Operational power performance of south-facing vertical BIPV window system applied in office building

Highlights

• Operational power performance of a-Si transparent vertical BIPV window is investigated.

• Big decrease of final yield in vertical BIPV was shown between April and August in Korea.

• Even short extrusion of louver next above BIPV can cause decrease in PV performance.

• PR can be decreased even by the effect of diffuse radiation due to adjacent obstructions.

Abstract

The purposes of this study are to analyze the power efficiency of BIPV system under actual operating condition and to reveal the factors of performance decrease through annual monitoring of the south-facing vertical BIPV window system (the capacity of 10.6 kWp) whose performance was affected by partial shading.

The study first investigated the monthly PR of each inverter to verify what caused the decrease in power performance by analyzing PR variation. Then, the shading analysis was performed using a simulation to analyze the capture loss of measured power performance and ultimately to find out the effect by partial shading components such as small overhang louvers of each floor, obstructions of adjacent building, and nearby hillock.

The one-year measurement of the power performance showed that the annual average reference yield was 2.15 h/day and the final yield was 1.52 h/day; moreover, it was analyzed that the annual average capture loss was 0.49 h/day and the system loss was 0.14 h/day. Monthly average reference yield in summer (between April and August) showed only 1.28 h/day which was 54% lower than the other seasons with average 2.77 h/day. The annual average of PR was 0.69 (the monthly maximum of 0.77 and minimum of 0.58); the average PR in the summer with low reference yield was 0.64, while the average PR for other seasons was 0.73. Whereas monthly variation of LS (system loss) did not show big difference of under 9%, monthly LC (capture loss) highly varied with fluctuation. These primarily arise from the effect of the partial shading and vertically installed angle of south-facing BIPV modules.

The BIPV system consisted of four arrays and installed on the same south façade. However, the power performance analysis per array showed that each array had different performances. The arrays located above the facade had the highest PR, from 0.74, 0.75, 0.66, and 0.62 respectively in order. In addition, LS and LC analysis of each array showed that there was performance difference mainly by LC, due to the influence of an adjacent building located in the south.

The analysis using the simulation showed the adjacent building did not cast any shading but affected on decrease in diffuse solar radiation whose amount was depending on the array location. When it comes to the lowest array, nearly 7% of annual insolation was blocked by front building. The shading analysis, furthermore, revealed that the overhang louvers caused a partial shading problem in spite of short extrusion of 40 mm depth all through the year, and particularly, showed a big effect during summer because of high solar altitude. The extruded louvers caused decrease in 4.5% of average insolation loss over the year.

Introduction

New and renewable energy systems in the zero energy building are regarded as the final stage of a technical application to manage residual load, and these play an important role in thermal and electrical load matching. In non-residential buildings, since the electric power consumption accounts for a big part of total energy consumption, there still exist a difficulty in reducing energy by energy conservation and energy efficient technologies. Thus, the new and renewable energy systems are getting more desirable in the non-residential building, particularly in view of electricity generation.

Building integrated photovoltaics (BIPV) systems, which also serves as building envelope material itself, can be a leading technology in terms of managing the argument of cost and efficiency issues. Recently, numerous market researches forecasted the rapid expansion of BIPV and PV market. The world PV market is expected to grow total global installed solar capacity from 229 GW in 2015 to 600 GW in 2020 (Solar Power Energy, 2016). The Installed capacity of BIPV was 0.3 GW in 2012 and the market expects to expend a compound annual growth rate (CAGR) of 18.70% per year, which will result in the capacity of 1.2 GW in 2019 (Transparency Market Research, 2016). Although current market share of BIPV is only 1.2% in solar energy market, it is expected to go up to 9.0% in 2017 (Philip and Kerry-Ann, 2012). Meanwhile, the size of BIPV market in South Korea is still small at the moment, which is between 3 MW and 5 MW. However, according to the recent research, the size of BIPV market is expected to highly increase in the year 2017, up to 100 MW (SNE Research, 2012).

The regulation for obliging newly constructed public buildings to apply certain proportion of new and renewable energy system took effect from 2004, and consequently many BIPV buildings are being supplied to the public in South Korea. Different from PV Power plants, most of BIPV modules are applied to a building envelope such as roof, wall and windows. Therefore, variables such as installation angle, shading and solar cell temperature become key factors limiting power efficiency. Over the past 10 years of its early stage of application, BIPV system required a great deal of work to establish guidelines for the BIPV design and construction (German Solar Energy Society, 2005).

In recent years, many theoretical and experimental studies have been conducted to determine how to maximize the benefits from the BIPV systems in terms of PV power generation, payback time and thermos-physical properties for the reduction of cooling load in the buildings (Li et al., 2009, Mercaldo et al., 2009, Sun et al., 2012, Lu and Yang, 2010, Zogou and Stapountzis, 2011, Han et al., 2010, Baetens et al., 2012, Tiwari et al., 2011; Sadineni et al., 2012).

In addition, in order to maximize the benefits, not only the efficient design, installation and construction of the BIPV system is important, but also the verification to ensure the power generation with maximum efficiency in operation is significant. These are especially necessary for BIPV systems whose power generation efficiency is affected by many factors. To sum up, investigation of actual power yield of BIPV systems in various installations are needed to maximize benefits.

The previous experimental study on operational power performance focuses on analyzing annual power yield and PR by collecting the long-term monitoring data of BIPV system installed on external wall or rooftop (Eke and Senturk, 2013, Lee et al., 2014, Essah et al., 2015, Sánchez and Izard, 2015; Wittkopf et al., 2012). Furthermore, an experimental study on temperature, shading effect, and solar incidence angle have been carried out, which are the elements influencing the performance of BIPV system (Maturi et al., 2014, Yoon et al., 2011, Masa-Bote and Caamaño-Martín, 2014, Eke and Demircan, 2015, Drif et al., 2012; Ding et al., 2015). The main purpose of this research is to investigate the power efficiency of BIPV system under actual operation and to determine the factors of performance decrease. The investigation was carried out by measuring annual electricity generation of the BIPV systems, installed in office building as a south-faced vertical curtain wall and affected by partial shading.