The document describes the design and components of a solar assisted bicycle. It consists of solar panels that charge batteries which power a hub motor on the front wheel. A voltage regulator monitors the battery charging from the solar panels. The motor is controlled through a motor controller and throttle. The bicycle is intended to reduce human effort and provide emissions-free transportation at a lower cost than other electric bicycles. It includes calculations for the solar energy potential and modeling the power needs for acceleration, overcoming air drag, rolling resistance, and climbing.

1. SOLAR ASSISTED BICYCLE
Department of ME, VAST-TC, Kilimanoor Page 1
CHAPTER 1
INTRODUCTION
As the crude-oil reserves are depleting day-by-day and pollution is the major
threat while using these energy sources, the human community has to move to
renewable sources of energy. Among the renewable sources, solar power is available
throughout the year in India and India has a solar power potential of 5gw. Inorder to
utilize the huge power potential we had designed a vehicle with solar power.
According to a source, India stands at fourth place after china with 3.2 lakhs barrels
in fuel consumption. With this large import India spends a huge currency from
foreign reserves and if this project is implemented with subsidies a large share of
foreign exchange can be saved.
Bicycle being the cheapest mode of transport in India it can be easily
affordable to the poor people. With sufficient alterations in design it can be used to
move at a higher speed than pedaled bicycles and also it reduces human effort. The
bicycle consists of solar panels and batteries. There is a provision in this vehicle to
charge the vehicle with the grid power, thus making it flexible when solar power is
not available. The solar assisted bicycle uses a 850w hub motor fitted with the front
wheel and potentiometer is provided to vary the speed of the vehicle. Solar charge
controller is used to monitor the charging of batteries using solar panel. It is free of
emissions and completely eco-friendly. Comparatively, this vehicle is of lower cost
than the commercially available battery operated bicycles .the reliability of
commercial battery bicycles with respect to riding distance/charge is lower than that
of our fabricated model.

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Department of ME, VAST-TC, Kilimanoor Page 2
CHAPTER 2
LITERATURE SURVEY
2.1 MAIN COMPONENTS OF SOLAR ASSISTED BICYCLE
The solar assisted bicycle consist of following components (Fig.1) - hub
motor, solar panel, voltage regulator, lead acid battery, motor controller, accelerator,
bicycle.
Fig 2.1- Block Diagram of a solar assisted bicycle
2.1.1 Hub motor
Brushless DC (BLDC) Motor is used because they are highly reliable and
mounted in the hub of the wheel. The rotor is placed outside of the stator and the
stator is coupled to the axle and wheel will be rotated by means of direct current
supplied through batteries. Hub motor has steel laminations with windings arranged
in two patterns: Delta pattern and Star pattern. The star winding can provide high
torque at low speed and other pattern can provide low torque at low speed. BLDC
motor uses Hall Effect sensors for detecting the speed of the vehicle and 3 sensors are
used in our model. The motor needs a position sensor for giving commutation
sequence for turning on the devices. The commutation senses the position of rotor and
the phases are energized to produce the maximum amount of torque.
Hub motors generates high torque at low speed, which is highly efficient and which
does not need sprockets, brackets and drive chains. This means they are very reliable

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Department of ME, VAST-TC, Kilimanoor Page 3
and have a long life. The main characteristics of Brushless DC Motors is that they
may be controlled to give wide constant power speed ranges
Fig 2.2-Hub Motor Rotor
Fig 2.3-Hub Motor Stator
2.1.2 Solar cells/panels
As the title suggests the bicycle is operated by solar energy. The lead acid
battery is charged with solar energy with the help of a solar cell. Solar cells convert
the energy of sunlight directly into electricity through the use of the photovoltaic
effect. The photovoltaic effect involves the creation of a voltage into an electro-
magnetic radiation.

