Conclusions Conclusions Cities occupy around 2% of the land surface area, use 60–85% of its energy, and emit 70% of the world's CO2 emissions. In the following decades, countries will become even more urbanized, with a global population of 70% expected to live in cities. In response to these patterns, the City of Sydney emphasized the significance of cities in climate change mitigation. Our cities are warmed by human-caused emissions of glasshouse gases, but the nature of urban form influences the surface energy balance, which is defined by a higher proportion of available energy being exchanged as sensible heat, adding to localized warming. Other than that, a large amount of remote-produced energy is imported directly to deliver energy services in the form of electricity and gas for domestic, industrial, and commercial consumers. This generates heat that contributes even more locally to the overall global warming trend. To lessen cities' and people's exposure to heat, a variety of approaches have been proposed, including surface geo-engineering, which involves painting surfaces with lighter colors to reflect more sunlight back into space, and vegetated roofs. These technologies have a high up-front cost and ongoing maintenance requirement, but the advantages to the environment can more than compensate for those drawbacks. Solar photovoltaic (PV) system deployment on a wide scale could be a geo-engineering solution for cooling cities. Solar power systems (mainly photovoltaic, although concentrating solar plants are also a possibility at the utility scale) are commonly investigated for their ability to generate electricity, with the related direct economic benefits and indirect impacts on CO2 emissions and climate16. Examples include the widespread use of solar panels in the desert, which can both decrease localized temperatures while also having minimal effects on global temperatures. According to estimations, there is a huge amount of solar energy that can be harvested. Large-scale urban PV installations can increase the heat absorption due to the low albedo of PV panels. This could enhance a city's solar energy load and thus the UHI effect. There is no need for energy to be generated remotely and subsequently imported if a city can produce enough power to meet its local needs using solar energy, including any higher energy demands because of the reduced albedo associated with solar panels. Because the solar panel does not effectively warm an urban surface, avoiding energy imports limits the overall amount of energy added to the system. An alternative would be to use the energy to generate electricity, which would be exported as heat over time and reduce the requirement for imported energy. When used in combination with white roofs, vegetated roofs, green facades, high albedo paints on the roads, solar panels can reduce daytime temperatures in a similar way as enhancing albedo, but they also generate useful electricity. The reduction or even removal of imported energy reduces the city's overall energy footprint, provides a financial return to PV system owners, and may cool a city to provide a free benefit to the environment and even a financial saving to individuals who do not have solar panels. This cooling can reduce construction and human health risks while also improving quality of life. The magnitude of these advantages and the value of the reduction in temperature and the generating of electricity are estimated independently.
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