Electrochromic glazing and facade photovoltaic panels: a strategic assessment of the potential energy benefits

This paper describes a methodology to compare the energy benefit that may result from the adoption of two very dfferent facade technologies in non-domestic buildings. A comparison is made of the energy benefit that might result from: (a) replacing conventional glass with electrochromic glazing; and, (b) installing PV panels across the opaque sections of vertical facade. The energy benefit from electrochromic glazing is predicted on the basis of displaced electric lighting usage against standard glazing with blinds, whereas the energy benefit from facade PV panels is equal to their delivered electrical output. The evaluation setting is a 'typical' six metre deep perimeter office space with vertical glazing. Office orientations for each of the four cardinal compass points are considered. Performance evaluations are founded on a full year's hourly meteorological data for fourteen locales across the world. The predicted energy benefit from electrochromic glazing and facade PV are related to the total annual vertical irradiation incident on the building facade. The findings indicate that the energy benefit that results from replacing standard glazing with electrochromic glazing may exceed that of facade PV for the majority of cases studied. Surprisingly, electrochromic glazings are found to provide the greatest energy benefit for those cases at the lower end of the experienced range in total annual vertical irradiation. The effectiveness of widespread deployment across multiple facades for each locale is examined. The likelihood that electrochromic glazing alone can offer sufficient solar protection without recourse to additional shading is assessed using the recently formulated useful daylight illuminance scheme.