Obviously there's a lot to debunk. The weight of waste is hardly the most important thing when you're comparing glass, aluminum, and silicon to radioactive waste.
But, anyway, two things come to mind:
The 800000 ton scary figure of potential waste by 2040 in the country of Japan per year isn't really that much. One land fill in Los Angeles County (Sunshine Canyon Landfill) takes 2.4 million tons a year right now.
And, Solar panels are very recyclable and when you try to find out how long they last you're going to get way way underestimates. Some of the oldest solar arrays like
this one are still operating after 40 years and some old arrays like
this one have been refurbished/recycled because it's worth it due to improvements in efficiency.