HYBRID SOLAR AND WIND OFF-GRID
SYSTEM - DESIGN AND CONTROL
Prasad GVT Srinivasan S* Sriram V*
*R.M.D. Engineering College (Affiliated to Anna University Chennai), Kavaraipettai, Tamil Nadu.
Abstract
This paper is aimed to improve the efficiency of a hybrid solar and windmill system by altering the design parameters. A complete prototype model has been designed and tested based on the altered features. In the designed model, solar PV module along with a wind turbine, the small prototype created powers a load of capacity 120 Watts. The design implementation consists of adding reflectors to the photovoltaic panel along with a dedicated sun tracking system. Further, a wind sensor detects the maximum wind flow direction to guide the windmill with plastic finished edges to improve the overall efficiency. The hybrid setup could be operated in manual and automatic modes. The former mode consists of a RF transmitter and receiver setup and the latter is effectively controlled by means of a microcontroller-AT Mega 162V. The entire setup can be extended for larger loads in order to electrify remote and inaccessible areas. Further, the project can be implemented in industrial and domestic sectors on a larger scale.
Keywords- Solar PV tracking system, reflectors, wind sensor, plastic finished edges. Introduction:
In the recent years, photo voltaic power generation has been receiving considerable attention as one of the more promising energy alternative. The reason for this rising interest lies in the direct conversion of sunlight into electricity. Photo voltaic energy conversion is one of the most attractive non conventional energy sources of proven reliability from the micro to mega watt level.
Its advantages are:
1. Absence of moving part
2. Ability to function unattended for long periods
3. Modular nature in which desired current, voltage and power level can be obtained by mere integration and
4. Long effective life and high reliability
The wide spread use of PV generation is however mainly hampered by economic factors. Efforts are being made worldwide to reduce the cost/watt through various technological innovations. Wind energy also is equally and effectively used in large scale wind farms to provide electricity to rural areas and other far reaching locations. Wind energy is being used extensively in areas like Denmark, Germany, Spain, India and in some areas of the United States of America. It is one of the largest forms of Green Energy used in the world today. Wind Energy is highly practical in places where the wind speed is 10 mph.
In the past 30 years, solar photovoltaic cells have increased in efficiency and the price levels have improved dramatically. Today the theoretical efficiency of a solar PV cell can be 25% - 30 % and a practical efficiency around 17%. Any improvement in efficiency of solar energy system will make a big difference in the use of solar panel. Developments are also taking place in finding new PV cells which can withstand high concentration of light and heat and produce more output per unit area. Small concentrating reflectors of a few cms across provide considerable concentration on cells made of special material and a number of such small concentrating units can be assembled to form a bigger panel. The panel as a whole is mounted suitably and tracking arrangements are made. In this work a simpler system of only one reflector on either side positioned at optimum angle is used which is found to enhance the light collection of conventional panels considerably and can be readily adopted in a wide scale. The elevation angle of sun remains almost invariant in a month and various very little in a year. Therefore single axis position control scheme may be sufficient in most of the application where economy and ease of maintenance are important
Outline of the proposed system
increase the collection efficiency. Details of the solar module, the microcontroller, system control mechanism and the driver circuits are given. A comparison has been made between stationary panel without reflectors and tracking type with reflectors.
Design of the Reflectors
Each reflector is inclined at 60 degree to the plane of the panel. The width of the reflector is equal to the width of the solar panel and the length matches that of solar panel. The tracking ensures that the plane of the panel is always perpendicular to the sun’s rays. This arrangement enables the light falling at the tip of the reflector to reach the edge of the panel and the all other reflected rays falling within the width of the panel. Thus there is no wastage and the collection efficiency is maximized. Theoretically this should double the light collection. It enables realization of the full potential of the panel.
Fig 1: Reflector design
Outline of the Wind tracking system
The distinguishing factor of wind tracking system is the usage of a wind sensor that identifies the direction along which the maximum intensity of the wind flows. The sensor itself is a small windmill whose output is in terms of milli volts. The maximum output value of the sensor is considered as the point of higher intensity of wind flow by the microcontroller and the wind mill is shifted toward the required direction. Thus the wind mill is rotated along the direction where maximum wind flows. A model of wind turbine is chosen, the model is an upwind and three blades turbine. The turbine’s pole is 3 m high and blade’s diameter is 35mm. The Generator used in this turbine is a 40 W wound-rotor induction machine.
