We have a number of recognized transmission and distribution experts serving on our board of "Grid Masters." Several times each month we’ll post what we judge to be the toughest questions that also have high interest to our readers. At least one of our experts will respond. Want to challenge our Grid Masters for a chance to win?

Q: As the government encourages more alternative energy installation such as wind and solar, what are the utility companies doing to assure their grids can handle the expansion of the solar generating farms? What are the problems with interfacing solar power systems with the utility grid? What is being done to overcome these problems?
Anonymous

A: There are a variety of distribution system problems that can be caused by the introduction of distributed generation resources – whether they be solar or wind – onto the electric distribution system. These include, but are not limited to:

  • Voltage levels outside normal operating levels.
  • Sudden voltage fluctuations due to variable cloud cover
  • Reverse power flow thorough typical radial protective devices not equipped to respond properly to such conditions
  • Misoperation of voltage regulators.
  • Excessive reactive power flow.
  • Public safety problems due to improper operation of overcurrent equipment and backfeed of downed circuits that are designed for radial operation.
  • Possible ‘islanding’ where generation capability approaches distribution system load levels, particularly during low load periods.

Many utilities successfully implement programs to review each proposed distributed generation project to make sure that it does not adversely affect the distribution system operation and reliability. The first step is to define reasonable operating criteria and incorporate these criteria in policy/regulatory statements applicable to distributed generation. If a system analysis finds an adverse impact attributable to the technical features of the proposed installation, the utility and the project developer negotiate the required changes to one (or both) systems to achieve satisfactory operation.
Ed Thomas
President, Utility Electrical Consultants, P.C.

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