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Old 06-03-2016, 08:03 AM   #21
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Thanks for the suggestions! While we may have space, I think budget will limit us!
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Old 06-03-2016, 08:26 AM   #22
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I wonder how the Tesla Powerwall solar battery would work for solar storage on a boat..?
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Old 06-03-2016, 09:17 AM   #23
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Originally Posted by djmarchand View Post
I would approach this differently than others have suggested with a Kill-a-Watt meter.


I would install an inverter probably 2,000 watts and a battery monitor. Then with your batteries fully charged (and paralleled- you don't need separate banks) run everything from the inverter for a typical day. The energy monitor will tell you how many amp hours of DC was required to power all of it- AC from the inverter and DC for lighting, etc.


Then base your decision on that value. Let's assume it is 200 amp hours. As a rule of thumb a typical flat solar panel will put out 1/3 of its watt hour rating on a sunny day in amp hours at 12V. So that means 600 watts of panels. But you need about 25% more due to Peukerts equation (losses in battery charging), so make it 750 watts. To be really comfortable and to deal with cloudy days, you might want to install 1,000 watts.


You probably will want to install 200+ watt panels, so that means the higher voltage ones that produce their maximum power at about 35 volts and have a Vmax rating of about 45. Pick a MPPT controller with a Vmax rating of 45 volts or more and an output current rating of the Imp of the panel times the number of panels plus a 20% safety factor. You might want to buy an even bigger controller if you think you may want to fill up your roof someday.


Then you have to size your conductors correctly, both the panel to controller run and the controller to battery run. Mount your controller near your battery bank to minimize losses and size that conductor to limit the voltage drop to a few tenths. The run from the panels to the controller will be ok with a half volt or so loss.


The design process isn't complicated but it all starts with your DC requirements. Figure that out and the rest is straightforward.


David
I totally agree with this for a land based system where you can generally install as many panels as you need. In that case the questions becomes "how many do you need". But I would be really surprised if the answer was anything other than "install as many panels as you can fit" on your boat. The loads always seem to exceed the available panel space. But let us know if that's not the case. And regardless, understanding your loads is critical either way. It's almost always cheaper and easier to lower your loads than to add more power, and even more so on a boat where you often can't add more power because of those pesky space constraints.
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Old 06-03-2016, 09:21 AM   #24
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I wonder how the Tesla Powerwall solar battery would work for solar storage on a boat..?
They are tempting, but would pretty much require a complete rework of the boat's charging, inverting, and DC power system. The Tesla batteries are high voltage (100-200V if I recall correctly). None of the usual marine alternators, chargers, charge regulators, inverters, battery monitors, or anything work at those voltages. There are industrial devices available, but if you think marine stuff is complex and expensive......
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Old 06-04-2016, 04:00 AM   #25
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Everyone has had their input into this subject, which is great because I am re-designing my solar setup too. There's been good input on size of banks /batteries vs. amount panels /wattage required vs. daily consumption /load and controllers.
However what about the type of solar panel to harvest all this free energy?
Can I generalize and say there is three types around ATM that are economical, being :-

Monocrystalline
– Good power-to-size ratio: efficiency typically within the range of 135-170 Watts per m2 (13-17%, with notable exceptions).
– Outstanding performance in cooler conditions.
– Some leading units now have over 18% conversion efficiency.
– Previously the most commonly used technology in the world, with over 50 years of technological development.
– Excellent life span / longevity. Usually come with a 25yr warranty.

Polycrystalline
– Good efficiency: typically 120-150 Watts per m2 (12-15%, with notable exceptions).
– Generally speaking, marginally less expensive to produce than monocrystalline.
– Slightly better performance in hotter conditions (lower heat derating coefficient)
– Excellent life span / longevity. Usually come with 25yr warranty.
NB: Monocrystalline solar panels are not necessarily ‘better ‘ or more efficienct than polycrystalline, as many in Australia believe. Read more: Monocrystalline vs polycrystalline silicon solar cells – Busting some myths.

Amorphous Thin Film
– Low conversion efficiency: typically 60-80 Watts/m2 (6-8%, with notable exceptions).
– Expected lifespan is less than crystalline panels.
– Optimal efficiency in hot weather, less effective in cooler conditions.
– 3-6 month ‘breaking in’ period where long term output is exceeded.
– Requires 2-3 times more panels and surface area for same output as crystalline.
– Ideal for example for inland Australia, where conditions are hot and vacant space abounds. (More about thin-film solar cell technology.)
How important is panel efficiency in your system?

Remember that, especially if you have a large roof, panel efficiency may not be the most important thing for you to worry about. It is more important to consider your system as a whole. The ultimate cost and performance of your system will depend not only on the panels you use.

So we have another can of worms to consider..........
My system on 'Nimiane' is a collection of panels both mono and crystalline collected over the years, setup with several PWM controllers to avoid conflict between the different panels - a real dog's breakfast.

What's your take on the type of panel to suit your particular weather conditions or will you just seek a happy compromise. Remembering some of us live in the tropics -ie. Florida/Queensland or the other hand Great lakes/Southern Australia. ?
Looking forward to some /any opinions.
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Old 06-04-2016, 06:36 AM   #26
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For many boaters a panel that can be partially blocked , and still create juice would be the best choice.

Installed on board efficiency is worth more than a theory.
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Old 06-04-2016, 07:50 AM   #27
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From what I've seen on boats, there is never enough space to install as many panels as your power needs would suggest. So the trick is to get as much power as possible out of the space available. This translates into a few things.

1) Use monocrystalline panels since they generate the most power per sq meter.

2) Use an MPPT controller to harvest the most power from the panels that you install.

3) Carefully pick panels so that you get max coverage of the available space. Panels come in lots of different physical sizes, and they don't always do a good job completely filling the available space. Picking different panels can get get you 10-20% more coverage and more power. This can be very tedious going through spec sheets and looking at dimensions.

4) Wire panels in series as much as possible. This reduces wiring sizes and number of conductors which is really convenient when you have to pull them through the boat. And it also helps mitigate the effects of shading. This last point can be controversial, and is not always true. Shade tolerance is very specific to the exact panels you select (cell arrangement, blocking diodes, bypass diodes, etc), their physical arrangement, how they are wired, and how shadows are cast over the panels. But for most of us who can only roll the dice and pick series or parallel wiring, I think series is the better bet. You might not win every time in every situation, but I think you will come out ahead over all.
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Old 06-06-2016, 06:33 PM   #28
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Thanks, I hadn't thought about #4.

Bojgranjac1, good stuff!
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Old 06-07-2016, 06:19 AM   #29
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IF the cost , expense and install for heavy DC wires ,is a bother the newest panels each have a built in inverter and much higher voltage output , so smaller wiring.
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