The kinetic retroreflective façade system (Kip, 2023) addresses the complex challenge of balancing visual comfort parameters including illuminance, daylight availability, glare mitigation, and view to the outside, while simultaneously potentially reducing short-wave radiative loading near the façade by redirecting incident radiation toward the sky. The project’s innovative approach centers on a kinetic retroreflective façade system that redirects incident solar radiation back toward the atmosphere, thereby avoiding problematic redirection into urban canyons that could exacerbate the urban heat island effect.

A cube corner retroreflector is an optical device that reflects incident electromagnetic radiation, particularly in the visible spectrum, predominantly back toward its source, maintaining this directional property largely independent of the device’s orientation relative to the incident beam (Hansen and Madhu, 1972). Figure 2 illustrates this principle for August 21 at four time points (11:00, 12:00, 13:00 and 14:00). This unique characteristic has made retroreflectors indispensable in diverse applications, including road safety devices, bicycle spoke reflectors and radar systems (CIE, 2024). The extension of retroreflective concepts from static devices to kinetic architectural systems, however, introduces substantial technical challenges. These include the integration of actuation and control mechanisms, as well as the performance-based metrics (illuminance, glare etc.).

Dubai, UAE, was selected as the case study location due to the recorded increase of 4 °C in average temperature between 2005 and 2019 (Mahanta and Samuel, 2020). Based on the global horizontal radiation map, the highest levels of solar radiation in Dubai occur between 11:00 and 14:00 during the months of May to August. Accordingly, the simulation studies for daylighting analysis were conducted for the hottest months on May 21, June 21, July 21 and August 21 using ClimateStudio plug-in (Solemma LLC, 2023) for Rhino3D/Grasshopper. Outdoor solar-radiation redirection and near-façade irradiance exposure (ray-tracing and cumulative irradiance analysis) was further evaluated using Ladybug plug-in and Honeybee Cumulative Irradiance Heat Maps (CIHM), respectively.

A preliminary comparative ray-tracing and cumulative irradiance analysis (Koukelli et al., 2023) was conducted to evaluate near-façade short-wave radiative performance of different façade configurations: baseline (glazed façade), horizontal louvers, biaxial rotation of quadratic panels (A1), monoaxial rotation of quadratic panels with a fixed horizontal axis set at 22.5° (A2), and six types of basic trihedral corner reflectors (S1, S2, S3 and T1, T2, T3) (Figure 3). The horizontal louvers were designed with a depth of 50 cm and a spacing of 50 cm. The square trihedral corner reflectors (S1, S2, S3) were analyzed in three distinct orientations facing the sky (Figure 3E), each with length of 50 cm and a row spacing of 50 cm. Specifically, the panels were oriented with their reflective surfaces tilted toward the horizon at three different angles: (i) S1 with the V-shape positioned centered symmetrically, (ii) S2 with the V-shape rotated horizontally and toward the left, and (iii) S3 with the entire unit laterally toward the left. The triangular trihedral corner reflectors (T1–T3) followed the same set of orientations. All retroreflector configurations were considered as fixed and did not track the sun path.

To evaluate the near-façade outdoor radiative performance of the basic trihedral corner reflectors (A1, A2, A3, S1, S2, S3, T1, T2 and T3) relative to the baseline and horizontal louvres, the simulation environment modeled an outdoor test space of 10 × 10 m, with a 5 × 4 m south-facing façade and a corresponding sensor grid at ground level to capture radiation exposure. This analysis quantifies radiation redirection and near-façade cumulative irradiance within a 10 × 10 m domain; it does not include coupled urban microclimate modeling (e.g., airflow, long-wave exchange, or temperature fields). Therefore, outcomes are interpreted as potential near-façade radiative effects, not as direct quantification of urban heat island mitigation. The glazed façade was assigned by visible transmittance (Tvis) of 54.6% and high reflectivity (R:1, G:1, B:1), with a Solar Heat Gain Coefficient (SHGC) of 0.52. All the trihedral reflectors are considered as double face textile material with a high reflectance on the outer side and high absorbance on the inner side to prevent reflection from the glass to the façade modules. The key performance metric for this study is the reflection efficiency (R [%]), defined as the percentage of reflected rays (R_p) with an angular deviation of 0°–45° relative to incident rays, normalized to the total number of rays (R_t). This metric ensures that solar radiation is redirected toward the sky rather than into the urban canyon, adjacent buildings, or pedestrian areas.

