Path-Q Solar
Should I use interval usage data rather than monthly bills to design solar?
Answer
Use interval data when it is available and reliable, especially when evaluating self-consumption, batteries, EV charging, time-based rates, or demand charges. Monthly bills are adequate for a preliminary annual-energy estimate but can hide when electricity is used.
Key points
- Monthly bills show total consumption and billing information but not the timing of loads.
- Interval data can reveal daytime usage, evening peaks, seasonal patterns, and opportunities to shift loads.
- Data quality, interval length, missing records, and the period represented still need review.
- Both sources can be useful: bills establish the annual baseline and interval data refines system and operating design.
What it depends on
- Availability and quality of interval data
- Rate structure and any demand charges
- Expected load shifting, battery use, or EV charging
- Whether the goal is energy offset, bill reduction, or backup
Risks and trade-offs
- A short or atypical interval-data period can misrepresent normal use.
- Detailed data can create false precision if future loads will change.
- Optimizing self-consumption may produce a different design from maximizing annual generation.
Information you may need
- At least several months of interval data if available
- Monthly bills and rate documents
- Operating schedules for major loads
- Planned EV, battery, heating, or other changes
Your next step
What to do next
Give the designer both bills and interval data, and request an explanation of how timing of use changes the recommended system and equipment.
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