Are there obvious signs of damaged components? Modules with broken glass are not common, but can occur. Hail damage is rare, unless you get hailstones larger than two inches. A module with shattered glass may keep functioning for some time, but eventually, water will infiltrate and corrode internal electrical connections, causing shorts or ground faults.
You will eventually have to replace the broken module, and finding an identical replacement can be quite difficult—especially for systems that are more than a few years old—due to changes in solar module construction and frame sizes. The longer you wait to replace modules, the more difficult it will be to find the same model. If the exact replacement module is not available, it may be possible to integrate another make and model, but it will need to have very similar physical and electrical characteristics to integrate into the solar array, and may affect the overall array aesthetics.
Depending on the inverter’s operating voltage range, it may be possible to simply remove the damaged module and rewire the array at a reduced system capacity. This will result in lower energy production, but will avoid the problem of having mismatched modules. In the case of multiple damaged modules, a full replacement may be required. Any undamaged modules could be used in another project or sold to offset some of the costs of the new modules.
What is the inverter’s make and model? Inverters typically last between five and 20 years, depending on the make, model, and production date. But it’s safe to assume that you will need to either make a warranty claim or replace the inverter within five to 10 years. A qualified solar contractor can tell you the expected lifespan, warranty coverage, and reputation of your inverter. A quick call to the manufacturer, providing the serial number of the inverter, can also determine whether it is still under warranty and whether there are any recalls or service bulletins on it.
Were there any recent upgrades to the system? The modules may be 15 years old, but the inverter (or if the system is battery-based, the charge controller or batteries) may have been replaced recently. It is helpful to know if there’s a mix of newer and older equipment since some parts (such as modules) generally function longer than others.
If it’s a roof-mounted system, what is the roof’s condition? The PV system may be in perfect condition, but if the roof is worn out, you’ll need to replace it. To avoid a big budget surprise, get a cost estimate to have the array removed and then reinstalled on the new roof. If penetrations do not have flashings (as may be the case with some older installations), the extra cost of adding flashing will need to be considered when reinstalling (see “Evolving Installation Methods” sidebar).
Battery backup and off-grid systems are more complex, so there’s more to check. The system’s overall operation can be more obvious than with a batteryless grid-tied system—if it’s not working, there will be no electricity. But just because you flip the switch and the lights come on during your daytime walk-through doesn’t mean that the batteries will have enough storage to keep the house’s appliances running after the sun goes down, let alone through a three-day snowstorm.
Batteries are crucial components in any off-grid system, and costly to replace, so be aware of any upcoming battery replacement needs before you purchase the home. Batteries should be visually inspected for corrosion, age (check if they have manufacture date tags), and electrolyte level.
But none of these checks really give you a full picture. Ideally, perform a load test to see how much energy the batteries hold compared to their original rating. Systems can still be functioning with old batteries, but the batteries may be operating at a significantly reduced capacity. That capacity might be enough to power loads for a few hours without additional PV input, but may not be enough to support loads for an extended duration. Some off-grid houses are sold in the summer, when even marginally operating batteries might serve a few small loads through the night. It’s when shorter days and cloudier weather come that you’ll realize that you need new batteries. Also, because infrared cameras have been declining in cost, more installers have this tool and may be able to provide an IR inspection of the battery bank. This can quickly show failed battery cells (because they will be a different temperature) and bad connections.