1000x over a really inefficient type of solar panel, no comparison with the modern silicon panels, that article is trash.

Modern solar panels are cheap and efficient enough, the issue is energy storage, still expensive and unviable for large scale.

Thats an issue with the time library, not with timestamps. Actually timestamps are always in UTC, you need to do the conversion to your local time when displaying the value. There should be no possible off-by-one errors, unless you are doing something really wrong.