Path-Q Solar
How should I use my electricity bill to size a solar system?
Answer
Use the bill to identify electricity consumption over a full annual cycle, then combine that usage with the home's future demand, roof production potential, and desired offset. Do not size from the bill total alone: billing periods, estimated readings, seasonal variation, fixed charges, and changing rates can distort a simple calculation.
Key points
- Record energy usage in kilowatt-hours for each billing period, not just the amount paid.
- Check for unusual months, estimated readings, partial occupancy, and recent changes.
- Include planned loads such as heating electrification, electric vehicles, or additions.
- Use a site-specific production estimate to convert energy demand into system capacity.
What it depends on
- Annual and monthly kilowatt-hour usage
- Future changes in household demand
- Roof orientation, shading, and available area
- Target offset and billing arrangement
- Panel and system production assumptions
Risks and trade-offs
- Sizing to one unusually high or low bill can produce the wrong system size.
- A system sized for annual usage may not match seasonal or hourly demand.
- Oversizing may add cost without equivalent bill value under some export arrangements.
Information you may need
- At least a full year's usage history
- Detailed bill pages showing energy use and charges
- Planned changes in appliances or occupancy
- Roof and shade information
- Current billing and export terms
Your next step
What to do next
Build a month-by-month usage summary and provide it, along with planned future loads, to the designer for a production-based sizing analysis.
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