Comparative energy and greenhouse gas assessment of industrial rooftop-integrated PV and solar thermal collectors

Solar technologies are a clean source of energy with no emissions during their usage phase, however, not all solar technologies are created equal in terms of their total impacts over their life-cycle. While many life-cycle assessment (LCA) studies have investigated solar photovoltaics and-to a lesser extent-solar thermal technologies independently, there are very few direct comparisons between these technologies due to differences in their design/sizing, boundaries, location-specific performance, and several other factors. However, since electricity can be converted to heat (and visa-versa), it is clearly possible to make such a link to holistically compare different solar technologies with respect to an intended application. To address this, the following article provides an LCA methodology to comparatively assess the environmental impact of solar thermal (ST) and solar photovoltaic (PV) technologies from cradle through the usage phase (noting that end-of-life impacts for these systems are still uncertain). That is, characteristic collector types which could be employed on factory and commercial rooftops were evaluated based on their embodied energy payback time (EPBT) and greenhouse gas emission payback times (GHG(e) PBT). Characteristic geographical locations were also analyzed since the equivalent carbon dioxide impact can vary between regions and these technologies due to differences in the available solar resource and the primary energy mix, they offset. This research also presents new data and an original assessment for a linear Fresnel collector which is suitable for industrial rooftops. The analysis revealed that the EPBT and GHG(e) PBT varied between 1.2 and 15 years and between 2 and 17 years, respectively, for the solar technologies and geographical locations considered in this study. The results also indicate that an ST collector system has a lower EPBT in high direct normal irradiation locations than a monocrystalline PV system. However, in terms of the GHGe PBT, the findings do not reveal a conclusive verdict for or against ST versus PV technologies. Overall, this study provides a new, global comparison between ST and PV solar technologies for industrial applications. This work is significant since many manufacturers around the world are considering utilizing their factory rooftop space for solar energy harvesting. As such, the proposed LCA method provides guidance for manufacturers, policymakers, and future sustainability reporting standards, to determine which solar technology achieves the fastest EPBT and GHG(e) PBT if the local solar resources and primary energy mix are known.