Page 228 - Materials Chemistry, Second Edition

Comparing Various Indicators for the LCA 217
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Power = Total installed power, determined at STC [kWp]
The other is based on irradiation (R), efficiency (h) and performance ratio (p);
YEO ¼ R A h p ð2Þ

2
with R = Yearly irradiation [kWh/m /year]
2
A = Active Surface of the PV module [m ]
h ¼ Conversion Efficiency [%]
p = Performance Ratio [%]
The EPT [years] can now be calculated by dividing the CED by the YEO, on
the condition that both components are expressed in identical units (kWh or MJ of
primary energy);
EPT ¼ CED = YEOð Þ C ð3Þ

with CED=Cumulative Energy Demand [MJ prim ]
YEO = Yearly Energy Output [MJ el /year]
C = Conversion coefficient [MJ el /MJ prim ]
To convert the YEO from electrical energy to primary energy, one has to
include the efficiency of the electricity supply in the region of interest. The
Conversion coefficient (C) indicates how efficient the generation of electricity is,
on average, for the generations assets in a particular region (Gürzenich and
Wagner 2004; Alsema and Nieuwlaar 2000). In this chapter, a Conversion coef-
ficient of 0.35 [MJ el /MJ prim ] is used. It is remarkable that some authors do not
incorporate C (Koroneos et al. 2006; Pacca et al. 2007), a practice that results in
EPT’s that are approximately 3 times longer.
Keep in mind that conversion coefficient (C) has nothing to do with conversion
efficiency (h). The former is 30–40 % and refers to the grid electricity production;
the latter is 10–20 % and refers to the efficiency of the solar PV system.

2.5 Net Energy Ratio

Another indicator for energy efficiency which is commonly used is the Net Energy
Ratio. This indicator takes into account the total lifetime of a PV system. It can be
interpreted as: the amount of energy that a technology can produce relative to the
total amount of energy that was consumed, over the total life cycle.

NER ¼ lifetime=EPT ð4Þ
The NER is therefore an indication of the ‘‘life-cycle energy efficiency’’ of the
technology. If it is lower than 1, the technology is by definition not renewable, since
more energy was consumed than produced. In other words, this would entail a

2
STC = standard test conditions (25°C; 1,000 W/m; AM 1,5).