Page 418 - A Comprehensive Guide to Solar Energy Systems

428 A COmPREhEnSIVE GuIdE TO SOLAR EnERGy SySTEmS

FIGURE 22.1 The Life Cycle Stages of PVs.

extraction to end of life. The cycle typically starts from the mining of materials from the
ground and continues with the processing and purification of the materials, manufactur-
ing of the compounds and chemicals used in processing, manufacturing of the product,
transport, installation if applicable, use, maintenance, and eventual decommissioning
and disposal and/or recycling. To the extent that materials are reused or recycled at the
end of their first life into new products, then the framework is extended from “cradle to
cradle.” This life-cycle for PV is shown in Fig. 22.1.
The life-cycle cumulative energy demand (CEd) of a PV system is the total of the (re-
newable and nonrenewable) primary energy (PE) harvested from the geo-biosphere in or-
der to supply the direct energy (e.g., fuels and electricity) and material (e.g., Si, metals, and
glass) inputs used in all its life-cycle stages (excluding the solar energy directly harvested
by the system during its operation). Thus,



CEdmJPE-eq=Emat+Emanuf+Etrans+Einst+EEOL CEDMJ PE-eq   = E mat + E manuf + E trans + E inst + E EOL (22.1)
where, E mat [mJ PE-eq ]: PE demand to produce materials comprising PV system, E manuf
[mJ PE-eq ]: PE demand to manufacture PV system, E trans [mJ PE-eq ]: PE demand to transport
materials used during the life cycle, E inst [mJ PE-eq ]: PE demand to install the system, and
E EOL [mJ PE-eq ]: PE demand for end-of-life management.
The CEd of a PV system may be regarded as the energy investment that is required in
order to be able to obtain an energy return in the form of PV electricity.
The life-cycle nonrenewable CEd is a similar metric in which only the nonrenewable
PE harvested is accounted for; details are given in the International Energy Agency (IEA)
Photovoltaics Power Systems (PVPS) Task 12 LCA Guidelines report [2].
EPBT is defined as the period required for a renewable energy system to generate the
same amount of energy (in terms of equivalent PE) that was used to produce (and manage
at end-of-life) the system itself.