I get asked this a lot by clients: "should I be on a time-of-use rate?" Is there a quick way to evaluate whether TOU would save money without doing a full 12-month interval data analysis?
TOU vs flat rate — quick way to tell which is cheaper?
Quick screen: look at the ratio of on-peak to off-peak usage. If you have interval data, even one month will tell you roughly. If more than 60% of the client's kWh are consumed during off-peak hours, TOU is probably cheaper. If less than 40% is off-peak, TOU is probably more expensive. Between 40-60% you need to run the full calculation. For clients without interval data, look at their operating hours. A 9-to-5 office building will have most usage on-peak — bad for TOU. A warehouse running overnight shifts will be mostly off-peak — great for TOU.
The quick screen works for initial assessment but always run the full calculation before recommending a rate change. Pull 12 months of interval data, apply the TOU rate to each interval, sum the monthly totals, and compare to what the flat rate would have been. I've seen cases where the quick screen said TOU was cheaper but the full calculation showed it was more expensive because of a few high-demand on-peak days that the average masked. Seasonal variation matters too — a client might be off-peak heavy in winter but on-peak heavy in summer.
One shortcut I use: most utilities publish a TOU rate calculator on their website or will run a shadow bill for you. Duke Energy and Georgia Power both offer shadow billing where they'll show what the client's bill would have been on a different rate for the past 12 months. Saves you the interval data analysis.
Didn't know about shadow billing — that's a huge time saver. Going to request that from Duke for my Charlotte clients. Thanks Derek.