Warranties & Degradation
Generally speaking, within the industry the operational life of a solar panel is generally expected to be between 25 and 30 years. During this time, the efficiency of the panels will degrade; the amount and over which period would be determined by the quality of the manufacturing process. Most manufacturers expect a loss of around 20% from when they were first installed. However, as the technology and processes improve, expected lifespans of 40 to 50 years will become more commonplace and the level of warranty will have to keep pace.
Solar panel warranties are not all the same
Solar panels come with two different warranties: Performance and Product. However, these vary in clarity and unscrupulous installers often mis-sell based on their misleading assurances.
Performance warranty:
Sometimes called degradation warranties, these guarantee how much power a panel will retain after 25 years. All MCS certified panels require a warranty that guarantees they will retain at least 80% of their power after 25 years. Some manufacturers offer better warranties, so it is important to check the data sheet of the panels you are offered in order to understand what you are getting.
Product warranty:
This guarantees against any manufacturing defects, such as physical faults with the panels. On average 10-15 years long, these warranties usually offer a replacement panel or refund the cost of a replacement panel but don’t cover scaffolding, installation or the investigation to find the fault in the first place.
What the 25 year Guarantee could really mean:
Some solar salespeople focus on the 25 year performance warranty and neglect mentioning the product warranty. This can also cause problems because if you have a degradation issue with a panel after the product warranty has run out the manufacturer could say that the degradation is caused by excess corrosion owing to the sealant breaking down. They may then say that this is a product fault and the product warranty has lapsed, leaving you with a low producing panel and no warranty covering the fault.
Other degradation:
The remaining issues that cause degradation such as Output Lead problems, Junction Box problems, JBox Delamination, Overheated Wires and Terminal Strips, Mechanical Damage and Defective Bypass Dio are much smaller but still contribute to the overall loss of power from panels. These are less prominent in better quality panels which have better quality components and sealants.
Low light level performance:
When the light level drops, better quality panels will maintain more power. This is affected by the quality of the silicon and the clarity of the glass.
Differences between ‘kWp’ and ‘kWh’.
Solar panels are sized in kWp (kilo watts peak) which refers to their performance under STC (Standard Test Conditions). However, you need kWh (kilo Watt hours = units of electricity) because the more kWh your system generates the bigger the impact on your bills.
Temperature coefficient:
Everything electrical increases in resistance the hotter it gets. Increased resistance means reduced efficiency. Panels with a lower temperature coefficient are affected less by increases in temperature and are more efficient.
Heat capacity:
If a solar panel can dissipate heat better, it will give better results at high temperatures. So even if a panel has a good temperature coefficient, it may perform badly if it cannot dissipate heat effectively.