Integration and Testing of P/V – A/G Hybrid System in the Technological Educational Institute of Crete’s Building in Chania

GIORGOS RISTAS1), DIONYSIA KOLOKOTSA1), JOHN. P. MAKRIS2), JOHN CHATZAKIS2)

1) Department of Natural Resources & Environment, Laboratory of Renewable Energy Technological Educational Institute of Crete

3 Romanou St, Chalepa, 73133, Chania, Crete GREECE

http://www.chania.teicrete.gr 2) Department of Electronics

Technological Educational Institute of Crete 3 Romanou St, Chalepa, 73133, Chania, Crete

GREECE http://www.chania.teicrete.gr

Abstract: - We present the integration and testing, for research and educational purposes, of a hybrid system bivalve from photovoltaic cells and a small wind turbine which are able to produce enough amounts of electricity for the power demands of the Laboratory of Renewable Energy Engineering of the Technological Educational Institute of Crete, Greece. With the use of the appropriate equipment and batteries for the storage of the produced electricity, the system is capable to support the operation of a number of the laboratory’s devices. The more consumption of the stored en-ergy, the system works in higher grade. The overall system is continuously monitored via a set of sensors, the meas-urements of which are sampled and digitized by a data acquisition card installed in a system computer, running associ-ated software package that controls the acquisition process, analyzes and displays the collected data. The measure-ments are taken in real time mode, thus providing the study of the system’s performance. With this implementation, we are able to produce private electricity with low cost. The hybrid system pro-vides the possibility to have free energy during all the seasons of the year. In the summer, we absorb energy, mainly, through the PVs, and the winter with the wind turbine. The system is effective, with the batteries reaching the 99% of their charge level within one month of the system’s operation. Key-Words: - Photovoltaics, wind, hybrid system, renewable energy, data acquisition, real time monitoring.

1 Introduction Autonomous hybrid systems are independent and incorporate more than one power source. Renewable Energy System (RES) penetra-tion depends only on the economic feasibility and proper sizing of the components to avoid out gages and ensures quality and continuity of supply. One important application is the use of photovoltaics and wind generator to provide electricity to buildings [1]. The present work outlines the design and development of a small autonomous hybrid PV and wind system that is anticipated to successfully ad-dress the electricity demands for electric lighting in the Renewable Energy Engineering Laboratory of the Technological Educational Institute of Crete situ-ated in Chania, Crete I., Greece. The overall installa-tion is monitored via LabViewTM software [7] that drives a data acquisition card (DAQ) which is sam-

pling the measurements of the used current and volt-age sensors. 2 System Description The system consists of the following components:

6 photovoltaic cells 24V DC output 100Wp each placed on the roof of the building with 45° inclination, in order to achieve the best per-formance (Fig.1, Fig.2) [2].

1 wind turbine 24V, nominal power 400Wp in 12.5m/s (Fig.1, Fig.2) [1].

1 DC/DC controller 12/24V which protects the batteries from overcharge/discharge (Fig.1, Fig.2) [3].

1 DC/AC inverter with DC input: 24V, 38A, 900W and AC output: 220V, 3.6A) which con-verts the DC current to AC (Fig.1, Fig.2) [4].

10 fuses (3 doubles and 7 singles) which protect and secure the whole system in case that we have greater current flow than this that the cir-cuit can withstand (Fig.1, Fig.2).

4 current sensors (CSH-01) 20Amp, 100mV, 0.005Ohms which measure the current that flows in the circuit by converting it to voltage (mV) that can be easily sampled by the DAQ card (Fig.1, Fig.2).

4 voltage sensors (VAT-04) 56K, 4K which measure the voltage that after signal condition-ing is sampled by the DAQ card (Fig.1, Fig.2).

24 batteries 2V, 300Ah/C72. The batteries con-sist of antimonium plates which are very effec-tive because of the multiple charge-discharge cycles (Fig.1, Fig.2).

1 module providing terminal strips for wiring the sensors to the analog inputs of the DAQ card (Fig.1, Fig.2).

1 general purpose and low cost data acquisition card (NI-DAQ 6024E) by National Instruments, installed in a PCI slot of the system computer, which samples and digitizes the sensor signals in order to process the collected data and dis-play the measured time series via the appropri-ate software. NI-DAQ 6024E is a multifunction data acquisition device that provides full func-tionality for applications ranging from continu-ous high-speed data logging to control applica-

tions to high-voltage signal or sensor measure-ments when combined with signal conditioning. It was selected for the developed system mainly for the following important features: (i) meas-urement and instrument class amplifier that guarantees settling times at all gains, (ii) precise voltage reference included for calibration and measurement accuracy, (iii) software controlled self-calibration, (iv) optimized data transfer for multiple simultaneous operations using bus mastering, (v) internal noise floor that maxi-mizes the resolution, (vi) minimized effect of

temperature changes on measurements and a higher immunity to noise and jitter and of course (vii) low power consumption. Further-more, it provides 16 single-ended analog inputs (or 8 differential), ±0.05V to ±10V input range software selectable, 12bits input resolution and up to 200kS/s sampling rate.

1 system computer that has installed in its PCI bus the DAQ card and is running LabViewTM software that controls the acquisition process, analyzes and displays the collected data. Lab-ViewTM software was selected because provides powerful tools for distributed monitoring sys-tems [6], [7]. It is an open environment de-signed to make interfacing with measurement hardware from many vendors, delivers a power-ful graphical development environment for sig-

Fig.1 Τhe assembly of the various components of the hybrid system installation.

nal acquisition, measurement analysis and data presentation and visualization. It is designed es-pecially for engineers and scientists that can take full advantage of its measurement-specific user interface design tools [7]. It has a great col-

lection of built-in functions designed specifi-cally for extracting useful information from any set of acquired data and for analyzing measure-ments and processing signals through underly-ing sophisticated algorithms [7]. The open LabViewTM environment provides superior con-nectivity to third-party software, having simple transitioning and coexisting and thus can be eas-ily integrated and upgraded to a powerful soft-ware package [6], [7].

