Solar/generator inputs and order

[Amart]

Trying to figure out the order of energy on a new to me boat. I'm planning on upping the solar to hopefully completely run a watermaker. Currently I have 400w of solar and I'm planning to add another 9-1200. I have 500 mah of AGM battery and I'm on the fence of going to lithium, which I would go even larger if/when I switch over; probably so 600-800mah.

My big question I'm asking myself is if ac or DC is the better way to go for a watermaker. I'm not totally sure the route the energy takes with the wm being the final destination. With DC would it run directly to the wm or does it have to go into the battery bank first and then run back out? With the ac would it go directly to the inverter then to the wm or would it still go to the battery first?

My apologies if this is a silly question or if every boat was wired differently but I was hoping there was a typical route for the energy to flow.

[sailorboy1]

well you didn't say whether a DC system met an energy recovery type system (Spectra type), so assuming that is what you met (because you can use a DC motor on the AC type of systems)

you save $3k by going AC WM
you make much more water in a shorter period
the AC WM is much less complex
in my experience the power/gal isn't as much as it looks on paper
you sound to have lots of power so what difference does power even make
with AC WM you can make so much water it changes lots of boat life

I had a Spectra 120 gpd system for a year and replaced it with a 40 gph Seawater Pro AC system. So that is my thoughts having had both.

[Amart]

My apologies for not specifying more. I'm planning on going with a seawater pro system and I have a victron 3000 inverter. The price between DC or ac is about the same. The ac has a much higher gph but also a much higher energy usage. My thinking was running a lower gph system longer would allow me to run fully off solar instead, perhaps I'd be fine either way though.

[HeywoodJ]

Originally Posted by Amart

... I'm not totally sure the route the energy takes with the wm being the final destination. With DC would it run directly to the wm or does it have to go into the battery bank first and then run back out? With the ac would it go directly to the inverter then to the wm or would it still go to the battery first?

The answer to this part of your question depends on how much power your generation source(s) are providing. For a typical setup, if your generation sources are putting out more power than you are using then the energy goes directly from generation source to device, the batteries are not really involved. If your batteries need charging, the the extra above what you are using goes to charging your batteries - i.e. charging your batteries is usually the lowest priority for energy that is traveling through your wiring, the consumers will take power off the bus before the power gets to your batteries. We have a DC watermaker and specifically run it during the day while the solar panels are generating to take advantage of ‘extra’ solar power and to avoid the inefficiencies of a round trip through the batteries.

If your generation sources are putting out less power than you are using then they will feed what power they are providing directly to the devices, and your batteries will make up the difference.

As to AC vs. DC watermaker, SailorBoy laid it out, that’s a bit like anchors or guns, there are opinions on both sides (I’m an energy recovery DC advocate myself) and the ‘right’ answer depends on the specifics of how your entire system is set up and operated.

[Edit] We we’re typing at the same time. With the additional information, if mostly operating with the solar panels I would go DC to avoid the inverter usage and size so that it could run from the solar panels. If planning a generator then the larger AC unit to reduce the time required running the generator just to fill the water tanks.

[Amart]

Yeah I'm not going to open a can of worms and ask which is better

The statement that the batteries are the lowest priority largely answered my question. My goal sounds very similar to what you're doing in that id like to convert excess power into water.

Edit: I do have a gen but the goal is really to use it as rarely as possible. I was pretty set on DC originally but after speaking with Mike at seawater pro he had me questioning it, he was very pro ac.

[sailorboy1]

Originally Posted by Amart

My thinking was running a lower gph system longer would allow me to run fully off solar instead, perhaps I'd be fine either way though.

It is really a small difference in the big picture and really doesn't matter. If you use too much power to make-up on 1 day you make it up the next day. In the end you make pretty use the same amount of water, using the same total power, whether you do it fast or slow.

