THE SHORT ANSWER
An assumption register names what the proposal treats as true, the evidence behind it, who verifies it and what changes if it is wrong.
Collect assumptions across the project
List annual usage, future loads, roof age and geometry, shade, equipment availability, electrical conditions, utility tariff, permit jurisdiction, property ownership and schedule. DOE shows that going solar involves technical, site, utility and financial factors. [1]
Give each assumption evidence
Attach a utility bill, photo, permit, model report, datasheet or written source where available. Mark homeowner statements and remote imagery honestly. “To be verified at survey” is more useful than converting an unknown into a confident fact.
Assign an owner and deadline
Identify whether the homeowner, designer, field surveyor, contractor, utility or lender resolves each item and by what milestone. Do not assign a utility approval to the installer as though it were already controlled or completed.
Describe the consequence
State whether a changed input could affect layout, equipment, production, price, financing, permitting or schedule. FTC guidance recommends understanding written agreements and promises. [2] Material consequences should trigger a documented proposal revision rather than an informal note.
Close or carry every item
Before installation, mark each assumption verified, revised, accepted with a defined risk, or still blocking. Keep the dated register with the final proposal. This modest project-control tool reduces ambiguity without pretending that every future condition can be guaranteed.
Before your next conversation
- List technical and commercial assumptions.
- Attach evidence or mark unknowns.
- Assign verification owners.
- Define material revision consequences.
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.
- Federal Trade Commission: Solar Power for Your Home
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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