Abstract
Assessment of mitigation strategies that combat global warming, urban heat islands (UHIs), and urban energy demand can be crucial for urban planners and energy providers, especially for hot, semi-arid urban environments where summertime cooling demands are excessive. Within this context, summertime regional impacts of cool roof and rooftop solar photovoltaic deployment on near-surface air temperature and cooling energy demand are examined for the two major USA cities of Arizona: Phoenix and Tucson. A detailed physics-based parametrization of solar photovoltaic panels is developed and implemented in a multilayer building energy model that is fully coupled to the Weather Research and Forecasting mesoscale numerical model. We conduct a suite of sensitivity experiments (with different coverage rates of cool roof and rooftop solar photovoltaic deployment) for a 10-day clear-sky extreme heat period over the Phoenix and Tucson metropolitan areas at high spatial resolution (1-km horizontal grid spacing). Results show that deployment of cool roofs and rooftop solar photovoltaic panels reduce near-surface air temperature across the diurnal cycle and decrease daily citywide cooling energy demand. During the day, cool roofs are more effective at cooling than rooftop solar photovoltaic systems, but during the night, solar panels are more efficient at reducing the UHI effect. For the maximum coverage rate deployment, cool roofs reduced daily citywide cooling energy demand by 13–14 %, while rooftop solar photovoltaic panels by 8–11 % (without considering the additional savings derived from their electricity production). The results presented here demonstrate that deployment of both roofing technologies have multiple benefits for the urban environment, while solar photovoltaic panels add additional value because they reduce the dependence on fossil fuel consumption for electricity generation.
Highlights
Many studies reveal that the large-scale deployment of roofing technologies is an effective means of reducing energy consumption (e.g., Akbari et al 2009; Oleson et al 2010; Menon et al 2010; Salamanca et al 2012a; Cotana et al 2014; Georgescu et al 2014)
We use the non-hydrostatic (V3.4.1) version of the Weather Research and Forecasting (WRF) model (Skamarock et al 2008) coupled to the multilayer building energy (BEP+building energy model (BEM)) system (Salamanca et al 2011) to characterize the diurnal cycle of near-surface air temperature and citywide air-conditioning electricity consumption
Our results demonstrate that the deployment of cool roofs and rooftop solar photovoltaic panels reduce near-surface air temperature and cooling energy demand at the scale of the metropolitan area
Summary
Many studies reveal that the large-scale deployment of roofing technologies is an effective means of reducing energy consumption (e.g., Akbari et al 2009; Oleson et al 2010; Menon et al 2010; Salamanca et al 2012a; Cotana et al 2014; Georgescu et al 2014). By virtue of increased reflectivities, absorb less incoming shortwave radiation than dark roofs, thereby promoting a lower skin temperature. The potential penalty associated with cool roofs is in general outweighed by the summer benefit and can be annulled if the roofs are typically covered with snow during the cold season (Bretz and Akbari 1997).
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