project on solar power air compressor

The Study of Solar Power Air Compressors

CHAPTER 1 INTRODUCTION

1.1 Air compressor

Air compressor, as the name indicates, is a machine to compress the air and to raise its

pressure. The air compressor sucks air from the atmosphere, compresses it and then delivers

the same under a high pressure to a place where the supply of compressed air is required.

Years ago, it was common to have a central power source that drove all the tools through

a system of belts, wheels and drive shafts. The power was routed around the work space by

mechanical means. While the belts and shafts may be gone, the use a mechanical system to

move power around the workspace still exists. It is based on the energy stored in air under

pressure and the heart of the system is the air compressor.

Air compressors are used in a wide range of situations - from corner gas stations to major

manufacturing plants. Many more kinds of air compressors are finding their way into homes,

workshops, basements and garages. Models are sized to handle every job - from inflating

pool toys to powering tools such as nail guns, sanders, drills, impact wrenches, staplers and

spray guns. These are now available through local home centers, tool dealers and mail-order

catalogs.

To run these air compressors, a lot of electrical energy is required depending upon the

output pressure of the air. The non-renewable resources to produce electricity have become

limited and are near extinction, leading to high energy cost or energy crisis. In such

situations, renewable sources like solar power are very helpful and the application of this

technology to run air compressor is known as solar power air compressor. Already many

non-renewable energy dependent companies have started implementing solar power air

compressors for their industrial applications.

Fig 1.1 Basic principle of Solar Power Air Compressor

1


The solar power air compressor has a number of solar panels that consist of photovoltaic cells.

These cells create direct current electricity by the reaction of photons with Silicon dioxide. This direct

current is used to power a motor that works the compressor unit. It can also be used to charge a

battery bank that can be used as a backup when the sunlight is considerably dim or at night.

1.2 Main components of air compressor system

Fig 1.2 Main Components of Air Compressor

2


1.3 Energy

1.3.1 Classification of ENERGY

RENEWABLE ENERGY

It is the energy from sources that are essentially inexhaustible.

It can be harnessed without the release of harmful pollutants.

Ex: Solar power, Wind power, Tidal power.

Fig 1.3.1 Renewable Energy Sources

NON- RENEWABLE ENERGY

It is the conventional fossil fuels, which are likely to deplete with time.

Ex: Coal, Oil and Gas.

Fig 1.3.2 Non-Renewable Energy Sources

3


1.3.2 Current Energy Scenario in India

Sector MW % age

State Sector 78,378.14 52.5

Central Sector 50,522.63 34.0

Power Sector 28,328.71 13.5

Table 1.3.1 Current Energy Scenario of INDIA

1.3.3 Source-wise distribution

Total Installed Capacity: 157229.48 MW

Fuel MW %age

Total Thermal 1,00,598.98 64.6

Hydro 36,863.40 24.7

Nuclear 4,340.00 2.9

Renewable Energy Sources

15,427.10 7.7

Table 1.3.2 Source-wise distribution

1.4 Fundamentals of solar energy

1.4.1 Need of Solar Energy

Developing countries in particular, face situations of limited energy resources - especially

provision of electricity in rural areas. There is an urgent need to address this constraint to the

social and economic development of our country. India faces a significant gap between

electricity demand and supply. Demand is increasing at an alarming rate when compared to

supply. According to leading Surveys, around 40 percent of India does not have electricity

provision.

4


1.4.2 Energy from sun

Fig 1.4.1 Earth’s energy budget

1.4.3 Insolation

Insolation is a measure of solar radiation energy received on a given surface area at a

given time. It is commonly expressed as average irradiance in watts per square meter (W/m2)

or Kilowatt-hours per square meter per day (KW.h/(m2.day)). In the case of photovoltaic, it is

commonly measured as (KWh/ (Kwp.y)) Kilowatt hours per year per kilowatt peak rating.

Types of Insolation:

Direct Insolation.

Diffuse and Reflected Insolation.

Fig 1.4.2 Types of Insolation

1.4.4 Direct Insolation

5


It is the solar irradiance measured at a given location on the earth with a surface element

perpendicular to the sun’s rays, excluding diffuse insolation.

