Roofing Materials Can Reduce Power Demand In Urban Spaces

Soaring temperatures are hard to ignore, and they are no longer limited to particular regions prone to heat waves. July 2023 was the hottest month on record for the entire globe, and several heat records were set throughout the summer. Cities, in particular, are vulnerable to heat and contain infrastructure materials that amplify it. Streets, high-rise buildings, and reduced foliage from development contribute to the bottling effect of heat within urban areas. 

 

   

Heat-reflecting white surface being applied to a roof. Image used courtesy of the U.S. Department of Energy

 

However, engineers are exploring roofing materials that can reduce temperatures inside and outside structures. Such reductions can significantly impact power demands as grids are strained from ubiquitous air conditioning usage. 

 

The Heat Island Effect 

Simple calculus explains the way heat becomes trapped in modern urban spaces. The materials used to build up cities absorb and reemit the sun's heat. Steel, asphalt, and other common materials raise ground temperatures even more, making the sun and urban building materials dual sources of the heat island effect. 

 

Comparative temperatures for rural and urban areas. Image used courtesy of ResearchGate

 

Fatalities are the most severe impact of the heat island effect, and one study that assessed 93 European cities found that 6,700 premature deaths were the result of urban heat islands (UHIs). Overall health is also compromised, especially for children and older adults. UHIs exacerbate respiratory conditions in children, and for the elderly, chronic heat exposure can increase the risk of stroke and impact cardiovascular demand, which is fatal in some cases. 

In addition to creating and exacerbating personal health challenges, UHIs compromise environmental stability. Urban infrastructure can raise stream water temperature by 7°F as stormwater runoff is heated by asphalt and other building materials on its way to natural bodies of water. Such abrupt temperature increases can compromise ecosystem stability and harm various species living in the water, causing cascading impacts on the natural environment. 

Carbon emissions also rise in UHIs from increased electricity use, so problems associated with UHIs span the human, animal, and environmental spectrums.

This increased electricity use places more demand on the utility grid, leading to large peak loads that can jeopardize grid function. Researchers have been able to quantify a precise relationship between these urban increases in temperature and the corresponding spike in electricity needs. Every time the temperature rises a single degree, the peak electricity load also increases, varying between 0.45% and 4.6%. 

The cumulative impact of increased electricity loads can lead to grid failure events, including blackouts, jeopardizing the safety of older people and those on medical support devices. A recent peer-reviewed article that analyzes a model designed to predict the consequences of power grid failures in urban areas found that if Phoenix experienced a power grid failure for five days, the death toll would rise to 13,000 residents. Such catastrophic grid failures are not outside the realm of possibility as temperatures soar and multiple sectors tax the grid. 

 

The Efficacy of Heat-Reflecting Cool Roofs

A research team at the U.S. Department of Energy's (DOE) Argonne National Laboratory has been investigating the impact of various types of roofing material to give stakeholders key information about how roofing strategies impact power demands.  

The team found significant statistical differences concerning the relative performance of three roofing materials. They studied cool roofs, green roofs, and solar panels. Cool roofs are treated with heat-reflecting white paint, and green roofs refer to foliage as roof coverage, which some may recognize from modern rooftop renovations.    

 

Temperature variations from different roofing materials. Image used courtesy of ScienceDirect

 

The data from the model shows the efficacy of the cool roof and how there is a significant difference in near-surface temperature for each type of roof. All three roof types lowered the demand for air conditioning during daylight hours, but cool roofs outperformed green roofs and solar panels. There was a 1.5°C drop in near-surface temperature for cool roofs, while green roofs caused a 1.2°C drop, and solar panels resulted in a 0.6°C drop.

While green roofs offer other benefits than cool roofs, including managing stormwater in areas prone to flooding, they cost more to maintain. They will use water unless local weather patterns are precipitation-heavy.

The cool roof was the cheapest and most effective option. 

 

The Power Payoff 

Argonne National Laboratory’s study also charted a corresponding drop in energy demand that matched the incremental decrease in temperature, showing a clear correlation between near-surface temperature changes and overall power demand.

Even marginal reductions in electricity use are a major gain for power grid function. As temperatures climb, the electric vehicle market grows, and other utility demands increase, it is imperative that engineers find new ways, such as innovative roofing strategies, to maintain grid function and manage utility allocation.