SUSTAINABILITY AND RENEWABLE ENERGY Lecture 2

Distributed Generation Technologies

hat are the characteristics of distributed generation (DG) systems

• Small in size (up to around 50MW) • Intermittent input resource • Stand alone • Grid connected at distribution or subtransmission levels of the power network • Extremely site specific inputs • Located nearer the loads than conventional large power plants • Remote locations from the power grid • Availability of energy storage and use at a later stage

advantages of DG technologies

• Less capital investment since the installation is a small one • Less capital risk • Easier to obtain planning certification, especially under the ever increasing restrictions • Their location nearer the loads decreases delivery costs and reduces transmission and distribution losses • Likely to result in improved reliability and availability • In open access and competitive markets, some DG technologies become competitive to large plants against the cost of power delivered

what is the higher heating value compared to lower heating value

The higher heating value (HHV) of a fuel includes the latent heat in the water vapour produced when the fuel is burned. The lower heating value (LHV) does not.

what is a reciprocating ICE

Dominate DG - including combined heat and power (CHP) - by installations that range from 0.5 kW to 6.5 kW, with (LHV) electrical efficiencies of about 37-40%.

what dose reciprocating ICE run on

Can run on gasoline, natural gas, kerosene, propane, fuel oil, alcohol, waste-treatment plant digester gas, and hydrogen.

benefits of reciprocating ICE

Least expensive DG technology and when burning natural gas, relatively clean.

step one for 2 stroke ICE

Fuel air explosion

step 2 for 2 stroke ICE

Piston is driven down - power stroke

step 3 for 2 stroke ICE

As the piston moves towards the bottom of it’s stroke, the exhaust port is uncovered

step 4 for 2 stroke ICE

Exhaust gases are driven out

step 5 for 2 stroke ICE

When the piston has bottomed out, the intake port is uncovered

step 6 for 2 stroke ICE

New fuel and air enters and is ready for compression and combustion

step 7 for 2 stroke ICE

As the fuel mixture is being compressed a vacuum is created in the crankcase

step one for 8 stroke ICE

The vacuum opens a reed valve and sucks air/fuel/oil from the carburettor into the crankcase

advantages of 2-stroke ICE

• Simplified construction • Great power to weight ratio - fire once every revolution for a significant power boost

disadvantages of 2-stroke ICE

• The engines do not last as long due to poor lubrication • Have to mix lubrication oil with the fuel • Do not use fuel efficiently • Two-stroke engines produce a lot of pollution

what is a diesel engine

A diesel engine is a heat engine of the internal combustion type that operates on the thermal cycle

what is a heat engine

A heat engine is a machine that its function is to convert heat energy into work. The heat energy can be taken from a medium of gas or vapour.

when is an engine classified as internal combustion

If the combustion of the fuel charge takes place inside the cylinder of an engine, and the resulting high pressure drives the piston downward on its working stroke

what is a compression ignition 4-stroke ICE

The diesel engine differs from other and more familiar types of internal combustion engines in its unique ignition feature: the fuel charge ignites when it combines with air, which has been raised to an appropriately high temperature by means of compression.

what are the 4 different types of diesel engine applications

industrial, public services, marine, power for equipment

In the context of a diesel engine used as part of a diesel based power generator what auxiliary equipment is needed:

• Starting system • Speed governing system • Voltage regulator • Cooling system • Exhaust system • Lubricating oil system • Fuel supply system

what are the roles of AC generators driven by diesel engines

• Supply base load in remote locations or as an uninterruptible power supply in case the mains fails • Peak-shaving in order to reduce the cost of the generated electricity • Standby

what are the power ratings of diesel power generators

• Continuous power • Overload power • Fuel stop power • Service power

what is continuous power

the power that an engine is capable of delivering continuously between the normal maintenance periods stated by the manufacturer, at stated speed and under stated ambient conditions, as long as the prescribed maintenance is carried out.

what is overload power

the power the engine may be permitted to deliver, at stated ambient conditions, immediately after working at the continuous power

how is overload power expressed

It is usually expressed as a percentage of the continuous power for a given period and speeds. Typically 110% of continuous power is allowed for 1hr

when do ICE’s adjust there power

An ICE tends to adjust its speed so that its power output will match the load demand.

when is an automatic speed control required for engines

When the engine drives a generator which furnishes electrical current for one or more motor driven machines

what dose an automatic speed control do for engines

automatic control of the speed of the engine is necessary to prevent stalling if the load increases, or overspeeding if the load decreases

what speed control is required for generators with alternating current type

When the generator is of the alternating current type, the service may require closed speed control in order to maintain the current frequency within permissible limits

what is a speed governing system

A speed governing system consists of a speed sensitive element together with other component elements that translate the signals of engine speed changes into changes in the amount of fuel supplied to the engine cylinders.

