Green-Roof Photovoltaics

he combination of green roofs and photovoltaics (green-roof PV) offers both ecological and economic benefits. Green roofs serve as natural insulation and contribute to improving the climate in towns and cities by lowering temperatures in urban areas, reducing energy consumption, and improving air quality. They also promote biodiversity, provide habitats for plants and animals, and reduce rainwater runoff.

PV modules on green roofs efficiently utilize existing space and offer additional benefits. The combination of green roofs and PV not only enhances ecological sustainability but also opens up economic opportunities. Photovoltaic electricity generation helps to reduce CO2 emissions and allows building owners to generate their own electricity and reduce energy costs. Our work focuses on urban climate modeling, economic evaluation of green roofs and green-roof PV, yield prediction, monitoring of PV-specific and biological Key Performance Indicators (KPIs), and life cycle assessment (LCA).

Our R&D Services on the Topic »Green-Roof Photovoltaics« Include:

• Techno-Economic Evaluation of Green Roofs and Green-Roof PV
• Simulation, Yield Assessment, and Monitoring of PV Green-Roof Systems
• CFD Wind Simulation Coupled with Thermal and Mechanical FEM Simulations
• Planning Support for Green-Roof PV
• Expert Opinions and Consulting on Mandatory Green-Roof Requirements

We conduct techno-economic evaluations for both green roofs and the combination of green roofs with photovoltaic systems for individual roofs as well as for typical roof sizes under different boundary conditions. The results can be used, for example, for individual economic decisions or the preparation of green-roof or PV green-roof cadasters.

In economic assessment, costs and benefits are weighed up against each other. A green roof not only causes installation and maintenance costs, but also offers economic and other benefits. These benefits include an extended lifespan of the roof sealing, savings on rainwater drainage fees, and reduced heating and cooling costs, which can also contribute to the economic viability of a green roof.

When combining a green roof with photovoltaics, special conditions arise that also influence economic viability. For example, the PV yield can increase due to the cooling effect of the green roof on the solar panels. Additionally, the optimal orientation and inclination of the photovoltaic modules should be determined, as the spacing between the modules must meet the requirements for maintaining the green roof.

Using our in-house simulation platform "ZENIT©," we conduct simulations to estimate the yield of your green-roof PV project. Light availability behind or beneath the modules can be modeled using ray-tracing approaches. Our monitoring determines key performance indicators of the system from the measured data. The PV systems are continuously monitored to ensure they operate efficiently and to quickly detect potential failures or performance losses – for example, due to soiling. Meteorological parameters such as wind speed, rainfall, and solar radiation can also be measured to monitor the microclimate around the PV system. Thermographic images of the system can be quickly and comprehensively recorded using drones.

We use multi-physical simulations based on the Finite Element Method (FEM) to investigate the specific effects of the PV modules on the green roof and vice versa. For example, we couple fluid dynamic wind simulations with thermal simulations to evaluate the influence of the PV modules on the temperature of the green roof and simultaneously assess the cooling effect of the plants on the PV modules. We also evaluate the impact on mechanical loads from wind conditions through coupling with mechanical FEM simulations. Additionally, we assess hotspot risks, such as from bird droppings, using electro-thermal simulations to evaluate the suitability of different module types.

We participate in the planning of green-roof PV projects and are responsible for clarifying technical questions and obstacles. One of our focal points is analyzing construction processes. We also deal with the different trades (actors, roles) and their interactions, as well as the construction subprocesses and their structured workflow. Moreover, we support planning by simulation, for example, for technical planning as well as yield and economic analyses.

With the ongoing climate change, more and more cities are asking what specific measures can be taken to adapt to new climatic conditions. One way to combat local heat islands in cities is to install green roofs. For this reason, there are already some cities in Germany and other countries where green roofs have become mandatory or this is currently under discussion. In this case, the installation of green roofs for new buildings or roof renovations is mandatory. The combination of mandatory green roofs with a requirement to install PV systems is also possible. We consult expert opinions to examine how such regulations should be structured and to determine the roof sizes for which the green-roof requirement or the combined solar green-roof requirement (PV or solar thermal) is economically viable.