For week 12, continue the report project proposal with chapter 2
4.0 LITERATURE REVIEW
Nowadays, there are several approach and
method used for generating electricity from energy harvesting. The most common this
method used to generate electricity is by using piezoelectric effect. Piezoelectric
is generating electricity from pressure or vibration when something stresses
that piezoelectric. However, amount electricity that produced form
piezoelectric is quite small in the range 2 to 10mV. London-based Pavegen
system describe another approach method energy harvesting is using Pavegen
energy harvesting tiles that from piezoelectric effect. The Pavegen is a hybrid
block box technology to convert the energy of a footstep into electricity. However,
a foot stomp that depresses a single tile can produce between one and seven
watts.
February 2009, speed bump as energy
sources. Speed bumps that will generate electricity as cars drive over them are
to be introduced on Britain's road. The traffic passes over it, the panels go
up and down, setting a cog in motion under the road. This then turns a motor,
which produces mechanical energy. A steady stream of traffic passing over the
bump can generate 10-36KW of power.
Energy harvesting proposed method used
in this project by using electro kinetic road ramp able to produce 7300watt
from one car compared Pavegen energy harvesting tile method.
4.1
Energy Harvesting
Energy harvesting or
also known as power harvesting is the process by which energy is derived from
external sources solar power, thermal energy, wind energy, salinity gradients
and kinetic energy captured. Energy harvesters provide a very small amount of
power enough for low-energy device. While the energy source for energy
harvesters is present as ambient background and is free.
Some of the energy
harvesting systems which use different sources to generate electrical energy
and their efficiencies are given below
·
Mechanical energy into
electricity-generators (20-70% efficiency), piezoelectric systems (0.5-15%
efficiency)
·
Chemical into electricity; fuel cells
(25-35% efficiency), primary batteries, rechargeable batteries
·
Heat/cold into electricity;
seebeck-elements (2-5% efficiency)
·
Electromagnetic radiation into
electricity; photovoltaic systems.
Figure
1: Energy Harvesting Sources
4.2 Alternator
Figure
2: Alternator
One of the most important main
components in this project is ac generator or alternators. They operate same
principle as dc generators. An alternator is a rotating electric machine, it
converting mechanical energy from the rotor drive machine for electric energy
in form of alternating current. The principle of operation an alternator occurs
when magnetic field lines cut across a conductor, a current is induced in the
conductor. In general, an alternator has a stationary part (stator) and a
rotating part (rotor). The stator contains windings of conductors and the rotor
contains a moving magnetic field. The field cuts across the conductors then
generate an electrical current. The mechanical input causes the rotor to
turn.
4.3 DC to AC power
converter (Inverter)
Since this project target
output is able to produce Ac, so it need to be converted from dc to ac. Power
inverter, or inverter, is an electrical power converter that changes direct
current (DC) to alternating current (AC). The converted AC can be at any
required voltage and frequency with the use of appropriate transformers,
switching, and control circuits. Inverters are commonly used to supply AC power
from DC sources such as solar panels or batteries. Inverter is use in this project
because the output of an alternator is DC source and need to be converted to Ac
source.
Figure 3: DC to AC power converter (Inverter)
4.4
DC Booster
Figure
4: Schematic DC Booster
DC-to-DC power converter
is use in this project since the output of an alternator depends on the vehicle
passes on the ramp, so the value output might be is smaller. By using with an
output voltage greater than its input voltage means that the input voltage can
be boost. DC-to-DC power converter It is a class of switched-mode power supply
(SMPS) containing at least two semiconductor switches (a diode and a
transistor) and at least one energy storage element, a capacitor, inductor, or
the two in combination. Filters made of capacitors (sometimes in combination
with inductors) are normally added to the output of the converter to reduce
output voltage ripple. Power for the boost converter can come from any suitable
DC sources, such as batteries, solar panels, rectifiers and DC generators. A
process that changes one DC voltage to a different DC voltage is called DC to
DC conversion. A boost converter is sometimes called a step-up converter since
it “steps up” the source voltage. Since power (P=IV) must be conserved, the
output current is lower than the source current.
4.5 Rechargeable
Battery
The rechargeable battery is use as backup
power supply if there is no vehicle run over on the ramp. In this project, maintenance-free
battery with valve regulated strongly recommended. Even though lead-acid
batteries are commonly used for this project, but nickel-cadmium batteries are
also used in some special circumstances. In the term of economy, the nickel
cadmium batteries are more expensive compare to the lead-acid type. The
important features of these of these batteries are designed specially for deep
cycle and low self-discharge. The lead acid battery was the most commonly used
of group, due to its low cost, and the efficiency of charging and dis charging
is 90%.
There are two types of lead acid
batteries, standard and gel filled. The standard batteries have a limited range
in the amount that can be discharges, the higher the daily discharge, the lower
the number of recharging cycles the battery will have in its lifetime. Lead
acid gel batteries are designed to handle discharges down to 20% before serious
damage occurs, and are able to handle the daily long term needs. Nickel Cadmium
batteries have a lower efficiency of 85%, and are more expensive than lead acid
types, but have a wider temperature range and are less susceptible to
over-charging.
Figure
5: Rechargeable Battery
