SOLAR POWERED STIRLING ENGINE

Dept of EEE

N HIMA GIRI

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERINGMADANAPALLE INSTITUTE OF TECHNOLOGY & SCIENCE

(Approved by AICTE, New Delhi and Affiliated to J.N.T.U.A, Anantapur) Madanapalle , Chittoor (Dist.), A.P.

An ISO 9001:2008 Certified Institution2013-2015

CONTENTS: INTRODUCTION

BASIC STIRLING ENGINE

TYPES OF STIRLING ENGINE

STIRLING ENGINE WITH SOLAR

CONCENTRATING SOLAR PLANTS

CARNOT CYCLE AND STIRLING CYCLE

CONCLUSION

INTRODUCTION The Stirling engine were invented in 1816 by Robert

Stirling in Scotland, some 80 years before the invention of diesel engine.

Stirling engine is a heat engine which converts heat energy to mechanical energy.

In this report stirling engine working is reviewed and is associated with solar power in various applications are discussed.

BASIC STIRLING ENGINE A Stirling engine is a device, which operates on a closed

regenerative thermodynamic cycle, with cyclic compression and expansion of the working fluid at different temperature levels.

The flow is controlled by volume changes so that there is a net conversion of heat to work.

CUT VIEW OF STIRLING ENGINE:

Pink – Hot cylinder wall Dark grey – Cold cylinder wall Yellow – Coolant inlet and outlet pipes Dark green – Thermal insulation separating the two cylinder ends Light green – Displacer piston Dark blue – Power piston Light blue – Linkage crank and flywheels

Operation Since the Stirling engine is a closed cycle, it contains a

fixed mass of gas called the "working fluid", most commonly air, hydrogen or helium.

The Stirling engine, like most heat engines, cycles through four main processes: cooling, compression, heating and expansion.

fig: pressure vs. volume

TYPES OF STIRLING ENGINE There are two major types of Stirling engines that are

distinguished by the way they move the air between the hot and cold sides of the cylinder.

1. Alpha type

2. Beta type

3. Gamma type

ALPHA TYPE ENGINE The two piston alpha type design has pistons in

independent cylinders, and gas is driven between the hot and cold spaces.

BETA TYPE ENGINE A beta Stirling has a single power piston

arranged within the same cylinder on the same shaft as a displacer piston.

GAMMA TYPE ENGINE: A gamma Stirling is simply a beta Stirling in

which the power piston is mounted in a separate cylinder alongside the displacer piston cylinder, but is still connected to the same flywheel.

APPLICATIONS A Stirling engine can function in reverse as a

heat pump for heating or cooling. Other uses include: combined heat and power,

solar power generation, Stirling cryocoolers, heat pump, marine engines, and low temperature difference engines.

STIRLNG ENGINE WITH SOLAR

Placed at the focus of a parabolic mirror a Stirling engine can convert solar Energy to electricity with efficiency better than non-concentrated photovoltaic cells.

By a mirror to focus the sun’s rays on the receiver end of a Stirling engine. The internal side of the receiver then heats hydrogen gas, which expands.

The pressure created by the expanding gas drives a piston, crank shaft, and drive shaft assembly much like those found in internal combustion engines but without igniting the gas. The drive shaft is connected to a small electricity generator.

CONCENTRATING SOLAR PLANTS

Concentrating solar power plants uses parabolic trough collectors or central tower concentration arrangement.

Concentrating solar plants:

SOLAR STIRLING WATER PUMP: The Sun pulse, a innovative water pump using solar concentrator and stirling

engine. At the front of the pump is a solar collector; this reflects sunlight towards the middle where it heats up the front of a Stirling Engine.

Sunvention's unique design

of Stirling engine uses air at

atmospheric pressure as the

working fluid, and pulses

at a slow 30-60 times

per minute. It can pump

water from depths as deep

as 100 m .

CARNOT CYCLE and STIRLING CYCLE:

The Carnot cycle has a low mean effective pressure because of its very low work output. Hence, one of the modified forms of the cycle to produce higher mean effective pressure is stirling cycle.

EFFICIENCY

The efficiency is defined to be:

Where W is the work done by the system (energy exiting the

system as work)QH is the heat put into the system (heat energy entering the

system)Tc is the absolute temperature of the cold reservoirTH is the absolute temperature of the hot reservoir

The estimated overall efficiency of the system would be about 9.6%.

CASE STUDY A practical solar stirling engine developed by the SES(stirling

energy systems), in which solar energy is focused on the Solar Receiver that is converted to 25kW of electricity for a peak conversion efficiency of approximately 31.25 percent.

SES(stirling energy systems) holds the world record of 31.25% efficiency for solar insolation to grid commercial power.

Fig: practical SES kit.

ADVANTAGES AND DISADVANTAGES If heat comes from a renewable energy source stirling engines produce no

emissions like solar. They run very silent and they don’t need any air supply. Heat source is available with free of cost. It has high efficiency when compared to other techniques. Theoretically having carnot efficiency. Some of the disadvantages are they need to be modeled as hybrid for

continuous operation.

Observation From Study

The best (and presumably most expensive) of current practical photovoltaic systems convert about 22% of the available solar energy into electricity. This mechanical system claims 24%, and all using ordinary low-environmental-impact materials and manufacturing techniques. Unlike fancy semiconductor solar panels.

Thus use of this scheme should be developed.

REFERENCES www.wikipedia.com www.stirlingenergy.com www.authorstream.com www.solarmagazine.com

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