Archivo para enero, 2016

Conceptual Framework of Smart Grid Alternatives

Microgrids are both partand beneficiariesof the smart-grid concept. Is evident thatthere are objectives
shared between microgrids and the smart-grid concept: reduce the costs of energy and the reliability, efficiency and security improvement. Also, there are benefits which are linked to the useof smart-grid technologies: the deployment ofgreen technologies, different levels of quality and the use of demand response strategies

René B. Martínez-Cid. “Renewable-Driven Microgrids in Isolated Communities”. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering. University of Puerto Rico. Mayagüez Campus. 2009.

Schematic of a typical wind diesel hybrid system with storage

One of the most promising applications of renewable energy technology is the installation of hybrid
energy systems (HES) in remote areas, where the grid extension is costly and the cost of fuel increases drastically with the remoteness of the location. Recent research have shown that HES have an excellent potential, as a form of supplementary contribution to conventional power generation systems. In figure, one of the most common hybrid renewable system implemented and studied is described.

Francisco Goncalves Goina Mesquita. “Design Optimization of Stand-Alone Hybrid Energy Systems”. A Dissertation submitted under the scope of Mestrado Integrado em Engenharia Electrotécnica e de Computadores Major Energia. Fevereiro de 2010. Facultade de Engenharia da Universidade do Porto.


Topology of a generic VPP showing the integration of energy, electrical and information system

The figure shows the minimum requirements for a VPP: a number of small participants (consumers or DERs); a communications network (the internet or dedicated lines); a communication platform with a common information model and a consensus on the communication architecture; a primary energy supply network; and a link to the energy market. The primary energy supply is the foundation of the VPP, the communication system forms the glue holding the VPP together, and the market link is the incentive which drives the system to service the needs of its owners and customers.A VPP may be dispersed over a large area, though in the case of islands and other microgrids it may equally well have tight geographical limits.

Riso Energy Report 8. “The intelligent energy system infraestructure for the future”. Riso National Laboratory. Technical University of Denmark. September 2009. ISBN 978-87-550-3754-0

National renewable energy UE targets as a percentage of final energy consumption

In Europe this growth is driven by both national and EU policies. By 2008 the EU member states had adopted longterm targets in three different areas of energy policy:

• a binding reduction in greenhouse gas emissions of 20% by 2020 compared to 1990; this target can be raised to 30%  subject to the conclusion of binding international climate change agreements;

• a mandatory target for renewable energy sources such as wind, solar and biomass, which by 2020 must supply 20% of the EU’s final energy demand; and

• a voluntary agreement to cut EU energy consumption by 20% by 2020, compared to a reference projection.

The EU has also set a target of 10% renewable energy, including biofuels, in transport by 2020.

This new policy, with its increasing reliance on renewable  sources, will change European energy systems radically within the next decade. Energy technologies based on variable sources, especially wind power but to a lesser extent also wave power and PV, are expected to play a large role in the future energy supply. For example, by 2020 wind power is expected to supply 50% of the Danish electricity consumption – implying that from time to time significantly more wind power will be available than Denmark can consume1. This challenge will require not only significant changes in energy system structure, but also the development of intelligence within the system

Riso Energy Report 8. “The intelligent energy system infraestructure for the future”. Riso National Laboratory. Technical University of Denmark. September 2009. ISBN 978-87-550-3754-0

gross energy consumption in Denmarks buildings during the period 1995 2060

A study of the potential savings in energy used for heating of existing domestic buildings in Denmark has shown that savings of 60-80% in the period up to 2050 are possible if extensive energy conservation measures are put in place whenever the buildings are renovated (see Figure). The assumption is that during this period the entire building stock is either replaced by new buildings or renovated to the energy standards of new buildings. This would cut Denmark’s total final energy consumption by around 30%. A major part of these savings up to 2050 come from renovation…

Riso Energy Report 6. “Future options for energy technologies”. Riso National Laboratory. Technical University of Denmark. November 2007. ISBN 978-87-550-3611-6

