Page 349 - A Comprehensive Guide to Solar Energy Systems

354 A COmPreHenSIVe GuIde TO SOLAr enerGy SySTemS

factor, χ, as listed in Table 17.2, where χ is a carbon intensity multiplier. If storage is 90%
efficient, the carbon intensity of the delivered electricity increases by 11%, χ = 1.11. manu-
facturing storage also incurs its own energetic and carbon costs.
despite higher energy and carbon intensities when compared to PHS, electrochemi-
cal storage technologies present one clear advantage: energy density. Batteries are able
to store several hundred times the amount of energy per unit mass and volume than PHS
(Fig. 17.2). Additionally, batteries do not require geological features, that is steep topog-
raphy, that PHS requires and therefore can be deployed anywhere including city centers,
residences, and commercial buildings (Fig. 17.3).

17.3 Net Energy Analysis of Storing and Curtailing Solar PV
Resources

Curtailing renewable resources results is an immediate and obvious forfeiture of energy.
However, flexible grid technologies can also consume significant amounts of energy in
their manufacture and operation. These embodied energy costs are not as immediately
apparent, but they are an energy sink from a societal perspective.
In this section, I compare the energetic costs of electrical energy storage (eeS) to the
energetic costs of curtailment. In lieu of storage or other means of grid flexibility, vari-
able resources are curtailed during periods of oversupply or of strong market disincentives
[19, 20]. Consequently, electricity is squandered, capacity factors are reduced and revenue

FIGURE 17.2 A plot comparing volumetric and specific energy densities for energy storage technologies. Technologies
considered for large-scale energy storage have labels in color (data obtained for PHS and CAES from calculations,
battery data [9] and flywheel data [18].