Power Generation with Solar Dish Stirling Engine

Prospect of Bangladesh

ABDUL FATTAH

071 421 045EECS DepartmentNorth South University, Dhaka

M Ashraful Haq

072 150 045EECS DepartmentNorth South University,Dhaka

Abstract—This electronic document is a “live” template. The various components of your paper [title, text, heads, etc.] are already defined on the style sheet, as illustrated by the portions given in this document. (Abstract)

I. INTRODUCTION

One of the major problems in bangladesh is power crisis problem. To get rid of this problem we have to adopt a new prower source. Renewable energy is the most capable power source available to us right now. And for that reason stirling is one of the most best solution to meet up our power crisis.The Stirling cycle engine has numerous natural benefits over other heat engines. A prime benefit of the engine stems from the ability to operate from any heat source including continuous combustion of sustainable fuels, solar energy, factory waste heat, geothermal energy, or numerous other sustainable energy sources.Stirling engines consists of a solar dish panel which is used as the heat source of the stirling engine and uses flammable liquid as the moderator. Here it recycles the flammable liquid by transferring it from the heat zone to the cool zone and again from the cool zone to the heat zone. By going from back and forth it will transfer the mechanical power into electrical power by the help of generator. Due to the external combustion, a Stirling engine produces little noise, allowing its use in locations that are not preferable for internal combustion engines, such as in homes or buildings for electric power generation or other noise sensitive areas such as submarines. The Stirling cycle also has the theoretical efficiency of the Carnot cycle, creating tremendous development potential.

II. THE DISH STIRLING ENGINE PLANT

The thermo-mechanical part of the Dish Stirling Engineis an external combustion thermo dynamical machine,whose thermal source is represented by insulation.The sun radiation is concentrated on the receiverby a concentrator, with a parabolic mirror (Dish) thatrotates according to the sun position (Figure 1).

The engine (see (Walker, 1980)) is based on the Stir-ling thermodynamical cycle (consisting of two isovolumic and two isothermal transformations) where the working gas is helium. The engine is a two-cylinderengine (in "V con_guration", see Figure 2). The helium

gas is delivered by two valves from the so-called

helium bottle to the compression cylinder where thetemperature is about 20_C (low temperature).The _rst (isovolumic) phase of the thermodynami-cal cycle takes place when the gas, in the compressioncylinder (cold cylinder) is pushed by the correspondingpiston to the chamber of the second expansioncylinder (hot cylinder), passing through a devicecalled regenerator (which gains heat while gas passesfrom the heat source to the cold cylinder, and .looses.heat while gas passes from the cold cylinder to the heatsource) and then the receiver (heat source). Along thispath, the temperature of the gas increases from about20_C (in the cold cylinder) to about 600_C-800_C (inthe hot cylinder). The second (isothermal) phase is theexpansion of the hot gas in the expansion cylinder.Such expansion is due to the heat accumulated in thereceiver and produces mechanical work. Then the hotgas goes back on the same path .loosing. heat, so performinganother isovolumic transformation. The lastphase is the isothermal compression taking place inthe cold cylinder. The cold cylinder's walls are kept ata low temperature thanks to a suitable cooling system.The produced mechanical energy is transformed intoelectrical power by an induction motor, by which theplant supplies energy to the power network. The wholeengine is equipped with a control system the mainscope of which is to keep the receiver's temperature constant, at a given set point value.

III. DISH STIRLING ENGINE SYSTEM

Dish-Stirling Systems transfer concentrated solar radiation with high efficiencies into electrical energy. Essentially the system consists of the following components:• Parabolic solar concentrator• Tracking system• Stirling engine with generator

Parabolic solar concentrator:

The parabolic concentrator reflects the incoming solar radiation onto a cavity receiver which is located at the concentrator’s focal point. The solar radiation is absorbed by the heat exchanger (receiver) and thus heats the working gas (helium) of the Stirling engine to temperatures of about 650C. This heat is converted into mechanical energy by the Stirling engine.

Generally speaking the concentrator delivers the fuel for the Stirling engine. It reflects and concentrates the direct solar radiation in the so-called focal point. For the operation of the Stirling engine, temperatures as high as possible are desired.

Therefore a large point-focus concentrator with an axial symmetrical shape is used for this system. The concentrator consists out of 12 single segments made out of glass fibre resin. When mounted the segments form a nearly perfect parabolic shell.The rim of the shell is stiffened by a ring truss to which later on the bearings and the Stirling support structure are attached. Thin glass mirrors, 0.8 mm thick, are glued onto the front side of the segments in order to obtain a durable high reflectivity of around 94%.

