Solar Energy - Environmental Impacts of Renewable Energy - page 82

for utility-scale solar systems can be minimized by siting them at lower-quality
locations such as brownfields, existing transportation and transmission corridors, or
abandoned mining land (AML) (Hand et al., 2012; USEPA, 2011).
w ater r esoUrces
Just as with the production of energy from all other sources, in one way or another
solar energy production has a water footprint , defined as the total volume of fresh-
water used to produce energy and the services consumed by the production process.
Water consumption for solar generation varies by technology and location. For our
purposes in this text, water consumption is defined as the amount of water that is
“evaporated, transpired, incorporated into products or crops, consumed by humans
or livestock, or otherwise removed from the immediate water environment” (Kenny
et al., 2009). Water consumption is distinct from water withdrawal. Water with-
drawal is the total amount of “water removed from the ground or diverted from a
surface-water source for use” (Kenny et al., 2009) but which may be returned to the
sources. Both water withdrawal and consumption are important metrics, but con-
sumption is a very useful metric for water-scarce regions, especially in the context of
future resource development, because consumption effectively removes water from
the system so it is not available for other uses (e.g., agriculture, drinking).
Table 3.1 s hows estimated water-consumption ranges for solar deployment in 2030
and 2050 under a U.S. Department of Energy scenario. These values represent esti-
mates of gross water consumption for deployed solar technologies only; that is, they
do not consider the amount of water consumption avoided due to replacement of other
electricity-generating technologies by solar. Table 3.2 g ives water use estimates for
solar, wind, fossil fuel, and nuclear generating technologies. Biomass and co-fired bio-
mass power plants have cooling/generating water consumption similar to that of com-
parable coal plants, but water consumption related to growing biomass fuel is highly
variable (Gerbens-Leenes et al., 2009; Macknick et al., 2011). As Table 3.2 shows,
many solar configurations can reduce water consumption dramatically compared with
conventional technologies that use evaporative cooling systems (i.e., cooling towers).
Solar cooling towers regulate temperature by dissipating heat from recirculat-
ing water used to cool process equipment. Heat is rejected from the tower primar-
ily through evaporation; therefore, by design, cooling towers consume significant
amounts of water (see Table 3.2 ) . The Achilles heel of solar cooling towers is two-
fold: (1) equipment failure and (2) operator and/or management error. The thermal
efficiency and longevity of the cooling tower and equipment used to cool depend on
the proper operation and management of water recirculated through the tower. Water
leaves a cooling tower system in any one of four ways (EERE, 2013):
1. Evaporation —This is the primary function of the tower and is the method
that transfers heat from the cooling tower system to the environment. The
quantity of evaporation is not a subject for water efficiency efforts (although
improving the energy efficiency of the systems being cooled will reduce the
evaporative load on the tower).