Distributed Generation

The Distributed GenerationThe Distributed GenerationIntroductionDefinitionTypes

Typical Power System Structure

Typical energy sources used by power plants include fossil fuel (gas, oil, and coal), nuclear fuel , and hydro energy .

Typical Power System Structure

Typical Power System Structure

Power system arrangements with distributed generation

2.DefinitionDistributed generation occurs when power is generated (converted) locally and sometimes might be shared with or sold to neighbors through the electrical grid (or over the fence)Distributed generation avoids the losses that occur in transmission over long distances; energy is used nearbySupply is robust, but automatic precautions are required to protect electricity workers when main base-load power is out, and a local system might feed back into power lines.Distributed Generation Diagram

3.Types

Potential DG SourcesDiesel engines with very large storage tanks (five days are common)Reciprocating engines similar to diesels that burn natural gas from a pipelineMicroturbines on natural gasWind turbinesSolar arraysGeothermalStream turbine from a small local streamWaveTideHuman or animal powered (really retrogressive)103.1 Diesel EnginesBackup and remote power has traditionally been supplied by diesel engines due to their long life and low maintenanceLarge systems have been invited to share metered power by pushing energy into the grid when utility power is stressed or limitedUnfortunately, this puts more pollution into the air than when occasional outages and weekly test runs were the only sourceSmaller diesels are inefficient compared to large 20-cylinder systemsAuto starting engines need less attention04040611Multiple Generators

12Multiple Generators

Reciprocating engines can run on natural gas to drive alternators133.2 Microturbines Small - scale Microturbines can be used for DG, alone or in combined heat and power systems. The generated electric power ranges from 30 to 400 kW to feed (local or nearby) loads or to be interconnected with utility grid. The output exhaust thermal energy can be used for heating purposes, which some loads need (industrial processes, hospitals, air - conditioning, etc.). Natural gas is mostly used as a primary fuel (more economic) for microturbines in spite of the validity of using a variety of fuels such as gasoline, diesel, kerosene, digester gas, and methane

14Generator interconnection to local loads or utility grid

Control system of microturbine

3.3 Hydroelectric Pumped Storage SystemsThis type of storage system is widely used when large energy storage is required. The principle of operation is based on utilizing the potential energy (PE) of water at a specific head. The head is established by pumping process during periods of surplus electric power

3.4 Fuel CellsFuel Cells generate electricity through an electrochemical process In which the energy stored in a fuel is converted directly into DC electricity.Because electrical energy is generated without combusting fuel, Fuel cells are extremely attractive from an environmental stand point.

18Attractive characteristics of Fuel Cell High energy conversion efficiency Modular design Very low chemical and acoustical pollution Fuel flexibility Cogeneration capability Rapid load response It consists of three components - a cathode, an anode, and an electrolyte sandwiched between the two. Oxygen from the air flows through the cathodeA fuel gas containing hydrogen, such as methane, flows past the anode. Negatively charged oxygen ions migrate through the electrolyte membrane react with the hydrogen to form water, The reacts with the methane fuel to form hydrogen (H2) & carbon dioxide (CO2).

Fuel cell workingThis electrochemical reaction generates electrons, which flow from the anode to an external load and back to the cathode, a final step that both completes the circuit and supplies electric power. To increase voltage output, several fuel cells are stacked together to form the heart of a clean power generator. Fuel cell workingFuel cell working

Applications of Fuel cells

Problems with Fuel CellsThe fuel cell uses oxygen and hydrogen to produce electricity. The oxygen required for a fuel cell comes from the air. The hydrogen is not so readily available, however. Hydrogen has some limitations that make it impractical for use in most applications. For instance, you don't have a hydrogen pipeline coming to your house, and you can't pull up to a hydrogen pump at your local gas station. Hydrogen is difficult to store and distribute, so it would be much more convenient if fuel cells could use fuels that are more readily available. 3.5 BiomassBiomass is a renewable energy source that is derived from living or recently living organisms. Biomass includes biological material, not organic material like coal. Energy derived from biomass is mostly used to generate electricity or to produce heat. Biomass can be chemically and biochemically treated to convert it to a energy-rich fuel

Biomass Types

Biomass cycle

Biomass Energy PlantBiomass Energy Plant

ENVIRONMENTAL ADVANTAGESRenewable resourceReduces landfillsProtects clean water suppliesReduces acid rain and smogReduces greenhouse gasesCarbon dioxideMethane

GEOGRAPHIC AREASComes from the forestCan also come from plant and animal wasteWood and waste can be found virtually anywhereTransportation costs

3.6 Wind Power - Introduction Wind power is good renewable, clean and free source of energy for power production

Reduce dependence on fossil fuels including imported oils

Reduce emission of greenhouse gas and other pollutant

One major concern is the noise can be improved

Intermittency and variability of the wind

The Basic Wind Turbine Configurationsvertical-axis wind turbines, in which the axis of rotation is vertical with respect to the ground (and roughly perpendicular to the wind stream), horizontal-axis turbines, in which the axis of rotation is horizontal with respect to the ground (and roughly parallel to the wind stream).

Parts of a Horizontal Axis Wind Turbine

The Basic Wind Turbine Configurations

Control Strategy to Extract Maximum PowerPole-Changing Induction GeneratorsMultiple GearboxesVariable-Slip Induction GeneratorsIndirect Grid Connection SystemsControl Strategy to Extract Maximum PowerConstant Tip-Speed Ratio Scheme This scheme is based on the fact that the maximum energy is extracted when the optimum tip-speed ratio is maintained constantly at all wind speeds. As shown in the figure, the wind speed is measured and the required rotor speed for maximum power generation is computed. The rotor speed is also measured and compared to the calculated optimal rotor speed, while the resulting error adjusts the load torque

Control Strategy to Extract Maximum PowerPower Control Scheme. This scheme based on power comparison as shown in the figure. This topology requires the wind turbine optimal power versus the rotating-speed characteristic. The wind turbine rotating speed is measured then the optimal output power is calculated and compared to the actual output power

Variable-Speed Wind TurbineThe system presented in the figure. consists of a wind turbine equipped with a converter connected to the stator of the generator. The generator could either be a cage-bar induction generator or a synchronous generator. Synchronous generators or permanent-magnet synchronous generators can be designed with multiple poles which imply that there is no need for a gearbox

Variable-Speed Wind Turbine with DFIGThis system consists of a wind turbine with doubly-fed induction generator (DFIG). This means that the stator is directly connected to the grid while the rotor winding is connected via slip rings to a converter.

3.7 Photovoltaic SystemPV systems convert solar radiation into electricity. They are not to be confused with solar panels which use the suns energy to heat water (or air) for water and space heating. A solar cell works, most simply, by absorbing sunlight. The photons from the light run into the solar cell and are absorbed by some sort of semiconducting material. Most contemporary solar cells are made out of silicon. PVs respond to both direct and diffuse radiation and their output increases with increasing sunshine or, more technically, irradiance .Structure of a Photovoltaic System

Ideal Solar Cell Equivalent Circuit

Solar Cell Equivalent Circuit

Solar cell module

Solar cell arrays

The I-V characteristics of the system

The P-V Characteristics of the System

Photovoltaic operation

Current-Voltage curves for loadSimple resistive-load I-V Curve

Current-Voltage curves for load