Adapting Mirror Concentrators and Tracking Mechanisms for PV Arrays Using CompactRIO and LabVIEW

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"Rugged and modular CompactRIO hardware and LabVIEW software proved the best approach to analyze tropical environmental impact for solar PV performance. We easily integrated most of the sensors for our system with the wide range of modules available for the CompactRIO platform."

- Effendy Ya’acob Mohammad, Universiti Putra Malaysia

The Challenge:
Designing a synchronized and reconfigurable real-time monitoring system for monocrystalline solar photovoltaic (PV) arrays installed in the tropics and rated at 1 kW with multiple configurations of mirror concentrators and tracking mechanisms.

The Solution:
Integrating PV output with weather station and thermocouple sensors using NI LabVIEW software and NI CompactRIO hardware to measure, log, monitor and analyze all data in real-time and synchronization mode.

Effendy Ya’acob Mohammad - Universiti Putra Malaysia
Hizam Hashim - Universiti Putra Malaysia
Sheikh Mohd Mustaffa Sheikh Ezaiddin - Virtual Instrument and& System Innovation Sdn Bhd

The Malaysian government works hard to attain energy independence and promotes the efficient use of renewable energy resources. One key source of renewable energy in our tropical climate solar photovoltaic (PV) energy which abundant, free sunlight produces electricity via photonic effect.

Mirror concentrating elements and tracking mechanisms have been investigated and widely adapted in solar PV technology. The main goal of this approach is to increase the daily energy generation from PV generators despite fluctuating sun irradiance, which is the sole source of photonic effect in PV electricity conversion process.

In this study, which took place in Serdang, Selangor, Malaysia, we installed PV arrays with mirror concentrators and tracking mechanisms and compared their performance to a PV array equipped with only a two-axis tracking device and a reference fixed PV array. We took samples for 10 months in this equatorial region that features uniform temperature, irradiance, high humidity, rainfall, and generally light winds. We monitored, recorded, and analyzed the data in real-time with NI LabVIEW software and the NI CompactRIO platform. We based our analysis on standard testing conditions (STC) data per unit array generation in which we analysed power contributions from mirror reflecting elements and tracking mechanism. We discovered an increase of more than 12 °C on the concentrating PV array surface with an AE of 24 percent. We referenced this information to design a PV array configuration for installation in the tropics.

Field Setup

We successfully set up 10 PV array units in Serdang, Selangor with coordinates of N 2°59’10”, E 101°43’30” in September 2011 (Figure 1). The PV arrays included  CEEG monocrystalline 95W PV modules connected in a series to meet the 30 grid-tied requirements . The pilot plant consists of the following elements:
• Six concentrating PV (CPV) generator systems
• Two tracking flat (TF) PV generator systems
• Two fixed flat (FF) PV (FF) generator systems
• One Stevens Met Station One weather station        
• One Apogee Instruments (pyranometer)         
• One Xylem global water rain bucket
• One Photasgard AHKF light intensity sensor
• One Type K thermocouple installed on top of and under the PV modules

DAQ and Monitoring System Setup:

Figure 2 illustrates the system configuration and data flow of the solar PV monitoring system with real-time targets. Due to the modular nature of CompactRIO, we can easily integrate signals such as RS-485 serial, current (4 to -20 mA), and high voltage into a single platform for data logging and streaming purposes. Additionally, we can capture and synchronize the power generated from the PV panels and the surface temperature of the PV with the environmental data.  

We programmed the CompactRIO system to automatically measure and log data based on a real-time event, which normally occur from 7 a.m. to 7 p.m. every single day. The system could operate in stand-alone mode and stream data every time we connected a PC to the system. We structured the LabVIEW Real-Time program using the following elements:

• A communication module for interaction between the CompactRIO system and the host PC
• A DAQ module to acquire data from each sensor and station
• A data logging and streaming module for streaming data from the CompactRIO system to the host PC
• A reboot module with a setting for automatic reboot for system safety prevention

Mirror Concentrators and Tracking Mechanisms

Mirror concentrators are a unique approach to enhance power output from PV modules on a per-area-basis. Concentrators use less cell material in a PV system. They also take advantage of relatively inexpensive materials such as plastic or glass lens to capture the solar energy shining on a fairly large area and focus that energy on a smaller area, where the PV module is installed. This approach reduces the use of semiconducting material which is an expensive part of a PV system, as well as increases the concentration ratio. The tracking PV array implies a two-axis tracking mechanism via self-adaptive control and pre-tightening algorithm for error rectifications.

Results and Discussion

Figure 3 shows the power contribution from mirror concentrators and tracking mechanisms for 65 data samples of STC with 5 percent tolerance based on field measurement. The total power generated from each PV arrays for 63 sample days is 53.0 kW for FF, 58.5 kW for TF, and 38.2 kW for CPV.

From the analysis, we calculated that the dual-axis tracking mechanism contributed as much as 5,485 W or 9.4 percent of the total generation from TF PV array with the FF PV as reference. The tracker contribution throughout the sampling period seemed unstable and sometimes experienced rapid fluctuation. This condition was comparable to the power contribution from the mirror reflector, which was more stable and consistent. The mirror concentrating element contributed approximately 8,929 W or 23.4 percent of the total generation from CPV array with TF PV as reference. The high contribution from mirror reflector was due to the increase of surface temperature (Table 1).

The modular nature of CompactRIO combined with the power of LabVIEW offers an expandable system we can improve in the future. We plan to add the web monitoring feature to the system to view results via the Android platform. With this feature, researchers can monitor data through a web browser from anywhere. We also plan to add financial analysis to the reporting system to highlight the PV Feed-in Tariff (FiT) rates endorsed by the Malaysian Parliament. We can adapt the LabVIEW Datalogging and Supervisory Control (DSC) Module or professional presentation of the research outcomes.

Our system uses the CompactRIO platform for monitoring, but we may extend it to also control tracking the CPV system. This simplifies the system by using only one platform for a complete solar station system.

Rugged Modularity, Flexible Performance

Rugged and modular CompactRIO hardware and LabVIEW software proved the best approach to analyze tropical environmental impact for solar PV performance. We easily integrated most of the sensors for our system with the wide range of modules available for the CompactRIO platform. Data synchronization was a crucial part in this research as we needed to study and analyze the relationship between the I-V curve of PV output with different array configurations and the environmental data. We addressed this challenge with CompactRIO and LabVIEW.

There are still solar PV research areas to explore to determine if it is the best energy source for Malaysian climate conditions. We can expand and modify our flexible system when the research approach changes, saving us time and money compared to off-the-shelve instruments.

Author Information:
Effendy Ya’acob Mohammad
Universiti Putra Malaysia
Faculty of Engineering, Universiti Putra Malaysia, Serdang, Selangor
Tel: 60196787178
Fax: 60386567099

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