what are the advantages of a diesel power plant

• High efficiency • High availability • Easy to expand when load increases • Planning, generation and installation periods required are very short • Good behaviour under low load conditions • They serve base loads up to 200 MW quite well

how can the efficiency of ICE be improved

Efficiency of ICE can be increased by pressurizing the air/air-fuel mixture, before it enters the cylinder (charged aspiration), which also helps lower combustion temperatures and emissions.

how does a concentrating solar power technologies work

With concentration, sunlight can provide high enough temperatures to make the thermodynamic efficiency of a heat engine worth pursuing

where are bio-fuels derived from

Bio -fuels are derived from decaying vegetable matter produced by agriculture or forestry or from waste materials from the industry.

how dose bio-fuel function as an energy source

As an energy source, they are burned to produce heat which contributes approximately 14% of the world’s energy requirements.

how dose bio-fuel produce electricity

• By burning in a furnace to produce steam to drive a turbine. • By allowing fermentation in landfill sites or in special tanks. This produces methane rich gases which can be used as a fuel for a gas turbine

what is hydro-electric power

electricity produced by the movement of water from rivers and lakes.

how dose gravity effect hydro-electricity

Gravity causes the water to flow and the difference in the kinetic energy can be converted into mechanical energy. The mechanical energy can then be converted into electrical one using a hydro-electric powerhouse

what are the classifications of small hydro power systems

Small hydro power systems can be classified into three categories as follows: micro (less than 100kW), mini (100kW – 1MW), and small (1MW – 10MW).

advantages of hydro-electric power

 Price of fuel and associated charges for the cost of electricity generation is not a problem and no fuel is needed.  They are also classified as part of the renewable energy systems, as the energy source, being the water, is renewable and does not pollute the environment while operating

what are is micro hydro systems

Micro-hydro systems are particularly suitable as remote area power supplies for rural and isolated communities.

advantages of micro hydroelectric power

the only economic way to provide electricity to such communities as opposed to extending the power grid. Moreover, these systems provide relatively inexpensive, independent and continuous power without degrading the environment in their vicinity.

how do micro-hydroelectric power

Micro-hydro systems usually operate by diverting the flow of a river through a penstock (or pipe) and a turbine which drives a generator to produce electricity.

how dose the function of micro-hydroelectric power not affect the enviroment

Typically the water runs back to the river which allows the river flow to continue. This has a number of advantages from an environmental point of view as seasonal river flow patterns downstream are not affected and there is no flooding of valleys upstream of the system

how is the power output of micro-hydroelectric system determined

The power output of the system is not determined by controlling the flow of the river, but instead the turbine operates when there is water flow and at an output governed by the flow. This means, there is no need for a sophisticated mechanical governor system, which further reduces the cost and maintenance requirements.

disadvantage of micro-hydroelectric power

the excess power generated is wasted unless an electrical storage system is installed or a suitable “off-peak” use is available in the surrounding area.

what do hydro-electric units consist off

water turbine and electric generator

what dose a water turbine do

Water turbine to convert the energy of flowing water into mechanical energy

what dose an electrical generator do

Electric generator to convert mechanical energy into electrical energy.

what does The amount of energy available from water depends on

• The quantity of the available water. • The water’s pressure at the turbine. The pressure is referred to as the head, and is measured as the height that the surface of the water is above the turbine. The greater the height (head) of the water above the turbine, the more energy each cubic meter of water can impart to spin a turbine.

how dose a water turbine work 1

Blades are attached to the shaft and when flowing water presses against the blades, the shaft rotates.

how dose a water turbine work 2

The water exchanges energy with the turbine and once this happens, the water is discharged through drainage pipes or channels called the tailrace of the power station.

what are the three main types of water turbines

• Pelton wheels • Francis turbines • Kaplan or propeller type of turbines

what do impulse turbines do

Impulse turbines capture the kinetic energy of high-speed jets of water. Most commonly used in micro-hydro systems (Pelton wheels).

what dose reaction turbines do

It is mostly the pressure difference across the runners, or blades, of reaction turbines that creates the desired torque (Kaplan/propeller type turbines).

when is a pelton wheel used

The Pelton wheel is used in the following case: • Small flow of water is available. • Large head

how dose a pelton wheel function

 It has small “buckets” all around its rim.  Water is fed through nozzles at very high speed hitting the buckets and pushing the wheel around.

what are propeller type turbines designed to operate for

• A small head of water is involved (up to 60 m). • Applied to river and bondage stations.

how are propeller type turbines used in/with water turbine

The only difference in the case of water turbine application is that the angle (pitch) of the blades can be altered to suit the water flow.

what dose the variable pitch feature permit

permits the machine to operate efficiently over a range of heads. This is important in applications were the water supply is not constant, therefore seasonal variation of water levels in a dam can be dealt with.

what are fuel cells

Fuel cells are electrochemical devices that can convert energy into electricity and heat without combustion

what do fuel cells consist off

• Cathode (negatively charged electrode). • Anode (positively charged electrode). • Electrolyte. • External load.

what is the role of anode (in fuel cells)