1.4.5 Diffuse and Reflected Insolation

Diffuse insolation is the solar radiation that is scattered or reflected by atmospheric

components (clouds, for example) to the earth’s surface.

1.5 Basics of solar Photo-Voltaic system

Fig 1.5.1 showing parts of SPV system

1.5.1 Solar Panels

Solar panels are devices used for the conversion of solar energy into other form of

energy like electrical or heat or light. This can be broadly studied under three categories.

Panels used to generate electricity

Panels used to generate heat

Panels used to heat water in homes

1.5.2 Solar cells

6


Solar cells were originally developed to provide electrical energy for space satellites. Photovoltaic energy uses photoelectric cell that converts light into electricity.

Fig 1.5.2 Solar Cells

Solar photovoltaic power or PV takes the advantage of the photovoltaic effect in which solar cells

convert sunlight into electricity.

Types of Silicon Cells

Comparison of various Types of Solar Cells

7

PHOTOVOLTAIC CELLS

Thick Si (200-500µm)

Single-Crystal-Si

Multi-Crystal-Si

Thin film (1-10µm)

Hetero-JunctionCopper

SulphideCadmium Sulphide

Homo-junction

AmorphousMonoCrystal

linePolyCrystalli

ne

Fig 1.5.3 Types of Silicon Cells


Solar module Efficiency Price Power/Area

Monocrystalline 10-13% High High

Polycrystalline 9-13% Moderate Moderate

Amorphous 6-8% Low Low

Fig 1.5.4 Comparison of various types of solar cells

1.5.3 Inverter

Converts D.C to A.C power, at desired output voltage and frequency.

The output voltage of practical inverters is non-sinusoidal and certain harmonics.

Square wave voltage acceptable for medium and low power application in standalone

PV street lighting system.

Switching techniques of power semi-conductor devices reduces harmonics.

1.5.4 Battery

Most commonly used is Lead Acid Battery.

Fig 1.5 (e) Lead Acid Battery

Fig 1.5.5 Battery

8


1.6 Basics of Air compressor

Classification of Air compressors

Positive Displacement Air Compressors

Positive displacement air compressors are most common and include the

models used for domestic purposes and also by woodworkers, mechanics and

contractors. Here air pressure is increased by reducing the size of the space that

contains the air.

Examples:

1. Reciprocating Air compressor

Fig 1.6.2 Reciprocating Air Compressor

2. Rotary Air compressor

Fig 1.6.3 Rotary Air Compressor

9

Classification of Air compressors

Positive Displacement

Reciprocating

Rotary

Dynamic

Centrifugal

Axial

Fig 1.6 Classifications of Air Compressors


1.6.1 Reciprocating Air Compressors

Most of the compressors use a reciprocating piston. It has a small internal combustion

engine. The conventional piston compressor has a crank shaft, a connecting rod, a piston, a

cylinder and a valve head. Reciprocating compressors for general purpose use are

commercially obtainable in sizes from less than 1 HP to about 30 HP.

The crankshaft is driven by either an electric motor or a gas engine. While there are

small models that are comprised of just the pump and motor, most compressors have an air

tank to hold a quantity of air within a preset pressure range. The compressed air in the tank

drives the air tools, and the motor cycles on and off to automatically maintain pressure in the

tank. At the top of the cylinder, you'll find a valve head that holds the inlet and discharge

valves. Both are simply thin metal flaps–one mounted underneath and one mounted on top of

the valve plate. As the piston moves down, a vacuum is created above it. This allows outside

air at atmospheric pressure to push open the inlet valve and fill the area above the piston. As

the piston moves up, the air above it compresses, holds the inlet valve shut and pushes the

discharge valve open. The air moves from the discharge port to the tank. With each stroke,

more air enters the tank and the pressure rises.

10

Fig 1.6.4 Cut Section of Reciprocating Air Compressor


Double Acting Air compressor

These are the work horses of the compressed air circuits, so named, because

compressed air is used to both extend and react rod – a double action. Single acting air

cylinders use an internal spring to either extend or retract the cylinder rod. The first graphic

depicts a double-acting air cylinder in which compressed air has entered the cylinder port at

the rod-end of the cylinder.

The piston and rod combination are shaded in purple, and the compressed air is shown

in blue, for ease of identification.

