How large is the potential of rooftop PV systems in industrial properties and can such systems be operated economically? These questions can be answered with little effort using the simulation tool SimStadt. It provides reliable information for the decision-making process on the basis of available 3D building models.
Researchers from the Center for Sustainable Energy Technology at HFT Stuttgart demonstrate this using the example of an industrial property at the Schwieberdingen site of Robert Bosch GmbH.
Although photovoltaic systems with a capacity of 53 GW were already installed in Germany at the end of 2020, there is a large potential of 400 to 500 gigawatts in total for additional systems, especially in the rooftop sector, according to the Fraunhofer Institute for Solar Energy System ISE in "Current Facts on Photovoltaics in Germany" of December 19, 2020.
Industrial properties with large roof areas and low installation costs are particularly attractive. In order to be able to develop these in a targeted manner, tools are needed that provide reliable information on costs and potential early in the planning and decision-making process on the basis of a small amount of input data. A software tool developed in a lead role at the Stuttgart University of Applied Sciences enables the determination of hourly generation profiles and costs for rooftop PV systems based on available 3D building models. The entire calculation process was recently successfully validated for industrial plants at the Schwieberdingen site of Robert Bosch GmbH.
The studies have shown that reliable information on the installable potential and costs of rooftop PV systems can be determined on the basis of just a few key data. If an up-to-date 3D building model is available, reliable results can be obtained in just a few hours, even for a larger property. "This makes the decision-making process for or against PV systems at the site much more transparent and cost-effective, and avoids either relying purely on standard values for specific installation costs and solar yield or commissioning detailed planning at the very beginning of considerations," emphasize Andreas Biesinger, Tobias Fischer and Bastian Schröter in a recent article in the trade journal "ew – Magazin für die Energie-Wirtschaft" (2-3; 2021). Furthermore, it is advantageous that in SimStadt, based on the same 3D building models, heat consumption can also be modeled, for example, and thus integrated energy scenarios can be investigated. In addition, islanding models can be used to consider the effect of the benefits of battery storage in the event that potential on-site electricity generation exceeds consumption.
Due to steadily decreasing module prices, rooftop photovoltaic systems are becoming increasingly interesting even without EEG subsidies. However, the economic efficiency of a system depends on many factors in each individual case. For operators of an industrial property, it is therefore desirable to obtain a reliable estimate of the costs and potential of a rooftop system early in the decision-making process. On the one hand, this should take into account local specifications such as roof size, solar radiation and shading, but on the other hand it should not require the effort, data requirements and costs of detailed system dimensioning.
The simulation environment SimStadt, which was developed under the leadership of the Stuttgart University of Applied Sciences (HFT), provides such an initial assessment on the basis of 3D building models that are generally available throughout Germany. PV rooftop potential analyses using SimStadt have so far been successfully carried out mainly in the residential building sector, for example in a reference study Ludwigsburg Grünbühl for SimStadt.
Recently, the methodology was validated for the first time for an industrial property at the Schwieberdingen site of Robert Bosch GmbH (Fig. 1). In addition to installable capacity and expected hourly electricity generation, the installation and electricity production costs of the plants were simulated on the basis of dynamic specific costs, and the extent to which the results can be used for a basic investment decision as well as a basis for a detailed analysis was investigated. The study was carried out as part of the iCity research partnership at HFT Stuttgart, in which Robert Bosch GmbH is a major participant. The aim of the iCity projects is to develop holistic, sustainable solutions for urban neighborhoods and regions.
SimStadt is an urban simulation platform that supports project developers, real estate owners, energy providers, municipalities or districts in determining electricity and heat demand as well as the potential of renewable energies at the neighborhood level. The aim of SimStadt is not to compete with the accuracy of detailed planning tools, but rather to provide reliable information on the costs and potentials of targeted solutions early in the decision-making process based on a small amount of input data. In SimStadt, 3D building models in the file format CityGML are used (Fig. 1) to create demand and potential analyses in workflows, such as heating requirements, energy-related renovation options, dimensioning of (renewable) heating technologies, PV potentials, water consumption as well as biomass potentials, and to analyze them continuously from the neighborhood to the district. The application scenarios are continuously developed further. In addition to the existing desktop version, a browser-based web version is currently being tested.
For the rooftop PV analysis in SimStadt, the hourly solar irradiance on the 3D building model is first calculated over a year from local weather data sets, for which the dynamic simulation environment Insel is used. Due to the use of 3D models based on CityGML, much more accurate potential calculations can be performed compared to the use of models generated from aerial photographs or floor plans. Above all, different radiation models as well as shading effects from neighboring buildings and different roof heights within a building can be taken into account. The installable potential (in kWp) is calculated from the hourly surface irradiation via the ratio of module surface to roof surface. The 3D building model in CityGML format is sufficient as input for these analyses.
In principle, this data can be obtained throughout Germany from the state land surveying offices. Despite continuous data updates, however, as in the case of the Schwieberdingen site, outdated or incomplete data may be available, especially for larger industrial properties, due to frequent additions and conversions. Missing building information is naturally present for properties that are in the planning stage. In order to close the gap of missing building information, it was first investigated to what extent a 3D building model can be updated using freely available software such as Google Maps/Earth and OpenStreetMap (OSM) in conjunction with the widely used 3D building design software SketchUp.
With a defined area factor of 0.3 for the suitable buildings, this results in an installable capacity of 1.5 MWp for the Schwieberdingen site in addition to the existing capacity of 0.8 MWp. A further potential of 7 MWp (area factor 0.6) can be realized on the parking lots of the property by roofing them over, which means that an additional 9.2 GWh of electricity can be generated annually in total if the modules are oriented to the south. In the case of the Schwieberdingen site, 99.5% of the electricity generated can be used on site. An installation of battery storage is thus not planned for an optimization of self-consumption. The solar coverage of the electricity demand reaches an annual average of 16%.
In addition to the installable capacity, an early estimation of investment costs, payback period and levelized cost of electricity (LCOE) of a plant is crucial. In SimStadt, constant specific installation costs were previously replaced by a degressive cost function. This means that the specific installation costs (in €/kWp) decrease with the size of the system (from 1775 €/kWp for 1 kWp to 1328 €/kWp for 100 kWp). The values can be adjusted individually. For the Schwieberdingen site, this results in installation costs of €3.2 million for the usable building areas. Assuming that the specific installation costs for parking lot roofing are similar, this results in total costs of 10.2 million euros. The electricity production costs vary between 12.7 Ct/kWh and 18.9 Ct/kWh for an assumed system lifetime of 20 years and are below the electricity procurement costs at the site from a system size of 45 kWp, so that the systems are thus economically interesting.
The unabridged article can be found in https://emagazin.ew-magazin.de/ March 2021
SimStadt – Overview and project goals: https://simstadt.hft-stuttgart.de/de/
Reference study Ludwigsburg Grünbühl for SimStadt: http://simstadt.hft-stuttgart.de/de/examples.jsp
Research project iCity: http://icity.hft-stuttgart.de/#/