Vegetation monitoring between the PV panels. © Stuart Connop
Cities dominated by impervious artificial surfaces experience numerous negative environmental impacts. Incorporation of nature-based solutions, such as restoration of green infrastructure, is a mechanism for reducing these environmental impacts enabling cities to transition towards more sustainable futures. Building rooftops often represent the greatest potential for widespread roll out of green infrastructure in high-density urban areas. Urban rooftops also provide prime locations for photovoltaic (PV) systems. Initially viewed as two technologies competing for roof space, there is increasing recognition that these two technologies can be combined to deliver reciprocal benefits in terms of energy efficiency and biodiversity targets. Scarcity of scientific evaluation of the interaction between PVs and green roofs means that the potential benefits remain poorly understood and rollout has therefore been limited.
Whilst studies are beginning to emerge about the beneficial effects that growing vegetation around rooftop PV systems can have on the improved energy efficiency of the panels, very few studies have investigated how PV panels interact with green roofs in terms of enhancing the biodiversity value of the roof. PVs have the potential to enhance the range of habitat niches available on green roofs by creating varied microclimates that plants, insects and other wildlife can exploit. A team of TURAS researchers from the University of East London Sustainability Research Institute have carried out a study on a substantial (0.25 ha) biosolar roof created in the Queen Elizabeth Olympic Park, London, to investigate just this. The roof was originally designed to be a biodiverse green roof supporting a mosaic of habitats to enhance biodiversity. PV panels were added later in order to meet carbon efficiency targets. Initial results have been published as part of a green roof ecology special edition journal.
Biosolar roof on the Queen Elizabeth Olympic Park, Stratford, London, UK. © Stuart Connop
The study involved recording vegetation and invertebrate communities and measuring habitat structure in relation to habitat niches on the roof, including those created by the PV panels. Results have been very positive with ninety-two plant species being recorded on the roof and variation in vegetation structure associated with proximity to PV panels. In addition to this, almost 50% of invertebrate species collected across the biosolar roof were designated of conservation importance. Invertebrate species recorded during surveys of particular interest included the UK Biodiversity Action Plan bumblebee species the brown-banded carder bee (Bombus humilis), the Olympic Park Biodiversity Action Plan target species the toadflax brocade moth (Calophasia lunula), and a spider that has never been recorded in the UK before (Tegenaria hasperi). Other species utilising the roof included the Wildlife & Countryside Act protected and London Biodiversity Action Plan listed black redstart (Phoenicurus ochruros), and the UK Biodiversity Action Plan species the linnet (Carduelis cannabina).
Results of the initial study supported the theory that PV panels can contribute to the overall niche diversity on a green roof. Results were so encouraging that further detailed study was carried out to fully characterise the microclimates associated with the PV panels.
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Black redstart perched on a PV panel. © Stuart Connop
Biosolar roof in full bloom © Stuart Connop
Toadflax brocade moth caterpillar in front of a PV panel. © Stuart Connop