A Vienna high-rise building’s architecture required a variety of solar modules in different shape and sizes, thus demanding a power electronics solution that could go beyond the typical PV design.
The University of Technology Vienna (TU Wien) had a lofty goal of making its high-rise chemistry building super energy efficient and powered by solar.Howeverr, solar on a high rise is a challenge. Roof space tends to be limited in proportion to the amount of energy needed to power such a tall building. As a solution, the designers decided to implement building integrated photovoltaics (BIPV) right on the building’s façade, making full use of all of that vertical space and generating a maximum amount of energy from the sun.
The lead designer on the project was Florian Jamschek, who was head of the photovoltaic department of fiegl und spielberger that installed the high-rise project, and is currently CEO at ehoch2 energy engineering. He said they had aimed to use standard modules, but “architecture and the existing building parameters forced the use of a variety of modules.” To increase the energy generation, power electronics technology that breaks through the typical PV design limitations was required to enable the integration of 332kW PV into 2,199 sqm of the building’s façade.
Flexible inverter solution
Jamschek chose the SolarEdge DC optimized inverter solution, which includes power optimizers, inverters, and a cloud-based, module-level monitoring platform. This system allowed for installation of 49 different module types to be easily placed in the system like Lego’s without the standard design limitations. While the module-level MPPT overcame module-level mismatch therefore increasing energy production of the original system designed with a traditional inverter, the SolarEdge solution further increased system size by 5% as it enabled use of the entire façade. This was achieved through its design flexibility, which allowed strings up to 44 modules, 49 different module types in the system, and strings of different lengths. This flexibility increased the site’s specific production from 30 to 40 kWh because most of the panels are two glass panes (2x6mm) in different length and width (some of the different variations: 200x1055mm, 200x735, 1860x1055, 1860x735, 1640x1055, 1640x735, 1560x1055, 1560x1115, 1905x840, 2045x840).
On the building facade, different types of insulated glass panes with 2x6mm (thickness) for photovoltaics and 2x 1x5mm normal glass panes with distance from each other for insulation were also used. On the roof, the panels are both standard framed modules and framed modules with glass panes used for the canopy. Because of the shape of the roof and the façade on the east side, a few dummy modules were used for appearance. Most of these modules are triangle in shape. Most of the modules on the east side, even if they are odd shapes, are also connected to the inverters and produce energy.
Solar panel test and installation
The solar modules are from PVP an Austrian producer. They specialize in glass panes made in specific shapes and sizes for each customer. Jamschek said that this is one reason they chose PVP. “It is not very easy to find a company that produces such a wide variety of different modules and dummy modules.” Another reason was that they had to put the modules through a very strict fire safety test in Linz, where they had to rebuild a part of the façade in a room and engineers “burned” the façade with different temperatures to find out how long is the resistance of the flames. Having the module manufacturer be relatively local was an advantage because they had to react quickly to supply the modules for the test.
The modules are attached like a normal glass façade with special cover strips. While the installation and attachment of the modules was not challenging, because it was handled as any other glass installation, careful handling was required due to the fact that solar panels cost more than simple sheets of glass.
As the building was built around 1970, it presented additional challenges to the installation of BIPV. For example, the distance from one window to the next required fitting in different modules of different sizes. Jamschek said that “If the building had been designed for a BIPV system, then it would have been easier to use more of the same modules and reduce costs.”
The system consists of 19 SolarEdge SE17K inverters and 1,135 SolarEdge power optimizers. Through the use of the SolarEdge DC optimized inverter system the wiring was much simpler than previously expected, Jamschek noted. “The installer only had to use special seals to get through the tight layer of the façade. At first there was a normal inverter layout planned, but after the installation the architect was very happy of the advantages of the SolarEdge system.” The SolarEdge solution allows <11.25kWp/string, thus enabling longer strings and therefore fewer strings for <50% reduction in BoS costs.
Another key issue with safety was the module-level shutdown. SolarEdge’s SafeDC which meets the R11 safety standard without any additional measures, provides automatic module-level shutdown to safe voltage, which is key with panel integration.
The SolarEdge module-level, cloud-based monitoring platform offers transparency into the system’s energy production, which enables researchers at the University of Technology Vienna to use the results to create a new standard for sustainable building renovation.
The project was completed in November 2014, which has given the university plenty of data, not the least of which is knowing that it has saved >54,000 kg of CO2 emissions saved, which is the equivalent of nearly 200 trees planted or nearly 420,000 lightbulbs powered for a day. The indirect benefits are the potential future sustainable building standards that will be developed from this project. The example provided by the University shows not only the possibility of PV, but the ability to create energy-plus commercial buildings from existing infrastructure. By overcoming module-level mismatch and providing design flexibility, the SolarEdge DC optimized inverter solution increased the site’s specific annual production by 30 to 40 kWh, which provides the University with a quicker RoI for the system.
Written by Anne Fischer, Managing Editor, Solar Novus Today