420: What size and number of solar panels needed

[adlib2]

Originally Posted by 1tviere

I am putting solar panels on my 420 which I intend to live aboard and cruise in the Caribbean. How much solar do I need and where is a good place to get what I need?

Don't overlook a wind generator in addition to Solar. I have 300w of solar and much more from wind in the Caribbean.

[motion30]

I have 3. 275watt panels feeding a outback 60 amp mppt controller. It is a new installation ,so for I have been averaging 2.5 To3 Kw a day into my batteries.

[EllisElectric]

Originally Posted by PaulinOz

The Panels output in round figures 50 volts DC at 6 amps

Is each solar panel output 50 VDC or do you have them wired in series?

[sailsw00]

FWIW, I've got 700 watts on my 43' cat. I have separate fridge and freezer. Mostly LEDs, use radios (VHF, SSB, FM) a fair amount, A/P 100% of the time while under way. I never use engine(s) for charging batteries unless it's been raining for a week or so with no sun. Batteries only drop about 10 to 15% of total after a long night ancchored, maybe 20% wit A?P working. 700 watts is more than enough for me.
-Steve
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[TacomaSailor]

I've lived with solar panels on our boat since early 2000. I've helped install panels on a lot of other boats. I've worked on them on even more boats.

It is not that complicated!

Install as many panels as you are comfortable with based on how you feel about the following:
- cost of panels
- mounting space and location
- cost and location of wiring and control hardware
- cost of battery bank
- mounting space and location of battery bank

Monitor battery state over a couple months time

If your batteries are being pulled down further than you want, more often than you want, add more panels.

There is no penalty for starting small and incrementally adding panel or battery capacity.

OR... ignore cost and:

Fill all the available space with panels
Put in as much battery capacity as there is space

Live with the results

Again - there is no penalty for making the array too big

[kapnkarl]

Great thread, Thanks everyone! Glad there wasn't much jabbing or poo slinging . That could end up creating a mess of shading on our arrays

[sy_gilana]

Get 24 Volt panels, they are cheaper (more produced) and more efficient (Voltage drop over wiring) and get as many as you can fit, you can't have too much power. Its about lifestyle, we run our washing machine off the inverter on a sunny day and still charge.

[EllisElectric]

Originally Posted by motion30

I have 3. 275watt panels feeding a outback 60 amp mppt controller. It is a new installation ,so for I have been averaging 2.5 To3 Kw a day into my batteries.

What does the MPPT (Maximum Power Point Tracker) controller do in your system?
How much is the loss for input wattage vs output wattage using an inverter, meaning if solar panel power output is 300 watts @ 12VDC, would you get 25 watts @ 120VAC?

[mstrebe]

Originally Posted by EllisElectric

What does the MPPT (Maximum Power Point Tracker) controller do in your system?
How much is the loss for input wattage vs output wattage using an inverter, meaning if solar panel power output is 300 watts @ 12VDC, would you get 25 watts @ 120VAC?

MPPT controllers use an adjustable DC-DC converter to match the output voltage of the panel to the charge voltage of the battery bank without loosing amperage to heat.

Consider this: If you simply tied a solar panel to a lead-acid battery, it would charge. But the optimal charge voltage for a battery is around 14VDC, whereas the natural output of the panel is somewhere between 16 and 18 volts, depending on the time of day and insolation. Those "extra" volts are lost as waste heat.

An MPPT charge controller uses a circuit to match the precise charge voltage of the battery by converting those "extra volts" into amperage. Remember that watts=volts * amps. With a DC-DC converter, you can adjust the voltage down and the amps up to get the same wattage, and this is what an MPPT does. You get extra charge, less heat, and therefore higher efficiency.

An inverter will waste about 10% to 20% depending upon its efficiency and the amount of power being converted. Figure 15% as a safe bet.

[a64pilot]

Originally Posted by EllisElectric

How much is the loss for input wattage vs output wattage using an inverter, meaning if solar panel power output is 300 watts @ 12VDC, would you get 25 watts @ 120VAC?

A watt, is a watt. In other words 10W at 12V is the same power as 10W at 120V.
Your confusing amps with watts, a common mistake.
Make me King for a day, and I'd dispense with all this amp nonsense, since voltage is part of the equation, but a watt, is a watt.
In other words, 10 amps at 120V is equal to 100 amps at 12V, it get's flaky of course as no battery except dead ones are 12V, normally in the high 12's, low 13's and that makes amps variable.

[EllisElectric]

Originally Posted by a64pilot

A watt, is a watt. In other words 10W at 12V is the same power as 10W at 120V.
Your confusing amps with watts, a common mistake.
Make me King for a day, and I'd dispense with all this amp nonsense, since voltage is part of the equation, but a watt, is a watt.
In other words, 10 amps at 120V is equal to 100 amps at 12V, it get's flaky of course as no battery except dead ones are 12V, normally in the high 12's, low 13's and that makes amps variable.

So a 300 watt solar panel is go for 2.5 amps @ 120VAC and with efficiency loss make that two amps. @240VAC the amperage on each leg would be one amp.

So to get a 20 amp service @120VAC, you would need eight 300 watt solar panels or for 240VAC, you need sixteen 300 watt panels. Is this correct?

[EllisElectric]

To figure what the amount of amp-hours for battery capacity, one needs to know there daily amp-hour usage. Don't you need to add up all the items that use power and attach a time period for that usage daily? Then convert the watt-hour to amp-hour for needed battery capacity. Is this right?

[monte]

Simply add the amps used for the time used. Fridge uses 6A for 12 hrs, etc. the OPs use might be similar to mine, around 180A per day at anchor and 350A on passage. I'd suggest a larger than standard battery bank also. At least 80% total Ah /W of solar. i.e 800Ah bank for a 1Kw array.

[EllisElectric]

Originally Posted by monte

Simply add the amps used for the time used. Fridge uses 6A for 12 hrs, etc. the OPs use might be similar to mine, around 180A per day at anchor and 350A on passage. I'd suggest a larger than standard battery bank also. At least 80% total Ah /W of solar. i.e 800Ah bank for a 1Kw array.

Hi Monte, what do you use to determine the amount of time the fridge uses 6 amps and other individual pieces of equipment that use electricity?

[monte]

The simple way is to turn it of when it's running and check the Ah difference on the battery monitor. This can be done for most equipment on board to get a handle on daily usage. The fridge is a bit of an unknown as to exactly how long it runs for so a guesstimate is good enough for rough calculations. The power budget can be modified over time to give you a clear indication. Ill upload ours shortly if anyone wants to use it as a base spreadsheet.
One important point often overlooked is the battery bank. Assume we have a 800Ah bank that we don't want to run lower then 60%. That leaves 480Ah usable. Above 90% charge the batteries won't accept as many Amps and input will be limited to maybe 10 amps. That leaves us realistically with 240Ah useable battery capacity between charges, assuming we can put the 240Ah back in. A couple of cloudy days can throw a spanner in the works if relying on solar, or days without wind if relying on a wind gen, so it's best to allow for those when estimating usage.