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 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
|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.