Another beaten to death Solar question. Please help!!

[Sgeorge]

I have read every post that I can find regarding solar charging for an RV. The amount of information out there is insane. Amp hours, PWN vs. MPPT, voltage loss, Amp storage etc…. I am overwhelmed at this point. I guess I’m just not very smart because I am at a loss. Someone please just tell me how many watts of solar panels to install on my trailer. Here is the scenario:

We typically dry camp for two week spans.
We have converted every bulb in the trailer over to LED’s.
2 standard group 24 12v batteries.
We like to listen to the radio most days.
We will watch an occasional movie.
If it is cold we will run the furnace to take the chill off, not make it so hot you could bake cookies.
The trailer has all the standard stuff that needs to be run.

In general what size panels do I need so I won’t have to run my generator? I will buy for x amount over just to be sure, but at this point I don’t know where to start.
Thanks

[Bruce_H_]

To achieve your goal of not having to run the generator, the battery bank needs to be significantly upgraded to provide the amps to hold you over when charging conditions are poor (shade, cloud cover, rain). The most cost effective approach is 2 golf cart (6 volt) batteries from Costco.

I agree with the recommendation of 250 watts of solar. Under ideal conditions, that will provide about 13 amps per hour of charging power.

Recommend that you install a good battery monitor, such as Trimetric or Victron, so that the battery state of charge, amp usage, and performance of the solar system can be monitored.

Bruce

[Golden_HVAC]

Hi,

200 watts should work well in your situation.

If you have a laptop that will play the DVD, it will only use about 20 watts, much less than a typical TV set, if you want to go that option.

You would also need a 150 - 300 watt inverter to run the TV set or laptop, and I would recommend just hooking up a new cigarette lighter outlet someplace with #10 wire and a 20 amp fuse. Run both a +12 volt and ground wire in copper to the plug, just tying to the frame will not provide as good of ground and will cause greater voltage loss.

SunElec.com is one place that has difficult to beat solar prices.

I would recommend a 12 volt (nominal 12 volts is actually about 21 volts open circuit (with no load on it)) solar panel, and a PWM controller, it is much lower cost. Pulse Width Modulation. MPPT is more energy efficient, however with the low cost of solar panels today, PWM works out less expensive overall, because the controller cost is about 1/2 the price.

I would recommend 100 to 175 watt solar panels, unless you really find a great deal on the larger panel, and it will fit in a good area in your roof. Many who select a larger panel regret it due to the difficulty in locating a large enough space to mount it. My 120 watt panels where also difficult to locate too, the 75 watt and pair of 45 watt where an easy fit.

Back in 94, the cost of a pair of 45 watt panels where over $500. Now days spending more than $2 a rated watt is no good deal at all!

Installing the system is really easy, you just hook up the +12 to the right locations, and ground -12 in the other side. From the panel, you hook up the + and - to the controller, and then + and - to the batteries.

For panel mounts, I cut 2" angle aluminum from Home Depot to 6" long with 3- 3/16" holes for #10 screws into the roof, and 5/16" hole for a 1/4-20 bolt into the solar panel. Lots of rubber roof sealant prevents any leaks, and also helps hold the panel mount in place.

Your refrigerator, CO meter and propane leak detector together use about 35 amp hours per day, about what the single 120 watt panel can provide. The next panel will run all the lights, pump, and other loads like the radio and TV.

Water pump load is really insignificant. In a 2 week trip, it can pump 2 gallons per minute, pumping 120 gallons while using less than 8 amp hours.

Good luck,

Fred.

[time2roll]

220w done like this:

MX Solar 220W 24V Solar Panel MX60-220 $154

MorningStar SunSaver SS-MPPT-15L Charge Controller $230

100' MC4 cable $71 Cut in half and the MC4 connectors click onto the panel and the cut end hits the controller.

Two hole strain relief $5 to get down fridge vent

Add some angle aluminum to mount and some misc to connect and You are 220w for about $500 self install. It is about 100 mile drive to go pick up in person and save the shipping. Call first to make arrangements.

It is a big panel so measure and cut out some cardboard to see where it fits best if at all. Try to stay 12" to 24" away from the air conditioner etc that might give shade.

Same place has some 12v panels and PWM controller that may save some money if you want smaller.

Forum Members Solar Installations With Pics

[rexlion]

150W might get you by, but might not. 200W should do it. 250W certainly. 300W probably overkill for just 2 group 24s.

[handye9]

On my TT, I have two 128 watt (24 volt) panels (256 watts at 24 volts total), two group 24 batteries, and a 30 amp MPPT controller (room for more panels if needed). On my TC, I only have one 150 watt panel (18 volt), one group 24 battery, and a 15 amp PWM controller.

When you shop for the panels and controller, watch the voltage on the panels. Some put out 24 - 48 volts, and higher. PWM controllers won't take the higher voltage and drop it down to 12 volt. MPPT controllers do.

With MPPT controller, you hook it up to battery bank first. That tells the controller to put out 12 volt power. Then your panels can input up to 48 volts, into the controller.

If you buy 18 (or less) volt panels, you can use a PWM controller.

[SteveAE]

Our two 150 watt panels (300 watts total) with MPPT controller is more than adequate for year round camping in the Northwest...for us. Panels are not tilted and, except in the winter, I do not go out of my way to orient the trailer for optimal solar exposure.
If you anticipate more than just a few days of cloudy weather, you may want to consider adding two more batteries.

Have fun with your new system,
Steve

[hmknightnc]

Agree with the above. Around 250 watts is a good place start and will keep your ~160 AH battery bank charged daily on good summer days. That size will also service a twin 6v GC2 battery bank when you upgrade those grp24s

Start with 250 watts and good 20 amp controller (like morningstar sunsaver) and you can add a little more solar in the future if you need to.

I have 265 Watt solar with a morningstar prostar 15amp controller and the 265 watts will come close to maxing it out if the bank is low

[JiminDenver]

We are low power users also and run a 230 watt panel. It can have our battery back up to float level within hours of sunrise.

[2oldman]

250 watts.