Path-Q Solar

How can I estimate electricity use if my household will grow after installing solar?

Answer

Start with your actual bills, then build a forecast from expected occupants, appliances, heating and cooling, water heating, EV charging, and changes in behavior. Use a range rather than one precise number, because household growth affects electricity use differently depending on occupancy patterns and equipment.

Key points

  • Separate current base use from specific future loads that can be estimated individually.
  • Review monthly data because seasonal heating, cooling, and occupancy effects may be substantial.
  • Include planned electrification and major appliances, not just additional people.
  • Model low, expected, and high-use cases and show how each affects solar sizing.

What it depends on

  • Current monthly or interval electricity use
  • Number, schedule, and habits of future occupants
  • Planned heating, cooling, water heating, cooking, laundry, and vehicle loads
  • Efficiency of the home and its equipment

Risks and trade-offs

  • Per-person rules of thumb can be misleading when equipment or occupancy patterns differ.
  • Overestimating future growth can increase system cost; underestimating it can leave the system smaller than desired.
  • Future occupants may use electricity at different times, affecting financial value even when annual use is similar.

Information you may need

  • At least a year of monthly bills, preferably interval data
  • Expected household size and occupancy schedule
  • Inventory of planned appliances and electrification projects
  • Efficiency or energy-use estimates for major equipment

Your next step

What to do next

Create a low, expected, and high future-load forecast and give all three cases to the solar designer for comparison.

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