Are Used Solar Panels Worth Buying? What to Check First

Used solar panels are worth buying when the price per watt is low and you can test them, especially for off-grid, shed, RV or power station projects. Panels lose output slowly, a median of about 0.5% a year in NREL’s review of field data, so age matters less than hidden damage. Expect no maker warranty, and inspect every panel.

How much output an older panel keeps

Solar panels wear slowly. An NREL analysis of nearly 2,000 field measurements gathered over 40 years found a median output loss of 0.5% a year. At that rate a 10-year-old panel still makes about 95% of its rated power, and a 20-year-old panel about 90%.

That median hides a wide spread. Climate is one cause: a later NREL study of about 8 GW of U.S. systems, reported by pv magazine, found systems in hotter climates losing 0.88% a year against 0.48% in cooler ones. Damage, poor handling and cheap materials push some panels further. As EnergySage puts it, when you shop for used panels you are on your own, so testing matters more than the age on the label.

The percentages are simple arithmetic on the NREL median, not a promise for any one panel.

What to inspect on a used solar panel

Look at every panel in daylight before you pay, on both sides:

• Glass and frame. Cracks or chips let water in. A bent frame can stress the cells.
• Snail trails. Dark, branching lines under the glass often follow microcracks in the cells. EcoFlow notes they sit under the glass and cannot be cleaned off.
• Dark spots. EnergySage says dark spots may signal delamination, where the panel’s bonded layers separate.
• Backsheet and edges. Peeling, lifting or cracking at the back or edges can let moisture in.
• Junction box and cables. The box should be firmly attached, and the connectors free of corrosion or cracked insulation.

EnergySage’s guide to panel defects explains that hot spots, where part of a panel runs much hotter than the rest, can come from cracks, poor soldering or built-up dirt. Because the difference is heat, a thermal camera shows them and the naked eye does not.

Testing used panels before you buy

Bring a multimeter and test in full, clear sun with the panel facing the sun:

1. Open circuit voltage (Voc). Read DC volts across the leads and compare with the Voc on the label. A hot panel reads a little lower than the label, which is normal.
2. Short circuit current (Isc). If your meter measures current at that level, check Isc against the label too.
3. Compare panels side by side. Same model, same time, same angle. A panel that reads well below its neighbors is the one to skip.

A good voltage reading does not clear a panel by itself. Sinovoltaics, a solar quality-control firm, notes that a visual check alone does not reliably find microcracks, which can lower a panel’s current and efficiency, while electroluminescence (EL) testing shows them. For a large lot, or panels headed for a roof, ask the seller for thermal or EL test results.

Warranties on secondhand panels

EnergySage says most used panels from individual resellers come with no warranty at all. Some makers allow a transfer through a formal process: Panasonic, for example, has a warranty transfer form for a new homeowner after a home sale. A panel removed from a roof and resold on its own is a different case, so assume it carries no maker warranty unless the seller shows otherwise. Incentive rules can also exclude used panels: EnergySage notes the federal solar tax credit required equipment that was new or used for the first time.

That makes the seller’s return policy your main protection. On eBay, look at the seller’s feedback, the condition notes, the photos of the actual panels and the return terms before you buy. Our guide to refurbished power stations covers the same trade-off between price and warranty for batteries.

Where used solar panels make the most sense

Used panels fit best where you control the whole system and no permit or rebate depends on the equipment:

• Charging a portable power station. Check the panel’s Voc against the station’s maximum solar input voltage first. Our guide on how to charge a solar generator explains the input limits. Solar panels for solar generators covers voltage windows and connectors.
• Off-grid sheds, barns and cabins. Larger residential panels give a lot of watts per dollar if you have space to mount them.
• Ground mounts and DIY projects where a slightly lower output per panel is fine.

For a permitted roof system tied to the grid, your installer, inspector or utility may have equipment rules, so new panels are usually the simpler path. Plug-in balcony solar kits also have their own state rules. More panel guides are in our solar panels section.