Fig 1.6.5 Double Acting Compressor (a)

Air has pressurized the inside of the cylinder barrel, and in so doing, has driven the

cylinder piston to the rear. In so doing, the rod, which is attached to the piston, is retracted,

and whatever tooling is attached to the rod end, does some work.

The air that was in the rear of the cylinder has exited from the rear-cap cylinder port,

through the exhaust port in the air valve, and out to atmosphere.

Fig 1.6.6 Double Acting Compressor (b)

11


The second graphic shows that the reverse has occurred. Air has entered the rear

cylinder cap port, driven the piston to the rod end, and the rod has extended, allowing it to do

some sort of work.

Advantages of Reciprocating Air Compressors

Good for small applications.

Use no or little power when unloaded.

Cheap and small to operate.

Operates over a wide range of pressures.

Available in sizes less than 1HP.

Disadvantages of Reciprocating Air compressors

Noisy and are not available in sizes more than 30HP.

Maintenance can be an issue.

Oil-free air units are expensive.

1.6.2 Rotary Air Compressors

Rotary air compressors are similar to the reciprocating ones but piston and cylinder is

replaced by rotors. These air compressors are available in sizes ranging from 30HP to

200HP. Rotary air compressors are further classified as follows:

Fig 1.6.6 Types of Rotary Air Compressors

1.6.2 (a) Rotary Screw Air Compressors

Rotary screw compressors have gained popularity and market share (compared to

reciprocating compressors) since the 1980s. These units are most commonly used in sizes

ranging from about 5 to 900 HP.

12

Rotary Air Compressors

Screw Compressor

Vane Compressor


The most common type of rotary compressor is the helical twin, screw compressor.

Two mated rotors mesh together, trapping air, and reducing the volume of the air along the

rotors. Depending on the air purity requirements, rotary screw compressors are available as

lubricated or dry (oil free) types. Depending on the purity requirement, rotary screw

compressors are available in lubricated or dry (oil free) types.

Lubricant Injected Rotary Screw

The lubricant injected rotary screw compressor is the dominant type of industrial

compressor for a perse set of applications. For lubricant injected rotary screw compressors,

lubricants may be a hydrocarbon composition or a synthetic product.

Typically a mixture of compressed air and injected lubricant exits the air end and is

passed to a sump where the lubricant is removed from the compressed air. Directional and

speed changes are used to separate most of the liquid. The remaining aerosols in the

compressed air then are separated by means of a separator element within the sump, resulting

in a few parts per million (ppm) of lubricant carryover in the compressed air. With two stage

compressors, interstate cooling and the reduced internal losses due to a lower pressure across

each stage increase the compression efficiency. Consequently, less energy is required to

compress the air to the final pressure.

Dry Type Rotary Screw

In the dry type, the intermeshing rotors do not contact one another, and their relative

clearances are maintained to very close tolerances by means of external lubricated timing

gears. Most designs use two stages of compression with an intercooler and after cooler.

1.6.2(b) Rotary Vane Air Compressor

A rotary vane compressor uses an elliptical slotted rotor situated within a cylinder. The

rotor has slots along its length, each slot contains a vane. The vanes are forced outwards by

centrifugal force when the compressor is rotating, and the vanes move in and out of the slot

because the rotor is eccentric to the casing. The vanes sweep the cylinder, sucking air in on

one side and ejecting it on the other.

13


In doing so, it drives the vane mechanism inside the tool in a rotary motion. The

compressed air ‘tries’ to get from an area of high pressure back to atmosphere, thus moving

the vanes as it drives to the exhaust port of the tool. As the shaft in the vane-housing rotates,

the vanes inserted into that housing slide in or out, depending on where they are in the cycle.

Centrifugal force ensures that the vanes are always in contact with the inside of the outer

cylinder, creating a seal.

Air flows from an area of high pressure to an area of low pressure, so the high pressure

air in the small vane-compartment moves to the larger area vane, and ultimately, out. The

shaft inside of the vane-housing extends through seals to the outer end of the tool, and is

attached to tooling on the end. As a result, rotary motion of that tooling is got.

