The Heat Island Effect in cities has the potential to reduce quality of life in many of the world’s most populous cities by locally raising outside temperatures. At the heart of the problem is the energy intensity of indoor climate control that requires ever increasing amounts of energy to sustain. Inconvenient facts of thermodynamics drive a positive feedback that exaggerates the problem. The detailed management of heat gains and losses using new technologies of vacuum glazing and the next generation of transparent high efficiency thin film photovoltaics is the best way to reduce the importation of energy into cities, assisted by convenient facts of optics. In this paper, I will discuss ways to make better use of available light using customised photovoltaic design and ways in which energy flows can be managed using glass-integrated thin film devices that incorporate metal-halide perovskite solar cells. These solar cells can be designed to maximise the use of parts of the solar spectrum for energy production. A key aspect of the designs is the underlying science of glass, which has ion diffusion properties that allow in glass fabrication of devices for energy transport and signal transmission.