Losses for 800kV HVDC systems are typically documented at ~3.5%/1000km or ~5%/2000km[0], and state-of-the-art 1.1MV systems have losses of ~1.5%/1000km[1][2]. Lower voltage systems have higher losses but I’m not sure why a lower-voltage system or AC system would be used in a project like this.
I can’t find any information about increased losses in submarine cables at all; where is that information from, and what is the mechanism that causes that added loss?
For solar panels, as far as I can tell, capacity loss occurs at a rate of ~0.3-1% per year depending upon the type of panel, with a median of 0.5%[3]. More modern panels have lower losses than older panels, presumably due to manufacturing improvements. So, after 10 years, you’re talking about something that will produce—on average—5% less power than it did when it was brand new. That’s not something that is broken and needs to be replaced the way you seem to be suggesting.
[0] https://publications.jrc.ec.europa.eu/repository/bitstream/J...
[1] https://news.ycombinator.com/item?id=29232512
You also are unlikely to have enough space and enough raw materials to construct solar panels that can provide the entire earth's energy needs all-day round, given the huge transmission losses.
Furthermore, solar panels have a very short life span - barely 10 years for a decent yield - which means that you would have to constantly mine hevay metals to build new solar panels at a rapid pace just to maintain this setup.
It's perhaps a possibility for a distant future, but definitely not something that can be contemplated as a serious solution to the 0-emissions world that we need to hit in the next 30 years.