Photovoltaic Facade Performance Evaluation

A high-rise building façade with integrated photovoltaic panels, located in the Central European region with temperate climatic conditions was tested. The PV façade was monitored for three years. Results of the PV system monitoring show that the façade positively influence the energy efficiency and reduction of carbon dioxide emissions from the building operation.


Introduction
Energy efficiency and applications of renewable energy technologies represent major issues for sustainable building constructions [1,2]. The conversion of solar energy into electricity due to photovoltaic panels has found wide applications in building industry [3,4]. The PV systems are installed separately or integrated into building constructions. Building-Integrated Photovoltaic Systems -BIPS [5,6] are designed for new buildings as well as for building renovations [7,8]. They are installed for roof and façade applications [9].
The PV system efficiency for the electric energy conversion is influenced by many factors like availability of solar radiation in the climatic locality, topographical features, shading obstructions and neighbouring buildings, etc. [10][11][12]. The BIPS installation depends on the PV system type (materials, grid-tied system) dimensions and geometry, tilt and orientation to the cardinal points [13,14].
The photovoltaic systems are highly efficient for direct solar radiation but they also respond to diffuse sky radiation. The building integrated PV modules should be installed in positions of maximum insolation. They must be ventilated for their proper performance. Apart from the main design and installation demands, the facade aesthetic appearance plays also important role for the BIPV system integrations. Design optimisations and modelling of the BIPS have been topics of research projects [15,16].
A post-occupancy survey of a building with integrated photovoltaic façade was performed. The paper shows main results of the building PV façade monitoring. This monitoring was provided under a university research project focused on smart region technologies for sustainable development.
The studied building is located in city Brno in the Czech Republic. The multi-functional building was constructed in 2013 [17].

Method
The post-occupancy evaluation of the studied building was focused on a monitoring of energy generated from the PV integrated façade. Photovoltaic panels are integrated into the south façade of the high-rise building, figure 1 [18]. That orientation gives potential of intensive solar irradiation in case of clear sky with direct solar radiation. For these conditions the façade is highly efficient. Lower efficiency is monitored for diffusive solar radiation during cloudy sky conditions. The studied building is in the locality with temperate climatic conditions. Outdoor conditions like global horizontal irradiance (monitored by pyranometer CPM KippZonnen) and outdoor temperature (local meteo-station data) were monitored for the building evaluation.   Figure 3 [20]. Threephase inverter Sunny Tripower is used for the PV system of total power is 89.7 kW. The generated electricity is used as a complement for the building electric energy consumption [21].   Annual profiles of the electric energy generated from the PV façade were tested for three years [21]. Results of the monitoring are summarized in figure 6 and Table 1. It is obvious that the façade efficiency varies in dependence on local climatic conditions. Minimum generation of electric energy is in winter seasons from November to February. Maximum energy production is between March and September.
The PV system highest efficiency appears to be in March and April as well as in July and August. Solar radiation of higher altitudes in May and June is substantially reflected on the vertical façade compared to lower solar altitude situations. It means that the energy conversion is lower for these months.  The PV generated energy has positive impacts on the building environmental classification. The clean technology of the PV solar panels represents potentials for reduction of emissions of CO2 and SO2 and NOx compared to the electricity production from traditional sources [22], Table 2.

Conclusion
The post-occupancy evaluation of the photovoltaic façade prove its energy efficiency. Despite the climate conditions with prevailing overcast days, the façade energy conversion is more than 65 MWh per year. The total electric energy generated from the façade photovoltaic system during the three-year The PV facade system is supportive to the building energy efficiency and positively influences the reduction of emissions from the building operation. The utilization of solar radiation for the building electricity substantially decreases CO2 emissions compared to traditional energy sources.