Living in a self contained unit makes you acutely aware of how much energy you use. This covers right from head torch batteries (we use them for night watches, in the dinghy, ashore...), to diesel for the main engine, petrol for the two dinghy outboards (both two stroke), to gas for cooking.
We carry 360 litres of diesel, the main engine using between 0.7 and 2.2 depending on whether we’re charging batteries or going flat out. I’m not sure how the 80 litres of petrol will last, as I’ve used the new outboard so little I have no idea on the consumption. If worst comes to worst, we’ll have one of the hottest RIBs in the anchorage... with the small (back up) 3.3 hp engine on the back. Not a good look, but it’ll get you from A to ..... B ..... slowly. For cooking we have a range of gas- primus tanks (four) for the main oven, a back up camp stove, and separate small cylinders for the pushpit BBQ.
I installed an inverter (500W), so we can take 230V off the 12V house batteries- ideal for charging camera batteries, rechargeable printer, dive torches... etc.
When the house batteries are fully charged, they can run the fridge (big consumer), water pumps, miscellaneous lights etc, for about two and a half to three days at anchor. On a typical passage, we’ll run the engine enough to fully charge the batteries without even thinking about it. The problem comes when we’re at anchor for extended periods- after the initial two-to-three days, we need to run the engine for about two hours each day. It’s hardly efficient, running a 40hp engine (although, of course not at full output) to run a 25 amp alternator, but that’s the compromise we have to live with for the moment. Either that, or buy 2,100 miles of shore power cable...