Path-Q Solar

How should solar be designed when two units in a duplex have different electricity use?

Answer

Design the system around separately measured usage and a documented allocation method, rather than dividing capacity equally by default. The practical design depends on whether there is one meter or separate meters, who owns the system, how energy is allocated, and what the utility and agreements permit.

Key points

  • Collect usage histories for each unit and account for common-area loads separately.
  • With separate meters, determine whether each meter can receive or be credited for solar production under the applicable arrangement.
  • With one meter, define how costs, benefits, maintenance, and future changes are allocated between units.
  • Size for expected future occupancy and loads, not only the current imbalance.

What it depends on

  • Meter configuration and utility billing arrangement
  • Ownership structure and landlord-tenant agreements
  • Each unit's historical and expected electricity use
  • Solar allocation, interconnection, and credit rules

Risks and trade-offs

  • Equal allocation can overbenefit one unit and underbenefit the other when usage differs.
  • Allocation disputes can arise if occupancy, usage, or tenants change.
  • A shared system may create responsibility for maintenance, repairs, insurance, and roof access.
  • The proposed allocation may not be available under the applicable utility or regulatory structure.

Information you may need

  • Separate or combined meter details
  • At least a year's usage for each unit and common areas
  • Ownership, lease, and cost-sharing arrangements
  • Utility requirements and available allocation methods

Your next step

What to do next

Ask a qualified installer and the utility to compare designs for separate-meter and shared-meter arrangements, then document ownership, allocation, billing, maintenance, and change-of-occupancy terms.

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Some details may depend on your location, installer, utility, incentives, regulations, or specific property.

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