We're buying a house with 25-year-old solar panels. Should we have the system updated?

Asked by Michael and Amy Bergman, Alexandria, VA

We are considering buying a house with solar panels that were installed 25 years ago. The solar panels are the house's primary source of electricity. Should we have this system updated before we buy the home?


Ricky Cappe

Answered by Ricky Cappe

Santa Monica, CA

Green Built Consultants

July 3, 2007

Although great advances have been made in photovoltaic (PV) technology, a solar system that was installed 25 years ago may still be effective and may continue to generate power for a long time to come.

Find out how much electricity the system is generating for the current homeowners. Would that amount be enough for your family’s needs? Updating the system with new, more efficient panels would produce more electricity, but it would be very expensive and it could take years to recoup the cost in energy savings.

The advice I always give my clients is to reduce energy requirements before sizing the system. Are there appliances you could do without? Could appliances be upgraded to energy-efficient, Energy Star–rated products? Are there incandescent light bulbs in the house that could be replaced with compact fluorescent bulbs? Could insulation be added to reduce heating and cooling needs?

You will need to contact a local solar specialist who can look at the system and advise you about upgrades and repairs. I encourage you to do some research of your own on PV systems so that you will know what questions to ask.

Consider the individual components: the panels, the inverter, the wiring, the mounting system, and the battery bank (if the system is grid-tied, there may not be batteries).

  • Panels. The PV panels represent most of the cost. It is not uncommon for panels to continue working indefinitely as long as they are not damaged, and any damaged panels could be replaced. Ask your solar specialist what kinds of replacement panels you could use with your existing system and what they would cost.
  • Batteries. If there are batteries, when were they last replaced? Batteries should be replaced every five years, as their ability to hold a charge declines.
  • Inverter. Find out whether the inverter has been replaced recently, and if so, whether it is still under warranty. Inverters are made better now than they used to be, so an old inverter could be the weak link in your system. A new inverter could cost approximately $2,000 for a grid-tied system or $2,500 for an off-grid system.

Finally, when it comes to negotiating a fair price for the house, the current homeowners’ estimate of how much electricity the system generates can help guide you. For grid-tied systems, according to the National Appraisal Institute, for every dollar of electricity a solar system generates per year, it adds $20 to the value of the house. So if a system generated $1,000 of electricity per year, it would be worth $20,000 more.

Thanks to Paul Scott and Bob Siebert of Energy Efficiency Solar in Santa Monica, Calif., for their assistance with this question.

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