Denmark’s  gross energy  consumption  and  primary  energy

Denmark is the only net exporter of energy in the EU. In 2005, production from Danish oil and gas fields in the North sea exceeded the country’s gross energy consumption by 56%. At the same time Denmark has an environmentally-friendly energy profile that includes considerable amounts of renewable energy, especially wind power; strong energy efficiency measures; and widespread use of combined heat and power (CHP). For more than 20 years Denmark has kept its gross energy consumption almost constant, with an increase of just 4% since 1985, despite a 70% increase in gross national product in the same period. In short, Denmark is in a far better energy situation than most countries in the EU

Riso Energy Report 6. “Future options for energy technologies”. Riso National Laboratory. Technical University of Denmark. November 2007. ISBN 978-87-550-3611-6

Market Sector Revenue Breakdown North America 2015 Pike Research

Community/Utility Microgrids:The word “community” implies a geographical region  that includes residential customers. Most observers predict that this class of microgrids will not achieve widespread commercial acceptance until standards are in place and regulatory barriers are removed.

Commercial/Industrial:The first “modern” industrial microgrid in the United States was a 64 MW facility constructed in 1955 at the Whitling Refinery in Indiana. All told, 455 megawatts (MW) of these vintage microgrids are currently online in the United States. Unlike today’s conceptual state-of-the-art models, these initial designs for the petrochemical industry still feature centralizedcontrols and fossil-fueled generation sets. Japan is a modern leader in the commercial/industrial sector, though most of its microgrids include governmental and other institutional customers.

Institutional/Campus:Because of the advantage of common ownership, this class of microgrids offers the best near-term development opportunity. At present, 322 MW of college campus microgrids are up and running in the United States, with more sophisticated state-of-the-art microgrids on the drawing boards. In the U.S., 40% of future microgrids will be developed in this market segment, adding 940 MW of new
capacity valued at $2.76 billion by 2015.

Remote Off-Grid Systems:This segment represents the greatest number of microgrids currently operating globally, but it has the smallest average capacity. While many systems have historically featured diesel distributed energy generation (DEG), the largest growth sector is solar photovoltaics (PV). Small wind is projected to play a growing role, as well.

Military Microgrids:The smallest market segment, these microgrids are just now being developed. They are integrating Renewable Distributed Energy Generation (RDEG) as a way to secure power supply without being dependent on any supplied fuel. GE and Sandia are moving forward in this area and model prototypes are expected in 2010.

Peter Asmus. Adam Cornelus. Clint Wheelock. “Microgrids: Islanded Power Grids and Distributed Generation for Community, Commercial, and Institutional Apllications”. Research Report. PikeResearch. 2009.

Typical step response of a micro-turbine

Transient changes in load power demand may result from faults in transmission line or load switching. For instance, a 75-kW Honeywell micro-turbine took about 35 s to respond for a 50%change in power demand under the grid-connected mode of operation.On the other hand, some fuel cells require about 10 s for a 15% change in power output.Furthermore, a fuel cell also has a recovery period of a few minutes to establish equilibrium before it can meet another step change in power output. The typical response that can be expected of a micro-turbine for a step change in load demand is illustrated in Figure. In the figure, PL denotes the load power demand, PS is the response of the micro-turbine, and (PL-PS) is the short age in power that needs to be supplied through some means. Inthe grid-connected mode of operation, the grid supplies the shortage in power until the micro-source responds to a step changein power demand. However, in the island mode of operation, this sudden demand can be met only if
additional storage is included in the MSDG system.

