Generating solar power on building facades

Using photovoltaic elements on facades could be a useful way to supplement solar energy supply, new research suggests.

Researchers at the Fraunhofer Center for Silicon Photovoltaics CSP have discovered that if they are appropriately designed, these elements can be attractively integrated and deliver 50% more energy than existing types of wall-mounted PV elements. Even concrete walls are suitable.

While PV elements on roofs receive the most sunlight, it makes sense to have them on building facades. Firstly, they make use of otherwise unused space, and secondly, the energy they collect can usefully supplement the power supply. However, given that the sun usually shines on facades at an unfavourable angle, and the elements themselves tend not to be aesthetically appealing, little use has been made of this opportunity.

In their SOLAR.shell project, researchers suggested — alongside architects at the Leipzig University of Applied Sciences (HTWK Leipzig) — that there is a way to remedy these problems.

“The photovoltaic elements integrated in this facade deliver up to 50% more solar energy than modules mounted perpendicularly on building walls. Plus the facade offers visual appeal,” said Sebastian Schindler, Project Manager at Fraunhofer CSP.

© Fraunhofer IMWS The photovoltaic modules in the SOLAR.shell facade element deliver up to 50% more solar energy than conventional, planar-mounted solar modules.

The HTWK architects developed the idea and designs. How do the individual photovoltaic elements have to be tilted in order to capture as much solar irradiation as possible? How large should the modules be, and how many solar cells should they ideally include? The team’s findings were presented in a 2 x 3 m demonstrator made of aluminium composite panels featuring a total of nine embedded solar modules. The Fraunhofer experts offered their experience, advice and assistance, and the photovoltaic elements used in the demonstrator likewise came from Fraunhofer CSP.

Solar modules on concrete facades

In collaboration with HTWK Leipzig and TU Dresden, the Fraunhofer CSP researchers also developed suitable options for integrating photovoltaic elements in concrete facades — more specifically in facades made of carbon concrete, a material developed by a consortium of more than 150 partners in the ‘C3 — Carbon Concrete Composite’ project. The required stability of the concrete comes from carbon fibres rather than steel wires.

“At Fraunhofer CSP, we analysed how photovoltaic elements can best be mounted on these kinds of carbon concrete facades — that is, how to obtain the optimum result when combining this novel concrete with the production of solar energy,” Schindler said.

To this end, the researchers devised three different concepts and methods for integrating the PV elements in facade sections. The solar modules can either be included directly when casting the concrete sections or be laminated on or bonded to the concrete slabs. The modules can also be attached to the concrete slabs using stud fasteners, screw connections or other means, facilitating easy removal for maintenance or repairs.

“We were able to demonstrate that all three mounting options are technically feasible,” Schindler said.

One of the main challenges is ensuring that the method used to produce the concrete sections is compatible with the required dimensional accuracy of the PV modules. This is done, for instance, by casting the concrete parts with a depression that is perfectly sized to accommodate a module. In this way, the desired orientation with respect to solar irradiation and the overall design are preserved.

“The dimensional accuracy should be implemented directly in the concrete section,” Schindler said.

It must also be ensured that the PV modules aren’t fastened where the concrete is particularly thin or where the carbon fibres are located, as this would impair the strength of the facade elements. The project has since been successfully completed.

SOLARcon: concrete facades 2.0

In the SOLARcon follow-up project — likewise in collaboration with HTWK Leipzig and TU Dresden, as well as two corporate partners, and launched in November 2019 — the Fraunhofer experts are now establishing marketable solutions for integrating PV modules into precast concrete slabs.

Will the solar cell mounting hold permanently? To answer this question, the Fraunhofer researchers are conducting appropriate endurance tests on both the PV components and the interface with the concrete. How does the interface behave under various weather conditions? What do accelerated ageing tests show? In addition to the experiment-based approach, simulations are also on the agenda — more specifically, finite element methods. These allow the experts to calculate, for example, how the concrete and the attachment point of the PV element heat up at high temperatures, or what wind and pressure loads the solar module must withstand.

Top image credit: © A. Heller, Architektur-Institut Leipzig (ai:L) A faceted design significantly increases the electricity yield, but it requires small, flexible solar modules.