Page 351 - A Comprehensive Guide to Solar Energy Systems

356 A COmPreHenSIVe GuIde TO SOLAr enerGy SySTemS

FIGURE 17.4 Grid EROI grid values as a function of storage or curtailment fraction, φ, and EES technology paired with
solar PV. All technologies except for PbA perform better than curtailment on a societal energy cost basis.

Ideally, storage technologies that support generation resources should not diminish
energy return ratios below curtailment energy return ratios for reasonable values of . This
means that storage technologies with high round-trip efficiencies and long cycle life val-
ues such as PHS and Li-ion are much more favorable for storing electricity generated from
solar PV than short-lived batteries for example traditional lead-acid batteries.
Curtailment of solar PV resources during times of excess generation is a viable form of
grid flexibility. Curtailment of solar PV yield carbon and energy intensities that are lower
than respective pairings with low cost PbA electrochemical storage technologies. Although
curtailment appears to be an immediate waste of a resource, the life cycle energy costs of
storage should be considered. Avoiding curtailment may not lead to the most environ-
mentally sound decisions. Curtailment is not the only option, nor is it ideal. useful appli-
cations for excess electricity occur beyond the power grid. excess electricity could be used
for thermal storage, producing heat or ice for later use. Additionally, electricity could be
used to pump or desalinate water, smelt metal ores, or manufacture goods. The energy is
“stored”, that is embodied elsewhere in the economy.

17.4 The Carbon Footprint of Storing Solar PV

energy storage emits carbon to the atmosphere. direct emissions of carbon are those
associated with the round-trip efficiency and operation of the storage device. Indirect
emissions are those resulting from the process of mining the materials and manufacturing
the storage and flexible generation technologies. The carbon intensity values for energy