Page 407 - A Comprehensive Guide to Solar Energy Systems

416 A COmpREHENSIvE GUIDE TO SOLAR ENERGy SySTEmS

This relation expresses the energy delivered to society, in units of electricity, per one unit
of the sum of the energy carriers diverted from other societal uses (excluding energy
delivered to society), in terms of their total primary energy demand. There is no distinction
between renewable and nonrenewable energy inputs. The purpose of this metric is to
evaluate and compare its economical and effective use of available energy carriers from a
short­term perspective.

21.2.4.2 EROI PE-eq : Energy Output Expressed in Terms of Equivalent Primary Energy
When expressing energy output in terms of equivalent primary energy, the EROI of pv may
be calculated as:
=
EROIpE−eq=OutpE−eq/Inv=(Out EROI PE eq = Out PE eq− /Inv(Out/η G )/Inv = EROI/η G (21.5)
el
el
−
el/ηG)/Inv=EROIel/ηG
where η G is the lifecycle energy efficiency of the electricity grid (G) of the country or region
where the pv system being analyzed is deployed. It is calculated as the ratio of the yearly
electricity output of the entire grid to the total primary energy harvested from the environ­
ment for the operation of the grid in the same year: η G = 1/CED G .
This relation expresses the energy delivered to society, in units of equivalent primary
energy, per one unit of the sum of the energy carriers diverted from other societal uses
(excluding energy delivered to society), in terms of their total primary energy demand.
There is no distinction between renewable and nonrenewable energy inputs. The pur­
pose of this metric is to evaluate and compare its economical and effective use of avail­
able energy carriers from a short­term perspective. It is important to note that as the grid
performance is intrinsic to this metric, observed change in EROI pE­eq may depend not only
on the technological system being evaluated, but also on a change in the average life­cycle
efficiency of the grid (η G ).

21.2.4.3 The Cumulative Energy Demand (CED) Metric
CED per unit output may be operationally defined as:
+
=
CED=(pE+Inv)/Out CED(PE Inv)/Out (21.6)
where both pE and Inv are expressed in terms of primary energy, while Out is expressed in
direct energy units of the delivered energy carrier, which for pv is electricity.
This relation expresses the total primary energy harvested from nature per unit of
energy delivered to society as electricity. It is recommended to distinguish between renew­
able and nonrenewable energy. The purpose of this metric is to evaluate the efficient use of
primary energy resources from a long­term perspective.

21.2.4.4 The Nonrenewable Cumulative Energy Demand (nr-CED) Metric
LCAs keep track of all renewable and nonrenewable energy flows separately, which leads
to the possibility of calculating Nonrenewable Cumulative Energy Demand (nr­CED) per
unit output. It can be operationally defined as: