Path-Q Solar

How should I size solar if I expect to add electric heating later?

Answer

Include a realistic estimate of the future heating load, but do not simply add the heating equipment's rated power to annual electricity use. Estimate its annual and seasonal energy consumption, account for efficiency and operating conditions, and obtain designs for current use, future use, and any practical expansion path.

Key points

  • Use the planned heating technology, efficiency, climate, building insulation, and operating pattern to estimate energy use.
  • Consider whether heating will shift demand into seasons or hours when solar production is lower.
  • Check roof area, inverter capacity, electrical service, and interconnection limits before reserving expansion capacity.
  • Compare installing a larger system now with installing a smaller system and expanding later.

What it depends on

  • Type, efficiency, size, and operating schedule of the future heating system
  • Building size, insulation, climate, and current heating fuel use
  • Roof, electrical, and equipment expansion capacity
  • Bill structure and treatment of exported generation

Risks and trade-offs

  • Heating estimates can be materially wrong if based only on equipment nameplate power.
  • A system sized for future heating may produce more than current loads can use before the heating is installed.
  • Waiting may allow better load data but may also affect project timing and future expansion feasibility.

Information you may need

  • Current heating fuel consumption and planned replacement timing
  • Heating equipment specifications or contractor load estimates
  • Building envelope and occupancy information
  • Current roof and electrical design constraints

Your next step

What to do next

Obtain a heating-load estimate and ask installers for comparable current-load, future-load, and expansion-ready designs.

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SQ00244