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Old 04-22-2018, 08:46 PM   #1
Mini-Skoolie
 
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What amp hr battery for the solar wattage?

Hi 🌞 I recently bought 4-290w panels. The price was right.
I'm not sure what amp hr batteries to buy, what wattage inverter and what controller. I read Mppt was better than pwm? The heaviest appliances I run are my freezer (on & off) and mini water heater-that one is 120v. That is only on about an hr a day. Also an ac but that's a 5000 btu plugged into shore power. I've read so much and doing online calculators but I just feel more and more confused.
Plz advise. It will be greatly appreciated 🙏💮
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Old 04-23-2018, 01:57 AM   #2
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6-800AH should be plenty, if weather isn't consistently sunny, for 1200W could even go to 1200AH but that's getting very heavy.
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Old 04-23-2018, 01:58 AM   #3
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Electric heat is very wasteful, consider propane or diesel.
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Old 04-23-2018, 02:00 AM   #4
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MPPT for sure, look at Victron's SmartSolar line.

If partial shading, consider one 100/20 per panel, or even 75/15 to save money, just wastes some panel output, but only in peak conditions.
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Old 04-23-2018, 07:58 AM   #5
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The learning curve for solar/RV electric is fairly steep but it all comes together pretty quickly. Fear not!

The best way to go is typically to establish your energy budget. This is done by measuring the power used by the various items/accessories and then adding in the time factor. You will then have a pretty good idea of how much power you need each day. You can then factor in the amount of reserve power you require and finally determine the battery bank capacity that you want/need.

The size of the inverter depends on the 120 VAC accessories that you plan to operate. If you have three items that each consume 500 watts (for example), you will need at least a 1500 watt inverter.

With 1200 watts of panels, you are likely to get a maximum of about 1000 watts under ideal conditions. If you have a 12 volt battery bank, you will need a solar charge controller (MPPT) that can handle 70-75 amps. If you have a 24 volt battery bank, it will need to handle half that.

I run my 11 gallon electric water heater (Solar to Power the Water Heater? - JdFinley.com) from solar/battery but it consumes a huge amount of power (when heating the water - not so much to maintain) so your solar/battery/inverter has to be able to handle that load.
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Old 04-23-2018, 09:15 AM   #6
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Quote:
Originally Posted by JDOnTheGo View Post
With 1200 watts of panels, you are likely to get a maximum of about 1000 watts under ideal conditions. If you have a 12 volt battery bank, you will need a solar charge controller (MPPT) that can handle 70-75 amps. If you have a 24 volt battery bank, it will need to handle half that.
That is talking about output amps, not input.

At 295W it is likely the panel Voc rating is higher than with nominal 12V panels, so need to first confirm the SC is rated for say 15-20% over that rating on input voltage.

If that happens to be say 40V, then input current is well under 8A each.

At the charging voltage, simplifying, output amps may sometimes get up to 18-19A, but average will likely be under 15A, which is why the Victron 75/15 at only $100-120 each would be a bargain.

But if you wanted to extract every watt in even peak conditions, the 100/20 version is ~$160 each.

Also, getting a single controller to handle all four panels is not optimal for shade handling, and the 150/85 at nearly $700 won't even save any money.

But yes less mounting space, cheaper wiring, and you can do temperature correction with a sense wire.

To really save wiring costs over a long distance, serial all four panels together with the 250/85 at ~$850, that is assuming they are indeed higher voltage.

OP, please link to the detailed electrical specs on these panels?
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Old 04-23-2018, 10:47 AM   #7
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Quote:
Originally Posted by john61ct View Post
That is talking about output amps, not input.
Yes, it is. In the case of the Morningstar MPPT charge controllers, the input amps are irrelevant (within reason), the maximum input voltage is 150 volts. The charge controller output rating is the maximum amps that you will get out of it, regardless of output voltage or input (voltage or amps). So, the TS-MPPT-45 will output 45 amps at 12VDC or 45 amps at 24VDC or 45 amps at 48VDC. This is one easy/convenient way to avoid having to use multiple charge controllers. Of course, it depends on your battery bank voltage.

At that rating (290 watts), the panels are almost guaranteed to be higher voltage panels which will require an MPPT charge controller. Wired in parallel, shading won't be near the problem (basically lose the output from the shaded panel(s) but not the others). Since they are 40+ volts to begin with, you can still run much smaller gauge wire (from array to controller).
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Old 04-23-2018, 10:27 PM   #8
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I can get 4-900ah. Would that work? When buying them I must make sure they are 12v? Or would that be determined by the controller?
I also need to know what size cables. I plan to set everything up relatively close, on the same side of the bus. Panels in parallel between roof hatches and everything going down right behind the driver. Batteries in a storage under the bus, same side.
I've read your emails over and over. They're incredibly helpful. Thank you!
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Old 04-23-2018, 10:28 PM   #9
Mini-Skoolie
 
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I can get 4-900ah. Would that work? When buying them I must make sure they are 12v? Or would that be determined by the controller?
I also need to know what size cables. I plan to set everything up relatively close, on the same side of the bus. Panels in parallel between roof hatches and everything going down right behind the driver. Batteries in a storage under the bus, same side.
I've read your emails over and over. They're incredibly helpful. Thank you!
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Old 04-23-2018, 10:39 PM   #10
Mini-Skoolie
 
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Also, regarding the Morningstar, can I do 2 controllers and what how many amps each?
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