THE SHORT ANSWER
A production estimate and a utility-bill estimate are different calculations. A useful proposal documents the Duke account inputs and does not guarantee future rates or savings.
Separate production from billing
Record the proposed annual generation, modeled household use, self-consumption, imported energy and exported energy. Ask which values are measured, estimated or assumed.
Use the current account
Confirm the Duke service address, rate schedule and 12 complete billing periods. Remove unrelated balances or fees from energy comparisons without pretending continuing utility charges disappear.
Preserve model inputs
PVWatts can make solar-production assumptions visible, but NREL does not approve the project or guarantee the result. [2] Save location, capacity, orientation, tilt, losses and dataset with the proposal version.
Stress-test the claim
Ask how the result changes with higher household use, different export timing, equipment downtime or a utility-rate change. Review financing separately from energy modeling and verify tax questions with a qualified adviser.
Before your next conversation
- Use 12 complete Duke bills.
- Separate production and bill models.
- Save PVWatts inputs.
- Test important assumptions.
Primary sources
- Duke Energy: Generate Your Own Renewable Energy
Primary source reviewed September 11, 2026. Utility rules, rates, forms and project requirements remain subject to the current account, equipment and property review.
- National Renewable Energy Laboratory: PVWatts Calculator
Primary source reviewed September 11, 2026. Utility rules, rates, forms and project requirements remain subject to the current account, equipment and property review.
- U.S. Department of Energy: Homeowner’s Guide to Going Solar
Primary source reviewed September 11, 2026. Utility rules, rates, forms and project requirements remain subject to the current account, equipment and property review.
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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