Sail and relaxed shipping deadlines? Sure. But the engine being removed saves 2.3 kilotons and the fuel being removed saves 3 kilotons. On a ship that weighs about 50 kilotons and holds 150 kilotons of cargo. You can probably get the solar panels installed at less than 1 kiloton, and a battery that can hold a day's power is also less than 1 kiloton.
But even with an optimistic estimate of saving 10 kilotons, that's only a 5% reduction in ship mass.
You're also going to need a much bigger sail. The biggest skysail can save you 2MW right now. This ship uses something like 40MW or 60MW and solar panels might very roughly also give you 2MW.
So what you really need is a sail 10x the size. And once you have that, the question of whether your backup drive is diesel or solar becomes a lot less important.
But even with an optimistic estimate of saving 10 kilotons, that's only a 5% reduction in ship mass.
You're also going to need a much bigger sail. The biggest skysail can save you 2MW right now. This ship uses something like 40MW or 60MW and solar panels might very roughly also give you 2MW.
So what you really need is a sail 10x the size. And once you have that, the question of whether your backup drive is diesel or solar becomes a lot less important.