROI” and “power return on investment.” power is
the ability to do work over time and King argues that if the units in the equation are that
of (energy per year output)/(energy per year input) then that constitutes “power return
on investment.” According to Hall [8], as EROI is a ratio and the units cancel out, the
distinction is most important when discussing rapidly shrinking or growing technologies.
The second distinction made by King involves cases where energy output includes that
invested in getting the fuel or not. For example, if natural gas is used to pressurize oil fields
for extraction, is that gas subtracted from the output? Although this distinction may not
seem relevant to pv EROI at the moment, it is possible that it can become an issue in the
future and it might be when comparing pv to other fuels for electricity.
Specific to pv EROI, confusion from results has been mainly due to a lack of clear objec­
tives, gaps in data availability, and inconsistencies in energy input accounting or issues of
analysis boundaries. Original studies into pv energy costs related an EROI in the range of
3–10:1 with an average of about 6.5:1 [17,25,26]. Since then, however, a growing number of
calculations are appearing well below this range. prieto and Hall [27] estimated an EROI of
2.45:1 for Spanish pv; palmer [28] estimated a similar EROI for rooftop systems with bat­
tery back up in Australia; Weissbach et al. [29] for pv in Germany; and recently Ferroni and
Hopkirk [30] in Switzerland and Germany. After some clarifications and arguments about
methods, objectives, and definitions [21,31,32], Leccisi et al. [33] and Raugei and Leccisi
[34] estimated an EROI of 9:1 for the same system Ferroni and Hopkirk claimed had an
EROI below unity in their study. How can two EROI analyses of the same systems reach
such drastically differing conclusions?
Sorting through all of the data, calculations and sources of information is outside the
scope of this chapter, but a summary is available in Hall [8]. Instead, what follows are les­
sons learned from exchanges in subsequent pv EROI, publications. First, correcting for
energy quality was inconsistently defined. In a simplified example, for the case of measur­
ing EROI for crude oil, the output is measured at the wellhead in barrels whereas for pv
EROI electricity is measured as output in kilowatt­hours. Important to note is that crude
oil in this case is a primary energy source and electricity from pv is an energy carrier.