It was sooner than twenty years ago, probably close to 8-10 IIRC. I looked into it because my dad asked me to as he was thinking about putting solar on his roof. At the time they were still not (as a practical matter based on the real world, not a panels theoretical output under ideal conditions) not there. Theoretically in ideal conditions they were close, something like 95% if you used sun tracking near the equator with defect free cells that never degraded faster than expected and never had any cloud cover.
We found he could spend about 6500 to save about 7800 over 10 years if he got all the tax breaks and bought the cheapest reputable brand he could and did all the installation himself. Or he could put in a 4 hours overtime a week for 3 months and make more.
The horrible toxic wastes that making the cells generate were just salt on the wound for him.