Page 388 - A Comprehensive Guide to Solar Energy Systems

396 A COMPrEHEnSIvE GUIDE TO SOlAr EnErGy SySTEMS

contrasts abundant sunlight levels optimal for solar energy production. Wet-cooled CSP
facilities, which need steam to generate electricity and water for cooling, may use between
−1
3
−1
5551 and 17 886 m a MW (4.5–14.5 ac-ft of water per year per MW of electricity pro-
duced), where "a" refers to annum [15]; this amount equals or exceeds nuclear and coal
power plants [17]. Alternatively, dry-cooled CSP technology requires between 247 and
−1
−1
3
−1
−1
1234 m a MW (0.2–1.0 ac-ft year MW ) of electricity produced [15]. Additionally, CSP
−1
3
−1
installations require water for mirror washing, potentially equating to 617 m a MW
−1
−1
(0.5 ac-ft year MW ) or more [15]. It is noted that Pv in the southwestern United States
uses marginal amounts of water for panel washing, and therefore, has a clear advantage to
any thermoelectric power generation in arid areas.
20.2.5 Changes in Land-Surface Temperature, Albedo, and
Microclimate
Photovoltaic panels have low reflectivity, owing to a large proportion of solar radiation
that reaches them being converted to electricity and heat [18]. There is growing concern
that Pv installations may cause a “heat island” effect similar to those that occur in urban
areas, especially in desert environments, whereby mean air temperatures surrounding the
installation increase due to a decrease in albedo. The effective albedo of a Pv panel (cur-
rent upper maximum >35.2%) is the sum of its reflectivity (e.g., 0.06–0.1) and solar con-
version efficiency (e.g., 0.12–0.252 [e.g., SunPower panels for upper limit] [19]). Ultimately,
the variation in the albedo of natural and built environments where solar energy installa-
tions are sited and the variation in the effective albedo of Pv can lead to different results;
thus additional research in diverse environments is needed to determine generalized pat-
terns of altered land-surface temperature by solar energy. A modeling study by Taha [19]
found that a large scale Pv installation in los Angeles—characterized by common roofing
materials, concrete, and asphalt—would reduce the urban heat island effect and cool cit-
ies up to 0.2°C. Another modeling study in the desert found that local night-time tem-
peratures were 3–4°C higher in solar facilities than nearby control areas [20]. Furthermore,
panels and mirrors may create an insulation effect due to physical shading and airflow
alterations. This was demonstrated at a CSP plant in China, where soil temperatures were
reported as being 0.5–4°C lower in spring and summer and higher by the same range in
winter relative to control sites [21]. However, nemet [22] found that the effect of albedo
change due to widespread deployment of Pv globally would be negligible in comparison
to the benefits of reducing greenhouse gas emissions from the same deployment intensity.

20.3 Ecological Impacts and Responses

Ecological responses to disturbance and development are well studied, although few stud-
ies have quantified effects of displacive installations on the biota, habitats, and ecosystems
occurring within or near their footprints. Displacive and large (e.g., USSE) installations may
negatively or positively affect a diversity of biota (Table 20.1). Effects likely depend on the