local authorised suppliers and installers of SunPower high efficiency solar panels, Alternative Technologies Ltd,   have just launched the first combined 25-year product and power warranty on the new SunPower modules installed by the company. 

This is 15 to 20 years longer than conventional solar warranties of standard solar panels. The performance warranty states that the SunPower PV modules should still provide at least 87% of their original rated output after 25 years.
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The new warranty is available only to residential, commercial and industrial customers installing SunPower solar panels purchased from authorised agents.