Power Quality Field Measurements on Photovoltaic System

Abstract

Solar energy is the main driving force of climate cycles and all life cycles on Earth. It is inexhaustible and it can be used in each country all over the world. Bosnia and Herzegovina is in line with EU guidelines on mandatory reductions of greenhouse gas emissions required to increase production of electricity from the renewable energy sources. The main scope of this paper is to investigate the power quality parameters measured during different periods and weather conditions on the first photovoltaic system “Eko Energija” connected to the distribution power network in Bosnia and Herzegovina. The results of these measurements are analysed and presented in this paper.

1 Introduction

Due to increasing environmental awareness, the legal regulations and international agreements that require reduction of carbon emissions and improvement of energy efficiency, there is need to increase the share of renewable energy in the total energy balance of the community. Bosnia and Herzegovina is in line with EU guidelines on mandatory reductions of greenhouse gas emissions required to increase production of electricity from the renewable energy sources. Beside hydro power, solar energy is one of the most suitable renewable energy sources in Bosnia and Herzegovina, due to favourable natural conditions [1].

Following EU guidelines and recent worldwide trends, the use of photovoltaic systems as a safe and clean source of energy from the sun has been increasing in Bosnia and Herzegovina. The application of photovoltaic systems can be divided in 2 fields, off-grid and grid-connected applications. Off-grid systems are being used to provide power for remote loads and do not have power exchange with the grid. On the other hand, grid-connected photovoltaic systems are used to provide power for local loads and have the exchange of power with local utility grid [2].

Photovoltaic systems can enhance the operation of power systems by improving the voltage profile, but comparing with other renewable sources, photovoltaic systems still have major difficulties and may have negative effect to the system in terms of power quality [3]. Power quality measurements during different periods and weather conditions have been performed on the first photovoltaic system in Bosnia and Herzegovina. The results are presented in this paper.

2 Photovoltaic Market Development

The history of photovoltaics (PVs) began in 1839 when Edmund Becquerel was able to cause a voltage to appear during his experiment with metal electrode in a weak electrolyte solution. Almost 40 years later, Adams and Day were the first to study the photovoltaic effect in solids. They were able to build cells made of selenium that were 1–2% efficient. Russell Ohl patented the modern junction semiconductor solar cell in 1946 [2].

The first practical photovoltaic cell was developed in 1954 at Bell Laboratories. They used a diffused silicon p-n junction that reached 6% efficiency, compared to the selenium cells that found it difficult to reach 0.5%. Due to the high production costs, solar cells found their first commercial applications in the 1958 in space stations. During the oil crisis in the 70-ies of the last century, when it was noticed that supplies of fossil fuel are limited, solar cells found their use on Earth [2].

Europe has set off intense effort to deal with issues such as climate change, a growing dependence on imported energy, fluctuating oil and gas prices and increasing energy consumption. European energy policy is built on sustainability, competitiveness and security of supply through a series of measures such as promoting renewable energy sources and energy efficiency. The European Union has committed to cut greenhouse gas emissions, to decrease energy consumption due to increasing energy efficiency and to increase share of renewable energy sources in total energy consumption all by 20% until 2020 (“Target 20-20-20”) [4]. Final priority of these European energy strategies is to achieve an energy efficient Europe and to build pan-European integrated energy market. Solar photovoltaic technology has proven in recent years that, with the appropriate regulatory framework in place, it can be a major contributor to reaching the European Union’s target of increasing share of renewable energy sources by 2020.

Photovoltaic technology shows the potential to become a major source of power generation for the world—with robust and continuous growth. That growth is expected to continue in the years ahead as worldwide awareness of the advantages of PV increases. At the end of 2009, the world’s PV cumulative installed capacity was approaching 23 GW. It was 40.3 GW 1 year later and later in 2011, more than 70 GW are installed globally and could produce 85 TWh of electricity every year. In 2012, the 100 GW mark was reached and by 2013, almost 138.9 GW of photovoltaics had been installed globally. In only 5 years, from 2010 to 2015, the total global photovoltaic capacity jumped over 450% from less than 41 GW. Looking back 10 years, photovoltaic’s development has been even more impressive—from 5 GW of total commissioned PV capacity at the end of 2005 the market has grown 45 times in just one decade [5]. This amount of energy is sufficient to cover the annual power supply needs of over 45 million households. Evolution of global cumulative installed capacity from year 2000 to 2015 is shown in Fig. 1.

Fig. 1.

Evolution of global cumulative installed capacity 2000–2015 (MW) [5]

After having scored the top position in the European Union in terms of new installed capacities in 2011 and 2012, photovoltaics were in the second place in 2013 ranking, after wind systems. With more than 21 GW connected to the grid for photovoltaics and wind, these 2 renewable electricity sources together beat gas and all other sources of electricity. If we count decommissioning (which remains marginal in the PV sector—less than 40 MW were replaced by new capacities), wind and photovoltaics both come ahead of gas. All of the other sources, both renewable and conventional, are far behind [5].

Solar energy is one of the most suitable renewable energy sources in Bosnia and Herzegovina due to the natural conditions. Southern parts of Bosnia and Herzegovina have mediterranean climate, while the north has a continental climate. Solar radiation is about 1600 kWh/m² in the southern parts of the country, while it is about 1250 kWh/m² in the north [1]. An important characteristic is the number of sunny hours per year. The number of sunny hours is 1900–2300 h in southern parts of the country, while there are between 1800–2000 sunny hours in the northern part [6]. According to these data, it can be estimated how much solar energy is applicable in an observed area.

According to Regulatory Commission for Electricity in Federation of Bosnia and Herzegovina (FERK) data from year 2013, approximately 75 MW of distributed renewable energy sources (small hydro and solar photovoltaic power plants) were connected to the distribution network of Bosnia and Herzegovina.

Interest in the construction of photovoltaic power plants in Bosnia and Herzegovina is noticeable. According to FERK, 65 requests for approval to build electric solar power plants of different power (from 3.8 kW to 0.920 MW) were applied in 2013. By 2017, according to Operator for renewable energy sources and efficient cogeneration in Federation of Bosnia in Hercegovina, 224 photovoltaic plants have been built with cumulative installed capacities of 75 MW.

3 “Eko Energija” PV System Connected to the Distribution Network in Bosnia and Herzegovina

The first on-grid photovoltaic system in Bosnia and Herzegovina has been commissioned on 19th March 2012. The system is located on the rooftop of a gym in Kalesija (Fig. 2a) consists from 520 solar modules (Fig. 2b), and 8 inverters (Fig. 3a, b), and is directly connected to the power distribution network. Power of this photovoltaic system is 120 kW, and the forecasted annual production 140 MWh of electricity. Information on photovoltaic system in Kalesija is shown in Table 1. The inverter that is used to connect system to the low voltage (LV) distribution network is SMA STP 1500 TL-10 type [7].

Fig. 2.

PV system “Eko Energija”—model (a), modules (b) [7]

Fig. 3.

PV system “Eko Energija”—inverter (a), inverter screen (b)

Table 1. Information about first PV system in Bosnia and Herzegovina

Figure 4a shows total electricity production of photovoltaic system “Eko Energija” during hottest and sunniest month in 2012, August. Highest production was on August 13th, 2012, with amount of 850 kWh. Figure 4b shows total electricity production of photovoltaic system “Eko Energija” during winter, in December 2012. Highest production was on December 27th, 2012, with amount of 320 kWh. Production diagrams were taken directly from photovoltaic inverter.

Fig. 4.

Electricity production of the “Eko Energija” in August 2012 (a) and December 2012 (b)

4 Power Quality Parameters Measurement

Power quality determines the fitness of electrical power to consumer devices. Synchronization of the voltage frequency and phase allows electrical systems to function in their intended manner without significant loss of performance or life. The term is used to describe electric power that drives an electrical load and the load’s ability to function properly. Without the proper power, an electrical device (or load) may malfunction, fail prematurely or not operate at all. There are many ways in which electric power can be of poor quality and many more causes of such poor quality power [8].

The quality of electrical power may be described as a set of values of parameters, such as:

• Continuity of service,

• Voltage magnitude variation,

• Voltage and current transients,

• Harmonic content in the waveforms.

The main document dealing with requirements concerning the supplier’s side is the EN 50160 Standard, which characterizes voltage parameters of electrical energy in public distribution systems [8].

Since photovoltaic systems can produce a significant impact on the power system due to their electronic components, it is necessary to survey the power quality parameters. Power quality measurements were performed on the PV system “Eko Energija” several times, in different weather conditions, during different seasons. Measurements were performed during summer (July 20 to July 24, 2012), during autumn (October 12 to October 17, 2012) and several times during winter (December 6 to December 13, 2012 and December 28, 2012 to January 12, 2013). Measurement was performed with Fluke 434 Three Phase Power Quality Analyzer (Fig. 5). The instrument compares results with the European Standard, EN 50160:2004. Besides power quality parameters, voltage and current waveforms were recorded, in different weather condition. Connection of the instrument to the 3 phase system in shown in Fig. 6, and the particular set up to the distribution cabinet of the PV system “Eko Energija” is shown in Fig. 7.

Fig. 5.

Fluke 434 three phase power quality analyzer [9]

Fig. 6.

Test set up [9]

Fig. 7.

Power quality parameters measurement set up [10]

Figure 8a, b show voltage and current waveforms recorded on October 12th, 2012 at 14:00:22 h, respectively. It is noticeable that voltage waveform could be described by almost pure sin function, while that is not the case with current. Transformer less inverter by which the analysed PV system is connected to the distribution network needs to provide optimal operating point on the I-V curve for the system. During the day, the working parameters of the system are changing. Varying position optimal working point of PV systems is especially pronounced for devices without transformers. The inverter that connects presented PV system to the grid has 2 devices to track the maximum power point, and that is the reason for not having sine current waveform. Due to cloudy weather conditions, low amount of electricity production can be noticed. Almost identical situation related to the voltage and current waveform is on snowy and cloudy day, on the December 6, 2012 at 16:43:21 h (Fig. 9a, b, respectively). When the weather was sunny on January 12, 2013 at 13:26:26, voltage waveform is sine again (Fig. 10a), and the current is almost ideal sine waveform (Fig. 10b), and there is greater electricity production than in previous cases. The voltage and current waveforms on April 29, presented in Fig. 11a, b respectively are very similar with those presented in Fig. 10a, b even though it was different season (winter- spring).

Fig. 8.

Voltage (a) and current (b) waveforms, October 12, 2012, cloudy [11]

Fig. 9.

Voltage (a) and current (b) waveforms, December 6, 2012, cloudy [11]

Fig. 10.

Voltage (a) and current (b) waveforms, January 12, 2013, sunny [11]

Fig. 11.

Voltage (a) and current (b) waveforms, April 29, 2013, sunny [11]

It can be concluded that productivity of PV system does not depend on outage temperature, but solar irradiation angle [11]. The main condition for good production is solar irradiation that is higher during sunny days. It is not important if a sunny day is on summer or any other seasons. It can be noticed that current on the sunny day of January (Fig. 10b) was 92 A, and current on the sunny day of April (Fig. 11b) was 116 A while during cloudy days of October (Fig. 8b) and December (Fig. 9b) current was 11 A and 1 A, respectively.

Figure 12a shows voltage harmonic components and total harmonic distortion (THDU) and Fig. 12b shows current harmonic components and total harmonic distortion (THDI) measured on October 12, 2012. Fluke 434 Power Quality Analyzer measures current harmonic component and THDI according to IEC 61000-4-30 Standard [9]. Current harmonic components are greater than voltage, but still in allowed values. Figure 13a shows the harmonic components and Fig. 13b shows the total harmonic distortion of current that PV system “Eko Energija” inputs into the distribution network. Harmonic components were in each case less than the allowable by the Standards, weather the wheatear is sunny or cloudy, and the dominance of fifth and seventh current harmonic is noticeable in both cases.

Fig. 12.

Voltage (a) and current (b) harmonic components and total harmonic distortion, October 12, 2012 [11]

Fig. 13.

Harmonic components and THDI on cloudy (December 6, 2012) (a) and sunny (April 29, 2013) (b) weather [11]

Figure 14a shows values of power quality parameters of PV system “Eko Energija” measured in July 2012. The results are shown in the form of columns, which is suitable to be compared with the EN 50160:2004 Standard. Looking from left to right the first 3 groups of 3 columns represent the effective value of voltage, harmonics and flicker, respectively, for each phase individually. Subsequent columns represent dips, interruptions, rapid voltage changes, unbalance, frequency and mains signalling respectively, each column summed up for all 3 phases. Height of column changes as the parameter value moves away from the nominal value. If the value of any parameter is greater than the prescribed, columns are about to change their colour from green to red. Fluke 434 Power Quality Analyzer can also specify the exact time when there was a disturbance such as flicker, voltage dips or swells. Figure 14b shows events that occurred related to the power quality. During this period of measurement, there have been 2 voltage dips and 5 flickers, but the summarized value for measuring time of any of these disorders was not higher than the Standard allowable values.

Fig. 14.

Power quality parameters (a) and events (b) according to EN 50160, July 20–July 24, 2012 [11]

Figure 15a–c show harmonic components and total harmonic distortion (THD) for phases L1, L2 and L3 respectively. THD is for every phase less that 8%, which is Standard allowed value. Dominant harmonic components are fifth and seventh, both in Standard allowed values. Third (a), fifth (b) and seventh (c) harmonic component trend, for measuring period July 20–July 24, 2012 are shown in Fig. 16a (third), Fig. 16b (fifth) and Fig. 16c (seventh).

Fig. 15.

Harmonic components and total harmonic distrorsion (THD) for phase L1 (a), phase L2 (b) and phase L3 (c), July 20–July 24, 2012

Fig. 16.

Third (a), fifth (b) and seventh (c) harmonic component trend, July 20–July 24, 2012

Power quality parameters measurements were preformed several times and the results are presented in Figs. 17a, b, 20a, b, and 21a, b. During the second and third measurement period (Figs. 17b and 20b, respectively) no disorder, neither from PV system itself or the grid, was observed. During the final measurement (Fig. 21b), there have been 8 voltage dips and 4 flickers, but the value of any of these disorders for measuring time was not higher than the Standard allowable values (Figs. 18 and 19).

Fig. 17.

Power quality parameters (a) and events (b) according to EN 50160, October 12–October 17, 2012 [11]

Fig. 18.

Harmonic components and total harmonic distrorsion (THD) for phase L1 (a), phase L2 (b) and phase L3 (c), October 12–October 17, 2012

Fig. 19.

Third (a), fifth (b) and seventh (c) harmonic component trend, October 12–October 17, 2012

Fig. 20.

Power quality parameters (a) and events (b) according to EN 50160, December 28, 2012–January 4, 2013 [11]

Fig. 21.

Power quality parameters (a) and events (b) according to EN 50160, April 29–May 6, 2013 [11]

Figure 18a–c show harmonic components and total harmonic distortion (THD) for phases L1, L2 and L3 respectively. THD is for every phase less that 8%, which is Standard allowed value. Dominant harmonic components are fifth and seventh, both in Standard allowed values. Third (a), fifth (b) and seventh (c) harmonic component trend, for measuring period July 20–July 24, 2012 are shown in Fig. 19a (third), Fig. 19b (fifth) and Fig. 19c (seventh).

Photovoltaic system respects Standard given voltage criteria. Figure 22 shows voltage unbalance for period July 20–July 22, 2012 (a) and October 10–October 17, 2012 (b). In both cases, voltage unbalance is 0,2% in it’s highest value, which is way bellow limit of 2%. Example of measurement report from FlukeView—Power Quality Analyzer Software is given in Fig. 23.

Fig. 22.

Voltage unbalance, July 20–July 24, 2012 (a), October 10–October 17 2012 (b)

Fig. 23.

FlukeView—Fluke 434 power quality analyzer software measurement report, July 20–July 24, 2012

Analyzing the results of measuring the quality of electricity carried in all weather conditions, it can be concluded that the PV system “Eko Energija” meets all regulations set the EN 50160 Standard at point of connection to distribution network, and as such does not have global negative effect to the grid. Summarized results of all performed measurements are shown in Table 2.

Table 2. Measurement—summary

5 Conclusion

Global trends in energy are being characterized primarily by increased demand for energy, the increase in prices of conventional energy sources, and the pursuit of renewable energy sources. As a result of these initiatives, the rapid growth of the installed capacity of photovoltaic systems can be seen. Installed capacity of PV systems in the world doubles every 2 years, and photovoltaic systems are the leading technology of electricity production with the biggest growth trend.

In accordance with European Union guidelines Bosnia and Herzegovina is required to increase electricity production from renewable sources. Recently there is increasing integration of photovoltaic systems in the power system of Bosnia and Herzegovina. The first photovoltaic system with power of 120 kW was commissioned in March 2012 in Kalesija, Bosnia and Herzegovina. Due to the fact that photovoltaic systems and renewable energy could have an impact on the quality of the distribution network, measurement of power quality parameters were performed on photovoltaic system “Eko Energija”. Comparing the measured values of power quality parameters with the EN 50160 Standard, it can be concluded that observed photovoltaic system fully complies with the regulations set by the applicable Standards at the point of connection to the distribution network. Depending on the weather conditions the photovoltaic system during operation produced different amount of harmonic components. However, the values of harmonic current components are negligible, and in any case do not exceed the values prescribed by applicable Standards.