Expert Systems with Applications 42 (2015) 1730–1742
Contents lists available at ScienceDirect
Expert Systems with Applications journal homepage: www.elsevier.com/locate/eswa
Zigbee-based data acquisition system for online monitoring of grid-connected photovoltaic system Farihah Shariff a,c, Nasrudin Abd Rahim a,b,⇑, Hew Wooi Ping a a
UM Power Energy Dedicated Advanced Centre (UMPEDAC), Level 4, Wisma R&D University of Malaya, Jalan Pantai Baharu, 59990 Kuala Lumpur, Malaysia Renewable Energy Research Group, King Abdulaziz University, Jeddah 21589, Saudi Arabia c Dept. of Electrical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia b
a r t i c l e
i n f o
Article history: Available online 13 October 2014 Keywords: Zigbee Photovoltaic Online Monitoring Grid-connected
a b s t r a c t For grid-connected photovoltaic (PV) system, monitoring is considered as a crucial aspect for observing the stability and performance of the system. The simplest method is to have the data collected and transmitted across data cables. Due to the cost and technical limitations of the data cable, the monitoring station needs to be located reasonably close to the monitored plant. Apart being inconvenient, the use of data cable often adds capital and maintenance cost to the system. In this research project, a Zigbee-based wireless monitoring system is developed for online monitoring of a grid-connected photovoltaic system. Parameters like temperature, irradiation, PV power output and grid inverter power output are monitored. The implementation process, including design and development of the hardware and software, is explained in detail. A user-friendly web-application is also developed, such that the monitored data is easily accessible via internet. To validate the performance, the system has been implemented on 1.25 kWp grid-connected photovoltaic system. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction As the global energy demand increases with the growing world population, countries all over the world are putting more and more emphasis on the development of renewable energy. Among the many sources of renewable energy, solar energy is considered the most promising and reliable energy source (Tyagi, Rahim, Rahim, & Selvaraj, 2013). In the light of this, governments in many countries have provided various incentives to setup solar energybased power plants, to complement the existing power plants which are running on fossil fuel. In order to ensure stability and reliability of a PV system, monitoring system is often preferred. As matter of fact, many recent solar energy conversion systems have included monitoring function as an integral part of the systems to ensure data can be collected and analyzed in systematic manner. Conventional wired monitoring system provides reliable solution in data transmission but suffers from several limitations. Apart from the physical constraints during laying of the data cables, the use of these cables also increases installation and maintenance ⇑ Corresponding author at: UM Power Energy Dedicated Advanced Centre (UMPEDAC), Level 4, Wisma R&D University of Malaya, Jalan Pantai Baharu, 59990 Kuala Lumpur, Malaysia. Tel.: +60 3 22463246; fax: +60 3 22463257. E-mail addresses:
[email protected] (F. Shariff),
[email protected] (N.A. Rahim),
[email protected] (W.P. Hew). http://dx.doi.org/10.1016/j.eswa.2014.10.007 0957-4174/Ó 2014 Elsevier Ltd. All rights reserved.
cost. Besides, for outdoor application such as PV systems, continuous exposure to sun beam and rains may reduce the lifespan of the system (Spertino & Corona, 2013). To overcome these issues, wireless monitoring system is favored over its cable-based counterpart. In this project, a Zigbee-based wireless monitoring system is designed and built as a replacement to the conventional cablebased monitoring system for a grid-tied PV system. Various aspects of the system, from design to construction and testing, are detailed here. Besides that, a PC-based application integrated with webbased function is designed and implemented in order to allow remote control of the system as well as easy access of the data over the internet. 2. Literature review In order to develop an effective yet low cost monitoring system, a number of previous works, which are related to solar energy monitoring system, have been reviewed and summarized in Table 1. Even though the focus here is on grid-connected PV system, monitoring systems for similar applications such as weather station, stand-alone PV system as well as hybrid systems are also included, to gain a better picture on this area of work. Based on the surveyed literature, the main characteristics of these monitoring systems are categorized into six main aspects, i.e. the data transfer mechanism, controller, monitored parameters,
F. Shariff et al. / Expert Systems with Applications 42 (2015) 1730–1742
1731
Nomenclature
lC AC ADC CL DAQ DC Eac ED EEPROM Elec. Epv f FF FFD G G1 Go GC GPRS GSM GUI h Hyb Iac Ib Il Imax Ipv Isc LP1 LP2 LQI MAC Met. MCU OS p Pt Pac PAN Pb PC