Advantages of Rotary Air Compressors

The biggest advantage of screw compressors is that they can run at full load

continuously, where the reciprocating compressors must be used at 60% duty cycle or

below.

Rotary screws are also a lot quieter and produce cooler air that is easier to dry.

Good efficiency for oil flooded models.

Can run fully loaded for a longer period of time.

Disadvantages of Rotary Air Compressors

Can use 40%-90% of full load power when unloaded.

Not good for very small or very large load.

1.6.3 Centrifugal Air Compressor

The centrifugal air compressor is a dynamic compressor, which depends on transfer of

energy from a rotating impeller to the air. The rotor accomplishes this by changing the

momentum and pressure of the air. This momentum is converted to useful pressure by

slowing the air down in a stationary diffuser.

The centrifugal air compressor is an oil free compressor by design. The oil lubricated

running gear is separated from the air by shaft seals and atmospheric vents.

14


Fig 1.6.7 Centrifugal Air Compressor

The centrifugal air compressor is a continuous duty compressor, with few moving parts, that

are particularly suited to high volume applications, especially where oil-free air is required.

Centrifugal air compressors are water-cooled and may be packaged; typically the package

includes the after-cooler and all controls. These compressors have appreciably different

characteristics as compared to reciprocating machines.

Advantages of Centrifugal Air Compressors

Can be staged for high pressure applications.

Typically used for loads greater than 200HP and high volume applications greater

than 12,000cmf.

Part load performance is adequate.

Most frequently used for medium volume and medium pressure air delivery.

It is an oil-free compressor by design.

Disadvantages of Centrifugal Air Compressors

Inter cooling must be provided for high pressure applications.

Not as efficient as rotary screw air compressor.

Axial Flow Air Compressors

An axial flow compressor, in its simplest form, consists of a number of rotating blade

rows attached to a rotating drum. Air flow is parallel to the axis of the compressor. Drum

consists of air tight casing to which stator blade rows are fixed. When air flows from one set

of stator and rotor to another, it gets compressed.

15


Advantages of Axial Flow Air Compressors

Axial flow compressors are widely used in gas turbine such as jet engines.

High efficiency.

Large mass flow capacity.

Disadvantages of Axial Flow Air Compressors

Temperature of the compressed air is high.

16

Fig 1.6.8 Axial Flow Air Compressor


CHAPTER 2 LITERATURE REVIEW

Application of solar power technology to run the air compressor was successfully run

by BHEL Corporate Research and Development Division, Vikasnagar, Hyderabad.

This solar power air compressor was developed to use the produced compressed air to pump

the water from the bore well. This solar power air compressor unit consists of the following

sub units:

Array of Solar panels or Solar Cells.

Solar Charge Controller.

Battery Bank or Battery Back up.

Inverter.

At initial stage the compressed air was produced by a reciprocating air compressor that

was run by a 1HP DC motor, i.e., a 746 Watts DC motor (since 1HP = 746 Watts). To run

this set up an array of almost 20-25 solar panels were used each consisting of 30-36 solar

cells made up of Silicon generating a maximum no-load voltage, i.e., Open Circuit Voltage of

Voc=20V.

As the initial stage was successful, they increased the capacity of the motor according to

their requirement. They also introduced an inverter as a sub-unit and were able to run a 5HP

AC motor, which was used to run a reciprocating air compressor for pumping water into a

large tank at a great elevation. From here, the water was supplied to all over the township for

different requirements.

Fig 2.1 Solar Power Air Compressor

17


V-I Characteristics of Solar Cells

The behavior of solar cells can be analyzed from its current voltage characteristics. The

intercepts of the curve on X-axis and Y-axis are called the short circuit current ISC and open

circuit voltage VOC. The maximum useful power corresponds to the point on the curve which

yields the rectangle with largest area and the corresponding voltage and current values are

represented by Vm and Im respectively.

Fig 2.2 V-I Characteristics of solar cells

Fill factor

Fill factor is defined as the ratio of maximum power to the product of V ocand I sc

Fill Factor=V m I m/V oc I sc.

Ideal cell will have a fill factor of unity. In order to maximize the fill factor, the ratio of

photocurrent to reverse saturation current should be maximized while minimizing the internal

circuit resistance and maximizing the shunt resistance. Typically the value of the fill factor

for commercial silicon cell is in the rage of 0.5 to 0.83.