The interconnection and assembly of the various components is depicted in Fig.1 and Fig.2 presents real photos of the hybrid system sub-units and modules. The whole system is designed and integrated in order to meet the laboratory’s energy needs and will be used by students as an experimental exercise. Thus, for educational and research purposes, care-fully selected current and voltage sensors are used in order to provide the necessary measurements to monitor the system. Voltage sensors have a range of 0-1.8V. Current sensors have a range of 0-100mV.

Both types of sensors are connected to the DAQ card via RC low pass filters. The sensors signals are connected to a DAQ card in a PCI slot of PC that is running the Lab-ViewTM software in order to store and process the

measured data. 3. Experimental Results The LabViewTM software is used for monitoring and of measurements and calculations. Fig.3 depicts the graphical layout of LabViewTM during real time op-eration of the system. The scale is common for both Volts and Amperes. On the upper part of the displayed graph the time series of four voltage channels are illus-trated which measure: (i) the voltage of the PVs; (ii) the wind turbine’s voltage; (iii) the batteries and (iv) the voltage between controller – inverter. All chan-nels have voltage fluctuations at the level of about 25V. On the lower part of the displayed graph (Fig.) the time series of the four current channels are de-picted. The window below the graph is summarizing information concerning the device from which the program is receiving data, its sampling rate and the channels that are scanned.

Fig.2 Photos of the main components of the hybrid system installation.

The electrical load, that the hybrid system supplies with power, is 4 fluorescent lamps (each of 15W) that are used for electric lighting of the labora-tory. According to the number of the lamps that are turned on, the rise and drop of the current is ob-served. On the other hand, the voltage remains al-ways at the level of 24-25V.

Fig.3 LabViewTM layout for measurements. 3.1 Measurements under calm conditions In this section the behavior of the hybrid system is analyzed under calm conditions and during night that no sunlight is available. The graph depicted in Fig.4 indicates that the stored electricity in the batteries can cover the demands for electricity. The batteries provide 3-4A when there is no sunlight or wind available. The batteries current is reduced as soon as the electric lights are off.

Fig.4 Measurements of current under calm wind conditions and during night.

3.2 Measurements under sunlight Under sunny conditions, the photovoltaic panels provide the necessary energy through batteries stor-age (Fig.5). When lights are turned on current is flowing from the inverter to the lamps (light blue line). PVs provide 4 to 5A to the load (blue line). Simultaneously, the batteries’s current (yellow line) is negative. Therefore, PVs produce enough electric-ity to support the load as well as to charge the batter-

ies. This occurs mainly during summer conditions when the sun radiation is quite high.

Fig.5 Measurements under sunny operation and no wind.

3.3 Windy conditions The turbine’s rotor has to rotate with more than 500rpm in order to produce electricity and thus to charge the batteries. The following graph is charac-teristic of how the wind speed affects the wind power production. As it can be observed in the graph, the red curve represents the wind speed, that reaches 10m/s, and the blue curve depicts the tur-bine’s current that is changing in phase with the wind speed (Fig.6).

Fig.6 Measurements under windy conditions. 4 Laboratory training The hybrid PV-wind turbine system is incorporated in the laboratory training of the courses Renewable Energy Sources II and Management and Planning of Renewable Energy Sources of Department of Natural Resources and Environment at Technological Educa-tional Institute of Crete. The objective of the labora-tory exercises, that the hybrid system is used, is to train students in the following topics: Sizing of PV-wind turbine hybrid system. Comparison of the actual energy production by

the wind turbine with the theoretical production based on site’s wind data analysis in conjunc-tion with wind turbine’s power curve.

Evaluation of PV system’s energy production and calculation of the Fill Factor, the coefficient of performance and the impact of ambient tem-perature to the performance of the PV system.

Calculation of the batteries and inverter per-formance and estimation of the total energy losses.

Familiarization with the use of LabView in data monitoring and management of PV-wind hybrid systems.

5 Conclusions The described hybrid PV-wind turbine sys-tem is installed to reduce the electricity dependence of the Laboratory of Renewable Energy Engineering of the Technical University of Crete from the power distribution net. Another important reason for this system design and development is its educational potential to demonstrate to the students how these systems are sized and operate in real time. Therefore, the system is a very powerful educational tool for the students laboratory practic-ing, where the indispensability and value of the re-newable energy sources is revealed.

6 Acknowledgements This work is supported from the project “Reformation of Undergraduate Studies Programs & Environment” of Technological Educational In-stitute of Crete, action category 2.6.1.g, in the frame of Op-erational Programme for Education and Initial Voca-tional Training II (O.P. "Education"). References: [1] E. Tzen, D. Theofilloyianakos, M. Sigalas, K.

Karamanis, Design and development of a hybrid autonomous system, Desalination, 166, 2004, pp. 267-274.

[2] AIR-X Manual, Land Southwest Windpower, USA.

[3] Shell Solar SM110 General Instalation Manual. [4] Steca Tarom 245 Manual. [5] Steca Fronius SOLARIX 900I Manual. [6] LabView, User’s Manual, National Instruments,

2000. [7] LabView, Measurements Manual, National Ins-

truments, 2000.