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Department of ME, VAST-TC, Kilimanoor Page 4
The photoelectric and photovoltaic effects are related to sunlight, but are different in
that electrons are ejected from a material’s surface upon exposure to radiation of
sufficient energy in photoelectric, and generated electrons are transferred to different
bands of valence to conduction within the material, resulting in the build-up of
voltage between two electrodes in photovoltaic.
Solar cells are electrically connected and fabricated as a module with a sheet
of glass on top to allow light to pass and protect the semiconductor from the weather.
To obtain a desired peak DC voltage we will add solar cells in series, and to obtain a
desired peak current, the solar cells are put in parallel position
Fig 2.4-Solar Panel
2.1.3 Voltage regulator
It is essential to regulate the voltage output from the solar panel before it is
supplied to the battery. A voltage regulator is a power converter with an output DC
voltage greater than the input DC voltage. This is used to regulate an input voltage to
a higher regulated voltage.
The output of the solar panel is not always be stable due to fluctuations in
intensity of sunlight, angular changes with respect to the direction of sunlight, as well
as other environmental factors. This is the voltage regulator/Boost Converter comes
into SAB. The output of the solar panel is the input of the boost converter, which then
outputs into the battery for charging. Because the output of the solar panel will be

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varying constantly, we need a voltage regulator/boost converter that will take an input
from a wide range of voltages and output a specific, constant voltage value.
A voltage regulator/boost converter is a power converter that will take in a DC
voltage and output a higher value DC voltage. Our voltage regulator/boost converter
requires output of the solar panel, which can range from 0V to 27.2V, and output for
charging of the battery.
Fig 2.5-Voltage Regulator
2.1.4 Lead acid battery
Lead-acid batteries are the most widely used batteries in electrical
applications. Although the energy density of lead-acid batteries is much lower than
the lithium ion batteries, they are much safer than the former provided the safety
measures are met. Current supplied from battery is measured in Amperes. In
accordance to the amount of current supplied the rate of discharge depends. Batteries
are generally rated in terms of Amp-hour and this is called the battery capacity. As
compared to the existing battery systems lead acid batteries are the most efficient and
suitable for the desired application. Sealed lead-acid batteries are used in our model.
Current supplied from battery indicates the flow of energy from the battery
and is measured in amperes (or Amps). The higher the current flow faster the battery
will discharge. A battery is rated in ampere-hours (abbreviated Ah) and this is called

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the battery capacity. This project revolves around supplying and utilizing energy
within a high voltage battery. It demands for a battery with longer running hours,
lighter weight with respect to its high output voltage and higher energy density.
Among all the existing rechargeable battery systems, the lead acid cell technology is
the most efficient and practical choice for the desired application. The battery chosen
for this project was a high capacity lead acid battery pack designed specifically for
vehicles. Plastic casing is provided to house the internal components of the battery.
Fig 2.6-Parts of lead acid battery cell
2.1.5.Motor controller
The motor controller is considered to be the heart of the electric bicycle as it
controls the amount of power required to drive the hub motor. It converts the DC
Voltage into alternating voltage with varying amplitude that drives the motor at
variable speeds. It consists of transistors and microprocessor that detects any defects
in functioning of hall sensors and to protect against any high or low voltage problems.
It basically consists of MOSFET transistors and small microprocessor that
vary from detecting any malfunctions with the motor hall sensors, the throttle, to
protect functions against excessive current and under-voltage, which are ideal for
protecting the system.

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Department of ME, VAST-TC, Kilimanoor Page 7
2.1.6 Accelerator/throttle
The speed of the bicycle is required to vary depending upon the road
conditions & traffic. Therefore an accelerator or a throttle is necessary. Throttle
allows us to drive the motor from zero speed to full speed. The throttle is fitted on
right side of the handle bar and is connected to controller. The throttle converts DC
voltage from battery to an alternating voltage with variable amplitude and frequency
that drives the hub motor at different speeds. It consists of MOSFET transistors and a
small microprocessor. This throttle is technically referred to as a Hall Effect type. The
throttle has three wires contains a black, red, and green. The supply voltage is via red
and black wires and is usually around 4 volts. Green wire voltage increases as the
throttle is turned.
Fig 2.7 Throttle/Accelerator