The conversion efficiency of solar cell is given by

η=V m I m /(Solar Power )

18

Shadowed portion Illuminated portion

Active cell Portion Passive

Rectifiers

Fig 2.4 Showing Effect of partial shadowing


2.1 Effect of Variation of Insolation and Temperature

Voltage

Current

70°C

50°C

20°C

Figure 3.5 a shows characteristics with insulation kept constant and temperature

varying

Figure 3.5 b shows characteristics with temperature

kept constant and insulation varying

Current

4

0 10

8

6

4

2

20

2

0 10

20

30

30

6

8

1000w/m2

800w/m2222

600w/m2

400w/m2

Voltage

2.2 Effect of Shadowing

The operation of module under the condition of:

Partial shadowing of a cell is an open circuited series string of cell. It may completely

damage the module due to HOTSPOT effect.

Complete shadowing of one cell is short circuited series string of cell.

19

Fig 2.3 Effect of variation of Insolation and Temperature


2.3 Energy Losses and Efficiency

Conversion efficiency of solar cells is ratio of electrical power output to incident solar

power. Highest conversion efficiency of single crystal solar cell is 24%. Conversion

efficiencies of commercially produced single crystal solar cells are in range of 12-15%.

Energy losses are due to the inherent nature of internal physical process and available input.

2.4 Solar irradiance Measurement

Pyrometer

A pyrometer is sometimes called as solar meter, is used to measure broad band solar

irradiance on a planar surface and is a sensor that is designed to measure the solar radiation

flux density in W/m2 (Watts per meter square) from a field view of 180o.

Thermo electric pyrometer

Measures solar irradiance from 300-4000nm.

Sensor Blackened copper constantan thermopile covered with two concentric glass

domes which are transparent to the radiation 300-4000nm.

Generated emf by thermopile is proportional to the incident radiation. The typical

value is approximately 5 microwatts/watt/m2.

Used for instantaneous measurement and continuous recording of Global, Diffused,

Reflected Solar irradiance.

Fig 2.5 Pyranometer

20


Typical pyranometers do not require any power to operate and are frequently used in

meteorology, climatology, solar energy studies and building physics. They can be seen in

many meteorological stations, often installed horizontally and next to solar panels, and the

sensor is mounted in surface plane of the panel. The pyranometer has a glass dome shaded

from suns beam and the shading is accomplished either by an occulting (concealing) disc or

shading arm.

Pyrheliometer

In Pyrheliometer, the black absorber plate is located at the base of the tube which is

aligned with the direction of sun’s rays with the help of a two axis tracking mechanism and

an alignment indicator. Thus, the black plate receives only direct radiation and small amount

of diffuse radiation falling within the ‘acceptance angle’ of the instrument and hence this

instrument can be used for the measurement of direct radiation only.

Sunshine Recorder

Duration of bright sunshine in a day is measured using sunshine recorder. The sun’s

rays are focused by a glass sphere to a point on a card strip held in a groove in a spherical

bowl mounted concentrically with the sphere. Whenever there is a bright sunshine, the

image formed is intense enough to burn a spot on card strip. Through the day as sun moves

across the sky the image moves along the strip. Thus, a burnt trace whose length is

proportional to the duration of the sunshine is obtained on the strip.

21


CHAPTER 3 ASSESSMENT OF AIR COMPRESSOR

3.1. Capacity of Compressor

The capacity of a compressor is the full rated volume of flow of gas compressed and

delivered under conditions of total temperature, total pressure, and composition prevailing at

the compressor inlet.

It sometimes means actual flow rate, rather than rated volume of flow. This is also

called free air delivery (FAD), i.e., air at atmospheric conditions at any specified location.

This term does not mean air delivered under identical or standard conditions because the

altitude, barometer, and temperature may vary at different localities and at different times.

Due to ageing of the compressors and inherent inefficiencies in the internal

components, the free air delivered may be less than the design value, despite good

maintenance practices. Sometimes, other factors such as poor maintenance, fouled heat

exchanger and effects of altitude also tend to reduce free air delivery. In order to meet the air

demand, the inefficient compressor may have to run for more time, thus consuming more

power than actually required.

