Path-Q Solar

How should a home's previous owner's electricity use be adjusted before sizing solar?

Answer

Treat the previous owner's use as a starting point, then adjust it for differences in occupants, schedules, heating and cooling, appliances, EVs, water heating, and planned improvements. Do not assume the prior annual total represents the next household's demand.

Key points

  • Occupancy and behavior can change both annual use and the time of use.
  • Fuel switching or new electric equipment can make historical bills obsolete.
  • A home that was vacant, unusually occupied, or operated with unusual thermostat settings may not have representative data.
  • Use monthly or interval data when available to identify seasonal patterns.

What it depends on

  • Number and habits of prior and future occupants
  • Heating, cooling, and water-heating systems
  • Appliances, EVs, and planned renovations
  • Quality and duration of the prior billing history

Risks and trade-offs

  • Simple proportional adjustments can miss large individual loads.
  • Recent renovations or equipment changes can make older bills unreliable.
  • Sizing to prior use can understate future electrification or overstate use after efficiency improvements.

Information you may need

  • At least a year of prior bills and interval data if available
  • Prior and expected occupancy
  • Current and planned equipment
  • Planned changes to the home's operation or envelope

Your next step

What to do next

Create a baseline from the prior bills, list every material difference in future use, and ask for a revised load model rather than a direct bill extrapolation.

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