Wind Sensor
The Model 50.5 Solid State wind Sensor is used in our system. This sensor series has offered high quality performance. This gives a 4 bit output to a microcontroller that could be controlled through manual and auto modes.
No moving parts
Digital and Analog outputs Time-proven design Sensor emulation
16-point wind tunnel calibration Microcontroller
The ATmega162 is a low-power CMOS 8-bit microcontroller based on the AVR Enhanced RISC architecture. By executing powerful instructions in a single clock cycle, The ATmega162 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed. The AVR core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers.
The ATmega162 provides the following features:
16K bytes of In-System Programmable Flash with Read-While-Write capabilities, 512 bytes EEPROM, 1K bytes SRAM,
An external memory interface, 35 general purpose I/O lines,
32 general purpose working registers, A JTAG interface for Boundary-scan,
On-chip Debugging support and programming, four flexible Timer/Counters with compare modes, internal and external interrupts,
A programmable Watchdog Timer with Internal Oscillator,
An SPI serial port
Five software selectable power saving modes.
The Idle mode stops the CPU while allowing the SRAM, Timer/Counters, SPI port, and interrupt system to continue functioning.
Modes of Operation
We are operating the solar and wind tracking system by means of two modes. Auto mode
Manual mode Manual operation and initial settings
The microcontroller clock generates 4MHZ clock pulses. Pulses at 1 sec interval are derived from this clock. The clock time can be manually set by pressing the minute switch or hour switch alone at a time. When both hour and minute switches are pressed simultaneously, the time clock starts running, time is added to the set time and the panel position moves to match the indicated time. The panel can therefore be tested to move to any desired position by setting the time suitably and activating the clock. The system operates from the same 12V battery which is used to collect power from the panel. The Radio Frequency Transmitter and Receiver This works at a frequency of 2.4Ghz. (CC2500). A dedicated microcontroller is employed for USART. The receptor has a remote control to coordinate the manual and auto modes.
worm and worm gear arrangement ensures that the panel is held and does not move away from the set position when the control execution is complete and power is taken off the motor. Thus no power is consumed in the idle condition of the panel and power is taken from battery only during actual movement. Even this energy consumption is negligible compared to the daily collection.
2.7 RESULTS AND DISCUSSIONS
USER REFERENCE CHART Impact of Reflectors & Solar Tracking Manual
Mode
POSITI ON
1 2 3 4 5 6 7 8 9 10 11
Power Output With out Reflector (watts)
11 AM 6.27 18.22 27.62 28.56 31.67 33.74 32.4 30.38 28.52 28.36 25.25 12 PM 6.44 18.47 28.73 30.59 32.43 33.85 35.8 34.47 32.52 30.35 26.72 1 PM 8.66 20.59 30.98 29.50 29.51 33.04 33.5 36.17 34.24 33.04 28.56 2 PM 6.38 18.21 23.78 25.23 27.09 31.17 31.3 31.82 33.91 31.12 26.54 3 PM 4.75 12.98 16.33 17.35 19.18 19.41 20.3 21.23 22.27 23.73 22.12 4 PM 3.17 10.57 10.99 11.45 11.87 11.98 13.7 13.98 14.88 15.90 16.95
Manual Mode
POSITI ON
1 2 3 4 5 6 7 8 9 10 11
Power Output With Reflecto r (watts)
11 AM 6.82 19.81 30.03 31.05 34.43 36.6 35.2 33.3 31.1 30.8 27.4
12 PM 7.01 20.08 31.23 33.25 35.25 36.8 38.9 37.4 35.3 32.9 29.0
1 PM 9.42 22.39 33.68 32.08 34.82 35.9 36.4 39.3 37.2 35.9 31.0
2 PM 6.90 19.80 25.85 27.43 29.45 33.8 34.0 34.5 36.8 33.8 28.8
3 PM 5.17 14.11 17.75 18.86 20.85 21.1 22.1 23.0 24.2 25.8 24.0
4 PM 3.45 11.49 11.95 12.45 12.91 13.0 14.9 15.2 16.1 17.2 18.4
Output of the Solar Panel
Open Circuit Voltage = 19.75 V
TIME FIXED PANEL
(Watts)
WITH REFLECTOR AND TRACKING (Watts)
11 AM 31.67 36.68
12 NOON 32.43 38.98
1 PM 29.51 39.32
2 PM 27.09 36.86
3 PM 19.18 18.43
4 PM 11.87 25.80
Output of the Wind mill
TIME WIND
DIRECTION AND SPEED
FIXED WITHOUT TRACKING (Watts) ( )
WITH WIND SENSOR AND TRACKING MECHANISM (Watts)
Morning 18 km/h 0.671 1.452
Afternoon 13 km/h 0.561 0.992
Evening 27 km/h 4.148 4.148
Night 25km/h 2.452 3.705
Courtesy: http://www.kea.metsite.com/
http://www.timeanddate.com/weather/india/chennai
Economics of the system
By using reflectors combined with tracking, the collection efficiency of the solar panel increases substantially. Even if we include the cost of tracking arrangement, there is still considerable overall saving as brought out in the calculation below, The cost of electrical energy per unit will come down and the subsidy also can be reduced leading to wider deployment for the same funds.
