Recommendations for solar setup

Keep in mind that keeping a 90%-100% SOC battery fully charged is different than re-charging a 50% SOC battery bank.

Charging Batteries with a solar controller is much the same as using your on-board converter unit.

When I re-charge a 50% battery bank my converter supplies 14.4VDC to my 255AH battery bank. The three batteries in this bank then immediately want to draw around 53AMPS DC current for a good 15-20 minutes and then start dropping back. Then after two hours of the 14.4VDC charge period the batteries are demanding around 8AMPS of charge from the converter. Then after two hours the converter switches down to 13.6VDC which drops the battery demand down to around 6AMPS DC Current. This will continue for another hour before returning my three 85AH batteries to a 90% charge state.

A single 120WATT Solar panel with a controller will only give you around 6 AMPS of Dc Current so this will take many hours to obtain a 90% charge state on your battery bank. If you start out with your batteries discharged down to their 50% charge state it ain't going to work to get your batteries back up to their 90% charge state in the remaining high SUN DAY.

Keeping the battery fully charged using solar is another story if it starts out at 100% charge state. If your consumption is low a single panel should be able to keep the charge up during the 8 hours of the SUN DAY.

For me this would not work as my battery demand is too high between 8PM and 11PM along with the 24/7 parasitic drains which equates to around 250-300WATTS of use. My batteries will drop from 90% SOC to 50% SOC by 8AM the next morning as read on my installed Battery Meter Panel. I do not think a single 120WATT SOLAR panel will replenish this SOC in the 8 hours of full sun time available in the one SUn DAY.

My rule is too never start using my 255AH battery bank for the day/night battery run unless it is at the 90% SOC.

My plan is going to be to install 360WATTS (three 120WATT PANELs) and do the initial battery charge each morning using the generator to get over the high 53 AMP charge cycle for two hours and then allow the solar panels to finish my 90% SOC rate before I run out of time of the high SUN DAY. When my 255Ah battery banks drops to around 12.0VDC I will turn it off to keep from doing damage to my battery bank.

This is my plan at any rate... The Solar guys are telling I will probably do great with my 360WATTS of solar panels giving me around 18AMPS of usable DC current during the high SUN DAY (Maybe around 108AHs total re-charge capability).

Just my thoughts for my upcoming SOLAR PANEL Project

Roy Ken

Shiltsy wrote:

Basically want a system with max output per square foot of roof space consumed. If I can fit a 2x4' panel will 100w serve my purposes well?

Yes. Without any problem as long as there is sunshine. In the winter, you will want to knock snow off the panel.
As a side benefit, the number of days you can stay out without power may even double.

Hum, I wonder if you could put a flexible panel (or lots of little panels) on the top of your cargo carrier? Might be worth looking into. Someone on here will know.

Enjoy your solar system,
Steve

Thanks for the quick feedback. I am really looking for a system strong enough to give me a full charge while the rig is in storage. The 3-4 days of dry camping will get me through most camping weekends. I just want the system to be topped off without plugging in during storage.

Basically want a system with max output per square foot of roof space consumed. If I can fit a 2x4' panel will 100w serve my purposes well?

I have a similar problem dry camping with my Class B and I also have limited roof space. On a recent camping trip I experimented with a portable 120w panel and found it was capable of keeping my batteries fully charged. (Like you I could only go 2-3 days before needed to recharge.) There are some 100, 120, and 135W flexible solar panels available that are 21" wide and anywhere from 40 to 56" in length. Would they fit in the space you have available?

BTW, I think I have room to install two of the 135W panels on my roof and I'm looking at doing that to solve my dry camping power issues.

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.

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 Spread Sheet N8GS

For a nice explanation of solar, try this link:

Golden rules of solar

wholesale solar.com

So this is strictly a trickle-charge setup? Probably easier just to disconnect the battery.