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Over a century ago, power engineers designed the majority of what we see in the today’s power system infrastructure, based upon significant research during the infancy of wide-scale electric power generation, transmission and distribution.  At the time, utilities built centralized electrical generation under the assumption of unidirectional power flow from the plant to the customer.  These concepts were appropriate for the demand and complexity of the power system during that time; however, with growing electrical demand of modern society, we must take a closer look at these assumptions.  Increasing fuel costs for centralized generation as well as changing social attitudes is leading to increased distributed generation from renewable resources including solar and wind.

Distributed Generation

Distributed generation has changed the way that the power system operates, allowing many small generation facilities to contribute power in order to meet current electricity demand collectively.  Consequently, utilities anticipate that distributed generation systems will introduce new problems since it violates the previous assumption of unidirectional power flow.  Distributed generation introduces the phenomenon of bidirectional power flow, resulting in adverse effects on conventional protection and voltage regulation equipment in the existing power system.

Indeed, many American states have adopted renewable portfolio standards, which require a pre-determined amount of electricity to come from renewable sources by as early as 2013 (for details, see Appendix A: Renewable Portfolio Standards).

Plug-in Electric Vehicles

With dwindling supplies of fossil fuels and increasing prices for crude oil and petroleum products, electric vehicles are steadily gaining momentum.  Although electric vehicles are not yet mainstream, they are expected to have a significant impact on the method and amount of power distribution in the near future as drivers begin switching from gasoline-fuelled vehicles to their electric equivalents en masse.  The increasing popularity of plug-in electric and hybrid-vehicles introduces issues to the power system since it effectively doubles or triples power consumption in already strained residential areas.

There are several problems faced due to the way in which the current power system is configured.  The problem lies not with the method by which the electric car is charged, but rather the number of electric cars being charged, as well as the total amount of energy required to charge each car on a daily basis (see Appendix B: PHEV Demand Increase Example).  This large increase in electrical demand will require additional generation facilities to meet the demand, and require new equipment to deal with the increased demand of consumers.  This paradigm shift will severely affect distribution utilities since the current generation of residential transformers is not rated for such high peak demands.

By implementing smart grids, local distribution utilities will be able to mitigate the problem by staggering the charging sequence of each electric vehicle.  Furthermore, utilities can explore the use of hybrid vehicles as a distributed storage technology or as a power factor controller.  Indeed, the smart grid has the potential to reduce loading on residential substations and small distribution transformers, which eliminate the necessity for expensive high-capacity equipment.

Appendix A: Renewable Portfolio Standards

State Amount Deadline Program Administrator
Arizona 15% 2025 Arizona Corporation Commission
California 20% 2010 California Energy Commission
Colorado 20% 2020 Colorado Public Utilities Commission
Conneticut 23% 2020 Department of Public Utility Control
District of Columbia 11% 2022 DC Public Service Commission
Delaware 20% 2019 Delaware Energy Office
Hawaii 20% 2020 Hawaii Strategic Industries Division
Iowa 105MW Iowa Utilities Board
Illinois 25% 2025 Illinois Department of Commerce
Massachusetts 4% 2009 Massachusetts Division of Energy Resources
Maryland 9.5% 2022 Maryland Public Service Commission
Maine 10% 2017 Maine Public Utilities Commission
Minnesota 25% 2025 Minnesota Department of commerce
Missouri 11% 2020 Missouri Public Service Commission
Montana 15% 2015 Montana Public Service Commission
New Hampshire 16% 2025 New Hampshire Office of Energy and Planning
New Jersey 22.5% 2021 New Jersey Board of Public Utilities
New Mexico 20% 2020 New Mexico Public Regulation Commission
Nevada 20% 2015 Public Utilities Commission of Nevada
New York 24% 2013 New York Public Service Commission
North Carolina 12.5% 2021 North Carolina Utilities Commission
Oregon 25% 2025 Oregon Energy Office
Pennsylvania 18% 2020 Pennsylvania Public Utility Commission
Rhode Island 15% 2020 Rhode Island Public Utilities Commission
Texas 5880 MW 2015 Public Utility Commission of Texas
Utah 20% 2025 Utah Department of Environmental Quality
Vermont 10% 2013 Vermont Department of Public Service
Virginia 12% 2022 Virginia Department of Mines, Minerals and Energy
Washington 15% 2020 Washington Secretary of State
Wisconsin 10% 2015 Public Service Commission of Wisconsin

Source: The Smart Grid: An Introduction – For Utilities.  Published by the Office of Electricity Delivery and Energy Reliability, United States Department of Energy.  Page 19.  Retrieved on March 20, 2010 from http://www.smartgrid.gov

Appendix B: PHEV Demand Increase Example

Gasoline car energy

Energy density of gasoline = 32MJ/L*50L/tank = 1600MJ/tank

Gasoline energy per month = 1600MJ/tank * 4tank/month = 6400MJ/month

Note that 50L/week = 200L/month would result in a monthly cost of: 200L/month @ $1.00/L = 200$/month

Electric car energy

1kWh = 3.6MJ

6400MJ/3.6MJ = 1778kWh/month

1778kWh/month @ $0.058/kWh = $103/month

Not only is the total electrical energy usage of the family almost tripled for every month, but charging peaks at night-time would exceed the peaks during the daytime and also prevent transformers from cooling down at night (in case they are being run above rated conditions during the daytime).

A partner and I originally wrote this article for a report submitted to ECE4439: Conventional, Renewable and Nuclear Energy, taught by Professor Amirnaser Yazdani at the University of Western Ontario.

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