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Department of ME, VAST-TC, Kilimanoor Page 8
Chapter 3
METHODOLOGY
3.1 SOLAR ENERGY CALCULATIONS
It is important to define a coordinate system that can be used consistently to be able to
keep track of the position of the solar panel relative the sun and the urban
surrounding.
Fig 3.1 Definition of angles between the sun and a solar panel.
γ indicates azimuth angles (0° is north and 90°, east); αsun is the altitude angle of the
sun and αpanel the tilt angle of the panel, both relative horizon; αi is the angle of
incidence between the direct irradiance and the solar panel's normal and θzenith is the
zenith angle (i.e. 90°- αsun).
The Figure 3.1 defines all the important angles for the sun and a solar panel.
γpanel and γsun notes the azimuth angle of the panel and the sun respectively, both
are defined as 0° to north and 90° to the east; αpanel and αsun notes the angle relative
ground for the panel and the sun respectively; αi is the angle of incidence between the

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Department of ME, VAST-TC, Kilimanoor Page 9
sun's direct irradiance and the normal of the solar panel and last is the zenith angle,
θzenith, which indicates the angle between zenith and the sun.
3.1.1 Losses in the solar cell
Due to the nature of semiconductors, there will be an increase in internal
resistivity of a solar cell with increased cell temperature. Commonly, the response of
this is referred to as the Temperature Coefficient (TC) in solar panel datasheets.
Typical TC values for crystalline solar panels is around -0.3 %/°C to -0.5 %/°C
relative 25 °C (Skoplaki & Palyvos, 2009). If the cell temperature is higher than 25
°C, the solar panel will thus generate less power than its nameplate states. This is
often the case as the more irradiance, the higher the cell temperature. Various
simplified models have been presented to estimate the solar cell temperature based on
a number of different parameters (Jakhrani, et al., 2011). Temperature data was
collected from the Swedish Meteorological and Hydrological Institute, SMHI (2014).
The proverb: 'A chain is not stronger than its weakest link' is unfortunately
true for solar panels. As a solar panel is constructed by series-connected cells, if only
one cell is shadowed, the whole panel's output will change drastically. This does not
only affect the power output but also puts the panel at risk as the shaded cell will start
to dissipate power (Rauschenbach, 1980, p. 77). The easiest way to deal with this is to
design the system so that series connections are avoided as much as possible. By
parallel connecting panels and adding a blocking diode on each panel, you prevent the
whole system to be affected if one panel is partially shaded. This will however not
solve the problem with individual panels losing much of their power during partial
shading, as often will be the case in urban environment. A possible solution is to
employ diodes at strings of cells or even at each cell; but as panels are enclosed they
must be manufactured in such way.
3.2 MODELING A SOLAR ASSISTED BICYCLE
This section focuses on the E-bike's power and energy use. Newton's second
law of motion states that,
𝑚𝑎=∑_i^n▒F_i ,

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Where m in the case of an E-bike is the total mass of the rider and the E-bike (kg), a
the acceleration (m/s2) and F all the different forces (N) that affects the E-bike. When
riding in constant speed there are three forces counteracting the input forces that
needs to taken into account: Air-drag, rolling resistance and climbing force. The sum
of the forces for an E-bike in constant speed is,
F_human+F_motor=F_air+F_roll+F_climb
where F_human is the force provided by pedalling, F_motor the force provided by
the electrical motor, F_air the air drag, F_roll the rolling resistance and F_climb the
force when climbing up- or downhill. The power (W) is the force times velocity,
𝑃=𝐹𝑣
Where v is the speed relative ground (m/s). If the input power is larger than the total
losses, the bike will accelerate until the equation is balanced. The following sections
will present each force and as well as the energy use during acceleration.
3.2.1.Power during acceleration and deceleration
Energy is stored in momentum of the rider. The stored energy of a moving
object can be expressed as,
E=1/2 mv^2
where E is the energy in Joules, m the mass (kg) and v its velocity (m/s). The energy
needed to accelerate an object from velocity v_0 to v_1 is thus,
Δ𝐸=1/2 1/(3.6*〖10〗^3 ) m(〖v_1 〗^2-〖v_0〗^2 )
where ΔE is the energy needed in Wh. Accelerating an E-bike with the total mass of
100 kg from 0 km/h to 25 km/h will for example need 0.7 Wh provided to the road
excluding all other forces. The power used during the acceleration depends on the
time of acceleration which is limited by the power the human and the electric motor
may supply.

