"Look at lord howe island who recently got funding for solar and...

"Look at lord howe island who recently got funding for solar and large battery that has to do overnight and they still have diesel generation backup"

The diesel is a backup - all systems would have some sort of generator as batteries don't charge if there is no sunlight. When you have prolonged overcast or adverse weather periods like in a cyclone then a diesel gen set would have to be used. Side note: I have a mate who says it is incredibly hard to design a system that maintains a minimum level of power (things like a cloud passing can significantly affect Panel output and battery and diesel systems have to take up load (as diesel lags ie 2mins to get up to full generation in which time cloud has passed and you can overcharge the system). With Lord Howe an investment into Wind and/or wave would be worthwhile. Usually when the sun isn't shining there tends to be more wind (on oceans where there is wind, there is waves). I suspect wind is out question as it is unlikely tourist would like to see 100m high wind turbines as a backdrop to pristine beaches although off shore systems (out of sight out of mind) could be an option although I suspect environmental issues would arise due to reef damage etc.

In the Danish sea etc where they have sea wind turbines the wave devices would complement the wind systems. They Wave Device could be moored between pylons. Although in littoral and near shore (AKA Shallow) areas the wave generation would be small. I guess barges with WITT style systems may pay off in these ares.