The power wastage depends on the percentage deviation of FAD capacity. For

example, a worn out compressor valve can reduce the compressor capacity by as much as 20

percent. A periodic assessment of the FAD capacity of each compressor has to be carried out

to check its actual capacity. If the deviations are more than 10 percent, corrective measures

should be taken to rectify the same.

3.2. Simple Capacity Assessment Method

Isolate the compressor along with its individual receiver that are to be taken for a test

from the main compressed air system by tightly closing the isolation valve or blanking it, thus

closing the receiver outlet.

Open the water drain valve and drain out water fully and empty the receiver and the

pipeline. Make sure that the water trap line is tightly closed once again to start the test.

Start the compressor and activate the stopwatch.

Note the time taken to attain the normal operational pressure P2 (in the receiver) from

initial pressure P1.

22


Calculate the capacity FAD:

Equation 3.1 Capacity of Air Compressor

P2= Final pressure after filling (kg/cm2a)

P1= Initial pressure (kg/cm2a) after bleeding)

P0= Atmospheric pressure (kg/cm2a)

V = Storage volume in m3 which includes receiver, after cooler and delivery piping

T = Time take to build up pressure to P2 in minutes.

3.3. Compressor Efficiency

For practical purposes, the most effective guide in comparing compressor efficiencies

is the specific power consumption, i.e., kW/volume flow rate, for different compressors that

would provide identical duty.

There are different measures of compressor efficiency that are commonly used

including volumetric efficiency, adiabatic efficiency, isothermal efficiency and mechanical

efficiency. We considered discussing only the isothermal and volumetric efficiency

calculation methods here.

3.3.1. Isothermal Efficiency

The reported value of efficiency is normally the isothermal efficiency. This is an

important consideration when selecting compressors based on reported values of efficiency.

Isothermal efficiency is calculated as follows

23

Isothermal efficiency

¿ Actual measured input power / Isothermal Power

Isothermal Power ( KW )=P1× Q1× loge (r

36.7)


Equation 3.2 Isothermal Efficiency

Where,

P1 = Absolute intake pressure kg / cm2

Q1 = Free air delivered m3/ hr

r = Pressure ratio P2

P1

The calculation of isothermal power does not include power needed to overcome friction and

generally gives an efficiency that is lower than adiabatic efficiency.

3.3.2. Volumetric efficiency

Equation 3.3 Volumetric Efficiency

D = Cylinder bore, meter

L = Cylinder stroke, meter

S = Compressor speed rpm

χ = 1 for single acting and 2 for double acting cylinders

n = No. of cylinders

24

Volumetric efficiency

= Free air delivered m3/min/Compressor displacement

Compressor displacement=π × D2/ 4 × L × χ ×n


3.4. Energy efficiency opportunity

3.4.1. Significant Inefficiencies

Compressors: 5 to > 50,000 HP.

70 – 90% of compressed air is loss.

3.4.2. Benefits of managed system

Electricity savings: 20 – 50%

Maintenance reduced, downtime decreased, production increased and product quality

improved.

3.4.3. Energy efficiency opportunities

Location

Significant influence on energy use.

Elevation

Higher altitude = lower volumetric efficiency.

Air Intake

o Keep intake air free from contaminants, dust or moist.

o Keep intake air temperature low.

o Every 4 oC rise in inlet air temperature = 1% higher energy consumption.

o Keep ambient temperature low, when an intake air filter is located at the

compressor.

Pressure Drops in Air Filter

o Install filter in cool location or draw air from cool location.

o Keep pressure drop across intake air filter to a minimum.

o Every 250 mm WC pressure drop = 2% higher energy consumption.

Use Inter and After Coolers

o Inlet air temperature rises at each stage of multi-stage machine.

o Inter coolers: Heat exchangers that remove heat between stages.

o After coolers: Reduce air temperature after final stage.

o Use water at lower temperature: Reduce power.

25


Pressure Settings

Higher pressure

o More power by compressors.

o Lower volumetric efficiency.

Operating above operating pressures

o Waste of energy.

o Excessive wear.

Minimizing Leakage

o Use ultrasonic acoustic detector.

o Tighten joints and connections.

o Replace faulty equipment.