G. Venkataramanan, M.S. Illindala, C. Houle, and R.H. Lasseter. “Hardware Development of a  Laboratory-Scale Microgrid Phase 1—Single Inverter in Island Mode Operation”. NREL. November 2002 • NREL/SR-560-32527

CBEMA curves specifying acceptable voltage sensitivity levels

Inthe recent past, dramatic improvements in productivity have been realized in the high technology sector as well as in the traditional industries. For the electric power supply to these industries, this hasled to a concomitant increase in the number of loads that are sensitive to power quality. Some of the industries that have such large sensitive loads include semiconductor manufacturing, textile mills, paper millsand plastic injection molding.Of course, a number of smaller but equally critical loads such as computers and electronic data processing equipment are also sensitive to power quality.Thetolerance
levels of computer equipment are specified by the Information Technology Industry/Computer and Business Equipment Manufacturers’ Association (ITI/CBEMA) curves. Figure illustrates theCBEMA curves. This figure gives thepercent of nominal voltage versus duration in (60-Hz) cycles. The CBEMA curves represent the boundary of the ac input voltage envelope that can be tolerated (typically) by most
computer-based equipment. The upper curve represents the maximum voltage below which the equipment will continue to function normally. The lower curve is the minimum voltage above which the equipment will continue to function normally.

As seen in Figure, the steady state range of tolerance for computer equipmentis ±10% from the nominal voltage, i.e., the equipment continues to operate normally when sourced by any voltages in this range for an indefinite period of time. Similarly, voltages wells to a magnitude of 120% of the nominal value can be tolerated for about 0.5 s or 30 cycles; voltage sags to 80% of nominal for 10 s, or 600 cycles, can be tolerated. When the supply voltage is outside the boundaries of the susceptibility curves, improvement of the quality of power supplied to sensitive loads is essential to avoid a possible failure in their operation.

G. Venkataramanan, M.S. Illindala, C. Houle, and R.H. Lasseter. “Hardware Development of a  Laboratory-Scale Microgrid Phase 1—Single Inverter in Island Mode Operation”. NREL. November 2002 • NREL/SR-560-32527

Optimum DG Penetration for Minimum Interruption Frequency

One question that most system operators are concerned with is the optimised DG penetration level. Relationship regarding different cost models between optimum DG penetration level and interruption frequency is indicated in Figure.

Optimum micro-source penetration level is positive related with the interruption frequency without DG penetration; especially for average interruption costs, the relationship is almost linear. This relationship is important for systemplanning; as the system interruption frequency without DG penetration is generally known, the system operator is able to roughly determine of the optimum DG penetration level from reliability point of view

System unavailability comparison of different countries EU

A reduction of system unavailability Q, as one example for system reliability indices, by the installation of micro-sources that enable (partial) island operation is demonstrated in Figure for selected European countries, compared to the case without DG.

The countries which have worse system reliability achieve higher improvements than the countries with high system reliabilities also in case without DG. For instance, in Portugal rural network the system unavailability decreases from more than 10 h/a to the value of below 1 h/a with maximum and average cost model; even with average cost model yearly unavailability is also reduced to approximate 4h/a. However, the improvement for German urban network and Holland network, which have already good system reliability without micro-sources, is not obvious, although system reliability is also improved to a certain extent in both networks. With higher interruption cost model, system reliability can be better improved. Higher interruption costs justify higher micro-source investment, thus achieving higher system reliability improvements.  Microgrid operation from reliability point of view is thus most beneficial in countries with lower power quality or in regions or for customer segments with comparably high outage costs.

Christine Schwaegerl. “DG3&DG4 Report on the technical, social, economic, and environmental benefits provided by Microgrids on power system operation”. Siemens AG. 2009

Economic Benefit Comparison of Microgrids on European Level

The figure compares the maximum economic benefits of different networks with x-axis as the multiplication of the total load of the network and the unavailability of this network in each year, which is symbolized by PQ. Benefits ineach country are almost linear related with PQ as interruption costs without DG increase with increasing total demand and unavailability, leading to higher benefits of Microgrid operation. The higher the outage costs assumed for reliability simulation the higher economic benefits can be achieved as shown for maximum, average, and minimum cost model.