Following the cumulative irradiance analysis, illuminance analysis was conducted for all basic types (Figure 4). As a next step, the best performing type was selected for further geometric investigations, such as size and depth gradation along the façade’s height. An office model was considered for the daylighting analysis with 13.6 m in length, 10.9 m in width, and 4.0 m in height, covering an area of approximately 115 m² with south orientation (Solemma LLC, 2023). Lighting Materials (LM) have been assigned for walls, floor and ceiling, and glazing with a U-value of 0.82 W/m²K and Visible Transmittance (Tvis) of 59%. Sensor points were placed 0.75 m above the floor level to evaluate the work plane illuminance distribution. For visual comfort, metrics include illuminance (target range: 500–1,000 lux for office spaces), daylight availability in accordance with EN 17037 (four compliance levels: Fail, Minimum, Medium, High), horizontal view angle analysis (14°, 28°, and 54° thresholds for compliance levels) and annual glare probability. To ensure consistency across outdoor and indoor performance assessments, a cumulative irradiance analysis was conducted considering the geometrically improved reflector (T60-40).

As shown in Table 1, S1 and S3 exhibit reflectance performance exceeding 80%, with S1 reaching an average of 88% over the examined hours and S3 achieving 81% over the same period. The triangular trihedral corner reflector variants (T1, T2, T3) generally maintain high reflectance, with the T2 and T3 reaching overall performance above 75% for the majority of the time. CIHM values indicate that the radiation load decreases slightly (Table 2). On average, values are reduced by approximately 0.4 kWh/m² compared to a glass façade without shading, showing that all reflector types reduce reflected radiation toward the urban canyon. This effect arises because all façade types are oriented roughly orthogonally to the façade, which limits direct reflection of solar radiation toward the ground. Among the variants, the greatest reduction in reflected radiation is achieved by T3, with reductions of 42.9% on May 21 and June 21% and 50.0% on July 21 and August 21, and was therefore selected for the daylighting analysis.

The illuminance levels were within the acceptable range (Table 3); however the results revealed a pronounced gradient, with high values near the façade, and much lower values toward the rear of the room, indicating insufficient light uniformity. To address this issue, further variations of T3 were analysed considering two different façade module sizes (60 cm and 80 cm) and depth gradient from 80 cm at the top row to 40 cm at the bottom row (T60-40 and T80-40) to allow more daylight admission by decreasing the depth.

The illuminance levels for T60-40 range between 456 lux, 482 lux, 428 lux and 404 lux, while for T80-40 range, between 438 lux, 465 lux, 412 lux, and 386 lux in May 21, June 21, July 21 and August 21, respectively. Overall, these deviations are small and can be considered negligible in terms of illuminance performance. The analysis of light uniformity further indicated that improvements were only marginal and not sufficient to achieve a fully satisfactory distribution, leading to the conclusion that reflectors are not suitable to function as light shelves. The variation T60-40 was selected for further investigation on daylight availability, glare, and view, instead of T80-40 due to the size.

The T60-40 variation with fully open modules achieves the minimum daylight availability threshold of 100 lux across 95% of the floor area, while an improved daylight level is expected when the modules are folded (Figure 5). In terms of view analysis, the proportion classified as “failing” is limited to 7.3% at 1.20 m and 4.0% at 1.70 m (Figures 5C,D). By contrast, 91.5% (1.20 m) and 93.9% (1.70 m) of the area fall within the highest category “High.” Therefore, it can be concluded that the T60-40 variant ensures a consistently good view to the outside. The red areas in Figure 5E indicate 1.6% of views with disturbing glare, occurring between October and February from 16:00 to 18:00.

