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Old 05-25-2023, 08:30 AM   #21
Sophiehaus's Avatar
2018 25' Flying Cloud
2007 25' International CCD FB
2006 23' Safari SE
Grand Junction , Colorado
Join Date: Jun 2006
Posts: 106
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Originally Posted by Ephraim View Post
Honestly, that sounds like something someone made up because they didnít want to take the time to do any calculations.

You need enough battery to get you at least 24 hours on battery. You need enough solar panel to charge that 24 hour usage back on an ďaverageĒ day. If you use a ďpeakĒ producing day on the panel calculations you will forever be in a hole. The only way to have too much solar is to have enough to charge your batts at higher than acceptable current levels. Thatís not likely to happen given the real estate we have to work with.

Bottom line is that you must know what your average 24 hour energy usage is and then size both battery AND solar to provide and recharge that energy within the 24 hour period. Design in a bit of margin for those below average sun days or above average usage days and you are good to go.

If you canít store/produce enough to make that 24 hour period, you will need to look for other sources of generation and/or cut down on usage.
I actually got that information from a solar site online. I agree with your more complex analysis, but the 1:1 ratio has worked flawless for me and I boondock a lot. I seldom use my inverter though and just use my coach in a normal manner. If I need to use the microwave or a/c I use my 4500 watt generator.
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Old 05-25-2023, 09:49 PM   #22
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2003 30' Classic S/O
Denver , Colorado
Join Date: May 2023
Posts: 9
Thanks Sandman227, appreciate the share. Having learned that formula, I think I might go up to 600w or 800w. Talking with link2dks also reminded me to at least build the system to grow into more panels later possibly (if I decide to build it in steps).

Originally Posted by sandman227 View Post
Did my own setup
- 3 x 100 watt Renogy slim
- victron BMV shunt monitor
- Renogy solar controller
- 2 x 12 volt 100 amp lithium batteries (SOK brand)

Did everything myself total cost approx $2500

My rule of thumb for solar wattage is
( battery amps total ) x 2 = solar panel wattage total
So 200 amp total battery needs at least 400 watt solar total
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