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Old 14-03-2016, 23:10   #1
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DC generator vs full solar/wind solution

Calling on the experience of those who are out there cruising far from civilisation: DC generator vs full solar/wind solution.

We are planning to leave Oz in around 5 years to take the kids to see the world. We have the boat, and are now busy planning the ideal setup for us. Currently the boat is setup with a truly ancient AC genset, 450 A/h of house batteries, 120w solar and a 1500w stackable inverter/charger. (The AC genset is going, too big, noisy and inefficient). We are going to need more DC capacity and charging sources for the level of comfort we are chasing, which will include making our own water, plenty of iPad charging for the kids, no forced lights curfew, and even a daily movie for the family. Hey, we're going cruising, not camping.

I'm currently on the fence whether to go with a DC generator charging the batteries and spinning a watermaker directly, or adding a whole lot of solar/wind and a (more expensive) DC watermaker like a Spectra.

So, to those who have actually done the big cruise, what would you do? DC genset or fully renewable? Keep in mind, space is no issue. This is a big boat, with a very big engine room, and plenty of space for a generator as well as for solar/wind. 1000w of solar would be achievable with the space we have available.
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Old 15-03-2016, 07:31   #2
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Re: DC generator vs full solar/wind solution

Typically solar is the way to go if you don't have heavy loads. The most common heavy load that pushes you into a generator is air/con. So far you didn't list anything that would suggest a generator is needed.


Wind is rapidly fading as solar is more cost effective and has no moving parts to fail and make a lot of noise. This assumes you have space to put in enough solar.


You need to start with an energy audit.
- Estimate how long each item will be on and multiply the number of hours in use by the amp draw.
- I would bump the resulting number up by 25-50% to give yourself some room for new items, items you missed or kids not turning things off.


This will give you your average daily amp-hr consumption.


Multiply by 2-3 to account for a couple cloudy days in a row. (If you wind up with 4-5 cloudy days in a row, you can always run the engine and have the alternator charge the batteries)
- Battery bank should be 2-3 times the amp-hrs calculated as deep discharge will quickly damage batteries.
- Solar should put out 1.5-2.0 times the amp-hrs calculated, so the system can catch up after an overcast day. Figure maybe 5hrs per day at the rated output as the solar output varies depending on the angle of the sun.


If you motor a lot or don't mind running the motor to charge the batteries, you can reduce some of these figures. If you are absolutely against running the motor, bump them up to reduce the odds you will need to use the motor to charge the batteries.
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Old 15-03-2016, 09:55   #3
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Re: DC generator vs full solar/wind solution

I agree with everything Valhalla360 said above. Solar is great, wind generators aren't really worth it.

Make sure you have no shading of the solar panels for best output, a little shade dramatically drops output. Consider high output panels, like Sunpower 327w or 435w panels, a few of those and you could be generating over 1.7kw of power if you have the room. 4 x 435 = 1740.

I suppose you could run a DC generator if you want, but I'd put it at a distant 2nd if you have enough space for solar. I'd also consider doubling your battery capacity.
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Old 15-03-2016, 14:00   #4
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Re: DC generator vs full solar/wind solution

Wife & I live aboard full time, 12 yrs on this boat. IMHO: I wouldn't call it a "this vs that" decision. I know, I know....

Solar for as much as possible, planning like there is nothing else available. Big array, good controller, and you can pretty much ignore it day-to-day. {As already mentioned, bigger battery bank, higher rated panels, etc.}

Add the Wind Turbine. Really. There are latitudes and wxr systems that have put us with minimal sunshine for days on end. "Windy" up there on its stick keeps chugging along & feeding amps. Technology changes & units are a lot quieter today. Example: Air Silent X https://www.emarineinc.com/categorie...X-Wind-Turbine

Genset. Ours died and we miss it. {Diesel, mounted in mtr room.) Bought an Engel 12 VDC fridge/freezer and learned to live without ice cubes for margaritas. Or pre-cook and freeze meat dishes while on the hook and near the butcher shop. Or run the water heater whenever without consulting the wxr charts... Still plan on replacing the genset when budget allows. Example: NEXT-GEN - Marine Power Units

Five years now without a genset and we've adjusted our lives to that. The 340 watt solar array & Air Breeze wind turbine power the boat. Life is good but I do miss having ice cubes in the drinks-glass on those really hot days!

My two farthing's worth from our experience. YMMV
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Old 15-03-2016, 14:08   #5
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Re: DC generator vs full solar/wind solution

Generally the best thing to do is first reduce consumption. So led lights, insulate the fridge, get used to cold showers, etc. Then add as many solar panels as you can fit to equal the reduced demand. Finally add a generator if you need to, mostly for AC. 12v ice makers are slow, but will eventually make enough ice for a few drinks.
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Old 15-03-2016, 14:08   #6
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Re: DC generator vs full solar/wind solution

Renewables all the way, with as much solar as you can fit. If your plans are truly 5 years away then don't fit the solar (just make general plans) now unless you need it for local cruising. The technology is changing quickly, and you'll be able to get more efficient panels (hence more power from less space) three or four years down the road.

