Complete set-up for power generation.
In boats you normally have a generator which provides off-shore power when you're tied out at anchor or a mooring ball. Gen-sets are ridiculously expensive to replace, and burn fuel. Its not as simple as buying one of those generators you see on construction sites. I thought it was at first, and quickly learned different.
RV and Marine gensets are a whole 'nother ballgame. A complete replacement of a genset can cost as much as $10,000, you could possibly shop it around and get a bargain for $5k. I was shocked. A marine genset is the equivalent of the furnace in your house. Theres a few name brands that continually surface. Onan, Westerbeke, Kohler. Northern Lights is supposed to be top shelf, and supposedly lasts twice as long - somehow. [citation needed-lol] The fuel they burn is necessarily the same fuel as your engines, they draw from the fuel tank. You don't want to fuckaround with propane genny and gas engine, it just makes things more difficult.
They kick on and off and power the battery bank, and you draw the power from the batteries. So when the batteries run low, the genny kicks on and charges the batts, then kicks off. All your electric stuff runs from this. Refrigerator is the biggest power drain, air conditioning is optional but nice to have. Plus, you've got your computer, nav systems, microwave, television, coffee maker, lights, water pump, all that jazz.
Quick elaboration on the batteries - you typically have maybe six batteries, deep cycle marine batteries are about the size of a cinderblock and are wired in a row. You can add to that row, they cost about $200 each. I need to look more deeper into the battery thing, but its a non-issue. They're basically the same as the batteries you'll use in solar house stuff. Big fuckers, heavy, and they're not cheap, but they're not hideously expensive either. You swap them out when they get lazy, and they last a good while in recharging cycles. Most boats would have good batteries if you made a wise purchase and the previous owner took good care of his shit.
If your generator dies, you are fucked. Bigtime. They have hour meters on them, and require maintenance. Once your genny reaches so-many-thousand hours, you're living on borrowed time. In an average day, it may run several hours depending on your electrical consumption. If you're tied to a mooring ball for a year, this is gonna add up to a lot of hours. Figuring 1gph fuel burn, 2 hours a day, thats 700 gallons in a year. At three bucks a gallon, you're talking $2,100. This is probably a very low low estimate. And thats just fuel, nevermind if the thing shits the bed.
You want to provide energy into the batteries to prevent the generator from kicking on as much as possible. You can't escape the necessity of a generator. But you can prolong its life. Theoretically you can introduce energy into the batteries and the generator will never kick on, until you run it for testing purposes to keep it fresh and prevent it from getting gummed up like all engines.
Heres how --
In one year, you will be completely energy independent if living off-shore. Unless you want to drive the boat around. Solar/wind hybrid kits are preferable to exclusive dependence on either method. Solar in itself is only efficient when the sun shines, which excludes at least half the day, and some days you get none. Wind often dies down, and windmills have kick-in speeds. Reliance on one is problematic, and tying into your system is a project. The dual-kits make the most sense to me, and they're designed to achieve that balance by green-power geeks, so I would defer to their area of expertise.