Given all the variables involved, it’s not surprising that predicting the efficiency of solar panels over time is so challenging. Every residential solar photovoltaic (PV) installation is unique. The amount of sunlight exposure and air temperature may not only vary from installation to installation, but from day to day.
In order to warranty products, however, solar panel manufacturers require an estimation of a system’s life, which is a hugely important solar rating for homeowners to know.
What’s Covered in Most Solar Warranties?
Until recently, the industry wisdom for solar panel efficiency has been that PV systems will operate at 90 percent% after 10 years, and at 80% efficiency at 25 years. A recent study at the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany, showed that efficiency degradation might be far less than previously thought. The study analyzed 17 systems that have been operating for more than five years, revealing no significant loss of efficiency.
Anecdotal evidence is even more impressive. A Swedish PV installation that has been operating continuously since 1984 has shown no significant loss in efficiency. Solar panels at the Technical University of Berlin have been running for 31 years. It’s becoming apparent that systems last longer and work better than standard solar panel warranties indicate. Top solar brands are beginning to respond with better warranties.
Suntech, the world’s largest manufacturer of solar panels, recently changed their warranties to ensure specific outputs:
- 95% at year 5
- 90% at year 12
- 85% at year 18
- 80% at year 25
This results in 6.7 percent more power than industry standard warranties.
Yingli Green Warranty
Yingli Green Panda panels are guaranteed to provide:
- 98% output during the first year
- 92% for 10 years
- 82% for 25 years
The company is also offering linear-based warranties that spread the decreased output expectation incrementally over 25 years.
Trina Solar Warranty
Trina Solar offers linear-based warranties for both polycrystalline and monocrystalline products, with slightly different percentages:
- Polycrystalline module output at 80.7% at 25 years
- Monocrystalline module output at 80.18%
Solar World also offers a similarly linear-based warranty.
SunPower Solar Warranty
Sunpower‘s warranty covers:
- 90% output at year 12
- 80% output at year 25
Other solar companies that now offer 25-year warranties, including First Solar, Canadian Solar, Sharp and Sanyo. As most homeowners now recoup upfront PV installation costs in less than 10 years, every additional year that their system operates efficiently means more money in their pockets.