I like having a windgen aboard to balance out the days when the sun isn't so bright, but it is definitely our secondary renewable source.
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Old 15-03-2016, 15:15   #7
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Re: DC generator vs full solar/wind solution

I'm a solar and 2kva Honda sort of guy. Just can't beat solar, more the better.

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Old 15-03-2016, 19:15   #8
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Re: DC generator vs full solar/wind solution

Seems the concensus is pretty overwhelming for solar/wind. But how about from a cost perspective?

Panels + controller + mounts + etc... ~$5k (guessing, definitely have not priced it properly)
Wind generator + controller + mount + etc... ~$5k
High efficiency DC watermaker ~$15k
Extra batteries ~$2k

vs

Aquagen DC genset with 210A alternator and 40GPH engine driven watermaker: $10,998
Installation: $500 (I already have an AC genset that I am removing, so installation costs will be minimal).

That's $15.5k less for the genset option. Sure, the genset will require fuel, but for $15.5k, I can make a heck of a lot of amps each week and still be ahead for many years to come.

There is also the flexibility of power on demand... guests over late for some sundowners and want some ice for their drinks? Just run the generator an extra hour the following day to recover. Can't do that with renewables.

Again, just talking out of my hat here, I am only planning at this stage, those out there doing it right will know more about this than I do.
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Old 15-03-2016, 19:28   #9
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Re: DC generator vs full solar/wind solution

Quote:
Originally Posted by pwillems View Post
Calling on the experience of those who are out there cruising far from civilisation: DC generator vs full solar/wind solution.

We are planning to leave Oz in around 5 years to take the kids to see the world. We have the boat, and are now busy planning the ideal setup for us. Currently the boat is setup with a truly ancient AC genset, 450 A/h of house batteries, 120w solar and a 1500w stackable inverter/charger. (The AC genset is going, too big, noisy and inefficient). We are going to need more DC capacity and charging sources for the level of comfort we are chasing, which will include making our own water, plenty of iPad charging for the kids, no forced lights curfew, and even a daily movie for the family. Hey, we're going cruising, not camping.

I'm currently on the fence whether to go with a DC generator charging the batteries and spinning a watermaker directly, or adding a whole lot of solar/wind and a (more expensive) DC watermaker like a Spectra.

So, to those who have actually done the big cruise, what would you do? DC genset or fully renewable? Keep in mind, space is no issue. This is a big boat, with a very big engine room, and plenty of space for a generator as well as for solar/wind. 1000w of solar would be achievable with the space we have available.
We have a DC genset (130A), solar and wind with a 2000W and spare 2500W inverter on our Liberty 458. Our spectra watermaker and frigoboat keel cooled fridge / freezer both run fine on 12V DC. Our house bank is 675Ahr of Trojans. This is plenty of house bank capacity.

We are not camping and we enjoy a hot shower each day. We also run a startup with an onboard network and I work remotely for a large tech company. We are working towards the world's slowest circumnavigation.

We now have only 2 persistent AC loads. The tv and laptop chargers. Getting rid of all the inefficient AC loads has reduced our average power consumption by half.

AC to DC conversion is very wasteful. It's typically responsible for at least 40% of household power consumption.

Intermittent AC loads, except hot water, include iron, barmix and toaster.

Solar meets 90%, genset 8% and wind just 2% of our off grid power needs here in San Francisco bay. The wind contribution will increase slightly while we are cruising.

We will be increasing our solar from 280W to 700W later this year. This will meet most of our daily needs and allow us to also heat hot water. Currently we use genset waste heat for hot water while off grid.

Priorities, for us, are solar and deep cycle lead acid, then genset then wind. Shading of solar is the biggest issue.

Our DC genset alternator and controller is also a spare for our engine. It has a 55A and 130A alternator.

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Old 15-03-2016, 19:54   #10
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Re: DC generator vs full solar/wind solution

Quote:
Originally Posted by pwillems View Post
...That's $15.5k less for the genset option. Sure, the genset will require fuel, but for $15.5k, I can make a heck of a lot of amps each week and still be ahead for many years to come.

There is also the flexibility of power on demand... guests over late for some sundowners and want some ice for their drinks? Just run the generator an extra hour the following day to recover. Can't do that with renewables.

Again, just talking out of my hat here, I am only planning at this stage, those out there doing it right will know more about this than I do.
Not sure I agree 100% with your numbers, but the AquaGen still probably leaves you ahead by $5-10K. Which is still a lot of diesel.

I can't stand running a generator, just don't like it. And can't carry enough diesel to power a generator, have already had problems just keeping the engine fed. But both of those are personal preferences; one is just the way I prefer things, the second is the places I prefer to go (and how long I like to spend there).

