# Analysis of development of a solar tracker engineering essay

## 1. INTRODUCTION

The need for development of the modern world has imposed an everincreasing energy demand. The gradual depletion of fossil fuels reserves combined with the irreversible environmental consequences of their widespread use resulted in an effort for the rational use of fossil fuels and in energy production from environmentally friendly technologies. One of these is the exploitation of solar energy, a photovoltaic phenomenon through which the solar energy is converted directly into electricity. Nowadays, it is commonly acceptable that environmental benefits may come from the energetic solar systems (photovoltaic systems, solar thermal) in contrast with conventional sources of energy that are not the same environmentally friendly. Energetic solar systems are necessary for the sustainable development of human activities. The use of fossil fuels causes serious problems in environment as it increases the pollution of air with the production of various quantities of carbon dioxide emissions and in general that leads to climate changes of earth. The electrical production with the PV applications helps in reducing significant amounts of CO2 emissions to the air and also it constrains the power transmission and distribution lines losses. The use of photovoltaic (P/V) systems for the production of electric energy is increasing and it evolves continuously. It becomes a technology widely widespread in all Europe. Photovoltaic (P/V) systems are discerned in grid-connected systems, which are connected to the network of electric power, and in autonomously systems, where accumulators (batteries) are used.

The earth rotates in 24 hours about its own axis, which defines the points of the north and south poles N and S respectively.¶ Latitude is defined positive for points north of the equator, negative south of the equator. Longitude is measured positive eastwards from Greenwich. The vertical north-south plane through P is the local meridional plane. More analytically we can see the Figure 2. 1 that shows the rotation of the Earth and illustrate the following points [1]:¶The axis of the poles is normal to the earth’s equatorial plane. C is the centre of the Earth. The point P on the Earth’s surface is determined by its latitude φ and longitude ψ. E and G are the points on the equator having the same longitude as P and Greenwich respectively. Figure 2. 1 Definition sketch for latitude φ and longitude ψ. [1]The hour angle ω at P is the angle through which the Earth has rotated since solar noon. Since the Earth rotates at /24h=, the hour angle is given by:(2. 1)The Earth orbits the Sun once per year, whilst the direction of its axis remains fixed in space, at an angle δ0 = 23. 45° away from the normal to the plane of revolution. The angle between the Sun’s direction and the equatorial plane is called the declination δ, relating to seasonal changes. Circles of latitude 0°, ±23. 5°, ±66. 5° are shown in the Figure 2. 2. Note how the declination φ varies through the year, equalling extremes at the two solstices and zero when the midday Sun is overhead at the equator for the two equinoxes [1]. Fig 2. 2 The Earth, as seen from a point further along its orbit. [1]δ varies smoothly from +δ0 = +23. 45° at midsummer in the northern hemisphere, to δ0 = -23. 45° at northern midwinter. Analytically,(2. 2)where n is the day in the year (n = 1 on 1 January). The error for a leap year is insignificant in practice.

## 2. 1 DEFINITION OF THE SOLAR BEAM

The scattered radiation reaching the earth’s surface and coming from all parts of the sky apart from the direct sun is called diffuse radiation. For the tilted surface of the collector represented in Figure 2. 3, define [1]: Figure 2. 3 Angles between sun and collector. [1]For the collector surface: Slope β (The angle between the plane surface in question and the horizontal). Surface azimuth angle γ (Projected on the horizontal plane, γ is the angle between the normal to the surface and the local longitude meridian). Zenith angle Θz (Angle of incidence θ, slope β and azimuth angle γ for a tilted surface). Angle of incidence θ (The angle between solar beam and surface normal). For the solar beam: Zenith angle θz (The angle between the solar beam and the vertical). Solar altitude αs (= 90°−θz) (The complement to the (solar) zenith angle and the angle of solar beam to the horizontal. Azimuth angle γs (Projected on the horizontal plane, the angle between the solar beam and the longitude meridian. Hour angle ω (as in (2. 1)) (The angle Earth has rotated since solar noon when γs = 0 in the northern hemisphere). 3. THE PROCESS OF DESIGNING A PV SYSTEMThere are many different types of PV systems available with different features and characteristics. The basic principles in the different types of the PV systems are the following: Stand-alone DC system (PV array, batteries, charge controller, DC loads). Stand-alone DC/AC system (PV array, batteries, charge controller, DC/AC inverter, DC/AC loads). Hybrid system (PV array, batteries, charge controller, battery controller, generator, system controller, DC/AC inverter, DC/AC loads). Grid-connected system (PC array, system controller, DC/AC inverter, AC loads, network). The main parts of an autonomous photovoltaic system to cover the electrical demand of the house appliances are highlighted to the following Figure 3. 1: Figure 3. 1 Stand-Alone DC/AC system. [13]The PV system will include some devices as PV array, control panel, charge controller and batteries. The different parts of the system will be described below:

## PV array

The PV array is constituted from many PV cells that are connected between them. PV cell is the elementary unit of PV system because there is converting the solar energy into electric energy. A PV array is made up of PV modules, which are environmentally-sealed collections of PV cells and these devices converting the sunlight into electricity.

## Inverter (DC/AC)

This is the device that takes the DC power from the PV array and converts it into standard AC power used by the house appliances. Inverters are electronic devices that are used in the grid-connected systems but also in autonomous systems with recharged batteries.

## Battery

Autonomous PV systems require storage of energy in order to have the possibility of functioning also in periods without or with few solar radiations, as at the duration of night or at the duration of shading.¶ However the experience has shown that in an autonomous PV system the battery¶ is the most impossible point, as the duration of life is generally much smaller compare¶compareefe all the other units of system. ¶Formally the battery in an autonomous PV system is sizing to ensure that provided the solar radiation does not suffice, the loads needs, they can cover for at least 3-4 days.¶ The result of sizing of this is the percentage of daily discharge battery of PV system it is roughly 25% with 30% of the theoretical capacity [3, 4].¶

## Charge controller

Its function consists on protecting the system of accumulation and avoiding extreme behaviour cases that could injure the batteries. 3. 1 FACTORS AFFECTING OUTPUTThere are many factors which affect the output electrical generation of the PV cells. More analytically these factors are:

## Standard Test Conditions

Solar modules produce DC electricity. The DC output of solar modules is rated by manufacturers under Standard Test Conditions (STC). These conditions are easily recreated in a factory, and allow for consistent comparisons of products, but need to be modified to estimate output under common outdoor operating conditions.

## Temperature

Module output power reduces as module temperature increases. When operating on a roof, a solar module will heat up substantially, reaching inner temperatures of 50-75 °C. For crystalline modules, a typical temperature reduction factor recommended is 89% [2].

## Dirt and dust

Dirt and dust can accumulate on the solar module surface, blocking some of the sunlight and reducing output. A typical annual dust reduction factor to use is 93% [2].

## Mismatch and wiring losses

The maximum power output of the total PV array is always less than the sum of the maximum output of the individual modules. This difference is a result of slight inconsistencies in performance from one module to the next and is called module mismatch and amounts to at least a 2% loss in system power. A reasonable reduction factor for these losses is 95% [2].

## DC to AC conversion losses

The DC power generated by the solar module must be converted into common household ac power using an inverter. Some power is lost in the conversion process, and there are additional losses in the wires from the rooftop array down to the inverter and out to the house panel. Actual field conditions usually result in overall DC-to-AC conversion efficiencies of about 88-92%, with 90% or 0. 90 a reasonable compromise [2]. 3. 2 MOUNTING OF PV MODULESThe sitting of the PV modules should be having the following characteristics: Resistance in air. Low cost. Reject of shading. Easy approach so that is possible to cleaning the PV units. The manufacture of PV should allocate height so the units not danger from the vegetation or from stones, but simultaneously to be possible the easy cleaning.¶ Because the PV units are very expensive it should be well mounted in order to be difficult their theft.¶ Finally the units should have a suitable distance between them and from the hedge for the avoiding phenomena of shadings. The construction sitting of PV arrays are separate in three categories: Constant structure. Structures with the possibility of rotation in axis. Structures with the possibility of rotation in two axes. The constant structures are the simplest. The modules are placed in concrete orientation and bent and they remain thus for all the duration of their operation. They have the lowest cost but cause their constant mounting have also the smaller production of energy. 4. DESIGN OF THE PV SYSTEMThere are many manufactures at the world market which design PV modules and solar cells [13]. The most common will be described in the table 6. 1: Table 6. 1 Summary of Current Photovoltaic Technology. [13]As can see in the table above there are four different cell types with different characteristics. The advantages and disadvantages, the efficiency of the solar cells and the cost are very important parameters for the choice the appropriate PV modules from the manufactures design. More analytically the Table 6. 2 shows the features of the different solar modules:

## Area

Monocrystalline10 – 13%25 years 90% rated power 30 years 80% rated power typicalhighhighPolycrystalline9 – 13%10 years 90% rated power 25 years 80% rated power typicalmoderatemoderateAmorphous6 – 8%10 yearslowlowTable 6. 2 Monocrystalline, polycristalline and amorphous modules features. [14]The choice of the appropriate PV module depends on many electrical and mechanical parameters as the peak power, the material, the dimensions, the weight, the temperature, the voltage, the current e. g. After research from different types and manufactures the two monocrystaline solar panel characteristics for the prototype is mentioned in table 6. 3:

10Watts

286 x 406 x 25

1. 5

16. 8

0. 59

21

0. 66

## SLA battery Voltage (V)

12Table 6. 3 Characteristics of the PV modules. In order to reduce the costs, two appropriate servo motors have been taken from an older project and their characteristics is mentioned in the table 6. 4:

4. 8-6. 0 V

3. 3Kg. cm

4. 1Kg. cm

## Current Drain (4. 8V):

8mA/idle and 150mA no load operating

## Current Drain (6. 0V):

8. 8mA/idle and 180mA no load operationTable 6. 4 Characteristics of the Servo motors HS-425BB