I think it is negligible. In particular, PV is much more than 10% cheaper than many other options, and this would be a replacement for whatever the round-trip cost is even in a zero-$ storage system.
My default number for HVDC is 5%/1000km, but I think that's out of date now; at that level, antipodal power would be 1-(0.95^20) = 64% loss, and while that's certainly something I'd avoid if possible, it's still good enough to make PV beat the TCO of batteries or fossil fuels or nuclear… if you ignore the TCO of installing and maintaining the cable, geopolitics, and all the other reasons we've not done that yet.
(I have no idea what the TCO of undersea HVDC cables is).
My default number for HVDC is 5%/1000km, but I think that's out of date now; at that level, antipodal power would be 1-(0.95^20) = 64% loss, and while that's certainly something I'd avoid if possible, it's still good enough to make PV beat the TCO of batteries or fossil fuels or nuclear… if you ignore the TCO of installing and maintaining the cable, geopolitics, and all the other reasons we've not done that yet.
(I have no idea what the TCO of undersea HVDC cables is).