MONETARY ANALYSIS OF THE COLOCATION OF SOLAR AND GREEN ROOFS IN SINGAPORE

Abstract

Singapore's densely populated, and highly urbanised landscape exacerbates the Urban Heat Island (UHI) effect, amplifying the impact of rising global temperatures stemming from climate change. Curbing the cooling load demand of indoor occupants is becoming increasingly crucial, and this can be seen in the recent developments of various infrastructures and even buses implementing greenery in its facades to keep interior temperatures lower (Building Construction Authority, 2010). On the other hand, reducing greenhouse gas (GHG) emissions encourages the switch to solar energy, it being the only viable renewable energy source for Singapore, given its geographical characteristics. With plants capability to reduce ambient temperatures, research overseas has explored the collocation of PV green roofs to improve panel efficiency. In Singapore's context, this integration of PV-green roofs also navigates the competition for roof space between the separate PV roof and green roof systems. While much research has explored the lower temperatures, improved energy efficiency and lower energy consumption of the collocation, little research has quantified these on a common monetary scale, much less explored it with the consideration of Singapore's monsoon seasons and building occupancy periods. This study aims to compare and quantify the benefits of a collocated PV-green with a PV-concrete roof, by tagging a dollar value to the renewable energy generated and the avoided energy consumed from reduced cooling load demands. This was done by calculating the energy generated and energy avoided from lower cooling demands and multiplying it with Singapore's electricity tariff. It was found that regardless of monsoon seasons, indoor temperatures below PV-green roof were indeed lower than PV-concrete. However, energy generation was not always enhanced with the collocation, and PV-green roof generated lower energy during Northeast monsoon and inter-monsoon (October and November) seasons. As the bulk of monetary savings is contributed by energy generated, this meant that during these monsoon seasons, PV-green roof did not present greater overall monetary savings compared to PV-concrete roof. These findings highlight that there is a trade-off for the collocated roof, and provides a greater emphasis on the need for deeper analysis into whether collocation has an overall net benefit.