All solar panels should come with 2 types of warranty:

• Power Output Warranty : usually 20-30 years
• Material Warranty : usually 2 to 10 years

1. The Power Output Warranty

This covers the power from the panels. Usually if the power drops to less than 80% of the specification in the first 20-30 years, you can make a claim on the warranty.

That’s all well and good but you need to be confident that you will firstly be able to measure and prove that the power has dropped, and secondly be able to contact the correct company to get any warranty claims honored.

Ask to see the warranty details in writing. Get the installer/salesperson to show you where it states how the power from your panels will be measured if you suspect that the power has dropped, who will measure it and if they will charge you for the privilege.

Also ask them to show you where it says how the warranty claim will be handled, who is responsible for honoring it and what costs you might incur. Will they charge you to remove, ship and test the faulty panel and then ship and install the new solar panel.

If your solar installer or salesperson can’t answer these questions then that is a sign that they are badly trained or inexperienced or both.

If the warranty is covered by the installing firm, ask what the backup is if they are not around in 20 years – (This even applies to the bigger solar installers – one thing the world has learned recently is that even huge companies can go bust if the economy changes…). If you have to go back to the solar panel manufacturer, then go to the manufacturers website and see if you can find warranty details. If you can’t find the website or the warranty details that is a bad sign…

Another great question to ask is: “What % of your revenue do you put aside for future warranty claims?” and also “What % of the solar panel manufacturer’s revenue is put aside for future warranty claims”.

The final thing to check out is whether this warranty is “linear” or “stepped”. A linear warranty of 80% (i.e. a 20% power drop) over 20 years would cover you if the output dropped by more than a twentieth of that 20% in the first year (i.e. 1%), then 2% in the second year and so on… at that linear rate of 1% per year until the solar panels were 20 years old.

Linear warranties are rare, but some of the more expensive panels do have them. The more common “stepped” warranty means that, for the “80% over 20 years” example, your panels can lose 19% in the first year and you won’t be covered unless they lose another 1% in the remaining 19 years to get under that 80% threshold.

2. The Material Warranty

The material warranty (2-10 years) is usually for defects that may cause the power of your panels to drop – but don’t cause the power to drop below the “power output warranty” threshold.

So if you have a power output warranty of “80% over 20 years” and some water gets into one of your panels causing the overall system power to drop 19% – this would be covered by the “material warranty”, not the “power output warranty”.

This can be for stuff like delamination of the backing sheet, discoloration of the solar panels (can look really naff!), solder joints coming undone and bypass diodes failing.

Again – ask your solar installer or sales person to give you a comprehensive list of things that are covered by this warranty.

Finally: watch out for get out clauses

In some of the small print in the terms and conditions published by the bottom end of the solar market, I’ve seen clauses that say your warranty isn’t valid unless you get your system “serviced” every 2 years.

If you have one of these clauses, find out exactly what defines “serviced” and how much it is going to cost. This is especially important if you are buying a really cheap solar system with panels of questionable lifespan. The last thing you want is for your panels to fail after 3 years and then have the warranty knocked back because you didn’t get your panels “serviced” within 2 years!