INTRODUCTION
Renewable energies are those forms of energy that derives from the natural movements and mechanisms of the environment – sunshine wind, the heat of the earth, the growth of plants and animals, the movement of the seas and rivers. They are classified into 1) Solar Energy, 2)Bio-mass Energy, 3) Hydro Energy, 4) Wind Energy, 5) Ocean Energy, 6) Geothermal Energy.
Among these SOLAR Energy has the distinctive features that are clean, environment friendly, inexhaustible and readily available energy everywhere and so on. The density of solar energy is low but it is suitable for a distributed utilization. More conventional forms of energy, the fossil fuels. Recovered their Solar energy input eons ago and possess the energy in a greatly concentrated form.
Applications of Solar Energy
1) Solar water heating, air heating, Solar cokkers.
2) Solar engines for water – pumping.
3) Photo voltaic conversion.
4) Solar fumaces, Solar thermal power generation.
SOLAR TRACKERS
Solar tracker is a PV array support structure following the sun during the day. As a result of the movement, the modules face the sun directly the whole day thus give much more electricity compared with fix mount modules. The original TRAXLE tracker was purpose developed and patented on most of the world markets.
Function of the Sun Tracker
The sun tracker is an apparatus which can follow the sun’s track from its rising in the east to its setting in the west. The TRAXLE solar tracker is an assembly consisting of aluminum profiles and stainless steel. Photovoltaic panels are attached to this assembly. Because the solar tracker turns after the sun, the photovoltaic panels face the sun directly all day long and their performance is thus substantially enhanced.
Technical Solution
The technical solution of the TRAXLE tracker is unique, with two patents issued, valid worldwide. The main load bearing part of TRAXLE is an aluminium or stainless stell pipel oriented slantwise on the north/south axis. Arms with photovoltaic panels are attached to the pipe. The pipe has a built in DC motor with tunrs the entire assembly with a worm gear unit. The motor is powered by PV module attached to the bottom part of the pipe. The module is mounted perpendicularly toward the sun and contains PV cells on both sides. The TRAXLE sun tracker to that side of the small PV module which is exposed to the sun.
Advantages of TRAXLE
• enhances performance of photovoltaic modules by 30%
• enhances performance of water pumps by 70%
• robust construction from stainless steel and aluminium profiles
• easy installation, unattended operation
• no maintenance of the assembly required
• works even in winter
• self-locking gear protects against gusty winds
THE TRACKER
At least one solar cell is fixed to rotary axle of the tracker and its plane is declined, from the plane parallel to the axle and perpendicular to the collectors of solar energy, approximately by 20o eastwards. The solar cell is connected directly to a DC electromotor. Both the motor and the self-locking transmission are integrated in the tracker axle.
Figures show principle of the tracker. Solar collectors are oriented eastwards. As the sun moves from the east to the west, angle of incidence of solar radiation of sensing / driving cells increases until power of the driving DC motor, connected to these cells, is high enough to move solar collectors. Then the angle of incidence starts to decrease until the power of the DC motor is lower than the necessary to move solar collectors. Additional antiparallel solar cells, placed in the same panel, enables back tracking of the tracker from any position.
Integration of antiparallel solar cells in one “bifacial” panel makes the tracker more compact, more reliable and less expensive. Antiparallel solar cells can be even manufactured monilitically on single substrate. Backtracking time of the new tracker is a few minutes only even in cold climate while by passive trackers the backtracking time is more than one hour at the same temperature.
The efficiency of the tracker increases with efficiency of solar panels. Force necessary to overcome friction and aerodynamic drag remains constant while the area related output power of driving / sensing solar panel increases.
SPECIFICATION
General description: Single axis solar tracker based on antiparallel “bifacial” driving/sensing solar panels connected directly to the reversible DC motor.
Weight of tracker Max. 8 kg/m2
Standard size 1-25m2
Length of the TRAXLE TM 2-8M
Weight of Collectors Max. 15 kg/m2
Tracking accuracy 100
Backlash <20
Tracking angle 1200
Max. static torque 500 Nm
Area related torque 2 Nm/m2
Max. windspeed 140 km/h
Backtracking time 5 min.
Temperature range -30 + 800c
Water & dust protection IP67
Main advantages of the new tracker over other systems
• Works also at low temperature down to –300c
• Collectible energy surplus up to 40% over fixed arrays.
• Pumping capacity surplus up to 80%
BIFACIAL SOLAR PV MODULES
Bifacial PV modules are modules utilizing the sunshine from both the “front face” and the “back face” of the module. The use of the reflected light from the back side gives bifacial modules the advantage against standard PV monofacial modules. Bifacial modules simply collect more light and give more power. When installed on a TRAXLE solar tracker, the PV energy gain can be up to 50%.
Because there is either no or low price difference in the price of such bifacial and monofacial modules it is reasonable to use bifacial modles which could produce 5-20% more energy. Additionally solar trackers/ concentrators are usually oriented to the west, before backtracking in the morning. The bifacial modules enable to collect direct back side solar radiation before backtracking. According to local climate the resulting energy gain coul be 2-5%.
It is also very advantageous that bifacial PV modules transparent for infrared radiation, has lower operating temperature against monofacial ones. It is especially advantageous by solar trackers and tracking soft concentrators where PV modules are exposed to higher solar radiation than on fixed racks. As indicated above solar trackers/concentrators are always mounted on high support structures which improve cooling of PV modules by air flow. The reduced
temperature is also very important for lifetime of PV modules in soft concentrators. It should help to avoid degradation of polymer encapsulants of modules cased by higher temperatures of monofacial modules. The new bifacial PV modules with reduced temperature sensitivity can further increase the system energy gain by up 10%. The polar axis solar tracker with c-Si bifacial PV modules will therefore deliver by about 50% more energy than fixed c-Si monofacial PV array with the same rated output power.
Concentrator
In the PV industry, a concentrator is a mirror that reflects additional sun shine to the PV modules. By this, the modules get more light and produce more electricity. The concentrators can be produced from various materials such as stainless steel, aluminum alloys, silver coated polymers or silver coated hardened glass.
Why track the sun?
The power generated by a PV panel is directly related to the amount of light it intercepts. More light = more power; its as simple as that.
The threeidentical PV panels at left are oriented in different directions relative to the sun’s rays. Panel “A”, faces the sun directly and its large shadow shows that it intercepts the maximum possible solar energy. Panel “B” does not face the sun, but is diagonal to the sun’s rays. It smaller shadow shows that panel “B” intercepts much less energy than “A”. Finally, panel “C” is aimed perpendicular to the sun’s rays and its tiny shadow shows that it intercepts very little of the available energy.
Pump 50% more water with a Sun Tracker 8!
Solar pumping systems which use a Sun Tracker 8 to keep their PV panels aimed at the sun can produce 50% more water than pumping systems using stationary PV panels. The Sun Tracker 8 allows the pump to turn on earlier and stay on later – this means more hours of pumping and produced by the very low light levels of dusk and dawn, we have developed a system which will return east in time to catch the early morning sun – without batteries! As a result, we no longer include internal batteries with our systems. This new feature is especially useful in well pumping applications where pumps are connected directly to PV panels and batteries are not needed or desired.
More Light = More Power
The amount of power produced by a photovoltaic panel depends upon the amount of sunlight it is exposed to. More light means more power. To intercept the most sunlight, a photovoltaic panel must be positioned so that the sun’s rays arrive at the panel directly; perpendicular to its surface. When a photovoltaic panel is not aimed directly at the sun, it does not intercept as much light as it can. And consequently, it does not produce as much power as it can.
Fixed vs. Tracking
Because of the earth’s constant motion, fixed (unmoving) photovoltaic panels rarely (if ever) aim directly at the sun. consequently, fixed panels intercept far less sunlight than they can. And as a result, they produce much less power than they are capable of producing. Photovoltaic panels mounted on a Sun Tracker 8 solar tracker, on the other hand, are always aimed directly at the sun from sunrise to sunset. As the sun’s position changes throughout the day, the Sun Tracker 8 continually adjusts the orientation of the panels so they are always aimed precisely at the sun. And as a result, photovoltaic panels on a Sun Tracker 8 collect the maximum amount of sunlight and product the most power possible.
The Sun Tracker 8
Sun Tracker 8 is a pole mounted electronic solar tracking system which needs no battery. Our weatherproof solid-state tracking electronics sense the sun’s position and control one or two heavy-duty actuator motors which keep the array aimed directly at the sun. at nightfall, Sun Tracker 8 turns the array east so that it is ready for the first rays of the next sunrise.
Consumes Very Little Power
Sun Tracker 8 is designed to consume very little power. Because the apparent motion of the sun across the sky is very slow, the Sun Tracker 8’s motion must also be very slow. Consequently, the periodic position adjustments made by Sun Tracker 8’s motor(s) normally last only a fraction of a second. As a result, total daily power consumption is very small. The solid – state tracking electronics themselves draw maximum of 7.5mA at 12V for a total of .15W or 3.6 watt hours per day. Consider that in just one hour a 25-watt light bulb uses 7 times the power that the Sun Tracker 8’s tracking electronics use
Durable and Reliable
Sun Tracker 8 is durable and reliable. Unlike passive tracking systems that use environmentally harmful Freon, the Sun Tracker 8’s performance is not adversely affected by cold temperatures or wind. The system’s heavy-duty linear actuators lock firmly on target, even in the iciest of winter gales. The Sun Tracker 8 is designed to withstand winds in excess of 100 mph and to operate in temperatures from –40F to 140 F. American Sun co backs every Sun Tracker 8 with a limited 10-year warranty.
Easy Installation
The Sun Tracker 8 is designed for quick, easy installation. In most cases, one person can install a Sun Tracker 8 in les than four hours. And because Sun Tracker 8 has full adjustable mounting points, almost any type of photovoltaic panel can be accommodated. Once the Sun Tracker 8 has been set up, there is virtually no maintenance.
Very Economical
The Sun Tracker 8 is economical. By keeping your array aimed directly at the sun, all day, every day, the Sun Tracker 8 makes the most of your photovoltaic investment. With a Sun Tracker 8, you get substantially more power from each PV panel in your array. And this increase in power results in a lower cost per watt and a shorter payback period for your entire system.
CONCLUSION
So, Solar tracking place a prominent role in production of electricity as:
• It can withstand winds in excess of 100 mph
• Operate in ambient temperature between –400F and 1400F.
• Turn east at night in preparation for the next day’s sunrise.
• Aim at the brightest area of the sky during overcast conditions.
• Limit “sun during partly cloudy conditions.
REFERENCES
1. ASME journal of Mechanical Engineering.
2. Solar Energy by SP Sukhatme.
URLs visited
www.solar-trackers.com.
B.V.RAMARAO
10H71A0256
Categories:
TECHNICAL ARTICLES(session-2)
