The impact of BIPV in high rise buildings

Researchers from Spain have simulated the effect building integrated photovoltaics (BIPV) will have on the energy consumption and the economics of high-rise office buildings in the Mediterranean area.

They presented three different BIPV integration scenarios for the GESA building, an office building built in the 1960s in Palma de Mallorca, in Spain's southern archipelago of the Balearic Islands.

“Despite of its iconic and protected status, the GESA building has been abandoned for several years, hence it requires a refurbishment that will also update its skin to the current energy efficiency standards,” the scientists explained. “The inefficient envelope, location (isolated and in a sunny climate), and representability of a typology of office building make it a good reference for studying the impact of refurbishing with BIPV.”

Via the TRNSYS simulation software, which is commonly used to simulate the behavior of transient renewable systems, the group simulated the impact of BIPV taking as reference a representative floor. As in the physical building, among the parameters inserted are the GESA building’s curtain wall structure, which is 77% composed of semi-transparent windows and 23% of non-window opaque areas. As the building, although abandoned, is protected by a local heritage commission, the façade design has to keep its original characteristics.

The reference scenario was based on the existing double-glazing Parsol Bronze window. It was compared to four other scenarios, one with only solar control windows; the second with solar control windows and BIPV modules in the opaque area; the third with only transparent BIPV windows; and the fourth with BIPV windows and opaque BIPV in non-transparent areas.

“The data for the transparent PV used in this study is based on a prototype currently in development, hence there is room to improve the thermal, optical, and electrical properties to better fit the building needs, as well as to increase the PV conversion efficiency,” the research group emphasized.

According to the results, the final energy consumption in the existing reference case was simulated at 51.3 kWh/m2. In the case of only solar control windows, this value reached 45.8 kWh/m2, with very similar results with the addition of opaque BIPV. However, in this case, the building will be able to use 5.8 kWh/m2 and export 2.6 kWh/m2 to the grid.

In the case of only transparent BIPV windows, the energy consumption will be higher, as that module will block more of the solar radiation and, therefore, result in higher heating and lighting demands. Overall, that system will require 49.8 kWh/m2 while consuming 5.1 kWh/m2 and exporting 2.2 kWh/m2. In the case of using window BIPV and opaque BIPV, the demand will reach 47.6 kWh/m2, while self-consumption will take 10.9 kWh/m2 and 5 kWh/m2 will be exported to the grid.

“The results show the potential of the BIPV solutions for improving the energy balance of the building. The transparent PV reduced the energy demand by 6.9% and the total energy balance by 21%,” the scientists added. “The opaque PV further improved the results of the two glazing system solutions, the energy balance improving to 28.1% and 38.3% with the solar control and transparent PV solutions, respectively.”

The researchers also conducted an economical analysis, which they claim showcases the “relevance of the electricity pricing schemes into the promotion of BIPV.” The components and installation cost of the components were mostly obtained from a construction materials database, while the cost of the prototype window BIPV was assumed at €200 ($210.65)/m2.

They looked into two tariff levels. The first is based on current Spanish tariffs and demand, while the second assumes a high penetration of PV into the national grid. In this case, the net load of high-penetration photovoltaics presents a very low price. Another variable was the compensation for the electricity sold to the grid by the building, which they estimated at either 0%, 30%, or 100% of the electricity price.

Currently, 30% of the electricity price is the typical export value in Spain. Under this assumption, with the current price profile, the discounted payback time for solar control will be 24 years, for solar control and opaque BIPV it will be 14 years, for window BIPV only it will be over 50 years, and the combination of both BIPV technologies will result in a payback time of 24 years. In the assumption of high PV penetration and 30% electricity price, however, the payback time in all systems may exceed over 50 years.

“The lower average electricity price and, more importantly, the timing of the generation in the ‘high PV’ scenario explain the significantly worse payback periods,” they concluded.

Their findings are available in the paper “Impact of building integrated photovoltaics on high rise office building in the Mediterranean,” published in Energy Reports, which also included an economic evaluation. The research group comprised academics from The Technical University of Catalonia and the Catalonia Institute for Energy Research.