This is not a plug, as I have no association whatsoever with this group or any other renewable energy supplier group, but talking about how long the tubes last, see this information for this particular brand, regarding warranty on the tubes.
Quote:
We are so confident in the foolproof design of our LaZer2 solar panels that should any of the tubes lose their vacuum during normal operation in the first 25-years of use we will replace them free of charge!
Solar Hot Water for the UK and Europe
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People can make of it what they want and please check themselves to satisfy themselves. I can't vouch on the correctness or otherwise of this information. Research the market broadly for yourselves. I have seen quite a few suppliers offering a 10 to 15 year warranty.