Sometimes also, how do you power your electronics?
We have a small battery bank and in a few months we are upgrading to a big battery bank. For the boaters reading, we are planning to buy Sears Diehard Platinum batteries which are AGMs and are made by Odyssey. For non-boaters, you should know that choice of battery is one of those instant fight topics on boating forums. It's like style wars in swing dancing or trad/sport/bouldering wars in climbing.
Most of the appliances on a boat run on 12V DC and so draw their power from our battery bank directly. For those few electronics that we run on AC power (like the laptops or power tools), we have an AC-to-DC inverter.
We have five main ways of putting power back into our battery bank organized from "least desirable" to "most desirable".
1) Plugging into shore while at a marina. This is mainly what we do right now but will become infrequent in the future.
2) Running our diesel engine. When we turn on the motor to drive in and out of a bay, prior to, hopefully, sailing, our alternator is set up to charge our battery bank. Carol just installed our new fancy alternator which does this more quickly and more efficiently. Charging while already motoring is very desirable, but turning on the big diesel engine while at anchor to charge batteries is not desirable which is why we have...
3) A small portable Honda 2000 gas generator. It still burns fossil fuels that we have to find a way to carry but it works without sun and without wind and (relatively) quickly charges us back to 100%.
4) Solar power. We are installing a 215W solar panel on top of the bimini. This is the best, not only because it is green, but because solar panels tend to work for 15+ years without breaking.
5) This is kind of trick answer: not taking energy out. Conservation is key on a boat - insulate the fridge, installation of LED lights in high use areas like the light on top of the mast that is on all night, and LED the lights on the sides of the boats that are on when we are sailing or motoring at night, turn down or turn off the fridge when you have run out of perishables and only have beer left in it, etc.