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The Urban Heat Island Effect

 

Our cities and towns are growing hotter as a result of replacing natural vegetation with buildings and roads. A study by the Lawrence Berkeley Laboratory describes what effect urban heat has on business, people and the planet. As the air temperature rises, so do our cooling demands, gasoline consumption, power plant emissions, electrical grid loads and ozone formation or smog. this heat is also linked to various health problems people suffer day and night. 

 

Asphalt and concrete absorb much of this solar energy, raising surface temperatures 50-70 degrees hotter than ambient temperature. This material then stores and releases heat all day and night. A parking lot with the sun emitting 1000 watts per square meter at the surface, can heat to upwards of 150 F on a warm, sunny day. Solar reflectance for old asphalt is about .10, which means 90% of the infrared of suns heat, is being absorbed by the asphalt. Another example is the surface temperature difference between a white car and a black car might exceed 50 degrees. Which one would you prefer riding in? 

 

A study on urban heat island estimates that about 20% of the national cooling demand can be avoided through a large-scale implementation of heat island mitigation. This amounts to a 40TW annual energy savings or over $10B per year in direct cost savings. The study suggests simple methods like reflective surfaces and trees for shade. 

 

Our 1MW energy system covers about 3 acres. It reflects heat at heights to allow cooler air circulation below the canopy and around buildings. By lowering ambient temperatures reduces building cooling demands. Imagine parking under a shade tree that casts a 3 acre shadow! The closest equivalent to our 1MW power plant, would be planting about 300 adult shade trees.

 

By taking the steps like these to reduce urban heat island, we move toward decentralized power, gain power independence and increase the health and comfort of the people who live and work here.

 

(excerpts from Lawrence Berkeley National Laboratory, americanforests.org)