A group of researchers in the Middle East has assessed how building-integrated photovoltaics (BIPV) may help reduce electricity consumption in high-rise buildings in Dubai, in the United Arab Emirates.
The academics explained that the city has 25 buildings of more than 300 meters, while 14 additional high-rises of this scale are currently under construction. “In Dubai, 38.9 % of the total energy consumption is related to buildings, and the high-rise building sector is key to energy efficiency,” they said. “BIPV can be a very efficient alternative in Dubai because of building load reduction and power generation. This paper aims to investigate energy efficiency according to the number of floors with BIPV application.”
The group conducted a series of simulations using the EnergyPlus and the TRNSYS software and considered a building where all floors have the same dimension – height of 3.6 meters, floor area of 400 m2, and window-to-wall ratio of 80%.
“The main setting conditions for simulation were assumed to be an occupancy density of 0.2 person/m2, sensible heat of 65 W/person, and a latent heat of 54 W/person,” they added. “Lighting density of 20.0 W/m2, device density of 22.0 W/m2, and ventilation factors through air conditioners per person were assumed to be 35 m3/person.”
Modeling
The scientists assumed the building to have a temperature of 20 C for heating and 26 C for cooling on work days under Duabi’s climate. Using previous academic literature, the scientists estimated the annual energy consumption of the building at 360 kWh/m2. A reference model was created with a low-emissivity (Low-E) double-layer PV window (LDW) and five BIPV system typologies were considered.
Three of them were systems for window replacement based on translucent amorphous silicon (a-Si) thin film modules. They add three different configurations dubbed double-layer PV window (a-si DW), Low-E double-layer PV window (a-si LDW), and Low-E triple PV window (a-si LTW).
Another BIPV system typology was a photovoltaic curtain wall based on crystalline silicon modules (c-si FMAT). The fifth and last option was a hybrid system, combining the FMAT with a-si LTW.
“As a result of the analysis, the window replacement type BIPV system is effective from the 15th floor, the exterior wall replacement type BIPV system is effective from the 12th-floor size, and the window replacement type and outer wall replacement type BIPV hybrid type is effective from the 9th-floor size,” the academics explained.
Comparison with rooftop PV
They also noted that the BIPV arrays do not only add energy generation to the building but also reduce its cooling and heating load, due to the materials used for their assembly. In the case of window replacement, the scientists also found that cooling and heating load reduction is more significant than conventional rooftop PV generation.
All three window-replacement configurations managed to produce an annual 20.2 kWh/m2, while load reduction was 27.2 kWh/m2, 33.6 kWh/m2, and 34.1 kWh/m2 in the a-si DW, a-si LDW, and a-si LTW, respectively. This compares to an annual consumption of 352.6 kWh/m2 in the case of the baseline LDW.
As for the c-si FMAT system, it was able to reduce the load by 20.1 kWh/m2 and support the building with the production of 26.1 kWh/m2. The hybrid configuration reduced the load by 24.9 kWh/m2 and contributed 34.9 kWh/m2 in generation.
The scientists compared then the performance of the different BIPV systems with that of a conventional rooftop installation, which in the simulated building could use a floor area of 400 me. They found this array may only be competitive with the BIPV arrays if the building doesn't exceed seven floors.
“The energy reduction rate is continuously maintained at 17.0% when a PV hybrid type is applied, and this result is equivalent to the 5-story scale (17.0%) of the rooftop-mounted system,” they said. “In addition, when compared with the energy reduction rate of 15.5% of the a-si LTW, it was analyzed that the version of the 6-story scale (14.2%) of the rooftop-mounted BAPV was shown. C-si FMAT also maintains an energy reduction rate of 13.2% regardless of the increase in the number of floors, which is close to the value of the 7-story scale (12.2%) of the rooftop-mounted BAPV.”
Their findings were presented in the study “Analyzing the effectiveness of building integrated Photovoltaics (BIPV) to reduce the energy consumption in Dubai,” published in Ain Shams Engineering Journal. The group included academics from the United Arab Emirates (UAE) Ajman University and Saudi Arabia’s Prince Mohammad bin Fahd University.
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