Path-Q Solar

How should I compare solar ROI with paying down my mortgage?

Answer

Compare the after-tax, risk-adjusted return and cash-flow effects of each use of money. Mortgage repayment provides a relatively predictable benefit related to avoided interest, while solar returns depend on production, utility prices, system costs, contract terms, and the value of retaining or selling the home.

Key points

  • Use the mortgage's applicable interest cost and repayment schedule, including whether payments are deductible or otherwise affect taxes.
  • Calculate solar returns using all-in ownership costs, expected bill savings, degradation, maintenance, and replacement assumptions.
  • Compare liquidity: money used for either option may be less available for emergencies or other investments.

What it depends on

  • Mortgage rate, balance, term, prepayment rules, and tax treatment
  • Solar installed cost, funding method, production, and savings
  • Expected ownership period and required return
  • Risk tolerance and need for accessible cash

Risks and trade-offs

  • Solar savings and home-value effects are uncertain, while mortgage interest savings may be more predictable.
  • Paying down a mortgage can reduce liquidity; financing solar preserves cash but adds interest and payment risk.
  • Comparing a nominal solar payback with a mortgage rate without matching time periods and tax treatment can mislead.

Information you may need

  • Mortgage statement and prepayment terms
  • Solar proposal, funding terms, and savings model
  • Tax treatment, emergency-reserve needs, and expected time in the home

Your next step

What to do next

Compare both choices in an after-tax, year-by-year cash-flow model using the same investment amount and time horizon.

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