I have been looking into this in detail on my
current boat and it totally depends upon how you intend to use the boat.
Unless you are going to
live aboard full-time with lots of power-hungry devices, or intend on going
diesel electric on
propulsion in the near future, a built in
diesel generator is not worth the
money. Bare in mind that in
Europe and similar places they are literally banning the
sale of new ICE personal vehicles from 2025-35 depending on country. This severely bites into the payback potential on any investment in new diesel onboard in
Europe.
Portable gasoline generators are noisy, difficult to use underway, a PITA to store, and require active management. They might be worth it as a
budget solution for a limited duration sabbatical trip, but only if you love the
noise of gasoline engines.
The new 150i EFOY can deliver 1.8kWh a day, if running 24/7 which is more than most sailors need. But if you do that then you will eat through the units working life expectancy at the rate of 1% every 2 days! As they cost 5000+ euros to start with it is an expensive solution even for a sabbatical trip (I worked out that the unit would be nearly dead after my planed sabbatical atlantic circuit), and totally outrageous for a
live aboard.
Solar is great and works well on catamarans, but is difficult to do well on monohulls without adding an arch at the back of your boat. Doing that significantly adds to the cost of doing solar. I looked into it and in
Sweden the cost of getting an arch made and fitted was going to make the diesel generator look
cheap in comparison (10-15000 euros). Even doing something off the peg and
cheap like
sun bar was going to be around 4-5000 euro fitted. That might be worth the investment if your home berth has no
shore power, or if you are
living aboard and don't mind the extra windage and aesthetic hit, but for a sabbatical
cruise or normal holiday cruising its simply not worth it IMHO. Add to this that present cell tech is going to be obsolete in about 5 years once multilayered cells hit the market (toward 50% efficiency) and it makes investing in substantial solar questionable for all except those who really are heading off into the blue for a very long time in the very near future.
I also looking into hydropower but there one has the problem that you only sail 5-10% of the time you are aboard when
living aboard and the things tend to have all sorts of issues with weed and deployment, particularly in the sarragosa sea, which is where I will be sailing.
Wind generators also have limitations. They require care in handling and maintenance and they produce surprising little power. I need about 1,5kWh a day when sailing and about half that when just sitting. To keep me charged a
wind generator needs to supply 60W on average which the silent
wind 12V unit requires 14kns apparent to do. For western Europe and
Caribbean cruising, and with a sufficiently large battery bank to buffer for the occasional lull, this is just about workable, but if you are in climes without something like the
gulf stream or
trade winds then you are going to be disappointed with a wind generator.
So again, it all depends on where you are and what you are doing.
If I were going to travel all over the world with a traditional diesel auxiliary
monohull without too many toys, then I would fit an arch and put lots of solar on it and perhaps also a wind generator. I would do the same on a
catamaran though now you can also have lots of toys.
If I were living aboard with lots of toys on a
monohull or going diesel electric on
propulsion and the
galley, then I would fit a diesel generator and maybe a few
panels for backup.
If I were cruising for a fixed period of time (say a year), then it would be toss up between fitting pole mounted wind and solar, or a fuel cell. Which would depend on multiple factors but mainly on what you will need once you return. If you just going to use the boat for normal holiday cruising and the odd weekend after the big trip and have
shore power at your home
mooring and in the environs, then a fuel cell is probably the easiest thing to live with albeit at about twice the price of the wind generator and
panels over the years. Over the sabbatical you will have run through much of the cell's working life, but enough will be left in it to give you some boosts on the rare occasions where you haven't been able to charge your
batteries by shore power or engine and it won't be cluttering the lines of your
dock queen, or bothering the neighbours. If you ever decide to up and go again for another sabbatical, you just replace the unit. If, on the other hand, you don't have ready access to shore power where you
cruise or at the home
mooring, then the wind and solar option on a pole is a better bet on a cost benefit analysis. Both systems will get the average cruiser around the pond so long as you are reasonable in what you ask of them, but they meet different needs once you return.
If you are just holiday cruising with the occasional weekend tossed in over the year and have shore power on the home mooring and in the environs, then you don't really need anything over and above a good battery bank and reasonable
alternator on the engine. A 300Ah
lithium bank will last you a good few days between charges, and you will recharge at around 60-120A per hour off the engine, or better off shore power.
If you are just holiday cruising with the occasional weekend tossed in over the year and you don't have shore power on the home mooring, and in a region where there isn't much shore power available, then you will need some combination of wind and solar to keep your
batteries charged, but you won't need much.
Under no circumstances would I ever do a portable petrol generator. There are just better options out there.
That's my two cents