Christine Schwaegerl. “DG3&DG4 Report on the technical, social, economic, and environmental benefits provided by Microgrids on power system operation”. Siemens AG. 2009

Microturbina power plant

More recently, a new generation of very small gas turbines has entered the marketplace. Often referred to asmicroturbines, these units generate anywhere from about 500 watts to several hundred kilowatts. The figure illustrates the basic configuration including compressor, turbine, and permanent-magnet generator, in this case all mounted on a single shaft. Incoming air is compressed to three or four atmospheres of pressure and sent through a heat exchanger called arecuperator, where its temperature is elevated by the hot exhaust gases. By preheating the compressed incoming air, the recuperator helps boost the efficiency of the unit. The hot, compressed air is mixed with fuel in the combustion chamber and is burned. The expansion of hot gases through the turbine spins the compressor and generator. The exhaust is released to the atmosphere after transferring much of
its heat to the incoming compressed air in the recuperator.

Gilbert M. Masters. “Renewable and Efficient Electric Power Systems”. Jhon Wiley & Sons, Inc., New Jersey. ISBN 0-471-28060-7. 2004

Typical Power Plant Power Output and End-Use Power Demands

In addition to economic benefits, other motivations helping to drive the transition toward small-scale, decentralized energy systems include increased concern for environmental impacts of generation, most especially those related to climate change, increased concern for the vulnerability of our centralized energy systems to terrorist attacks, and increased demands for electricity reliability in the digital economy.
A sense of the dramatic decrease in scale that is underway is provided in Table (top), in which a number of generation technologies are listed along with typical power outputs. For comparison, some examples of power demands of typical end uses are also shown. While the power ratings of some of the distributed generation options may look trivially small, it is the potentially large numbers of replicated small units that will make their contribution significant. For example, the U.S. auto industry builds around 6 million cars each year. If half of those were 60-kW fuel-cell vehicles, the combined generation capacity of
5-year’s worth of automobile production would be greater than the total installed capacity of all U.S. power plants.

Gilbert M. Masters. “Renewable and Efficient Electric Power Systems”. Jhon Wiley & Sons, Inc., New Jersey. ISBN 0-471-28060-7. 2004

Characteristics of Copper Wire

Wire size in the United States with diameter less than about 0.5 in. is specified by its American Wire Gage (AWG) number. The AWG numbers are based on wire resistance, which means that larger AWG numbers have higher resistance and hence smaller diameter. Conversely, smaller gage wire has larger diameter and, consequently, lower resistance. Ordinary house wiring is usually No. 12 AWG, which is roughly the diameter of the lead in an ordinary pencil. The largest wire designated with an AWG number is 0000, which is usually written 4/0, with a diameter of 0.460 in. For heavier wire, which is usually stranded (made up of many individual wires bundled together), the size is specified in the United States in thousands of circular mills (kcmil). For example, 1000-kcmil stranded copper wire for utility transmission lines is 1.15 in. in diameter and has a resistance of 0.076 ohms per mile. In countries using the metric system, wire size is simply specified by its diameter in millimeters. In Table gives some
values of wire resistance, in ohms per 100 feet, for various gages of copper wire at 68◦F. Also given is the maximum allowable current for copper wire clad in the most common insulation

Gilbert M. Masters. “Renewable and Efficient Electric Power Systems”. Jhon Wiley & Sons, Inc., New Jersey. ISBN 0-471-28060-7. 2004


Usually the microgrid used wind turbine (wind), PV (sun), battery (batt) and load, aditional it have a PCC with electrical network external (ene). Both the technical operation as the economic operation are important during performance microgrid. In the figure I show the results of optimization process with imaginary energy prices from diferent source mentioned. In top figure is the power distribution between sources and down figure the total cost of each state. Programming linear has been used in this modelling and simulations.

first steps in optimizing microgrids

This is first results of simulation in optimization microgrids. For variable electric load (4 states), the sources supply from diferents power plants. In a first moment, sun (blue line) and after is the wind. Other sources as battery and electrical network exterior not supply in this analysis for to get the minimum cost.

