Back Print

Ask Mr. Answer Person: "What are Alliant Energy's reliability numbers and how do those municipal numbers compare?"

Posted: Mon, Feb 12, 2018 1:53 PM

(Austin e-mails: "Decorah Power has noted that nationwide, municipals have a better reliability than investor-owned utilities? But what are Alliant Energy's reliability numbers and how do those municipal numbers compare to Alliant Energy specifically?")

Mr. Answer Person says: "Austin, you've asked a simple question--which has a very complicated answer!  That's because there are at least four different ways to measure 'reliability' when it comes to electric utilities.

The organization in charge of tracking statistics about reliability is a federal government agency--the U.S. Energy Information Administration (or "EIA").  Utilities fill out a form annually and submit it to Washington, D.C.  But because it's the federal government, the most recent statistics on reliability are from 2015.

EIA is interested in having utilities submit four different sets of statistics,  The first two are "CAIDI," which stands for "Customer Average Interruption Duration Index," and "MAIFI," which stands for "Momentary Average Interruption Frequency Index."  As these names imply, the indexes track how the average customer is affected by interruptions and how many times the electricity is interrupted even momentarily.

But experts in the field agree the two other sets of statistics are the most important--"SAIFI," which stands for "System Average Interruption Frequency Index," and "SAIDI," which stands for "System Average Interruption Duration Index."  Obviously, no one wants to be without electricity, even for a minute.  But what type of outage is more important to avoid--the momentary outage, which is better tracked with the SAIFI figure, or the longer outage, which is better tracked with the SAIDI figure?

In the feasibility study presented by Alliant Energy to the City of Decorah, the utility presented both sets of figures.  A chart showing frequency of outages showed investor-owned utilities--the category to which Alliant Energy belongs--to have had slightly more frequent outages in 2015 than municipal electric utilities--the category in which a new Decorah electric utility would belong.  But a second chart showing outage time in minutes shows investor-owned utilities doing slightly better than municipal utilities in having a lower total of outage minutes.

So are the two types of utilities even when it comes to "reliability?"  Alliant Energy submitted another set of figures which it says covered only the area served by the Decorah substation.  Those figures show a markedly better performance by Alliant in avoiding outages in Decorah.  However, the statistics are internal statistics from Alliant and not figures filed with the Iowa Utilities Board, so there's no independent third-party verification of the figures.  Alliant, of course, is touting these figures from the Decorah substation, while Decorah Power is touting a conclusion by the EIA that on a national basis, municipal electric utilities on average do a better job of providing reliable energy.

Making the question even tougher to answer is the fact that there are often forces outside the control of utilities--either investor-owned or municipally-owned--that have big impacts on outage figures.  A storm-filled year when branches knock down overhead power lines will make it look like a utility is doing a bad job of reliability, when it is literally "an act of God" that is affecting the statistics.  Reliability figures can also be lower in rural areas than in urban areas.  That's because there would be many more miles of electric wires needed to serve 1,000 customers in the country than there would in the city.

Austin, you're probably looking for a conclusion about "who's right?" on this issue.  You're probably not going to like this answer, but with the average electrical customer suffering just one outage a year, it seems like both investor-owned utilities like Alliant and municipally-owned utilities like the one Decorah Power is proposing do excellent jobs in keeping the lights on and our houses and businesses running.  In short, Mr. Answer Person is ruling that this question results in a tie."