I'm developing my audit methodology for time-of-use billing and want to make sure I'm being thorough. Working with a client who has Pacific Gas & Electric service on Schedule E-19 (medium commercial TOU). The rate has different pricing for summer vs winter and peak/partial-peak/off-peak periods. What's the best approach for verifying that usage is being allocated to the correct time periods? Should I be requesting interval data for the entire audit period or is sampling sufficient?
Methodology for reviewing time-of-use billing accuracy
For TOU audits, I always request at least 13 months of interval data to cover seasonal variations. PG&E's E-19 schedule is complex with different TOU periods in summer (June-Sept) vs winter months. Create spreadsheets that map the interval data to the rate schedule time periods and verify the billing calculations. Pay special attention to holiday scheduling - PG&E treats holidays as off-peak but some clients don't realize this. Also watch for demand ratchet provisions that might carry peak demand from summer into winter billing.
TOU billing verification is one of the most complex audits but also where you find the biggest errors. Beyond the interval data, make sure you understand PG&E's specific definitions of peak periods - they can change annually. I found a $2,800/month error last year where a client was being billed peak rates during what should have been partial-peak hours due to a tariff update that wasn't properly implemented. Also verify that daylight saving time transitions are handled correctly in both the interval data and billing calculations. The devil is definitely in the details with TOU audits.