After reviewing hundreds of interval data analyses over the past few years, I've noticed some recurring mistakes that cost clients money. Thought I'd share the top issues I see: 1) Not accounting for holidays in TOU schedules - utilities often treat holidays as off-peak even if they fall on weekdays. 2) Ignoring seasonal TOU schedule changes - many utilities have different peak hours in summer vs winter. 3) Mixing up demand window calculations - some utilities use rolling 15-min windows, others use fixed intervals. 4) Not validating meter multipliers when analyzing raw interval data. What other common pitfalls have you encountered?
Common mistakes in TOU rate analysis using interval data
Randy, excellent list! I'd add: 5) Forgetting to check if the utility applies TOU rates to both energy and demand charges - some only apply TOU to energy. 6) Not understanding coincident vs non-coincident demand billing. Pacific Power here in Oregon has both, and mixing them up can lead to significant calculation errors. 7) Overlooking minimum bill provisions that can override TOU savings calculations.
Great points Randy and Dave. Another big one: 8) Not checking if interval data is recorded in local time or utility time. Idaho Power records everything in Mountain Time, but some clients assume it's in their local time zone. Also 9) Failing to account for power factor in demand calculations when the utility bills for both kW and kVA. The interval data might show kW but billing could be based on kVA demand.
Adding from Alaska experience: 10) Not understanding cold weather billing adjustments that some northern utilities apply. Chugach Electric has provisions that modify both TOU periods and demand billing during extreme weather events. These adjustments often aren't clearly documented but can significantly impact bills during winter months.
From the Northeast: 11) ISO New England has capacity charges that many auditors miss when analyzing commercial accounts. The interval data is crucial for calculating these charges, but they're often buried in tariff schedules. National Grid applies them based on coincident peak during specific system peak hours, not just the customer's individual peak demand.
Virginia perspective: 12) Dominion Energy has ratchet provisions that carry forward peak demand for 11 months. I've seen auditors focus only on current month interval data and miss that the customer is being billed for a demand peak that occurred months earlier. Always check the full ratchet history when analyzing demand charges.
Wisconsin addition: 13) Madison Gas & Electric has different TOU schedules for different rate classes, and they're not always intuitive. A customer might be on Schedule Cg-5 but the auditor applies Schedule Cg-4 TOU periods. Small difference in rate class can mean completely different peak/off-peak definitions. Always verify the exact rate schedule and TOU provisions.
Ohio experience: 14) Duke Energy Ohio has transmission charges based on PJM coincident peaks that occur at unpredictable times. The interval data is essential for tracking these, but many auditors don't realize these charges exist. They can be significant - sometimes $3-5 per kW per month on top of regular demand charges.
Minnesota insight: 15) Xcel Energy has different demand billing for summer vs winter months, but it's not just the TOU periods that change - the actual demand calculation method can be different. Summer might use 15-minute intervals while winter uses 30-minute intervals for the same customer class. Always check both the TOU schedule AND the demand calculation methodology.
Texas perspective: 16) CPS Energy here in San Antonio has some of the most complex TOU schedules I've seen, with different rates for different seasons AND different customer voltage levels. A customer served at 4kV has different TOU periods than one served at 13kV, even if they're on the same base rate schedule. The interval data analysis has to account for service voltage, not just usage patterns.
Great thread everyone! 17) Idaho Power has what they call "irrigation season" rates that completely change TOU periods for agricultural customers from April through October. The interval data analysis looks completely different depending on whether you're in irrigation season or not. Many auditors miss this seasonal switch and apply wrong TOU periods for half the year.
This has become an invaluable reference thread. I'm copying all these points into my interval data analysis checklist. It's amazing how many utility-specific quirks can trip up even experienced auditors. The key takeaway is that generic TOU analysis doesn't work - you have to understand each utility's specific rules, seasonal adjustments, and calculation methods. Thanks Randy for starting this discussion!