Condensate Removal

o Condensate formed as after-cooler reduces discharge air temperature.

o Install condensate separator trap to remove condensate.

Controlled usage

o Do not use for low-pressure applications: agitation, combustion air, pneumatic

conveying.

o Use blowers instead.

Compressor controls

o Automatically turns-off compressor, when not needed.

Maintenance Practices

o Lubrication: Checked regularly.

o Air filters: Replaced regularly.

o Condensate traps: Ensure drainage.

o Air dryers: Inspect and replace filter.

26


CHAPTER 4 SOLAR POWER AIR COMPRESSOR

With rising energy costs and more awareness of the need to be environmentally friendly, companies and individuals are beginning to utilize the solar power air compressor.

4.1. Components of Solar Power Air Compressor

Solar power Air compressor is the effective assembly of all the components discussed in the above chapters. They are as follows:

Solar Photo-voltaic System Solar Charge Controller Battery Backup or Battery Bank Inverter Air Compressor

4.1.1 Solar Photo-voltaic System

Solar Photo-voltaic System is the source of energy generated from the irradiation from the sun. This system’s main function is to supply the energy required to run the air compressor.

4.1.2 Solar Charge Controller

Solar Charge Controller also known as SCC. It is the device that regulates the voltage and current from the solar photo-voltaic system to the battery bank. The no-load voltage, i.e., Open Circuit Voltage V oc of a photo-voltaic array increases more than 220 volts on a bright sunny day, which is very high for charging the battery bank and may also lead to the drying up of battery bank due to overcharging. To avoid the overcharging of battery bank, SCC is used.

SCC acts as an automatic switch in between solar photo-voltaic system and battery bank and also for AC supply and DC supply depending upon the type of motor used to run the air compressor.

27


Fig 4.1 Automatic switching by charge controller

4.1.3 Battery Backup

Battery Backup or Battery Bank is the temporary source of energy, which is used at

night or in cloudy weather, to run the air compressor. Most commonly, lead acid batteries are

used to run the air compressors.

The chemical reaction that takes place while battery discharges is as follows:

Positive plate : Pb O2+4 H+¿+SO4

2−¿+2 e−¿−−−−¿PbS O

4+2H

2O ¿

¿ ¿

Negative plate : Pb+SO 42−¿−−−−¿ PbS O4+2 e−¿¿ ¿

28

Sun

Solar Charge Controller

(SCC)

ChargingBattery Bank or

Battery Backup

Inverter

DC Air Compressor

Photo Voltaic Panel or Solar Panel


Fig 4.2 Battery

4.1.4 Inverter

Inverter is an electrical device that is used to convert DC voltage into AC voltage.

This is generally used when the motor used to run the air compressor is an AC motor. AC

motors are used when the distance between the source and load is relatively high, because DC

current cannot be effectively transmitted through longer distance.

4.1.5 Air Compressor

Air compressor converts solar power into kinetic energy by pressurizing and

compressing air, which is then released in quick bursts. There are numerous methods of air

compression, divided into either positive-displacement or negative-displacement types.

4.2Block Diagram of Solar Power Air Compressor Working

29


CHAPTER 5 RESULTS AND DISCUSSIONS

5.1 Assessment of energy and cost for running an air compressor with conventional energy.

The average electricity required to run an air compressor, which is running with a 1 HP motor, i.e., 746 watts motor (as 1 HP = 746 watts or 0.746 kilowatts) is as follows:

In India, the electricity bill is calculated on the basis of number of units of electricity utilized per month. This is calculated by the electricity meter provided by the government for each organization.

Therefore, 1 unit of electricity is utilized if a load of 1000 watts or 1 KW is run for a period of 1 hour.

i.e. 1 unit = 1 kilowatt-hour

Now, if we calculate for a load of 1 HP air compressor running for one hour we get,

1 HP = 0.746 kilowatts

But the amount of electricity utilized for a period of one hour is 0.746 kilowatts × 1 hour

i.e., 0.746 kilowatt-hours or 0.746 units

If the same compressor runs for about “t” hours per day, then the electricity utilized by the compressor per day is given by formula:

Eday=0.746 × t units.