microcontroller alternating current Analog-to-Digital Converter losses array capture data acquisition direct current AC energy energy detection Electrically Erasable PROM electrical PV energy frequency fill factor full-function device solar radiation irradiance on plane of PV array irradiance on horizontal plane grid-connected general packet radio service global system for mobile communications Graphical User Interface humidity hybrid AC current, grid current battery current load current maximum current PV array current short circuit current logging point 1 logging point 2 link quality indication media storage control layer meteorological microcontroller unit operating system barometric pressure active power AC power personal area network battery power personal computer
sampling intervals, program development software and monitoring method. 2.1. Data transfer mechanism In terms of data transfer mechanism, both wired and wireless systems have been introduced in the past. For wired systems, data transmissions are usually done using RS232 cable (Anwari, Dom, & Rashid, 2011; Forero, Hernández, & Gordillo, 2006; Mukaro & Carelse, 1999; Soler-Bientz, Ricalde-Cab, & Solis-Rodriguez, 2006) or RS485 cable (Ayompe, Duffy, McCormack, & Conlon, 2011), with the monitoring systems being PC-based. As mentioned earlier, wired systems have their limitations, and are considered less favorable than the wireless option for the monitoring of a solar energy conversion system. For system employing wireless data transmission, a wider variety of data transmission technology has been reported, such as the use of satellite (Krauter, 2004), GSM (Gagliarducci, Lampasi, & Podestà, 2007; Rosiek & Batlles, 2008), Zigbee (López, Mantiñan, & Molina, 2012; Ranhotigamage & Mukhopadhyay, 2011) and other unspecified RF devices (Benghanem, 2009a; Benghanem,
PF PHP PHY Pl PLC Pmax Ppv Fq PV Q RF RFD S Samp. SA SCADA SDir Sv Sw SWC Ta Tm Ts Vac VB Vb VI Vl Vmax Voc Vpv W/Gc W/Gs W/Gv WS WSN Z
c cr H
gave
power factor hypertext preprocessor physical layer load power programmable logic controller maximum power PV power soil heat flux photovoltaic reactive power radio frequency reduced-function device apparent power sampling stand-alone supervisory control and data acquisition wind direction wind velocity wind speed soil water content ambient temperature module temperature soil temperature AC voltage, grid voltage Microsoft Visual Basic battery voltage Virtual Instrumentation load voltage maximum voltage open circuit voltage PV array voltage wind generator current wind generator rotational speed wind generator voltage weather station wireless sensor network utility grid impedance array yield reference yield efficiency average efficiency
2010; Kalaitzakis, Koutroulis, & Vlachos, 2003; Papadakis, Koutroulis, & Kalaitzakis, 2005). Among these, data transmission via satellite was reported to be slow, taking around 8 to 12 min (Krauter, 2004) and require high cost of installation (Rosiek & Batlles, 2008). GSM on the other hand is more reliable with accuracy of data transmission via SMS up to 100%. It also exhibit low retransmission rate and low total data loss rate of approximately 2.73% and 0.66%, respectively. The main drawback of GSM is its high operating cost, as the user needs to pay for the data transmission service. As seen from the surveyed literature, RF data transmission was quite a popular mean of wireless data transfer. Radio communication has the possibility of sending and receiving a huge amount of information at a low cost of transmission, and it is also a good alternative in remote area which does not have telephone lines. Its main disadvantage is the difficulty in obtaining permission for the transmission frequency and the high price of its installation (Rosiek & Batlles, 2008). Bluetooth support simple wireless networking but only cover short distances (Hua, Lin, Xu, Li, & Ouyang, 2009). Wi-Fi is another alternative technology in wireless communication where it has high data transfer rate and supports star topology (Drake, Najewicz, & Watts, 2010). However,
1732
Table 1 Characteristics of previous monitoring systems. Work done by
PV system type
Controller
Mukaro and Carelse (1999) Pietruszko and Gradzki (2003) Koutroulis and Kalaitzakis (2003)
Wired: RS232 Wired Wired: PCI bus
ST62E20 DAQ unit PCI-6024E
1m 5m 1m
PC PC PC
Turbo C++, ASSEMBLY Not mentioned LabVIEW
Wireless: RF
Vpv, Ipv, W/Gv, W/Gc, W/Gs, Vb, Ib
1m
Web
Java
Krauter (2004) Papadakis, Koutroulis, and Kalaitzakis (2005)
Wireless: Satellite Wireless: RF
Ppv, Vb, Pb, Pac W/Gv, W/Gc, W/Gs, Vpv, Ipv, Vb, Ib
15 m 1m
Web Web
Not mentioned VB, SQL server 2000
Forero, Hernández, and Gordillo (2006) Soler-Bientz, Ricalde-Cab, and Solis-Rodriguez (2006) Gagliarducci, Lampasi, and Podestà (2007)
Wired: RS232 Wired: RS232
G Go, G1, Ta, Tm, Sv Ta, G, h, SWC, Ts, Fq, SDir, W/G speed, Sv, p DAQ unit Sw, SDir, Ta, h, p, G, Ts, Fq, SWC lC G PCI DAQ card Ta, H, p, G, Sw, SDir, Ts, Fq, SWC FP DAQ board Ta, G FP Tm, Ta, G
None Vpv, Vac, Ipv, Iac, Pac, Eac, Z, f Vpv, Ipv, Vb, Ib, W/Gv, W/Gc
Kalaitzakis, Koutroulis, and Vlachos (2003)
WS GC (1 kWp) Hyb: PV and wind Hyb: PV and wind SA (5 kWp) Hyb: PV and wind SA SA
Vpv, Ipv, Epv, Ppv, Voc, Isc, FF, g, Pmax Vpv, Ipv, Ppv, Vb, Ib