Following the improvement of indoor daylighting conditions through adjustments to the geometrical characteristics of the façade module, a further analysis of the cumulative irradiance map was conducted comparing the baseline with T60-40. As shown in Table 4, reflected radiation is reduced by 42.9% on May 21 and June 21 and by 50% on July 21 and August 21, behaving the same as T3 (Table 2). A visual assessment further confirms that radiation decreases significantly in the immediate vicinity of the façade, where red discolorations shift to yellow and, in some cases, even to blue (Table 4). At greater distances from the façade, however, no major changes are observed.

The system comprises seven rows of triangular trihedral corner reflectors (74 units) with a height of 45 cm and a width of 90 cm supported by a cable net system. To follow the daylighting performance criteria, the modules in the top row have a depth of 60 cm, while those in the bottom row measure 40 cm. The wings of the modules are connected to an elastic steel sheet at an angle of 45°, and to ensure optimal bending capacity of the elastic steel sheet, a clearance of 50 mm is maintained between the folding axis of the bar and the attached wing. Each module can be folded or unfolded (Figure 6) via two running cables. Since cable-driven actuation occurs horizontally in rows, individual rows can also be controlled independently. This enables, for example, the selective closure of rows at eye level to maintain outward visibility, following a clustered actuation strategy. A double-sided textile membrane is integrated into the wings’ frame, featuring high reflectance on the interior surface and high absorption on the exterior surface.

To experimentally assess the kinetic behaviour of the façade modules, a 1:3 scale prototype was fabricated to verify the kinetic behavior of the proposed system (Figure 7). The black elements were printed from Polyethylene Terephthalate Glycol (PETG) filament, while the elastic steel sheet was represented by an elastic joint fabricated from Thermoplastic Polyurethane (TPU) filament. The prototype provided insights into the actuation mechanism of the wings. By pulling the cables, the wings could be folded with minimal applied force; upon release, the wings returned to their initial position, demonstrating the elastic restoring capacity of the system.

The design project, developed by Jiuyuan Liu, Simon Göbel and Tobias Steiger, introduces an adaptive kinetic façade system inspired by the Hortenkachel geometry, originally designed by Helmut Rhode and later developed by Egon Eiermann. The Hortenkachel is a distinctive façade system used in the Horten department stores, consisting 50 × 50 cm tiles, initially made of ceramic and later of aluminum, each featuring a stylized “H” for Horten. The system comprises two main components: (a) the egg-crate frame of individual wings, and (b) the wings within the frame. Its application to the reference office model is illustrated in Figure 8. Technically, the original Hortenkachel was not conceived as a shading device. Therefore, the objective of this study was first to identify and optimize the geometric parameters of the Hortenkachel for solar shading aligned with user controllability (Figure 9a), and then to design a lightweight kinetic shading system using recyclable materials and a minimal number of actuators through module clustering.

Initially, the egg-crate system was analysed without the wings, however, this configuration lacked flexibility (Figure 9b). Subsequently, various wing geometries were explored, testing different arrangements, sizes, coverages, shapes, and depths. When applied without the egg-crate frame, the wings alone failed to meet the target illuminance levels, particularly during winter at 12:00, when the low solar altitude allowed direct sunlight to penetrate the office room (Figure 9c). These limitations highlighted the need for a new system capable of both shading and flexibility. To address this, a single-axis Tri-fold system was developed (Figure 9d), combining modules with the primary Hortenkachel wings and additional translucent side wings to control glare and regulate indoor illuminance, while preserving outward visibility and user adaptability (Figure 10).

A comparative parametric analysis was conducted between the baseline (glazed façade), the original Hortenkachel, various static geometric configurations, static Tri-fold modules (50% openness) and an adaptive scenario featuring single-axis Tri-fold modules (50 × 50 cm module size arranged horizontally) to assess their influence on daylight performance. The parametric analysis examined three types with side wings arranged: (a) mixed; (b) vertical; and (c) horizontal (Figures 11a–c), where the mixed type combines both alignments, meaning that one module is vertically positioned and the adjacent module, horizontally positioned. Four module sizes were subsequently analyzed: (a) 25 cm; (b) 50 cm; (c) 75 cm; and (d) 100 cm (Figure 11d), this was followed by four coverage and shape variations: (a) façade coverage of 50%; (b) façade coverage of 75%; (c) low mid-point; and (d) high mid-point (Figure 11e). In the sun-tracking scenario (Figure 12), the Tri-Fold modules dynamically track the sun’s position and configure their openness.

