ADVANCEMENTS IN SOLAR BASED LED STREET LIGHT
Electrical and Electronics Project by Ravi Devani
ABSTRACT
We are in the time where energy conservation & use of renewable
resources has become a necessity. Thus requirement of methods which are not
only highly efficient but also low in energy consumption has greatly increased
to keep a check on pollution factor. Keeping this in mind this paper focuses on
solar based LED Street light that uses automatic intensity controller with a
solar tracker. This type of LED street light not only adjust itself according
to the varying darkness but also keeps a track on overcharging, deep
discharging, automatic restoration of charging ,protecting the battery from the
over/under voltage. It comprised of solar cell and electric energy stored from battery.
The LED street lamp is lit at night automatically and changed into pulsed
lighting in low power after the setting time and then turns off in daytime. Since
only 20% of the total sun’s energy falls on earth and also the trajectory of
sun keeps changing thus a solar tracker is used so as to track maximum sun’s
energy.
Keywords: Solar panel, charge controller, Intensity regulator,
solar tracker.
INTRODUCTION
The surface of the Sun has a temperature of about 5,800 Kelvin (about 5,500
degrees Celsius, or about 10,000 degrees Fahrenheit),as per the say of NASA, At
that temperature, most of the energy the Sun radiates is visible and near
infrared light. At Earth’s average distance from the Sun (about 150 million
kilometers), the average intensity of solar energy reaching the top of the
atmosphere directly facing the Sun is about 1,360 watts per square meter,
according to measurements made by the most recent NASA satellite missions. This
amount of power is known as the total solar irradiance. (Before scientists
discovered that it varies by a small amount during the sunspot cycle, total
solar irradiance was sometimes called “the solar constant.”
Averaged over the entire planet, the amount of sunlight arriving at the top
of Earth’s atmosphere is only one-fourth of the total solar irradiance, or
approximately 340 watts per square meter.
SOLAR TRACKER
Solar tracking system is the most appropriate technology to enhance the
efficiency of the solar cells by tracking the sun. A microcontroller based
design methodology of an automatic solar tracker is presented in this paper.
Light dependent resistors are used as the sensors of the solar tracker. The sun
is the prime source of energy, directly or indirectly, which is also the fuel
for most renewable systems. Among all renewable systems, photovoltaic system is
the one which has a great chance to replace the conventional energy resources.
Solar panel directly converts solar radiation into electrical energy. Solar
panel is mainly made from semiconductor materials. Si used as the major
component of solar panels, which is maximum 24.5% efficient. Unless high
efficient solar panels are invented, the only way to enhance the performance of
a solar panel is to increase the intensity of light falling on it. Solar
trackers are the most appropriate and proven technology to increase the
efficiency of solar panels through keeping the panels aligned with the sun’s
position.
Solar trackers get popularized around the world in recent days to harness
solar energy in most efficient way. This is far more cost effective solution
than purchasing additional solar panels.
Fig.1: LED solar pathway light model LT-SOL10
TECHNOLOGY TO ENHANCE POWER OUTPUT FROM SOLAR PANEL
Increasing the cell efficiency, maximizing the power output and employing a
tracking system with solar panel are three ways to increase the overall efficiency
of the solar panel. Improvement of solar cell efficiency is an ongoing research
work and people throughout the world are actively doing research on this.
Maximizing the output power from solar panel and integrating solar tracking
system are the two ways where electronic design methodology can bring success.
Maximum power point tracking (MPPT) is the process to maximize the output
power from solar panel by keeping the solar panel’s operation on the knee point
of P-V characteristics.
A number of MPPT algorithms have been developed and employed around the
world. MPPT technology only offers the maximum power that can be received from
a stationary array of solar panels at a particular time; it cannot, however, increase
the power generation when the sun is not aligned with the system. Automatic
solar tracker increases the efficiency of the solar panel by keeping the solar
panel aligned with the rotating sun.
Solar tracking is a mechanized system to track the sun’s position that
increases power output of solar panel 30% to 60% than the stationary system. A
few design methodology of solar tracking system has been proposed in recent
days.
Electrical and Electronics Project by Ravi Devani
MICROCONTROLLER
The ATMEGA32 microcontroller has been used in the prototype.
Microcontroller is the heart of overall system.ATMEGA32 microcontroller
requires a 5 volt regulated voltage supply. „7805‟ voltage regulator is used to
provide fixed 5 volts supply to the microcontroller .ATMEGA32 has some features
such as analog comparator (AC), analog to digital converter (ADC), universal
synchronous asynchronous receiver transmitter (USART), times etc.
Utilization procedure of these features is given below:
Fig 2: schematic of solar tracker circuitry
1) Analog comparator:
There are two pins which are known as analog input 0 (AIN0) and analog
input 1 (AIN1). Two analog voltage signals coming from two junctions of photo
resistor circuit are fed to these pins. There is a bit called analog comparator
output (ACO) which is set to either „1‟ or „0‟.
VAINI> VAIN0
2) Analog to digital converter:
Among 8 analog to digital converter input pins ADC0 and ADC1 have been
used; where VVt ,is expected. Differential input is converted into digital
value and the most 8 significant bits are defined
10 ADC as ADC_result to compare with threshold.
ADC_result = [VADC0 – VADC1]
This threshold value, set according to the photo resistor response against
the solar radiation intensity, is provided,
Since ADC_result alone might be insufficient for rotation of motor. And if
ADC_result> Threshold; motor rotates one step.
