Looking for Battery & Solar sizing spreadsheet

Don, PWM with 48V input is something to consider. That many 12V panels for a 2400KW array doesn't seem practical, I would rather use 24V panels. 10*24V panels in series/parallel, to make total 2400W/48V array and 60A PWM - maybe, yes.

Though I'm leaning towards MPPT, all panels in series. Don't like roof J-boxes and monstrous cables. Most trailers and 5-ers don't have room for more than 900W - you need to leave some room for walking and working there - so we are down to 20A controller with 48V battery. The difference btw quality 20A MPPT and PWM will be minor. I recall AM Solar J-box (for PWM) costs $60. So in the end it's a wash, in terms of cost. Efficiency of 48V PWM in series-parallel vs MPPT in series - don't know.

Hi Almot,

The biggest difference is being able to use a single high quality pwm controller. Wire from the panels to the controller can be smaller, too. (example 12 volts @ 200 amps = 2400 watts vs 48 volts @ 50 amps = 2400 watts). The first part of the example would require two Magnum pt-100 controllers @ $800 each. The second would require one Morningstar 60 amp pwm controller @ $240.00. Obviously wire to carry 200 amps is going to be a LOT thicker than that for 50 amps.

The conversion losses may be smaller as getting from 48 volts dc to 120 volts ac, is a lot easier to do.

There are quality dc to dc converters that are inexpensive.

Almot wrote:
With 48V bank only the wire to battery will be thinner (where it's not too important as it's short). The wire from panels to controller won't change, and the dance of parallel/series/Vdrop will be the same.

Controller will be smaller and cheaper, yes.

A DC-DC downconverter will have to be installed after the battery, to handle 12V loads of trailer - costs $80 or so.

With 48V bank only the wire to battery will be thinner (where it's not too important as it's short). The wire from panels to controller won't change, and the dance of parallel/series/Vdrop will be the same.

Controller will be smaller and cheaper, yes.

A DC-DC downconverter will have to be installed after the battery, to handle 12V loads of trailer - costs $80 or so.

If you really want to go "whole hog" on solar there is a case to be made for going to a 48 volt battery bank. You save on the controller, and wire size. Any inverter may run more efficiently.

My 6-something cu.ft Norwarm draws 12-13 AH when it's hot. DC circuit of propane fridge is one of the biggest 12V draws. Exhaust fans running 12-14 hrs on a hot day draw something too, but then you spend more time outside and day is longer in summer, so you burn the lights less. Yeah, can be more than 40 AH total for 12V loads if you are like Mr Trump and spend more than you have :)

Perhaps with LED lighting <40 amp hours. Thinlite fluorescent's sucked 4 amperes +. Some folks light up the inside of their rig like the Trump Tower. There is no way to guesstimate total usage.

Joisey gets hot and humid in the summer. What's a couple of fans, running all night, between friends? Like it or snot my 8 CF Norwarm sucked 14 amp hours a day confusing itself as to what it should do.

Music and TV! Hook them both into a currant bush? The last satellite system I got near required 50 watts for the LNA. Has this changed?

It's all guesswork until it is measured. To asssssssume a certain lifestyle and habit is inevitable leads the "assssssumptor" right over a cliff.

You mentioned "major conservation". If this is your way, and you want to avoid running generator completely or run it very occasionally - then in summer at your latitude the minimum array would be either 260-280W or 500-600W. And at least 200 AH battery - 2*6V @225 AH each will be it.

280W is the maximum for a simple install without complications of thick cable and roof junction box. 2*140W panels, 20A-25A PWM controller.

If you're thinking about future expansion - better do it now and forget 2*140W + PWM. Get two 250-280W and 45A MPPT controller. You can still get away without J-box then.

Unless you are in Az desert, you should expect rainy and cloudy days at times, and then 600W will harvest what 300W would on a good day. Or you park in partial shade. Or you have to run a furnace. A lot can be done to conserve energy, LED lights is not up to discussion. I replaced furnace with catalytic heater - silent, easy on propane and no 12V required. "Major conservation" may mean different things to different people. If you are running a fullsize computer tower and can't live without microwave several times a day, 1200W coffee maker and toaster - then you better cover the whole roof with panels.

ewarnerusa wrote:
No AC loads while boondocking? Already have all LED 12V lighting? 2 group 24's or 2 GC batteries. 300 watts of solar. Spec a charge controller and wiring with expansion in mind. Remember to park the trailer in the sun.

Sort of what he said. We boondock exclusively. 2x6 GC batteries, 200 watts solar, whole house wired inverter (tv, phone charge, occasional fan). LED lights. Everything else on propane.
Generator back-up and for the occasional toast or vacuum or power tools outside...

No AC loads while boondocking? Already have all LED 12V lighting? 2 group 24's or 2 GC batteries. 300 watts of solar. Spec a charge controller and wiring with expansion in mind. Remember to park the trailer in the sun.

Almot wrote:
Auditing DC loads, like lights, 12V radio and DC circuit of propane fridge? They account for less than 40 AH a day.

I didn't know that ... now I do. It really changes my thinking about this topic. Since I've been reading up on batteries, solar and how wimpy the plain old dealer installed 12v RV battery is I can understand why we always ran out of juice so fast even with major conservation ... there just wasn't much there to begin with!

Thanks for the enlightenment!