Daylighting simulations were performed for the summer and winter solstices at 12:00 and 15:00 in Stuttgart, Germany, using the office reference model described in Section 3.1.2, with south- and west-facing glazed façades. The analysis was conducted in Rhinoceros 3D and ClimateStudio under CIE clear sky conditions through point-in-time simulations. Opaque wood was assigned to the primary wings and polycarbonate with 30% light transmittance to the side wings.

A comparative analysis of the baseline, the Hortenkachel, the three arrangements (mixed, vertical and horizontal) and the single-axis Tri-fold system, shows significant differences in daylighting performance (Table 5). The baseline produces the highest illuminance levels (5363 lux in winter at 12:00), exceeding the target range (500–1000 lux). The Hortenkachel reduces illuminance however, the system is structurally complex for integrating adaptive feature, as it combines an egg-crate framework with additional wings, increasing material and fabrication cost. While the mixed and the vertical arrangement perform well on the winter and summer solstices at 12:00 and 15:00, mixed arrangements complicate actuation for clustering because adjacent modules have different orientations (vertical-horizontal), and vertical arrangements can lead to intolerable glare, especially in winter when the solar altitude is low. For this reason, subsequent simulations focused on the horizontal arrangement, in which the primary wings that face the sun are opaque, and the secondary wings are translucent to diffuse incoming radiation. The module-size variation had no significant effect on illuminance; however, the illuminance levels remain low and further improvement is essential. Therefore, a 50 cm module was selected as a balance between performance and human scale (Table 6). Coverage and shape studies showed that cases with high and low mid-points performed better overall, while 50% coverage yielded lower illuminance, because fully open modules already provide effective protection for south- and west-oriented surfaces (Table 7). The adaptive scenario addresses this limitation by employing a kinetic shading system that tracks the solar’s altitude to dynamically regulate illuminance. However, modules with high and low mid-points pose greater control challenges due to their asymmetrical geometry and non-uniform kinetic behavior.

Following the parametric analysis on illuminance regarding the arrangements, size, coverage and shape variations, another comparative study was conducted for the baseline, static Tri-fold and single-axis Tri-fold. The Tri-fold solar’s altitude tracking mechanism maintains indoor illuminance within the target range, achieving a mean value of 905 lux on the summer solstice at 12:00, outperforming both the baseline (2530 lux) and the static Tri-fold (1158 lux) (Figure 13). Glare analysis was conducted for the worst-case scenario in winter solstice at 12:00 presenting intolerable glare for the baseline and the static Tri-fold (Figure 13). The single-axis Tri-fold (altitude-responsive) system demonstrates robust daylight- and glare-control behavior under seasonal variations. In summer, when the sun is higher, the modules open to permit daylight and preserve outward views while preventing glare; in winter, when the solar altitude is lower, the modules remain closed to block direct sunlight and avoid visual discomfort. View analysis (Figure 13) following EN 17037 confirms that while views towards the southern sun are occasionally obstructed for glare control in winter at 12:00, west-facing views remain accessible, reflecting the system’s adaptive and occupant-centered design. Gray zones indicate no access to views; dark blue indicates minimal access; turquoise indicates moderate access; and green indicates full access to views.

In the daylighting analysis, vertical zoning plays a crucial role in achieving optimal visual comfort. Inspired by the classical blind mechanism, the proposed adaptive shading system, Tri-fold, operates through a single actuator controlling six modules per zone (Figure 14). The actuator engages by pulling a string connected to the lower edges of the modules, causing them to fold upward in an origami-like motion. Upon release, gravity restores the modules to their original closed position. Across the entire façade, a total of 33 actuators is distributed to generate various shading patterns responsive to the sun’s position and user preferences. The side wings of the modules are supported by an aluminum frame, while the joints between the elements are made of elastic 3D-printed TPU, enabling the characteristic foldable, origami-inspired transformation of each module (Figure 15). A 1:2 scale prototype was built to experimentally demonstrate the kinematics of the system.

