S. OzcelikDepartment of Mechanical Engineering

Texas A&M University-Kingsville

Outline Introduction Modeling PV Array Tracker Angles Solar Radiation Approach Results Conclusions

Introduction Photovoltaic solar power is one of the most promising

renewable energy sources in the world. At noon on a cloudless day at the equator, the power of

the sun is about 1 kW/m², as the sun rays comes perpendicular to a plane.

PV arrays can track the sun through each day to greatly enhance energy collection.

A remote home can be virtually self-sufficient with solar power.

Introduction A solar tracker orients a solar photovoltaic panel or

concentrating solar reflector or lens toward the sun to maximize irradiation.

The sun's position in the sky varies both with the seasons and time of day as the sun moves across the sky.

The solar energy intercepted by the solar panels during the course of the day is not maximized if the position of the panel is always static.

Dynamically oriented solar panels can track the sun throughout each day to greatly enhance energy collection.

Introduction The required accuracy of the solar tracker depends on the

application. Concentrators, especially in solar cell applications, require

a high degree of accuracy to ensure that the concentrated sunlight is directed precisely to the powered device.

Typically concentrator systems will not work at all without tracking.

Very large power plants or high temperature materials research facilities require very high precision similar to that used for solar telescopes.

Modeling the PV Array A solar PV cell equivalent circuit which mathematically

describes the I-V characteristics of the PV circuit is

Where 𝑅𝑠 is the series resistance, 𝑅𝑝 is the resistance in parallel ‘a’ is the diode ideality constant𝑉𝑏 is the thermal voltage of the solar cell 𝐼𝑜 is the diode saturation current𝐼𝑝ℎ is the photovoltaic (light-generated) current

Modeling the PV Array The light-generated current of the photovoltaic cell depends

linearly on the solar irradiation and is also influenced by the temperature,

Iph,nom, light generated current in solar cell circuit at nominal conditions (when temperature is 250 Celsius and irradiance of 1000 W/m2)ΔTem=T-Tnom, T is actual temperature and Tnom is the nominal temperature,G is the actual irradiation and Gnom is the nominal irradiation (usually 1000 W/m2).

The diode saturation current I0 and its dependence on the temperature may be expressed

Tracker Angles The position of the sun

during any time of day is calculated by knowing the azimuth and elevation angles. Both the azimuth angle φ, and elevation angle β measured from any pointon the earth’s surface

On the solar panel, these angles are

Tracker AnglesThe elevation angle β is the angle between the sun rays and the horizontal surface. It is complimentary to the zenith angle 𝜃𝑧𝑒𝑛.

Where L is the latitude angle of the location, δ is the declination angle, and ξ is the hour angle.

Tracker Angles For the horizontal coordinates, the azimuth angle φ, is

given as 00 in north direction, east +900, west 2700 and the south 1800.

The azimuth angle for True Local Time >12.00 hr,

Tracker Angles The azimuth angle for True Local Time <12.00 hr,

Where L- latitude of the location, β is the elevation angle and 𝛿 is the declination angle

Solar IrradiationThe radiation at the Earth's surface varies widely due to:

• Atmospheric effects, including absorption and scattering;

• Local variations in the atmosphere, such as water vapour, clouds, and pollution;

• Latitude of the location; and

• The season of the year and the time of day.

Solar IrradiationThe solar irradiation falling on the solar panel is composed of three main components,

Direct irradiance : The radiation passing through the atmosphere in a straight path.

Diffuse irradiance : The radiation due to undirected scattered light coming from any direction in the sky.

Reflected irradiance : The radiation reflected from the ground.

Solar IrradiationTotal irradiance on any inclined surface is the sum of direct irradiance, isotropic sky diffuse irradiance, and ground reflection

θ is the angle of incidence, β is the angle of inclination, and ρ is the reflection coefficient.

ApproachOne way to maximize the current generated by the solar panel is to achieve maximum total irradiation available at any given time. This is possible if panel azimuth and elevation angles are kept at those calculated (desired) values during the day.

Generate desired values of elevation and azimuth angles between 7am and 7pm.

Control actual angles and verify that result in maximum irradiation, G.

Approach

Results

Kyocera KC200GT PV Modules

Diagram representing Subsystem of the Solar Cell Array

Elevation angle

Azimuth angle

Total Irradiation

Overall System

At no load Speed 8884 Rpm

Current 2.03 Amp

At Stall Torque 1236.024 N-m

Current 104.079 Amp

At Maximum Efficiency- Efficiency 70.92 %

Torque 151.467 N-m

Speed 7795 Rpm

Current 14.53 Amp

Output 123 W

Motor Characteristics

Conclusions and Future Work Simulation results show that the simple approach is

effective.

Experimentally validate simulation results.

Design a tracking system using photo sensors placed inthe middle of each side of the panel

Compare the effectiveness of each tracking system.

Design a single actuator that control both elevation andazimuth angles.