Intelligent tracker 02

AN INTELLIGENT SOLAR TRACKING SYSTEM

Umer Adnan

Haroon Ashraf

Nada Masood

THE BASICS: SOLAR TRACKING

Solar Trackers Increase PV “POWER”

Peak Time

METHODS FOR TRACKING THE SUN

There are many types of trackers (Single axis, dual axis, Polar etc) but we will focus our attention on the method of tracking.

There are three basic methods that Solar trackers use to keep track of the sun. The goal is to get the “max possible power” averaged over a day.

1. Sensor based Employ photodiodes, LDRs and other light sensitive sensors

2. Chronological Take longitude/latitude and time/date and use pre-programmed data to set

the Sun angle at each point in time

3. Intelligent Sensor-less control Use advanced techniques for detecting where the panels achieves Max Power

and learn to optimize the tracking process over time.

SENSOR BASED TRACKING

Often used in Hobby / small scale projects.

Method is highly unreliable due to Incorrect data from sensors Dust, clouds, wind etc LDRs also get heated by and this affects the accuracy of the output they

provide.

Blindness in such trackers is a very common phenomenon

They track the brightest part of the ask , which may or may NOT be the orientation in which the panels produce max power.

CHRONOLOGICAL TRACKERS

These trackers use pre-programmed values to find the angle of the Sun. They have inputs like longitude, latitude, time and date etc fed into them for each location and produce a value for angle for each step.

No matter if its cloudy, sunny or its raining, the tracker will always position itself according to a “predicted value” of where the Sun will be.

Advantages: They stick to the sun like glue Data from the year 2000 to 2050 can be programmed in the inputs are

known. Produce fairly good results

CHRONOLOGICAL TRACKERS

Disadvantages: Its an open loop system. The tracking controller “Predicts” the angle at

which the Sun will be at a particular time. It doesn’t get any feedback if its doing a good job or not.

Doesn’t account for Clouds / Fog (diffused sunlight) Temperature of the solar cells Other factors like air mass , moisture etc Gives you the perfect angle, BUT…..

Unfortunately , tracking is NOT done to achieve a perfect angle, It is done in order to get the Max possible power.

SENSORLESS INTELLIGENT CONTROL

This is an intelligent system, which monitors , in real time, the photovoltaic energy (power) produced and avoids systematic failures coming from changes on assumed values (position, orientation, cleanliness on the cells etc) . Once turned ON it scans the sky and finds the point as which max power was produced. Uses a small 10-15 Watt panel for running operations, and calculating peak power.

This methodology resembles what goes on in the grid tied inverter , or other charge regulators , which can boost or suppress the voltage to maximize the power dynamically as the load varies.

This peak power tracking control once deployed , creates a set of data points in its memory and learns to adapt to its conditions. It gets smarter as it grows old.

WHY ITS BETTER ! Solar cells are non-linear devices, here is a plot of the average silicon solar

cell. It is usually plotted by varying the load across the cell.

WHY ITS BETTER ! Power : P= (V x I). MPP is at the “knee of the curve”

GETTING MAX.POWER Our goal will be to orient the panel in such a way that, it operates at or

near MPP. Typically the MPP is at 90% of the Isc (short circuit current) and between 70-75 % of the Voc (Open circuit voltage).

VARYING SUNLIGHT The system is unaffected by sunlight. It keeps track of the MPP.

VARYING TEMPERATURE As cell temperature varies, so does the Peak power point. The system is

immune to temperature , and will extract the max possible power at any given temperature.

DESIGN REQUIREMENTS FOR SINGLE AXIS TRACKEREngineering Requirements

Movement

• Slow Rotation , minimal Jerk , Efficient, Higher current rating than

Lorentz tracker

• Single axis (upgradable to 2D)

Demonstrational

• Immune to dust/Wind/clouds, Intelligence (Learning)

• Intriguing, Grasp Attention

Special Requirements

• Functions Autonomously, no other data required

• Faces point which produces max.power

• Self-Contained, very low power consumption

• Can Power itself indefinitely

STUDY OF LORENTZ ETA TRACK 1000

Price ~ 4700* US Dollars Weight 320 kg Angle 0-90 degrees East-West

Empirical testing on the controller Voltage conditioning circuitry , battery charge operation, current

and voltage signal conditioning, AVR pins operation(approx), Motor driver operation etc

Breakup of circuitry and methodology

Controlling the Linear actuator (0.1 degree accuracy or less)

ELECTRONICS- TASKS COMPLETED

The electronics sub-circuits have been tested in Proteus and are logically correct.