Get the AC system IMO

[howardatviking]

Ok im really intrested in this as i have 360 watts of solar and a 12 volt 300watt water heater. Can i feed the solar directly into the heater. Im concerned that the open circuit solar panels are likely to be 20 plus volts and will that harm the water heater, or do i supply through the mppt keeping my batteries out of circuit. I maybe overthinking this please help

[waterman46]

To answer OP's question about flow of energy: Your charge sources are all connected to the 12V battery bank (BTW it's 400AH not mAH), and your 12V loads (watermaker, lights, invertor, etc. are also connected to the battery. Whenever charging is taking place (sun on the panels, engine running, dock power battery charger running) then energy in the form of current (amps) from those sources is available for the battery as well as the loads. If the battery is already fully charged, then all charge source current is available for loads. If battery needs charging, then some of the charge current is going to go into the battery and the rest will go to any active loads.

Bottom line is, don't worry about the flow, it will automatically go where needed. The trick is to average your expected loads and your available charging over a period of one or several days. You do need to be sure to provide enough charging current, averaged over time, to be able to run your expected loads averaged over time, while not discharging your battery more than 50% (lead acid) or fully (lithium).

Now many people with lots of watermaker experience will tell you that it is preferable to run it at least a couple times a week. That will save you problems with biological growth in the filters, avoid having to use fresh water for a flush. And I found the intake line, which does not get flushed, can also be a source of problems if left more than a few days. That's an argument for a smaller watermaker, which is also a good thing for your batteries as they prefer longer, lower current loads rather than short duration high current loads.

There's really no reason I can see to have a 110VAC watermaker, unless you have an AC generator on board that you like to run every other day or so. Since you are going to add even more solar panels and bigger/better batteries, 12V is the way to go.

[vpbarkley]

I visited Seawater Pro at their facility in Fort Lauderdale about a year ago. I was positively impressed by what I saw.

They were working on a DC watermaker that used BLDC motor instead of the common brushed DC motor. I don't know if this is available but it would be more efficient.

If you're OK with running your generator to make water, then an AC watermaker is fine.

But if your generator craps out you have no water supply. And generators use fuel and make an annoying racket. And there is the requisite generator maintenance.

You could invert but there are losses there too.

Happy seas.

[Sailshabby]

Originally Posted by howardatviking

Ok im really intrested in this as i have 360 watts of solar and a 12 volt 300watt water heater. Can i feed the solar directly into the heater. Im concerned that the open circuit solar panels are likely to be 20 plus volts and will that harm the water heater, or do i supply through the mppt keeping my batteries out of circuit. I maybe overthinking this please help

Everything through the batteries, I’d suggest.

[howardatviking]

Thanks Sailshabby, its as i thought, just trying to save batteries

[zstine]

The Solar has to go through a charge controller and to the battery bank before use. You can run AC via and inverter or DC straight off the battery. Your 400W is enough to run a small Spectra 150 watermaker, and probably the next size up that makes 14gallon/hr. My spectra 150 only draws 10 Amps at 12V (only 120Watts) and makes about 7 gallon an hour. Our setup has 530W solar and 400amp-hr of Lead Acid which runs the refrigerator, watermaker, laptop, lights fans.. If you charge with solar, which is a slow charge, There's no real need for Lithium since you are not taking advantage of the quick charge capability. LA is more Amp-hr for the dollar. Also, keep in mind that you have to run the watermaker every few days to keep growth out. We use ~12 gallons a day and run our watermaker every other day for about 3 hours. these really high output watermakers still have to be run every few days, you just won't have to run them as long... But who cares if it runs 1 hour or 3 hours?
If you are power conscious, calculate the gallons per watt of the watermaker to compare which is most efficient. Also do a power budget for your boat... you are talking about a lot of solar! You can probably run induction cooking, a refer, icemaker, blender, TV and a watermaker with ~1400W!

BTW, your refrigerator is going to draw a lot more amp-hrs than a watermaker if you are in a warm climate.

[markcouz]

My Seawater Pro watermaker is powered by a 48v BLDC bicycle motor. It produces 40GPH at 750w - its great!