3) Timers:
Built-in timer of ATMEGA32 is utilized to create delay. The Earth rotates
on its own axis, with respect to the sun 360° in a day and so it rotates,
(360°/24=) 15° an hour or 3.75° in 15 minutes. Delay for 1.5 minutes and 15
minutes are required. These delays are mentioned as short delay and moderate
delay respectively. The last hour before sunset will provide additional energy
to rotate the panel in the initial position and so the tracker no more rotates
to the west rather it will rotate reversely. As 2 hours in day time are not
considered for tracking, (2Ҳ15°=) 30° of rotation is not required to be done by
the solar tracker. Half stepping of stepper motor is considered which gives
3.75° rotation in each stepping; approximately ((180°-30°)/3.75°=) 40 rotations
are required in each day to track the sun at daylight.
Count is used for counting the number of „wait‟ states when weather is
cloudy and ADC does not permit to rotate the motor.
Fig 3: operational flowchart of solar tracker
CHARGE CONTROLLER
A charge controller monitors the state-of-battery to insure that when the
battery needs charge-current it gets it, and also insures the battery isn't
overcharged. Connecting a solar panel to a battery without a regulator seriously
risks damaging the battery and potentially causing a safety concern.
Charge controllers (or often called charge regulator) are rated based on
the amount of amperage they can process from a solar array. If a controller is
rated at 20 amps it means that you can connect up to 20 amps of solar panel
output current to this one controller. The most advanced charge controllers
utilize a charging principal referred to as Pulse-Width-Modulation (PWM) -
which insures the most efficient battery charging and extends the life of the
battery. Even more advanced controllers also include Maximum Power Point
Tracking (MPPT) which maximizes the amount of current going into the battery
from the solar array by lowering the panel's output voltage, which increases
the charging amps to the battery - because if a panel can produce 60 watts with
17.2 volts and 3.5 amps, then if the voltage is lowered to say 14 volts then
the amperage increases to 4.28 (14v X 4.28 amps = 60 watts) resulting in a 19%
increase in charging amps for this example.
Charge controllers also offer Low Voltage Disconnect (LVD) and Battery
Temperature Compensation (BTC) as an optional feature. The LVD feature permits
connecting loads to the LVD terminals which are then voltage sensitive. If the
battery voltage drops too far the loads are disconnected - preventing potential
damage to both the battery and the loads. BTC adjusts the charge rate based on
the temperature of the battery since batteries are sensitive to temperature variations
above and below about 75 F degrees.
Electrical and Electronics Project by Ravi Devani
1) Battery:
The Deep Cycle batteries used are designed to be discharged and then
re-charged hundreds or thousands of times.
These batteries are rated in Amp Hours (ah) - usually at 20 hours and 100
hours. Simply stated, amp hours refer to the amount of current - in amps -
which can be supplied by the battery over the period of hours. For example, a
350ah battery could supply 17.5 continuous amps over 20 hours or 35 continuous
amps for 10 hours. To quickly express the total watts potentially available in
a 6 volt 360ah battery; 360ah times the nominal 6 volts equals 2160 watts or 2.16kWh
(kilowatt-hours). Like solar panels, batteries are wired in series and/or
parallel to increase voltage to the desired level and increase amp hours.
The battery should have sufficient amp hour capacity to supply needed power
during the longest expected period "no sun" or extremely cloudy
conditions. A lead-acid battery should be sized at least 20% larger than this
amount. If there is a source of back-up power, such as a standby generator
along with a battery charger, the battery bank does not have to be sized for
worst case weather conditions.
The size of the battery bank required will depend on the storage capacity
required, the maximum discharge rate, the maximum charge rate, and the minimum
temperature at which the batteries will be used. During planning, all of these factors
are looked at, and the one requiring the largest capacity will dictate the
battery size.
In this specific application, and taking into account the changes of solar
radiation during the day and, consequently, the energy available, the battery
bank charge algorithm will present three different modes:
• If the panel available current is lower than 0.1CAh, the converter will
find the maximum power point (MPPT)in order to provide the highest current
possible for the battery bank (area under the current level, see figure 2).
• If the panel available current is higher than 0.1CAh, the converter
limits the current to 0.1CAh, and disables the search for the maximum power
point.
• If the batteries are already charged, the control algorithm will apply a
constant voltage level, in order to keep the batteries charged.
Lead-acid batteries are the most common in PV systems because their initial
cost is lower and because they are readily available nearly everywhere in the
world. There are many different sizes and designs of lead-acid batteries, but
the most important designation is that they are deep cycle batteries. Lead-acid
batteries are available in both wet-cell (requires maintenance) and sealed
no-maintenance versions. AGM and Gel-cell deep-cycle batteries are also popular
because they are maintenance free and they last a lot longer.
CONCLUSION
This paper has studied about various advancements in the field of solar
based LED Street light. The use of solar tracking system has greatly increased
the system and has helped to increase its overall output.
Whereas the use of charge control circuit in the solar based LED street
light has not only helped in saving the battery power but also in preventing
the battery from getting deep discharged, overcharged, thereby conserving a lot
of energy.
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Electrical and Electronics Project by Ravi Devani
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