In real-world applications, TPU-based compliant mechanisms could be substituted with pneumatic joints which offer higher durability, scalability, and reliable performance under repeated actuation. Additionally, since the proposed system responds dynamically to the solar altitude, solar thin-film photovoltaic panels could be integrated on the primary upper wings to generate renewable energy while providing shading.

An adaptive unitized building envelope system incorporating thin-film photovoltaic PV modules was developed as part of a research project conducted at the University of Cyprus. The system integrates lightweight PV modules mounted on aluminum support plates and is designed for seamless application on both new and existing building façades. A key feature of the prototype is its minimal use of actuators, which are strategically positioned outside the main structural body. The configuration reduces the number of active components within the movable structure, thereby simplifying control and minimizing mechanical complexity.

The unitized structural system comprises a primary frame of aluminum profiles, within which a pre-tensioned cable net serves as the main supporting mechanism. This cable net carries a secondary assembly consisting of aluminum struts, interconnected via continuous cables on both the front and rear sides of the system. The PV modules are rigidly attached to the front-facing struts, ensuring that any rotational movement of the struts results in a synchronized reorientation of the PV panels. The system allows for bi-axial movement, with the struts capable of rotating within both the vertical and horizontal planes. These rotations are actuated by controlled adjustments in the relative lengths of the continuous cables, enabling the PV modules to track the motion of the sun in two degrees of freedom. This capability allows for real-time adaptation to the sun’s position, maximizing energy capture throughout the day. Figure 16 illustrates a small-scale prototype of the system in its initial configuration, where the struts are aligned horizontally, and the PV modules are oriented vertically. The overall dimensions of the prototype unit in actual scale are 540 cm in width and 365 cm in height. The assembly houses 20 PV modules, each measuring 66 cm in width and 50 cm in height. Due to the rigid connection between each module and its corresponding strut, any change in the strut’s orientation directly adjusts the PV panel’s inclination, thereby enabling uniform angular realignment relative to incident sunlight.

For synchronized movement, all cables within a plane (either horizontal or vertical) can be actuated in parallel, allowing the PV modules to reorient simultaneously and uniformly in response to changing solar angles. The continuous secondary cables are routed through a pulley system that includes a pair of counter-rotating pulleys at one end and a guiding pulley at the midpoint. This arrangement is driven by a single rotational actuator, such as a stepper motor, connected to the axis that links the paired pulleys within each row of cables. Importantly, only two actuators are employed in total, both mounted on the stationary aluminum frame and mechanically decoupled from the lightweight, movable system body. This approach maintains the low self-weight of the main structural components, ensuring efficient operation without compromising structural balance or dynamic response.

Following the initial evaluation of the dual-axis BIPV system (Phocas et al., 2024), which primarily targeted maximizing PV efficiency, while reducing the mechanical complexity (associated with dual-axis tracking), a supplementary daylighting and solar irradiance analysis was conducted.

Daylighting simulations were carried out in ClimateStudio for a CIE clear-sky condition in two distinct climatic contexts, Nicosia, Cyprus and Stockholm, Sweden, on March 20, June 21, September 22 and December 21 at 12:00, using the office reference model described in Section 3.1.2. To complement the spacing distance between the PV modules, an opaque material with a reflectance of 28% was assigned to the panels. The analysis on illuminance and glare focused on the fixed position, average optimum (static and optimized position for maximum PV power output) and sun-tracking positions for the four selected point-in-times (Figure 17). This step enables a combined evaluation of energy generation and indoor daylight quality, clarifying to what extent the dual-axis BIPV system can be redesigned to provide both high solar-energy yield and adequate daylighting and shading performance.

The transmitted solar heat gain was conducted for four façade types: (a) baseline, (b) fixed vertically positioned PV, (c) average optimum for Stockholm and Nicosia (fixed position), and (d) an orientation optimized for 21 June and then applied to the entire year. The fixed vertically positioned PV and the average optimum were chosen in a previous irradiance analysis and photovoltaic system power (Phocas et al., 2024). The third configuration was defined by first determining the façade orientation that minimizes incident solar radiation for summer solstice (June 21, 12:00) and subsequently applying this single orientation to the annual simulation. This scenario reflects a summer-driven control concept and allows a direct comparison with the two other single-state strategies (vertical and annual average optimum), without introducing hourly tracking. It also quantifies the annual effect of maintaining a summer-protective façade state even during periods when passive solar gains would be desirable.