Roadmap for microgrid development

Currently, an increasing number of microgrid pilot sites can be observed in many parts of the world. It is true, however, that up to now,cost, policy and technology barriers have largely restrained the wide deployment of microgrids in distribution networks owing to their limited commercial appeal or social recognition. However, these three barriers are currently undergoing considerable changes – they are very likely to turn into key enablers in the future, eventually leading to a widespread microgrid adoption worldwide.

Firstly, the cost factor might prove to be the most effective driving force for microgrids in the very near future. This might happen not only because of the reduction of microsource costs, but also because of the relative changes of external opportunity costs due to economic (fluctuating market prices), technical (aging of network infrastructure) and environmental (emission trading) factors.

When microsource penetration at a LV grid becomes significant, participants in the electricity retail business will consider the aggregated power from small generators as a new market opportunity. Unlike in the case of VPP, microgrid stakeholders will eventually recognize a unique feature of aggregated microsource units, namely locality: the microsource units can potentially sell directly to end consumers in an “over-the-grid” manner. In order to turn this potential into reality, however, the second factor – appropriate policy and regulatory environment – is needed to enable the operation of a local market within a microgrid.

Finally, the adoption of favorable selling prices in local retail markets will attract even more microsource units, allowing the microgrid to operate islanded, if beneficial. With the help of smart metering, control and communication technologies, the microgrid operator will eventually be able to coordinate a large consortium of intermittent and controllable microsource units, as well as central and distributed storage devices, to achieve multiple objectives and, at the same time, to cater for the interests of different stakeholders.

MICROGRIDS: Architectures and Control
Nikos Hatziargynou

Microgrid operation strategies

Currently available DG technologies provide a wide variety of different active and reactive power generation options. The final configuration and operation schemes of a microgrid depend on potentially conflicting interests among different stakeholders involved in electricity supply, such as system/network operators, DG owners, DG operators, energy suppliers, customers and regulatory bodies. Therefore, optimal operation scheduling in microgrids can have economic, technical and environmental objectives

Depending on the stakeholders involved in the planning or operation process, four different microgrid operational objectives can be identified: economic option, technical option, environmental option and combined objective option.

In the economic option, the objective function is to minimize total costs regardless of network impact/performance. This option may be envisaged by DG owners or operators. DGs are operated without concern for grid or emission obligations. The main limitations come from the physical constraints of DG.

The technical option optimizes network operation (minimizing power losses, voltage variation and device loading), without consideration of DG production costs and revenues. This option might be preferred by system operators.

The environmental option dispatches DG units with lower specific emission levels with higher priority, disregarding financial or technical aspects. This is preferred for meeting environmental targets, currently mainly supported by regulatory schemes. DG dispatch is solely determined by emission quota; only DG physical limitations are considered.

The combined objective option solves a multi-objective DG optimal dispatch problem, taking into account all economic, technical and environmental factors. It converts technical and environmental criteria into economic equivalents, considering constraints from both network and DG physical limits. This approach could be relevant, for instance, to actors that participate not only in classical energy markets, but also in other potential markets for provision of network services and emission certificates

MICROGRIDS: Architectures and Control
Nikos Hatziargynou

FACTS devices can enhance the power flow on existing power lines. For the transmission line shown in figure, the sending end voltage isVS∠δS, the receiving end voltage is VR∠δR and the equivalent impedance of parallel connected lines isX. The power transfer through the lines is given by:

FACTS equation

the figure also shows how FACTS devices act on the power transfer equation. The TCSC can change the impedance of the line, the STATCOM can control the voltage magnitude at

FACTS applications for increased power transfer

the terminal to which it is connected by injecting or absorbing reactive power and the UPFC can alter the phase angle of the sending end voltage, thus power flow through a line can be controlled in a number of ways.

Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication