Problems of Photovoltaic Power Plants Operation in the Czech Republic

(1)PETR MASTNY, (2)FRANTISEK BERNATH, (3)ZUZANA MASTNA

Brno University of Technology (1), (2)FEEC, Centre of Research and Utilization of Renewable Energy Sources

Technicka 10, 616 00 Brno (3)FCE, Institute of Building Structures

Veveri 331, 602 00 Brno CZECH REPUBLIC

(1)mastny@feec.vutbr.cz, (2) xberna07@stud.feec.vutbr.cz, (3)mastna.z@fce.vutbr.cz http://www.vutbr.cz

Abstract: - Regarding the development and the growing integration of renewable energy sources into energy systems, it is still important to acquire knowledge concerning the vice of their operational characteristics. The paper is primarily focused on the operation of photovoltaic power plants in the conditions of the Czech Republic. The paper describes the important operating indicators that relate to the integration of photovoltaic power plants into the electricity network. There is described the importance of compensation for photovoltaic power plants (PVPP), as well as the methodology for establishing the operating performance of photovoltaic applications and its impact on the economy of operation. Key-Words: - Photovoltaic, Performance, Solar Radiation, Fault Condition, Power Factor, Reactive Power Compensation 1 Introduction The development of photovoltaic (PV) power plants accelerated by such support is over the useful need and possibilities of the power engineering in the Czech Republic and also it is over meeting obligations towards the EU.

The development of renewable power sources is characterized by many doubts such as:

• changes in relevant legislation, • change the subsidy system, • changes in prices of individual technologies • limited integration of renewable power

sources to the electricity network • the issue of disproportion between

production and consumption from renewable energy sources (RES)

Figure 1 shows the progress of installed

performance of PV systems in Czech Republic (CR) during past 5 years. The behavior of installed capacity shows extreme growth in installed PV power in the period between years 2009 - 2011. The total installed capacity of PV in the CR is currently 1974 MWp (30th June, 2011) [8].

In the Czech Republic, in spite of an important increase in the installed capacity of solar

photovoltaic systems legislative measures have been recently adopted that stopped this upward trend. Currently, it is possible to install photovoltaic power plants only up to 30 kWp. Restrictions for connecting renewable energy sources in the CR are mainly in terms of power system operation.

2 Compensation for Photovoltaic Power Plants In ideal case integration of PVPP into ESS (Electricity Supply System) does not cause downgrade of power quality in access point (point of common coupling). Power quality is expressed by voltage quality. Ideal quality of electric power is achieved if energy is still available; voltage has its rated value, voltage waveform is a harmonic function with rated frequency and particular phases of voltage are symmetric.

Parameters of power quality [6]: • Root Mean Square (RMS) value of voltage, • Frequency, • Shape of waveform, • Voltage symmetry.

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Usually is by a supplier of photovoltaic power plant declared operational performance in the range of 80% - 90%. Minimum value of operating performance is usually set at 82%. Lower operating production rate would have a negative impact on the overall economics of photovoltaic power plant. This indicator is during the evaluation of the operation very important. Regarding the development of the installation of photovoltaic power plants in the Czech Republic there have been established new purchase price of electricity produced from such sources. As can be seen from Tab. 1, purchase prices fell in 2011 by almost 50%, which has a major impact on the economics of the operation of these power plants. This set purchase prices downward trend continues this year. Return of investment in PV power plants has by this step extended approximately about 5 years - from 7 years to 12 years.

Following the new measures there are increasingly controlled technical and operational parameters of photovoltaic power plants by its operators.

Most photovoltaic power plants providers guarantee five-year warranty on mechanical design of panels and 25-year warranty on performance parameters. But there are many options when photovoltaic panels may not correspond to the declared parameters, which have a negative impact on the overall energy and economic efficiency of the operated PV power plant.

Main causes of defects on the PV panels can be divided into several categories [11]:

• Different technological level of production for producers,

• Mechanical damage, e.g. during transport of PV panels,

• The effects of adverse environmental impacts,

• Improper installation of the PV system.

type of PVPP (kWp)

Purchase price of electricity(EUR/MWh)

2010 2011 2012 ≤ 30 kWp 500.00 306.12 251.43

30 – 100 kWp 495.92

240.82 ----- > 100 kWp 224.49 -----

Tab. 1 [11]

The following part of the paper will present the method of performance estimation of photovoltaic power plants on a real example.

3.1 Performance measuring of 16.6 kWp PVPP For the operation measuring there has been chosen PV power plant with 16.6 kWp capacity installed on the roofs of technical building (Fig. 2).

Within the PV power plant there have been installed 83 pcs. of panels with unit panel performance 200 Wp. Installation of power plant was proceeded in the first half of 2010 and the control measuring of quality of all PV panels was held on July, 2011 – after one year operation. This installation reported efficiency about 20% lower than it was guaranteed by the producer. Such decrease causes prolongation of return of investment and results in economically inconvenient operation of the PV power plant. This fact is even more apparent regarding decrease in purchase prices of electricity produced by PV power plants set by the beginning of 2011 (Tab. 1).

The following calibrated measuring devices were used in order to perform the analysis of the PV power plant:

• Pyranometer CMP21, • Temperature sensor PT-100, Class A, • LogBox SD. According to established methods there were

also used data from distribution network certified measuring device (electricity meter) and data from a solar sensor that is part of the PV power plant. The methodology used when calculating the total aggregated solar energy was based on the arithmetic average of the measured values of solar radiation and the solar sensors within the PV power plant (Fig. 3). The usage of both devices (pyranometer CMP 21 and the solar sensor) represents a correct solution in terms of the methodology since it eliminates any influence of the overall local cloud cover on a total aggregated solar energy. Both devices were located at various spots within the PV power plant. The pyranometer CMP 21 was placed within PV power plant at proper inclination (32°) and at the same orientation with PV panels (Fig. 4).

For photovoltaic power plant displayed on Figure 2, there has been established - on the basis of the operational measurements - operational performance at 65%, which is due to the declared parameters of the power plant

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ISBN: 978-1-61804-139-5 169

The result of the operation IR measuring was detection of defect parts of the PV panels within photovoltaic power plant. Of the total 83 pcs solar panels were detected 13 of defective panels. In 11 panels were defects in individual cells, two panels showed a total error. As is apparent from the above mentioned results, the entire PV power plant was detected 15% of defective photovoltaic panels. This number of defective panels caused the decline in the overall operational performance of the PV power plant by approximately 20%.

In the Figure 6 there are two panels that showed a total error and had the largest impact on reducing the operational performance of the PV plant. These panels have been connected in one string, which reduced real operating performance of PVPP by 10%.

Fig. 6 [2]

Necessity and importance of ongoing operating controls of photovoltaic systems can be shown on a simple economic evaluation of operation.

Analyzed photovoltaic power plant with the performance of 16.6 kWp with regard to its location and design is capable to produce approximately 15 MWh of electricity per year. Given that this photovoltaic power plant was opened in 2010, there is valid its electricity purchase price for the year 2010 (see Tab. 1) for 20 years.

Total gross revenues, therefore for the optimal operation could reach above 7500, - EUR / year. Payback period of the device was in this case, with regard to the purchase and operating costs, set at 11 years.

In the case that operational analysis was not performed and would be further operated defective PV modules, it would have a negative impact on the overall energy and economic aspects of operation. Defective panels with improper dimension of surge protection devices reduce the overall performance of

the PV power plant by up to 20%. This means that the total quantity of electricity reached values of 12 MWh / year. Total gross proceeds from the sale of electricity produced would therefore be only 6000, - EUR / year. Regarding this decrease and disturbance conditions associated with defective components, would extend payback period of the system to nearly 15 years.

4 Conclusion As stated in this paper, compensation power factor plays an important role in connecting photovoltaic power plants. Compensation power factor is an important step to reach voltage demand in connection point of photovoltaic plant. It is one of the ways that make integration of dispersed sources more performable.

Compensation unit has to be based on analyze of reactive power characteristics of photovoltaic plant. Some plant is pressed to dispose by compensation unit already before probation period. Then mathematical method to obtain reactive power balance can be realized. However the best solution is to measure powers and calculate needed powers according the connection conditions.

Reliable operation of PV plants is in terms of the operator (investor) one of the most important properties. It is therefore very important to perform regular inspections of the functionality of each component in PV power plants. The significance of these operation measurements within the environment of the CR increases with reduction of the purchase prices of electricity generated by PV power plants. As shown by a simple economic operation analysis, the defects on the PV panels have considerable influence not only on energy but also on the economic efficiency of its operation. Reducing the performance of PV power plant significantly extends the return of investment, which is for investors operating PV power plants with capacity of 100 kWp very problematic.

Acknowledgments The research was performed in Center for Research and Utilization of Renewable Energy Sources (CRURES). Authors gratefully acknowledge financial support from European Regional Development Fund under project No. CZ.1.05/2.1.00/01.0014.

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