Global solar technology optimization for factory rooftop emissions mitigation

The industrial sector consumes similar to 32% of the world's final energy demand, most in the form of heat which is derived primarily from fossil fuels. Two fundamentally different technologies exist for harvesting sunlight to offset fossil fuel use-solar thermal (ST) and photovoltaic (PV) collectors. The former convert sunlight into heat while the later convert sunlight directly into electricity (although electricity can be converted into heat via heat pumps and/or resistance heating). If/when factories transition towards utilizing their rooftops for solar harvesting, an essential question will be: which solar technology, or a mix of technologies, should be chosen for factory rooftops? This paper investigates this (as yet unanswered) question by assessing the global greenhouse gas emission (GHG(e)) mitigation potential of PV and ST collectors in a side-by-side mix (e.g. a percentage where 0% is solely PV and 100% is solely ST available roof area coverage) to supply medium temperature heat (150 degrees C-400 degrees C) for industrial processes. It was found that in most locations globally, a mix of both technologies optimizes the solar output. Globally, installing the optimum PV:ST mix can save up to 141.8 or 205.8 kt CO2e over installing solely PV or solely ST collectors, respectively. Another interesting finding of this study was that GHG(e) mitigation potential stems largely from where the solar collectors were manufactured (i.e. the embodied emissions from using local primary energy to fabricate the collectors). Thus, this study reveals that project managers, policymakers, corporate sustainability directors, etc could achieve maximum global GHG(e) mitigation through simply considering a mix of solar collector technologies and the best practices for manufacturing them.