## 2 Background
To gain a better understanding of the effects of PV shading on plants, studies related to agro-photovoltaics and studies in the context of shading in greenhouses were analyzed. One review study stated that shading by PV panels will influence the harvest: this can lead to declining crop yields, but may also lead to harvest increases, depending on the species type and intensity of shading [26]. Similar results were found in studies on the effects of shade on agricultural production. Tests on _Actinidia_[27] and _Solanum_ led to the discovery that the shading of plants increases their health, but too much shade can decrease their productivity. These publications mentioned that the effects also depend on the variety of the species. A Study on _Helianthus annuus_ showed that the grain number decreased with shading up to 20% of incident radiation [28]. While especially in urban environments, the implementation of green roofs (GRs) is increasing due to the growing understanding of the multiple benefits involved, renewable energy generation is similarly on the rise, as cities need to fulfill ambitious climate goals. In Austria, the contribution of PVs to domestic energy consumption has steadily increased from 0.1 PJ in 2005 to 3.9 PJ in 2016. In their climate and energy strategy, \"Mission 2030\", the Austrian government set itself a target of covering 100% of national electricity consumption with renewable energy sources by 2030. The strategy also states that optimum use should be made of all available surfaces for integrated photovoltaics [14]. Buildings play, in this context, a key role in providing suitable areas for implementing renewable energy systems such as photovoltaics (PVs). In dense urban environments, building skins, and in particular roofs, offer mostly unshaded surfaces to generate solar energy. The increased efficiency of PV systems [29; 30] and the reduced costs of PV modules [31] make it increasingly more economical to include mounted or building-integrated photovoltaic systems (BIPVs) [32] in construction projects. In Vienna, the recently updated building code supports the implementation of PV systems, as it covers requirements for highly efficient and alternative technical building systems [33]. As green infrastructure and renewable energy applications are essentially competing for the same surface areas, it is only logical that suitable solutions must be found that combine the benefits of both. A recent study by [PERSON] et al. stated that the onsite production of photovoltaics, as well as agro-urban production on rooftops, contributes to decreasing their environmental impacts [34]. So far, however, it seems that photovoltaic energy production as well as roof greening still constitute exclusive choices in terms of ecological uses for a roof [35]. Even though there are numerous benefits related to the symbiotic combination of vegetation and energy generation, the number of solar green roofs was still considerably small in 2018 and was practically nonexistent a few years before that [36]. Because the market has reacted to this gap, systems for the combination of GRs and PVs have been developed. Studies on the functionality of this combination have mentioned an increase in energy production due to the cooling effects of green roofs [24] and positive effects due to the species richness of insects [37] and plants [35], but they have also reported negative effects due to the shading of plants on PV panels and the mounting of panels (which hinders proper maintenance) [38]. On the ground,agro-photovoltaics (the dual use of land for both energy generation and agriculture) have solved this problem through the use of highly elevated panels, where machinery can work underneath to allow for plant harvesting or animal pasture. In addition, there is still a lack of technical solutions for the construction of intensive green roofs in combination with PVs (which would allow for higher substrate layers): this would be more suitable for storm water retention and biodiversity compared to shallow extensive green roofs.