Buying a Used Solar Inverter or Battery: What to Check Before You Pay

Second-hand solar gear looks like an easy win. Inverters and batteries are expensive new, plenty of good units come off roofs when houses are demolished or systems are upgraded, and the asking prices can be a fraction of retail. The catch is that solar is not a plug-in appliance, it is a grid-connected electrical installation, and a few checks before you hand over money will save you from buying something you can never legally or safely connect. Here is what to look at.

Is it on the CEC approved list

This is the first filter and it is not optional. In Australia, an inverter has to appear on the Clean Energy Council list of approved inverters to be connected to the grid, and to be eligible for small-scale technology certificates (the STC rebate). Batteries have their own approved-products requirements. A unit that has been delisted, or a grey-import that never appeared, cannot be signed off by an installer for grid connection. Before you buy, find the exact model number on the label and check it against the current CEC lists. If it is not there, walk away unless you genuinely only want it for an off-grid, standalone setup.

Be aware that most rebates do not apply to second-hand equipment anyway. The STC scheme is generally for new, approved gear installed by an accredited installer. Buying used can still make sense on price, but do not count on a rebate to sweeten it.

Age, warranty and what is left

Inverters are the part of a solar system most likely to fail first. A string inverter typically carries a 5 to 10 year warranty when new, and many are on their last legs by the time they come off a roof. Ask:

• How old is it, and how many years of manufacturer warranty remain, if any? Warranties are often non-transferable to a second owner, so assume you have none.
• Why was it removed? "System upgrade" is fine. "It kept faulting" is a red flag.
• Are there any error codes in the logs, and can you see it powered up and running before purchase?

Panels age gracefully and are usually a safer used buy than inverters, but inspect for delamination, cracked cells, burnt junction boxes and water ingress.

Batteries need extra care

A used battery is a different risk profile again. Lithium batteries degrade with every cycle, so a cheap battery that has already done thousands of cycles may have little usable capacity left. Check:

• The chemistry. Lithium iron phosphate (LFP) is the most common home chemistry and is more tolerant than older types.
• Cycle count and age, if the battery management system can report them.
• Physical condition. Any swelling, heat damage or corrosion means do not buy.
• That the battery management system (BMS) is intact and communicates, because a battery without a working BMS is both useless and dangerous.

Damaged lithium batteries are a serious fire hazard. If anything looks off, it is not worth the saving.

Panels: worth it, with eyes open

Second-hand panels are the easiest part of a system to buy well, because there is very little to go wrong that you cannot see. Look along the surface at an angle in good light for micro-cracks, browning of the cells, delamination where the laminate has lifted, and any moisture or corrosion inside the frame. Check the junction box on the back is sealed and that the leads and connectors are intact and of the same type as the rest of your array.

The practical catch is matching. Panels in a string need to be electrically similar, so a mixed pallet of odd modules is far less useful than it looks, and an older panel may be physically larger for less output, which changes how much roof you need. If a seller can give you the model and a datasheet, you can check the voltage and current figures against what your inverter expects.

Assume some loss of output with age. A panel around ten years old will typically be producing meaningfully less than its original rating, which is fine if the price reflects it and a problem if it does not.

Paperwork that changes the price

Ask for the original invoice, the installation paperwork, any warranty documentation and, for a battery, the BMS history. Manufacturer warranties on solar equipment are frequently tied to the original purchaser and the original installation address, so assume a used item comes with none unless proven otherwise. That is not a reason to walk away; it is a reason to pay a used price rather than a nearly-new one.

The hidden install cost

The purchase price is only part of the total. Solar and battery installation is licensed electrical work, and a compliant install includes DC and AC isolators, correct cabling, labelling, and often switchboard changes. Your distribution network (the DNSP) must approve the connection, and there are limits on system size per phase. If your board is old or full, you may be up for a switchboard upgrade before anything can be connected, and batteries in particular often need spare ways and specific isolation. Factor this in before the second-hand inverter looks like a bargain.

Compliance: who can connect it

Installing or connecting solar and battery systems is fixed electrical and often specialised work. In Australia it must be done by a licensed electrician, and for grid-connected systems, by a CEC-accredited installer if you want the connection signed off and any certificates issued. It is illegal and extremely dangerous to wire in your own solar or battery. Rooftop DC can be lethal even with the grid isolated, and a battery stores energy that cannot simply be switched off.

Any second-hand protective devices, isolators or components that come with the system must be tested before they are energised, as set out in the AS/NZS 3000 wiring rules for buyers. The same testing logic that applies to a used RCD or RCBO applies to solar isolators and connectors.

Buy from someone who can back it up

Ask for the original invoice, the compliance certificate from the first install and any monitoring history. A seller who has all of this is a seller who looked after the system. When you are ready, browse current listings for inverters, panels and batteries, and when you have gear you no longer need you can sell it on. Before you commit to any installer, verify their licence and accreditation using our guide to hiring a licensed electrician.