Cost of Panel: With Reflectors and Tracking
Cost of the Solar Panel (40Watts) = Rs. 8000 Cost of DC Motor worm gear = Rs. 1500
Cost for stand and Miscellaneous = Rs. 4500 Cost of Circuit and Driver Arrangement = Rs. 2000
Total Cost = Rs. 16000
Table 2: Output of Solar Panel
The above calculation is for installing 1 panel and this arrangement gives the power if 2 panels installed without reflectors and tracking arrangement (based on 50% increase in output considering evening readings of the Hybrid System)
Cost of Fixed Panels
Cost of 2 Panels =Rs.16000 Cost of Stand and Miscellaneous =Rs. 4500
Total Cost =Rs.20500
Saving in investment = Rs (20500-16000) = 4500
An investment of Rs.16000 gives the benefit of additional equivalent investment of Rs.4500. If more panels are connected together then the saving in capital will be higher because much of the drive arrangement can be made common for a group of panels.
2.8 APPLICATION AND FUTURE SCOPE
APPLICATIONS
Islanded system (remote areas) Hybrid vehicle (fuel less) Industrial power saver Distributed power generation ADVANTAGES
Green, environment friendly Efficiency improvement Higher output power Economical benifits User friendly control
Less interrupted continuous power FUTURE EXTENSION
Our system can be extended futher to an integrated solar wind system which can be used to power a vehicle. The vehicle can be started by means of solar power, and when it gains momentum, it can obtain sufficient wind energy to satisfy its fuel demands.
CONLUSION
In this work the collection of the solar panel was enhanced by 68.5% from that of the single panel with the help of reflectors and tracking. Further energy obtained using the windmill with addition of dedicated wind sensor and altered design together adds to an increase in the efficiency by an overall margin of above 50%. The working model of the hybrid system was successfully implemented and demonstrated. It is shown to be highly attractive economically. There is a strong case for providing new solar panel installations with reflectors and tracking arrangement along with the windmill with sensors in view of the above advantage.
REFERNCES
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[2] Specialists Conf., vol. 2, 23-27 June 1996, pp. 1027-1032J.Rizk and M H Nagrial. ’Implementation on solar energy Systems’- proceeing of world academy of science, Engineering and Technology Volume 31, July 2008. Page 131.
[3] Piao, Z.G.Park, J.M.Kim, J.H.Cho, G.B.Baek, H.L.,(2500) ”A study on the tracking photovoltaic system by program type,” page(s):971-973 Vol.2
[4] Pritchard,D., “Sun tracking by peak power positioning for photovoltaic concentrator arrays,”IEEE Control Systems Magazine, Volume 3, Issue 3, August 1983, pp.2-8.
[5] Wanzeller M.G.; Alves R.N.C.; Neto J.V.F.; Fonseca W.A.S.: Current Control Loop for Tracking of Maximum Power Point Supplied for Photovoltaic Array. IEEE Transactions on Instrumentation and Measurement, vol. 53, August 2004, pp. 1304-1310.