Annual incident solar radiation on the façade, obtained from ClimateStudio, was converted into transmitted solar heat gains using the common fenestration formulation: Q solar = I incident × S H G C × A where I incident is the solar radiation incident on the glazing kWh / m 2 · yr , S H G C is the solar heat gain coefficient of the glazing (0.52 in this study), and A is the glazed area (31.5 m²). This approach is consistent with the solar gain calculation methods in (ASHRAE, 2021) and with the definition of total solar energy transmittance in EN 410 and ISO 15099.

The mean illuminance values for the fixed position, average optimum and the sun-tracking system in Stockholm and in Nicosia are shown in Table 8. In Stockholm, the sun-tracking system shows a consistently lower mean illuminance than the fixed vertical position during periods of low solar altitude, with 34.9% lower (1875 vs. 2878 lux) on March 20, 29.2% lower (1992 vs. 2813 lux) on September 22, and 11.1% (786 vs. 884 lux) on December 21. The reduction is smallest on June 21 (0.36%), because the high solar altitude minimizes the kinetic feature of tracking. A comparable pattern is observed in Nicosia with the sun-tracking system, 2.5% lower (546 vs. 560 lux) on March 20, 5.0% lower (529 vs. 557 lux) on 22 September, 9.5% lower (2595 vs. 2868 lux) on 21 December and 11.6% (501 vs. 449 lux) on June 21. These results indicate that dual-axis sun tracking is most effective, in terms of differentiation from a fixed vertical system, when the solar altitude is low. In winter the difference diminishes, because the very low solar altitude combined with relatively large panel spacing allows more daylight penetration even in the fixed case.

The annual solar irradiation is 833 kWh/m²·yr in Stockholm and 1019 kWh/m²·yr in Nicosia, which corresponds (with the simulated SHGC of 0.52) to 433.2 kWh/m²·yr and 529.9 kWh/m²·yr of transmitted solar gains, respectively (Table 9). For the actual façade area of 31.5 m², this equals about 13.6 MWh/yr in Stockholm and 16.7 MWh/yr in Nicosia, confirming the expected effect of climate, with the Mediterranean location offering higher annual solar availability. The fixed vertical PV reduces annual gains by about one-third in both locations. In Stockholm, transmitted gains drop from 433.2 kWh/m²·yr to 282.4 kWh/m²·yr (34.8% reduction), which for 31.5 m² equals 8.9 MWh/yr, i.e., a reduction of roughly 4.75 MWh/yr compared to the baseline. In Nicosia, the same configuration reduces transmitted gains from 529.9 kWh/m²·yr to 348.9 kWh/m²·yr (34.2%), or from 16.7 MWh/yr to about 11.0 MWh/yr for the whole façade, a reduction of about 5.7 MWh/yr.

The average optimum fixed orientation achieves the lowest gains overall: 251.2 kWh/m²·yr in Stockholm (42.0% reduction), which is 7.9 MWh/yr for 31.5 m², and 329.2 kWh/m²·yr in Nicosia (37.9% reduction), which is 10.37 MWh/yr. The solstice-derived fixed orientation (i.e., façade position defined for 21 June and applied unchanged to the annual simulation) yields very similar results: 254.8 kWh/m²·yr in Stockholm (41.2% reduction) and 329.7 kWh/m²·yr in Nicosia (37.8% reduction), corresponding to about 8.0 MWh/yr and 10.38 MWh/yr for the full façade, respectively. This is relevant for designs that require strong solar protection in summer, but prevent over-shade in winter, when passive solar gains are desirable. It should be noted that the solstice-derived fixed orientation does not represent a continuously sun-tracking façade. A system that updates its position hourly or seasonally would be able to align the façade more closely with the incident solar vector and thus further reduce incident (and transmitted) solar gains during high-load periods. The present case therefore represents a conservative, single-state approximation of a summer-driven control strategy.