Tracking system

Since the concentrator always needs to be perfectly oriented towards the sun, it is mounted on a two-axial tracking system. Therefore a simple movable steel construction standing on six wheels has been developed. Both the horizontal and the vertical orientation of the concentrator are done by a small servomotor. The orientation towards the sun is either determined by a sun tracking sensor, or by a special computer program which predicts the position of the sun.

Stirling engine with generator:

In the simplest version, a Stirling engine consists of a sealed system with two cylinders (expansion and compression cylinder) filled with a working gas (helium). The pistons of these cylinders are connected to one crankshaft. If now the working gas in the expansion cylinder (working cylinder) is heated (by the sun) it will expand due to the increasing temperature; pushes the piston down (1-2) and thus induces power.

Part of this power is now used to push the hot working gas from the expansion cylinder into the compression cylinder (2-3): On its way the working gas passes through a regenerator where a major part of its heat is stored and also through a water cooled gas cooler, where it will be cooled further down. (2-3).Once completely in the compression cylinder, this piston will return due to the inertia of the crankshaft, and the working gas is compressed at low temperature (3-4). By reabsorbing the heat stored in the regenerator the gas is pushed back into the working cylinder. (4-1). Overall the expansion of the hot gas in the working cylinder delivers more energy than is needed for the compression of the cold gas in the compression cylinder. This surplus of energy can be used to operate an electric generator which is directly hooked to the crankshaft of the engine.

COOLING SYSTEM

The Cryocooler consists of two dual opposed linear compressors mounted on a central block, which is designed to retain a high proportion of the compression

heat. Surplus heat is removed via an external mounting fixture. The Cold Head is manufactured separately and can be mounted directly onto the central block of the Compressor in any orientation or separately with an intermediate transfer tube. The unit has a design life of 5 years continuous operation. This is based on the life testing of early experimental prototypes that have now exceeded 55,000 hours and many other examples in service. The Cryocooler requires an AC input to drive the linear motors of the Compressor. This is supplied by a Power Supply and Control Module that converts a DC supply into an AC output of the required amplitude to maintain reliable operation during cool down and steady rate running. This module is designed to achieve high levels of cold end temperature stability and ensures absolute temperature control over the life of the product. The control function is provided by a microprocessor that also allows control of the temperature set point.

REGENERATOR

A regenerator helps to capture and use some of the waste heat from a previous cycle to heat the current cycle, in order to have the highest efficiency. The idealized cycle consists of four stages: isothermal expansion and heat addition, constant volume heat rejection into the regenerator, isothermal compression and heat rejection, and constant volume heat recovery from the regenerator.

Link between Collector and Engine

The receiver is the link between the concentrator and the Stirling engine. It has essentially two tasks:

1. To absorb as much of the solar radiation reflected onto it from the concentrator as possible.2. To pass on this absorbed energy to the Stirling engine in form of heat with the least possible losses.

In general there are two types of receivers. One type is a solar-only receiver which can only be operated during sunshine. The other type is a hybrid receiver which is additionally equipped with a gas burner and can be operated the whole day.

Solar Receiver for the SBP/SOLO V-160/161 Stirling engine

As solar-only receiver, a tube receiver was developed which is directly connected to the cylinder heads of the Stirling engine. The receiver consists of very thin tubes, approx. 3mm in diameter, which resists very high temperatures. They form an almost closed area which is the absorber surface. The concentrated solar radiation heats the working gas to approx. 650C. In addition to the solar absorbing surface, the hybrid receiver is equipped with a gas burner. Thus the Stirling engine can be operated during times when the sun is covered with clouds or even in darkness.

The hybrid Dish-Stirling system thus has the advantage of being available 24 hours a day. Therefore this system can be the ideal substitute for Diesel engines which are currently used to high numbers.

IV. WHY STIRLING ENGINE

The Stirling cycle is the most efficient thermodynamic cycle to transform heat into mechanical or electrical energy. As far back as in 1826 the Stirling engine was invented by the Scottish Rev. Robert Stirling. In the 19th century thousands of engines of this type had already been in use. The Stirling engine has some extraordinary properties:

Compared to an Otto or Diesel engine, which runs on internal combustion, the Stirling engine depends only on external heat supply, with no preference on how the heat is generated. Thus the Stirling engine is the ideal candidate to convert solar heat into mechanical energy

In the Stirling engine a constant amount of working gas (helium or hydrogen) is constantly heated and cooled. Due to expansion when heated and contraction when cooled, the working gas sets two pistons in motion, which both are connected to a crankshaft, and thus delivers energy.

