Brief Concept Description

Lumiduct is an innovative building-integrated concentrating PV (BICPV) façade system that uses an array of movable panels located in the cavity of double-skin façades to guide the incoming sunlight, so to provide shading control to glazed building façades and harvest solar energy.

The Lumiduct panels consist of special optical modules that redirect direct sunlight, and concentrate it onto tiny, ultra-high-efficiency III-V solar cells. Since the Lumiduct modules have a concentration factor above 600, the electricity generation potential per m2 façade is similar to the output of vertically mounted regular crystalline PV modules. In order to track the sun over the course of the day, the technology includes a dual-axis tracking system. An example of a single module, including the sun-tracking structure, is presented in Figure 76 (left).

This solution is developed by the company Wellsun, in close collaboration with Eindhoven University of Technology and Radboud University Nijmegen. It is currently in the technology readiness level 7, which corresponds to a demonstration system operating in an operational environment at pre-commercial scale.

Architectural and Technological Integration into the Envelope

Lumiduct is designed as a facade integrated solution, and not as separate modules to be added onto existing façades. The modules are installed into several vertical pillars, which are in turn integrated in the cavity of a doubleskin façade. Figure 76 (right) presents an example of the installation of the modules into pillars. 
The Lumiduct façade system can be connected to the building’s HVAC system. In this way, the warm air in the cavity can be used to pre-condition ventilation air, thereby reducing energy demand for heating. Another possibility is to harvest heat in the cavity of the double-skin façade using an air-to-water heat exchanger, so that the extracted thermal energy can either be used for space heating, or to satisfy domestic hot water needs.

Figure 76. Lumiduct module on the left and integration of multiple modules into pillars on the right.

Integration into the Building: System and Comfort

Since Lumiduct tracks the sun over the course of the day (dual-axis tracking), the direct part of the sunlight is always absorbed while the diffuse daylight passes freely. In this way, Lumiduct acts as a selective solar shading device, addressing multiple needs at the same time. Apart from producing electricity, Lumiduct significantly reduces solar heat gains and thus the space cooling load of the building. It also functions as a glare protection system blocking the direct solar radiation, while the diffuse daylight still enters the room and reduces the need for artificial lighting. An important side-benefit of Lumiduct, compared to regular solar shading systems, is that the view to outside and an enhanced access to the many health and well-being benefits of daylight is guaranteed at all times. Figure 77 presents an artist’s impression of the indoor environment with a full-scale building integration of Lumiduct. Figure 78 shows a bottom view of a 40 m2 demonstrator façade integrating Lumiduct.

Figure 77. Artist’s impression, full-scale building integration of Lumiduct.

Figure 78. Bottom view of the demonstrator façade of the Lumiduct BICPV system.

Lessons Learned

The lesson learned are summarized as follows:

• The required accuracy of the tracking system is a major challenge. A maximum deviation of 0.9 degrees for both tilt and rotational motion is allowed in order to capture direct irradiation and generate electricity. Moreover, it is required to have an accurate adjustment of the individual pillars relative to each other. Overall, this high accuracy needs to be achieved with low-cost hardware suitable for series production.
• The pillars that integrate the modules should be controlled as a collective, so the system can be integrated in a façade. A two-way communication protocol needs to be developed, to exchange information between the control and the pillars.
• Implementation of optimization measures in the circuitry of the solar cells within the modules, and between the modules and the power optimizers (maximum power point trackers) is necessary, to minimize the losses caused by self-shading of modules and shading from the surroundings.
• The dynamic characteristics and physical phenomena that take place inside the Lumiduct façade are not compatible with the range of possibilities offered in building performance simulation software. Performance prediction of Lumiduct therefore requires modification of simulation models at the source code level. This is a time-consuming task that needs to be carried out by specialists.

Further Reading

Website company Wellsun: http://www.wellsun.nl/lumiduct-design-and-sustainability.html

Submitted paper for the VIII International Congress on Architectural Envelopes (ICAE) as part of a PhD research at Eindhoven University of Technology. This publication evaluates the thermal and daylight performance of the sun-controlling dynamic façade system Lumiduct (Saini, Loonen, & Hensen, 2018).  

Investigation performed by Radboud University Nijmegen (RUN) on the effect partially of shaded modules on the energy performance of the façade system, both by external elements or due to self-shading within the system

(Bunthof et al., 2016). Bunthof, L. A. A., Kreuwel, F. P. M., Kaldenhoven, A., Kin, S., Corbeek, W. H. M., Bauhuis, G. J., … Schermer, J. J. (2016). Impact of shading on a flat CPV system for façade integration. Solar Energy, 140, 162–170. https://doi.org/10.1016/j.solener.2016.11.001

Saini, H., Loonen, R. C. G. M., & Hensen, J. L. M. (2018). Simulation-based performance prediction of an energyharvesting façade system with selective daylight transmission. In VIII International Congress on Architectural Envelopes (ICAE).