Steve Dashew makes a pretty good argument that even for ocean crossing a power boat is cheaper than a sailboat once you factor in all costs. Not sure I agree with that, but either way I just prefer to sail, and listen to the silence as the solar charges things. Worth the extra cost to me, YMMV.
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Old 15-03-2016, 20:14   #11
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Re: DC generator vs full solar/wind solution

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Originally Posted by leftbrainstuff View Post
We are not camping and we enjoy a hot shower each day
Another major point in favor of the DC generator that I had not thought about.

Wife will appreciate.
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Old 15-03-2016, 21:21   #12
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Re: DC generator vs full solar/wind solution

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Not sure I agree 100% with your numbers, but the AquaGen still probably leaves you ahead by $5-10K. Which is still a lot of diesel.

I can't stand running a generator, just don't like it. And can't carry enough diesel to power a generator, have already had problems just keeping the engine fed. But both of those are personal preferences; one is just the way I prefer things, the second is the places I prefer to go (and how long I like to spend there).

Steve Dashew makes a pretty good argument that even for ocean crossing a power boat is cheaper than a sailboat once you factor in all costs. Not sure I agree with that, but either way I just prefer to sail, and listen to the silence as the solar charges things. Worth the extra cost to me, YMMV.
I call bs on Dashew's claims that a powerboat in use to cross oceans is cheaper than a sailboat. He's in the business of selling powerboats to sailors so he has an inherent bias.

To achieve any reasonable fuel consumption a powerboat, similar in size to sailboat, can't go fast. In fact long distance ocean crossing records are mostly held by sailboats. It's only recently some of the clipper ship records have been broken. By sailboats.

James Hamilton, distinguished engineer at Amazon, is currently near the end of a circumnavigation in a powerboat. He publishes frequently on fuel consumption.

mvdirona.com/2015/09/fuel-economy-and-range

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Old 15-03-2016, 21:41   #13
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Re: DC generator vs full solar/wind solution

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I call bs on Dashew's claims that a powerboat in use to cross oceans is cheaper than a sailboat. He's in the business of selling powerboats to sailors so he has an inherent bias.
I'd like to think you're right, but in part because I'm probably afraid to add up all of the actual costs of sailing. I might not like the answer.

Kind of ties into the OP's second question, would a genset be cheaper? Solar proponents (myself included) would probably like to think that the operating costs are zero, but are they really? Do we have bigger battery banks for instance? That get replaced more frequently because we go through deeper cycles? Or is that offset by the cost of generator maintenance?

For Steve's argument, if you have a carbon mast and high-tech sails he might win. If you have an alumin(i)um stick and plain white sails maybe not. With sails (and renewables) I think you have more choices; I have a 40 year old drifter that still works, maybe not as well as when new, but it still works. With a power boat you have no choice but to buy new fuel if you want to move on. With renewables and a reasonable sized battery bank I can modify my usage to match solar output, with a small bank I am obligated to run the generator each day even with minimal loads.
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Old 15-03-2016, 22:19   #14
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Re: DC generator vs full solar/wind solution

IMHO, solar panels are a much better investment for charging batteries than a generator, especially now that solar panels are getting so powerful and cheap. THey really do cost nothing unless damaged by a storm or something, they have no moving parts and are very reliable.

When I install solar panels for someone, it's a real eye opener for them to realize that during daylight hours, the solar panels are powering the loads and charging the batteries, so the battery bank is only being discharged during the night, as opposed to 95% of the time, when the generator isn't charging them. They basically only run the generator for the microwave or air conditioner, which is a huge drop in usage compared to daily battery charging.

The reason I'm not a big fan of wind generators is they cast a shadow, possibly limiting solar panel output or the number of solar panels you can install. They rarely put out much power, especially compared to rated output and only the very expensive ones start making power down around 5-7 kts, you could have bought a Honda 2000 generator with a lot of change left over.


The Kubota DC gen+watermaker+fridge compressor is a pretty interesting idea. I suppose every time the fridge cycles the compressor, it makes a bit more 12v power and some more water. It's still a diesel gen, so you'll have to carry fuel for it, but it is a pretty slick bit of packaging and a Swiss army knife type of solution to the perennial DC power, water and refrigeration problem.
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Old 15-03-2016, 23:05   #15
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Re: DC generator vs full solar/wind solution

Quote:
Originally Posted by leftbrainstuff View Post
I call bs on Dashew's claims that a powerboat in use to cross oceans is cheaper than a sailboat. He's in the business of selling powerboats to sailors so he has an inherent bias.

To achieve any reasonable fuel consumption a powerboat, similar in size to sailboat, can't go fast. In fact long distance ocean crossing records are mostly held by sailboats. It's only recently some of the clipper ship records have been broken. By sailboats.

James Hamilton, distinguished engineer at Amazon, is currently near the end of a circumnavigation in a powerboat. He publishes frequently on fuel consumption.

mvdirona.com/2015/09/fuel-economy-and-range

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Ya it's not like he has decades of contemporaneous records and receipts that show exactly what he and his wife spent every year on all of their boats... Er wait they actually do.

But Beowulf is not the average 45' cruising boat, and the FPB's are not the average LRC. Just because the numbers work out for them this way doesn't say much for the typical cruiser.
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