How Many Watts of Solar?

[newhaul]

Originally Posted by Captain Bill

Within the hour? Which hour are you talking about? You claim you are down 40 amp hours overnight. 400 watts of panels are not capable of producing 40 amp/hrs of power in any one hour period even with the sun directly overhead and that is never going to happen in the south of France. The maximum you can produce is 33 amp/hrs and even then charging is not 100% efficient. If you were claiming to have 40 amp/hrs by noon I might buy it, but within an hour?

exactly and that's why I asked about other charging sources .
I have 400 watts solar now I can do about 20ah into my lifepo4 bank per hour till full but there is no way possible even with NASA's extreme efficient panels to get 40 ah out of 400 watts in an hour.
Laws of physics and all.

[MVDarlin]

Best answer, as much as you can! And get a large battery bank. I have 12 panels advertised at 100 watts each. Never get that much. I generally get 30 amps pumping into the batts at peak hour from 12 x 5amp anels with sophisticated mppt controllers. So about 50% rated output!. I have 12 Optima D34M batteries for house. No maint. A 3,000 watt remote control inverter. Peak daytime output charges batts and has surplus for 1,500 watt water heater. Float voltage is 13.6v. But as soon as sun drops the batts drop to 12.6. I shut down inverter when I go to bed. Refer defrosts. 5 cf feezer has big bottles of frozen water for 50% of capacity. It stays cold. Voltage drops to 12v by morning. Then the charge cycle starts again. Check Amazon for easy to install flexible panels. About $1 per rated watt. Im cruising the Sea if Cortez.
MVDarlin

[john61ct]

Originally Posted by newhaul

there is no way possible even with NASA's extreme efficient panels to get 40 ah out of 400 watts in an hour

Higher voltage bank maybe?

[Reefmagnet]

Microwaves have very high start up loads. Even an inverter twice the size of the microwave's rated cooking output may not be enough to run it.

[john61ct]

Yes, some more than others. A soft start capacitor could maybe help.

But usually 2-3000W is enough.

Hate the idea myself, but some people really find them convenient.

[newhaul]

Waste of space to me on a small sailboat.
They are useful on passages as a faraday cage for electronics.

[Reefmagnet]

Great for softening butter or heating leftovers.



If using induction cooking would make a great accessory for cooking potatoes and other veggies. When we purchased our boat, the PO had installed a microwave and I did entertain the idea of installing one. Until I tested the small 700 watt unit's (about as small as practical to go) power requirements. Opted for a toaster instead.

[secrabtree]

Read the other opinions as guides to things that may be useful. But NO SOLAR is absolutely NEEDED.

[john61ct]

Even just a little helps with the long tail if off grid and you want to get to 100% Full for bank longevity.

Can't do that with ICE power, unless motoring 8 hours a day. . .

[newhaul]

Originally Posted by john61ct

Higher voltage bank maybe?

400 watts solar is 400 watts there is no way to get more than about 30 ah out of it even with an mppt controller.
As you well know a Fla battery will not fully charge from 80% to 100% in an hour .
( regardless of available amps. )

[john61ct]

Sorry did not think the discussion was limited to lead banks.

And 400W is under 14A for a nominal 24V AGM bank.

[john61ct]

Originally Posted by newhaul

As you well know a Fla battery will not fully charge from 80% to 100% in an hour

Yes of course, even with the highest CAR AGM.

I am not claiming that poster knows that though, just suggesting an alternative possibility for how low amps can mean high watts.

[AndyEss]

Originally Posted by newhaul

Waste of space to me on a small sailboat.
They are useful on passages as a faraday cage for electronics.

I tried firing up my 700W microwave sailing once - that was enough. Now I use it to store dishtowels. All cooking is on my propane stove - including toast and coffee. A 10lb tank lasts me almost a month (often single live-aboard at anchor) and that includes hot water for my shower (tankless water heater).
The only daily reason my inverter might be turned on is for my CPAP (can't find a 12Vdc one) and for video viewing (once/week avg). PO bought a large panel TV that only takes 110Vac. No time or desire to tear into it to see if it can run on DC.
I also use the inverter to run a small, oil-less compressor to feed my hookah dive regulator when I clean my bottom. I didn't want gasoline on my boat for the gas compressor, dink outboard has its own 5 gal tank.

[captainwd40]

My standard answer is 1000 watts. The inverter provides the 120 Vac. The batteries drive the inverter and the solar/controller recharges the batteries. The size of the battery bank determines how long the inverter will provide the 120 Vac. The size of the solar panels (100, 200, 300, 500 etc) determines how long it takes to recharge the batteries.

Simple Math:

If you count on 5 hours of full sun 5/24 = .21

If your inverter is 1000 watts and your 12 Volt DC (Vdc) battery is 100 amp hour (AH) you can get 1100 watts (full load) for one hour. 12 Vdc x 100 amps = 1200 watts x .90 efficiency (90%).

If you draw 100 watts continuously from your inverter......you will get about 11 hours.

If your battery is depleted and needs recharge (1100 watts) and you have a 1000 watt solar panel that will provide full charge for 5 hours per day you will get 1000 watts x .21 = 210 watts per day to recharge your batteries.

So conservation and power management is important.

If have more hours of direct sun or a bigger panel (more elements = more power) then the solar recharge watts go up. If you want more inverter run time increase your battery bank (add 3 - 100 amp hour batteries) ...... 4 - 100 amp hour batteries will give you 400 amp hours and about 44 hours of run time at 100 watts inverter load.

I always recommend multiple deep cycle batteries connected in parallel because they deplete much less overall, are easier to fully recharge, and last longer.

Hope this helps.

Cheers!

[john61ct]

On many boats, solar may be important, but especially using LFP, may not be the primary contributor.