• To provide an interface between the fuel and the electrolyte. • To catalyze the fuel reaction. • To provide a path through which free electrons are conducted to the load via the external circuit.

what is the role of cathode in (fuel cells)

• To provide an interface between the oxygen and the electrolyte. • To catalyze the oxygen reaction. • To provide a path through which free electrons are conducted from the load to the oxygen electrode via the external circuit.

what is the role of electrolyte (in fuel cell)

• To act as the separator between hydrogen and oxygen, to prevent mixing and, therefore, preventing direct combustion. • To complete the electrical circuit of transporting ions between the electrodes.

fuel cell principle of operation 1

Two catalyzed carbon electrodes are immersed in an acid electrolyte and separated by a membrane.

fuel cell principle of operation 2

As hydrogen and oxygen enter into the fuel cell, hydrogen and oxygen bubbles are formed across the surfaces of the fuel and oxygen electrodes, respectively.

fuel cell principle of operation 3

The hydrogen reacts with the catalyzed electrode and forms hydrogen ions and electrons.

fuel cell principle of operation 4

The hydrogen ions move across to the surface of the cathode passing through the electrolyte.

fuel cell principle of operation 5

The electrons flow through the external circuit to the cathode (current).

fuel cell principle of operation 6

The oxygen, hydrogen ions and free electrons combine on the surface of cathode to form water.

what is a fuel cell stack

Individual fuel cells can be combined into a fuel cell “stack”

in a fuel cell stack what does the number of fuel cells mean

The number of fuel cells in the stack determines the total voltage.

how is the total current in a fuel cell stack determined

The surface area of each cell

what is the differenece between a battery and fuel cells

The difference between a battery and a fuel cell however is that a fuel cell does not release energy stored in the cell.  The energy is converted into a hydrogen laden fuel directly into electricity.  The use of fuel cells does not emit pollutants.

what are types of fuel cells

 Phosphoric Acid Fuel Cell (PAFC)  Proton Exchange Membrane Fuel Cell (PEMFC)  Molten Carbonate Fuel Cell (MCFC)  Solid Oxide Fuel Cell (SOFC)  Alkaline Fuel Cell (AFC)

what is a phosphoric acid fuel cell (PAFC)

a fuel cell that uses phosphoric acid as an electrolyte

advantages of PAFC

• Stable electrolyte. • Ability to highly concentrate phosphoric acid. • Efficient anode performance.

disadvantages of PAFC

• Inefficient cathode performance.

what is the operating range of PAFC

The operating temperature range of PAFC is 200 celcius

what is the mechanism of PAFC

As phosphoric acid is a poor ionic conductor at low temperatures and other materials such as carbon, platinum, etc. used in the fuel cell may become unstable at higher temperatures so PAFCs do not work efficiently beyond this temperature range.

difference between Proton Exchange Membrance fuel cell (PEMFC) and PAFC

They differ in that their operating temperatures are relatively low (about 100oC).

similarities of PAFC and PEMFC

same mechanism and They have high power density (defined as power output over the volume they occupy) and can vary their output quickly to meet shifts in power demand.

what is a molten carbonate fuel cell (MCFC)

It uses an alkali metal carbonate (Li, Na, K) as the electrolyte.  However, this alkali metal carbonate must be in the liquid phase to function as an electrolyte

operating temp for MCFC

higher compared with others and approximately 650oC.

why does MCFC have a higher operating temp

The high operating temperature is required to achieve sufficient conductivity of the electrolyte

how does MCFC differ from PAFC

because of their higher operating temperature and nature of the electrolyte.

limitations of MCFC

The high operating temperature, however, imposes limitations and constraints on choosing materials suitable for long life time operations.

how are MCFC’s commonly refered as

The MCFC is referred to as a second generation fuel cell after PAFCs

what are solid oxide fuel cells (SOFC) made off

It uses solid, nonporous metal oxide electrolytes

what metal electrolyte is commonly used in SOFCs

The metal electrolyte normally used in manufacturing SOFCs is stabilized Zirconium.

what is the operating temp for SOFC

This cell operates at a higher temperature of about 1000 degrees celcius.

what is the purpose and advantages of high operating temp for SOFC

This high operating temperature allows internal reforming, promotes rapid kinetics with non-precious materials and produces high quality heat. The solid state character of SOFC components implies that there is no restriction on the cell configuration

what is alkaline fuel cell made of

AFC uses alkaline potassium hydroxide as the electrolyte

efficiency of SOFC

up to 60%

efficiency of AFC

up to 70%

environmental advantages of fuel cells

• Fuel cells are considered an excellent alternative energy resource from the environmental point of view. • Fuel cells are quiet and produce negligible emissions of pollutants.

efficiency advantages of fuel cells

• Different types of fuel cells have varied efficiencies. • Depending on the type and design of fuel cells, efficiency ranges from 40 to 60%. • Alkaline fuel cells can even achieve power generating efficiencies of up to 70%