One great thing about solar power is that generating it doesn’t involve any moving parts.
Of course, nothing lasts forever, and solar panels do gradually lose efficiency over time.
But because the processes involved in generating solar energy all occur at the subatomic level, the ordinary physical wear and tear that affects most of the other devices we use isn’t an issue.
The upshot is that, unless something extraordinary occurs, you won’t have to worry about your solar panels’ performance for the 25 to 30 years it takes the gradual loss of efficiency to become a problem.
Extraordinary circumstances, however, do sometimes occur. So, it’s worth understanding the different kinds of solar warranties and guarantees, as well as who’s contractually responsible for each.
There are three types that you can expect your panels and overall solar system to be covered by: a product warranty, a performance warranty, and a production guarantee.
Product warranties are sometimes also referred to as lifespan, equipment, or material warranties. They’re provided by panel manufacturers and cover the cost of replacing any panels that aren’t functioning properly due to physical defects or faulty construction.
Most panel manufacturers offer at least a 10-year product warranty, with some brands providing up to 20 or even 25 years.
It’s important to note that product warranties do not cover the natural decrease in efficiency all solar panels undergo over time, even if it turns out to be excessive. That’s where performance warranties come in.
Though all solar panels will gradually lose efficiency over time, for the first 25 years output shouldn’t decrease by more than 10-20%.
So, in addition to product warranties, manufacturers also offer performance warranties that guarantee their panels will keep generating close to their intended output.
Performance warranties typically run for 25 years. The most common type is called a linear performance warranty. That means that the amount of production guaranteed will decrease by a fixed percentage each year—usually around 1%.
Some manufacturers, however, offer what’s known as a step performance warranty, where production losses are fixed for an initial part of the warranty period and then lowered for the rest. A step warranty might, for example, guarantee that production goes no lower than 90% for the first 10 years and no lower than 80% for the remaining 15.
One of the most important factors determining whether going solar is a good investment will be your installer’s estimate of how much electricity you can expect your system to produce annually.
If the right methods are used, your production estimate ought to be very accurate. But, unfortunately, production estimates are also very easy to manipulate. [link to previous post on production estimates]
That’s why you should always make sure your installer is willing to guarantee their production estimate in your contract.
Any installer who won’t guarantee their production estimate in your contract probably doesn’t have much confidence in it themself. And should it turn out to be exaggerated, without a written guarantee you’re going to be the one left holding the bag.