1. Current measurement (I max)2. Open circuit voltage (V oc) , Nominal voltage (V max)3. Reverse polarity , Overcharge protection of battery4. Battery charging control5. Solar voltage signal instrumentation6. Reed sensor signal conditioning7. Motor driver selection and testing (LMD18200)

LINEAR ACTUATOR-DESCRIPTION

Reed Sensor

Limit switches

LINEAR ACTUATOR READING @ 12VDC

LINEAR ACTUATOR PROBLEMS

Initially we got errors in counting the pulses when using an 8051.Variation of 15-25 pulses on complete stroke length (compressing and expanding)

The sensor needed a de-bounce circuitry for proper operation as Lorentz have given this topic , some important significance.

Our options in Hardware: RC filter or Schmitt trigger

Our options in Software: ADC monitoring of signal to remove noise

Initially, results from an RC filter, greatly showed improvement in performance, but since Lorentz have used a Schmitt trigger , and fed the output to ADC pin, we are assuming they are doing both software and hardware checks to ensure a pulse is never missed at any time.

DE-BOUNCE CIRCUITRY SIMULATION Shows a very noisy signal being cleaned by our Schmitt trigger design.

CALCULATING PEAK POINT OF A PANEL AT AKHTER SOLAR At the Akhter solar factory, they use a SUN SIMULATOR to calculate the

MPP of a solar panel . This is done in order to calculate the efficiency of the panel by the following formula:

This term is calculated using the ratio of the maximum power point, Pm, divided by the input light irradiance (E, in W/m2) under standard test conditions (STC) and the surface area of the solar cell (Ac in m2). STC specifies a temperature of 25°C and an irradiance of 1000 W/m2 with an air mass 1.5 (AM1.5) spectrum. These correspond to the irradiance and spectrum of sunlight incident on a clear day upon a sun-facing 37°-tilted surface with the sun at an angle of 41.81° above the horizon.

The SUN SIMULATOR flashes a neon lamp @ 1000Hz and takes readings , compares it to a reference solar cell that is fitted besides the panel to be tested. It then gives the MPP of the panel/cell. (Will be verified in our next trip to Hattar)

MAX POWER POINT

A solar cell may operate over a wide range of voltages (V) and currents (I). By increasing the resistive load on an irradiated cell continuously from zero (a short circuit) to a very high value (an open circuit) one can determine the maximum-power point, the point that maximizes V×I; that is, the load for which the cell can deliver maximum electrical power at that level of irradiation.

Maximum power (with 45 °C cell temperature) is typically produced with 75% to 80% of the open-circuit voltage (0.43 volts in this case) and 90% of the short-circuit current.

The short-circuit current (Isc) from a cell is nearly proportional to the illumination, while the open-circuit voltage (Voc) may drop only 10% with a 80% drop in illumination, so only measuring the voltage wont give as very accurate results.

MAX POWER POINT- THE IDEA …..

In our case , we will short the solar panel outputs (almost) with 0.1 Ohms wire wound resistance for 50 milliseconds. This will give us a point near the Isc of the IV curve, and use PWM to generate the entire curve, for 0% PWM we will get Voc, similarly as PWM is increased to 100 % we get a point very close to Isc. In this way MPP can be located.

MAX POWER POINT- THE IDEA ….. From the given panel (10W) , closing the switch for very short period of

time and taking the reading, will also use to essentially make a virtual resistor.

A resistor by definition limits the flow of electrons in a circuit, we would limit the flow of electrons by varying the PWM duty cycle.