Path-Q Solar

How should I compare quotes with different expected system lifetimes?

Answer

Compare quotes over a common analysis period using each system’s stated degradation, warranty limits, maintenance, replacement needs, and expected residual value. Do not treat a longer modeled life as automatically better unless the additional production exceeds its added costs and uncertainty.

Key points

  • Use the same discount rate, energy-price assumptions, and treatment of incentives for all quotes.
  • Model production year by year rather than multiplying first-year output by the stated lifetime.
  • Include inverter, battery, monitoring, roof, and other replacement assumptions where relevant.
  • Distinguish equipment warranty duration from expected technical or economic life.
  • Show results using net present value, levelized cost, or another common metric in addition to simple payback.

What it depends on

  • Degradation assumptions
  • Warranty and replacement terms
  • Maintenance and operating costs
  • Analysis period and discount rate
  • Expected energy value and residual value

Risks and trade-offs

  • Long-range production forecasts become more uncertain over time.
  • A longer life can improve modeled return but may require unpriced repairs or replacements.
  • A shorter model life can understate value if equipment is likely to remain useful.

Information you may need

  • Annual production and degradation schedule
  • Warranty terms and exclusions
  • Replacement and maintenance assumptions
  • Itemized price and financing cost
  • Common financial-model assumptions for all quotes

Your next step

What to do next

Recalculate every quote over the same analysis period and run conservative, central, and extended-life cases.

Path-Q

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SQ02469