Solar panel battery charge

To really understand solar for rv's Google handybobsolar and read his words of advise. I followed his advise for a reasonably priced system that actually works.

It all depends on how much power you actually use. More is always better. As an example: If you drain your batteries half way that's about 100 Ah. It will take close to 500 watts of solar to do that in one day.
I hope you won't be draining them that far in one day. If you are you need a bigger battery bank.
100 watts is about the smallest panel that makes any sense to buy. The best deal on panels on a dollar/watt basis is usually in the 225 to 280 watt range. These will require an MPPT charge controller.

The charging rules are the same... If you batteries are down to 50% charge state then it will take 17-20AMPS DC charge for each battery from your solar panels if you want them to be back up to their 90% charge state in a three hour time frame. This will happen in around three hours time if you have that much DC Current going into them...

But since you only get 5-6 amps out of each 120WATT panel then you are not going to get them recharged in three hours and can only hope the high sun is there for several more hours during the day...

Where everyone gets saved is their panels start charging good probably around 9-10AM each morning and go all day to 6-7PM in the evening. this will top off your batteries BIG TIME...

My case is going to be different however as I know I will draining 20-22AMPS DC current from my batteries starting at 6PM to 10PM everyday running all my Ham Radio and momabears toys... I know I can get them recharged to 90% using the generator so that what I am going to do...

It could be for me that I may only have to run the generator for the first hour of my recharge cycle each morning until I get past the very high 52-55AMPS of DC Current demand when I first start my charging cycle. It starts tapering down after 15-20 minutes - then perhaps switching over to solar panel after the first hour I can get my batteries going to the full 90% charge state while still in the high sun all day...

As you can see if different for everybody haha...

Roy Ken

Here is a simple flow chart.

Budget-->Energy Audit-->Battery bank size-->number of watts-->PWM or MPPT. What ever type of controller is chosen, make sure it has adjustable set points and a temperature probe that is on the battery.

If you use solar as a battery charger, one rule of thumb is between 60 and 150 watts of panels per 100 amp-hours of storage. The smaller the battery bank the higher the wattage needed (per 100 amp-hours). Here is a link to the rather special spreadsheet which includes an energy audit, that N8GS has created to help size solar battery charging systems!

solar spreadsheet by N8GS

If you full time or use an inverter lots, then populate the entire unshaded area of the roof with panels. I'm considering replacing my awning with solar panels.

For a nice explanation of solar, try this link:

Golden rules of solar

Couple hundred should do it.