Technology

The weird thing is that in this scenario these panels are still applicable for replacement probably because the the solar panels of today compared to then are about ~40% more efficient. So compared to a new replacement it's at around 60% efficiency. A major site plans profit off of 30 years and plans to replace glass at that time, so while it may still be somewhat useful long term it's probably more profitable to replace them.

It’s good to know that they have pretty good longevity. One thing complicating this is that panel technology has gotten better and better during that time. There’s a graph on Wikipedia plotting how much better the various types of panel have gotten since the 70s. A lot of them have doubled in output since the early 90s.

So on the one hand, these old panels are outputting 75% of what they started with, which is good. But on then other hand they are only outputting about 37% of what new panels could.

Not that we should throw old panels away. There’s plenty of sun to go around (though I guess the average homeowner only has one roof to use). It’s just interesting how fast the tech has improved and how that might factor in to some longevity calculations.

This is gonna sound so dumb... But they had solar panels back then?!

Sounds like you should install double what you think you need. Reason? The panels will start losing efficiency over time and your electricity usage over time will do nothing but grow. That's very common.