Since the efficiency of the Stirling engine increases with increasing upper process temperature, this engine is the ideal combination to produce energy with a solar collector.

As there is no internal combustion, this engine produces almost no noise.

The potential life-cycle of a Stirling engine is extraordinarily high since there is no internal pollution of pistons and bearings due to combustion of fuels.

Due to the flexibility of the heat source, a Stirling engine can also be operated with a hybrid receiver. This means that with an additionally installed burner, the required heat can also be generated with fossil fuels (Bio-gas etc.).Thus the system is also available during cloudy periods and during night-time.

V. COST OF SOLAR DISH STIRLING ENGINE

Cost of power generation with solar dish stirling engine is very reasonable. The key capital expense is the power plant installation charge. Among them stirling engine cost bears the major expenditure of the entire cost. And the other expenses depend on solar dish, tracking system, cooling system and the required space. Operating and maintenance expense of solar stirling engine is very insignificant in comparison with the other existing power generation plant. As stirling engine is an evacuated system it does not require any maintenance cost, the only system that requires to be maintained is the cooling system in every five years. Apart from that the solar dish panel and the tracking system requires some accidental maintenance expense which is also very low.

Cost for 25 kw power plant(APPROXIMATION):

Cost of solar dish stirling engine-3,00,000 TK

Cost of cooling system – 80,000 TK

Cost of tracking system- 1,00,000 TK

Total installation charge-2,50,000TK/20 year

Operating cost-50000-60000tk/year

Cost of per kwh-

Technology COST/KWH

GAS 4 BDT

PETROL 8 BDT

SOLAR 20 BDT

SOLAR DISH STIRLING ENGINE

3.25 BDT

VI. PROSPECT OF BANGLADESH

In the country, presently state owned power plants generate only 3500MW of electricity per day, where as demand is 6000MW. Whereas demand is increasing by 500MW a year due to increase in industrialization. The Bangladesh government has estimated about 4.8 million metric tonnes of petroleum oil to be a requirement for the current calendar year (2011), up by 1.05 million tonnes from the previous year’s demand. Bangladesh Petroleum Corporation (BPC) will cost about US$ 5 billion (approximatelY Tk 35,000 crore) for the huge petroleum import.Bangladesh is not only suffering from power generation crisis. It has serious crisis of primary fuel. The major fuel is domestic natural gas which alone accounts for about 85% of power generation. Even over the last 2.25 years of present government there has been hardly any growth of gas production.

VII. TECHNIQAL DATA

Concentrator

Diameter 8.5 mProjected area 56.7 m²Focal Length 4.5 mAverage concentration factor 2500Reflectivity 94 %

Tracking and Control Partners

Suspension azimuth Stow position face down Max. Allowable wind velocity during operation 65 km/h

Survival wind velocity in stow position 1 60 km/h Drive velocity 60 °/min. Control system PC, micro controller Data transfer InterBus-SRemote control telephone / WWW

Stirling engine

Type single acting, 90° V-engineSwept volume 160 cm³

Gross power output 9 kWNet power output 8.4 kWGrid connection 400 V, 50 Hz, 3 phase

Receiver gas temperature 650 °CWorking gas heliumGas pressure 20-150 barPower control pressure control

REFERENCES

[1] G. Eason, B. Noble, and I. N. Sneddon, “On certain integrals of Lipschitz-Hankel type involving products of Bessel functions,” Phil. Trans. Roy. Soc. London, vol. A247, pp. 529–551, April 1955. (references)

[2] J. Clerk Maxwell, A Treatise on Electricity and Magnetism, 3rd ed., vol. 2. Oxford: Clarendon, 1892, pp.68–73.

[3] I. S. Jacobs and C. P. Bean, “Fine particles, thin films and exchange anisotropy,” in Magnetism, vol. III, G. T. Rado and H. Suhl, Eds. New York: Academic, 1963, pp. 271–350.

[4] K. Elissa, “Title of paper if known,” unpublished.

[5] R. Nicole, “Title of paper with only first word capitalized,” J. Name Stand. Abbrev., in press.

[6] Y. Yorozu, M. Hirano, K. Oka, and Y. Tagawa, “Electron spectroscopy studies on magneto-optical media and plastic substrate interface,” IEEE Transl. J. Magn. Japan, vol. 2, pp. 740–741, August 1987 [Digests 9th Annual Conf. Magnetics Japan, p. 301, 1982].

[7] M. Young, The Technical Writer's Handbook. Mill Valley, CA: University Science, 1989.