Similarly for one month, we get

Emonth=0.746 ×t ×d units.

Where,

t = Working time of the compressor per day in hours.

d ¿Number of days in a month.

If we assume that the air compressor runs about 5 hours a day, then the energy utilized will be

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Emonth=0.746 ×5 × 30units.

Emonth=111.9units .

Electricity charges in Andhra Pradesh for Non-Domestic Category/ Commercial category:

Slab 1: 0 to 50 units : Rs.3.85 per unit

Slab 2: 51 to 100 units: Rs.6.20 per unit

Slab 3: 100 and above : Rs.6.50 per unit

For Industries, apart from energy charge in Rupees/Unit, there will also be a fixed charge (Rupees/ HP).

So the electricity bill for one month will be :

Slab 1 0 to 50 units E1=50 × 3.85=192.50

Slab 2 51 to 100 units E2=50× 6.20=310.00

Slab 3 100 and above E3=347.6 ×6.50=2259.40

Emonth=E1+¿ E2+E3+¿ charges

Emonth=192.50+310.00+2259.40+¿Charges

Emonth=2761.90+¿Charges

If we assume fixed charges for 1hp is Rs100 then Emonth=Rs 2861.90

∴ E year=¿ 2861.90 ×12

E year=¿ Rs. 34,342/-

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5.2 Assessment of energy and cost for running an air compressor with solar energy

The cost for running the same 1 HP motor air compressor with solar energy is as follows:

To run a 1 HP air compressor, we need to have an array of solar panels that can generate 1 kilowatt of electrical energy, i.e., 1250 Watts of electrical energy.

We know that cost of solar power in India is very high (whole sale price is 1$/watt in U.S.A) i.e., about Rs. 85/watt.

Hence, to run an air compressor of 1 HP we need 1000 watts of solar panels that will cost about Rs.1,02,000/-. In addition to this cost, we need to have a solar power plant that consists of battery bank, solar charge controller and inverter for A.C air compressors. This will make the total investment to about Rs.1,40,000/-.

The payback period for this compressor will be as follows

Pb=

1 ,40 ,00034 ,342 . 80

=4 .07 years

As the air compressor does not require any maintenance cost for a period of 20-25 years, the savings will be as follows:

If we consider that the solar plant will work for 25 years, then the electricity bill will be saved for only 20.93 years since we have to subtract the payback period.

Savings are calculated as follows:

S=34,342.80× 20.93

S=Rs 7,18,794.80 /−¿

5.3 Advantages of solar power air compressor

Solar power can be useful in such industrial applications where small kilowatt energy

is required.

The most common application of this technology is the common or garden air

compressor.

Solar power air compressors are used in the regions where gas and oil companies drill

is remote and does not have a reliable source of power.

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Solar energy is clean, renewable (unlike gas oil and coal) and sustainable, helping to

protect our environment.

Low / no maintenance.

Reduces dependence on centralized sources of energy.

5.4 Limitations of solar power air compressor

High initial cost.

Photo-voltaic arrays are not easily available.

High capacity DC motors cannot be manufactured easily.

Using an inverter incurs some loss of energy due to conversion of DC to AC.

Solar charge controllers involve complicated circuits management.

With rising energy costs and more awareness of the need to be environmentally friendly, companies and individuals are beginning to utilize the solar power air compressor.

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CHAPTER 6 CONCLUSION

By studying “Solar Power Air Compressor”, it is clear that solar power air compressors

are the application of solar power technology to power the compressing of air that powers a

drill or other device. It is the classic theory of conservation of energy, where one form of

energy is transformed into another.

These systems provide a dependable source of pneumatic power for use in remote areas.

They include high efficiency photovoltaic modules, long life batteries and heavy duty steel

construction for rugged, reliable service.

Can be used in Turbo charging of automobile engines.

This technology can be used to supply the compressed air to the pneumatic tools in

any small or even medium scale workshops.

Applying this photo-voltaic compressor technology in modern construction may help

to provide refrigeration effect, i.e., Air Conditioning to the rooms of the building.

This may also be helpful in pumping up the water to higher elevation by using

submersible water pumps which in turn work on the same principle of centrifugal air

compressor.

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project on solar power air compressor

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