THE SHORT ANSWER
Keep a data gap visible. Obtain interval history from the utility when possible; otherwise label the replacement method, inputs and uncertainty before sizing solar.
Confirm that the month is truly absent
Check whether the utility portal groups statements by issue date rather than meter period. Look for a start or stop of service, revised statement, estimated read, or bill covering an unusually long interval. Record the account and meter dates without publishing private account identifiers.
Ask for the underlying usage record
Request monthly or interval kWh history from the utility for the service address and period. DOE recommends using electricity use when assessing rooftop solar. [1] A dollar estimate from a bank statement cannot substitute cleanly because electric rates and non-energy charges can change.
Choose an explicit placeholder only if needed
If a verified reading is unavailable, document whether the placeholder uses adjacent months, the same season from another year, or appliance information. Do not quietly copy an average into the gap. The proposal reviewer should be able to see which month is observed and which is estimated.
Keep weather and system modeling separate
NREL PVWatts estimates photovoltaic production from system and weather inputs. [2] It does not reconstruct a household’s missing consumption. Treat the usage-gap method as one assumption and the proposed array’s production model as another, then evaluate both instead of blending them.
Revise when better data arrives
Save the proposal version based on the placeholder. When the utility supplies actual kWh, request a revised annual total and design comparison. A small difference may not change the layout; a material difference deserves an explanation before contract scope or financing is finalized.
Before your next conversation
- Check meter-period dates for overlap.
- Request utility kWh history.
- Label any estimated replacement.
- Re-run the review when actual data arrives.
Primary sources
- U.S. Department of Energy: Homeowner’s Guide to Going Solar
Primary source reviewed September 10, 2026. Utility rules, equipment availability, project design and contract terms remain specific to the property and proposal.
- National Renewable Energy Laboratory: PVWatts Calculator
Primary source reviewed September 10, 2026. Utility rules, equipment availability, project design and contract terms remain specific to the property and proposal.
Planning examples and questions are Origin’s editorial guidance, not a property-specific diagnosis, engineering design, tax determination or promise of savings. Manufacturer and utility references do not imply an affiliation with Origin.
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