In Stockholm, the three investigated PV positioning strategies (fixed, average optimum, and sun-tracking) show that reorienting the system alone cannot eliminate glare for certain low solar altitudes. At 12:30 on March 20 all configurations reach Daylight Glare Probability (DGP) 1.00, and on December 21 the values remain clearly uncomfortable (0.79–0.81), indicating that the combination of low solar altitude and view direction creates inherently critical situations (Tables 10–12). When glare is evaluated over space and time, however, the average optimum configuration performs best (sDG = 15.1%) compared to the fixed position (19.1%) and the sun-tracking (Figure 18). This means that, relative to the fixed case, the average optimum reduces the share of views experiencing disturbing glare over the year by about 21%, while the sun-tracking case still achieves a reduction of roughly 16%. In high-latitude locations, even a limited-state adaptive façade (fixed ‘average-optimum’ or seasonal state), rather than continuous sun tracking, is more effective for visual comfort than a static vertical façade.

In Nicosia, the same set of configurations results in generally lower glare levels. The fixed position already yields a relatively low annual value (sDG = 11.5%) and only moderate DGP values for the four representative dates (0.42–0.54), which implies that a static configuration is sufficient to maintain acceptable visual comfort for most of the year (Figure 19). By contrast, the more sun-facing “average optimum” and the sun-tracking drive the winter case (21 December, 12:30) up to DGP = 1.00, without providing a clear annual advantage (sDG remains around 11%–12%) (Tables 13–15). In this low-latitude, high-irradiance context, orienting the PV surface toward the solar vector increases exposure to direct high-luminance sources during the short low-solar-altitude periods, without yielding any compensatory gains in annual spatial glare.

A further factor that helps explain the observed DGP peaks is the spacing between PV elements. Because the array is not fully continuous, the inter-panel gaps act as apertures through which direct sunlight can penetrate when the solar altitude and azimuth align with these openings. At those moments the gap, rather than the PV surface, becomes the dominant bright element in the field of view, leading to high point-in-time DGP even though a PVSD is present. This effect is more easily triggered in low-altitude locations (such as in Stockholm in spring and winter), but it can also appear in Nicosia in December when the sun is lower. Consequently, spacing should be treated as a glare-relevant design parameter reduced or supplemented by a secondary glare layer to block these beam paths.

Comparing the two climates, Stockholm benefits most from the static average-optimum PV orientation (the yearly energy-based position), because it reduces annual spatial disturbing glare by about 21% compared to the fixed position. Nicosia, by contrast, is already well served by a fixed configuration, and additional solar-oriented positions mainly penalize the few winter hours when direct sun can enter through panel gaps. This shows that PV/façade control rules should be climate-specific: in higher latitudes the aim is to balance solar access and glare over many potentially problematic sun positions, whereas in Mediterranean conditions the priority is to shield the space from a small number of low-sun situations that sun-tracking and PV spacing would otherwise expose.

The design of the structural components, control elements, and their interconnections follows a modular assembly logic, enabling both interchangeability of parts and facilitating straightforward assembly and disassembly processes. This modular approach supports flexibility in prototyping and potential scalability for real-world applications. In addition, a critical aspect influencing the control strategy is the configuration of the secondary cable system and its anchorage to the aluminum frame. The routing and termination points of these cables directly impact the number of actuators required for achieving the system’s adaptive motion. As such, the cable layout has been optimized to support transformability with minimal actuation, reinforcing the overall design goal of mechanical and control efficiency.

The primary design objectives include: (1) minimizing the number of actuators necessary to achieve the desired adaptability of the envelope, and (2) ensuring that the integration of control components does not interfere with the structural or gravitational behavior of the lightweight system. To this end, the actuators and associated mechanisms are deliberately decoupled from the movable body, allowing for a self-weight neutral control integration. An overview of the structural and kinematic configuration of the system is presented in Figure 20. Detailed investigations into the kinematic behavior, load-deformation response, and comparative energy performance of the integrated photovoltaic modules are provided in (Phocas et al., 2024).