Solar config opinions wanted.

[Lgboro]

I have two 100 watt solar panels pre bought for my future small standy build. I am considering two different configurations (1) a Morningstar Duo 25 amp capable of charging 2 batteries separately at the same time with the ability to set the percentage of charge sent to each battery or (2) a larger two battery system hooked together and charged as one large battery. I was thinking I could dedicate more amps to charging the 12 volt refrigerator battery on the 2 single battery system so that I would not run down the refrigerator battery and spoil its contents. If either battery were to go bad on an extended trip I could put the refrigerator on the good battery and deal with a more permanent fix when I return home (sometimes I leave with just enough money to make the trip and return home). I think the cost of either system will be substantially the same. I am leaning toward the 2 separate battery configuration and wanted to run this by forum members for some feedback to consider the pros and cons of the two choices.

[Bogo]

Don't separate, get two identical batteries to parallel, and manage your draw. Instead spend your money on a true MPPT type solar charge controller.

BTW: A single 100 Watt solar panel should easily keep ahead of the draw from most compressor based cooler style refrigerator/freezers.

[Shadow Catcher]

Amp hours are pretty much amp hours. I have one 150 AH lifeline AGM and a 180W high voltage panel which had to have an MPPT controller, (Morningstar Sunsaver). On our trip last summer with a Waeco refrigerator and a lot of electrical goodies, and camping in a number of cases in deep shade we never got below 70% state of charge. The only real advantage in having an MPPT controller is that you get a slight increase in usable current and with high voltage panels you get usable current at a lower light level. You could achieve this with your two panels in series. There really is not enough advantage to justify the additional cost of an MPPT, a good PWM will do very nearly as well for a lot less $$$. I do have a flexible 140W moderately high voltage panel that is rolled up (it is 18' long) and with voltage drop from the extension cord is compatible with a Steca PWM which will handle the higher voltage.
This summer we will be camping on the shore of Lake Superior in a wooded camp site for 8 days. This is why I wanted the additional panel to be able to stake it out on the beach to make sure we get up to 100% SOC.
Conservation is a large part of the equation, using LED's computer, case fans, not using resistance appliances i.e. coffee maker...monitoring usage with a Victron or Trimetric battery monitor.

[Lgboro]

My current tear has the all the above mentioned power friendly options built in and I too have yet to run a 55 amp hr Sam's Club marine/rv battery below 70% on my meter. My next build will add a composting toilet and a dc refrigerator / freezer that will only require me to add a couple of computer fan vents to assure ventilation for the add ons plus the refrigerator power needs which are around 2.5 amps or less per hour. I also have a 100 watt panel I can add if I feel the need as a portable pole unit just in case of a cloudy week . The Morninstar Sunsaver Duo 25 amp on sells for $155 and that is with a remote meter that will measure everything I use on my TriMetrec meter on my current tear. I may try it because I can set it up as either one or two separate batteries and have plenty of amps to handle an extra panel if needed.

[bdosborn]

The Morninstar Sunsaver Duo 25 amp on sells for $155 and that is with a remote meter that will measure everything I use on my TriMetrec meter on my current tear.

The Sunsaver Duo meter will display a lot of handy values but it won't replace your Trimetric. It doesn't track amp-hrs in and out of the battery, just the amp-hrs harvested from the PV panels. The Sunsaver Duo is really meant for motor homes that have a station battery and a start battery, I wouldn't spend the extra money for it on a single battery installation. Like SC said, at 200 watts you really don't have enough wattage to warrant the extra expense of an MPPT controller, unless your out of roof space and want to get every watt you can (I'm assuming you have 12V panels since you were looking at the Sunsaver Duo). I'd go with a a Sunsaver 10 for a single 100 watt panel or a Sunsaver 20 if you use both panels.

Why not use two 6V golf cart batteries if your looking at two batteries anyways? That seems to give the most amp-hrs and reliability for the money. FWIW, I don't think I've ever read about anyone having a battery fail on a camping trip on this forum....
Bruce

[bdosborn]

BTW: A single 100 Watt solar panel should easily keep ahead of the draw from most compressor based cooler style refrigerator/freezers.

It depends on how big the fridge is.

Our Tundra upright compressor fridge uses around 1 amp-hr in 80F weather. A 100 watt panel will harvest around 5 amps * 5 hours Peak Sun = 25 anp-hrs. That ignores shoulder hour contributions but a 100 watt panel just barely keeps up with only the fridge usage in perfect weather. I'd go with 200 watts to compensate for a few clouds, hotter weather that increases the fridge draw, lights, DVD player, etc.

Our Waeco chest style compressor fridge only uses 0.5 amp-hrs so a 100 watt would keep up with it.

Waeco CF-40 Tests

Tundra TJ22 Tests

Bruce