ECC noted the record storm season of 2020, pointing out that planning to keep customers online, or getting them back online after a storm, is a growing challenge. Weather is changing, and so must utilities’ ability to have flexibility, exacting planning, and superb execution.

Santee Cooper claims they rank among the most reliable utility companies in the country. Santee Cooper’s table says that on average, their customers were only without power for 21 minutes in 2018 compared to Florida Power & Light (FPL) whose customers lost power on average for 55 minutes.

Is this a forthright comparison? The question of which utility is more reliable is important.

ECC’s take – Santee Cooper cherry-picked the data.

FP&L and Santee Cooper – The Numbers (MED = Major Event Day):

YEAR FPL SAIDI W/ MED FPL SAIDI W/O MED SANTEE COOPER SAIDI W/ MED SANTEE COOPER SAIDI W/O MED
2018 60.36 54.59 518.41 20.56
2019 58.26 51.46 132.88 18.94

Check the comparison on Major Event Days. Santee Cooper shows significant increases in customer outages. In 2018 and 2019 FPL customers experienced 5.77 and 6.8 additional minutes of lost power during MEDs. Comparatively, Santee Cooper customers experienced 497.85 and 113.94 additional minutes of lost power during MEDs.

Again, just in 2019: FPL – 6.8 minutes; Santee Cooper – 113.94 minutes. Minutes may seem small; but more than 16 times the difference makes a difference. Not small. Not small when a company like Santee Cooper says it is among the most reliable in the country.

NextEra, the parent company of Florida Power & Light, submitted a bid for Santee Cooper in 2019. Included in this bid is the promise of investment for a stronger, more reliable utility for South Carolinians.

Some background.

How does the utility industry measure reliability?

Reliability is best gauged by System Average Interruption Duration Index (SAIDI) because it encompasses two other standard industry performance metrics for reliability: System Average Interruption Frequency Index (SAIFI) and Customer Average Interruption Duration Index (CAIDI), or, how often service areas experience outages and the duration of the outage.

How are SAIFI, SAIDI & CAIDI calculated?

  • SAIFI = # OF CUSTOMERS AFFECTED / # OF CUSTOMERS IN THE SYSTEM
  • SAIDI = (MINUTES OF POWER OUT) X # OF CUSTOMERS AFFECTED / # OF CUSTOMERS IN THE SYSTEM OR SAIDI = (MINUTES OF POWER OUT) X SAIFI OF EVENT
  • CAIDI = (MINUTES OF POWER OUT) = SAIDI / SAIFI

Here is a key issue: SAIFI, SAIDI, and CAIDI are oftentimes calculated both with Major Event Days (MED) and without MEDs. Major Event Days are classified as a catastrophic event which exceeds operational limits of the electric power system where at least 10% of the customers within an operating area experience a sustained interruption during a 24-hour period. Think major storms like hurricanes.

Our next blog: Why are reliability numbers important?