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3.2.2. Power to overcome air drag
One of the forces that is especially strong in high speeds is wind resistance. Its
power may be expressed as,
P_w=(C_d ρA)/2 (v_w+v_g )^2 v_g
where C_dis the coefficient of air drag, ρ the air density6 (kg/m^3), A the total area
of the rider and the bicycle as seen from the front (m^2), v_w the head wind speed
(m/s) and v_g the ground
speed (m/s) (Morchin & Oman, 2006, p. 24). A typical value for the coefficient of air
drag is 1 for an upright cyclist (Morchin, 1996), which is assumed to be the seating
position for E-bikes in an E-BSS. The frontal area can be assumed to be 0.50 m^2
(measured by Morchin and Oman (2006) for a male weighing 80 kg). Note that the
wind speed marks the head wind speed. Cycling north when the wind speed is 5 m/s
from northeast will for example result in a 3.5 m/s head wind speed due to the 45°
displacement. Wind coming from the back of the rider is represented by negative
values.
3.2.3 Power to overcome rolling resistance
The rolling resistance is caused by the tires, bearings and other moving parts
on the bicycle.It is thus independent on the bicycle design but also its speed and the
total weight of the rider
and bicycle. The power needed to overcome the rolling resistance is,
P_roll=gC_r m_tot v_g
where g is the gravitational acceleration (9.81 m/s2), C_r the coefficient of rolling
resistance, m_tot the total mass of the rider and bicycle (kg) and v_g the speed
relative ground (m/s) (Morchin & Oman, 2006, p. 26). The coefficient of rolling
resistance for an E-bike and a rider (mtot at 99 kg) has been measured to 0.0071 on
smooth asphalt by Morchin (1996).

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3.2.4 Power during climbing
When riding up- or downhill there are changes in potential energy that need to
be accounted for. An expression for the power during climbing is,
P_hill=gm_tot v_g G
where g is the gravitational acceleration (9.81 m/s2), mtot the total weight of the rider
and the bicycle (kg), vg the speed relative ground (m/s) and G the road grade (%)
(Morchin & Oman, 2006, p. 23). The road grade can for small hills be approximated
as the fraction between the rise and the bird's eye distance travelled. For steep hills it
may be computed by,
𝐺=sin⁡(tan^(-1)⁡(((△h)/(△l))/100) )
where Δh is the height difference of the hill and Δl the horizontal distance; both in
meters. Note that G is positive uphill, negative downhill and zero in flat conditions.
Table 6 shows examples of the slope grades for three steep roads in Gothenburg.
Going uphill in 20 km/h would for example require 245 W in pure hill climbing
power for rider weighing 75 kg with a 25 kg E-bike.

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Chapter 4
CONCLUSION
Solar assisted bicycle is modification of existing bicycle and driven by solar
energy. It is suitable for both city and country roads, that are made of cement, asphalt,
or mud. This bicycle is cheaper, simpler in construction & can be widely used for
short distance travelling especially by school children, college students, office goers,
villagers, postmen etc. It is very much suitable for young, aged, handicap people and
caters the need of economically poor class of society. It can be operated throughout
the year free of cost. The most important feature of this bicycle is that it does not
consume valuable fossil fuels thereby saving crores of foreign currencies. It is
ecofriendly & pollution free, as it does not have any emissions. Moreover it is
noiseless and can be recharged with the AC adapter in case of emergency and cloudy
weather. The operating cost per kilometer is minimal, around Rs.0.70/km. It can be
driven by manual pedalling in case of any problem with the solar system. It has fewer
components, can be easily mounted or dismounted, thus needs less maintenance.

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Chapter 5
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