Solar Questions, yes more solar questions

[KE6IRJ]

Okay, before you say it, I did search, and have been reading on this for days.

Here is my question.

I have a bonus coming possibly and am trying to decide if I want to use it for solar on our trailer. I intend to use the trailer mainly off the grid, and have fall hunting trip coming up for 7 days.
Currently, I have 2 GC2 batteries, plan to go to LED lights, and a propane heater other than the trailer heat.

So, in reading, I know I want an MPPT controller, remote monitor head, and probably 200-250 watts to keep my batteries charged for the week trip.

Is it better to shop around and piece together a system or stay with something put together by someone who knows?

I was thinking this one, because they are local to me and I have seen them in action on our last trip.
http://www.solar-electric.com/solar-panels-mounts-kits-accessories/prsy/rvandsmbasoc/rv-solar-kit-280-watts-mppt.html

I don't think I need an inverter right away, since I don't use other devices when camping right now. Do I need replace my built in power converter or is this all additional?

So, am I on the right track? Are there companies or brands to avoid? Better prices I have not found? Fill me in, what am I missing?

[Almot]

KE6IRJ wrote:
Am I on track?

More-less.

The audit is flawed, but yes, you need about 300W solar. Won't hurt getting more, for rainy days. Converting to LED is almost mandatory with a small solar.

Proper audit:
(watts)*(run time of EACH DEVICE SEPARATELY) =daily watt-hours. This is the minus side of the balance sheet.
The plus side is more complicated. As a rule of thumb, solar harvest in watt-hours = (panel wattage)*5 hours.

Those Ebay panels Link
are unknown stuff, but this is not uncommon. The industry is in disarray, reputed brands disappear. Everybody seems to cobble up panels in their back yard. I don't even see established Chinese brands like Trina anymore, not to mentioned old US and German brands. I don't like it being Monocrystalline, would prefer Poly, but the price is good with free S/H.

30A PWM is dangerously small for 3*160W.
2*160W have 18A current, so with 20% safety margin you need 21.5A PWM, the closest bigger size is 25A. If you add 3rd panel, you'll need 35A.
For a 35A PWM consider Xantrex aka Trace aka Schneider, with their optional remote temp sensor. Plus, digital Drok voltmeter. Don't be tempted with $4 meters on Amazon, Drok is about the only accurate meter. Or get Xantrex meter, costly but nicer. I wouldn't want bright LED display in the night.

As noted, you can also use MPPT, they are more expensive but will simplify the install as you will be able to wire panels in series and run same MC4 #10 cable to controller, without junction box. You can wire in series either 12V or 24V panels, it doesn't matter for MPPT, though 24V are cheaper. OTH, with PWM you are limited to parallel wiring, i.e. rooftop junction box and thicker cable.

[KE6IRJ]

Alright, so I did an energy audit again and found all my lights (not LED yet), water pump, water heater ignition, fridge control, stereo, and awning use 682 Watts. I think, that assumes constant operation, so I did a 50-percent adjustment and get 341 watts.

So I figure, 2 of these panels
ebay id 272008199222


With expandability for 1 more if needed.
Then I need a good PWT controller rated at 30 Amps.
Am I on track?

[time2roll]

pianotuna wrote:
Hi SMK,

When my upgraded battery bank was new, I could run the fridge on 120 volt while trundling down the road and still have plenty of power for a week long trip. As the bank aged I had to eventually abandon running on the inverter while traveling.

Now that I'm full time, I tend to run the fridge on propane, because I don't have enough panels to support the fridge.

You may have better luck as you have a much larger solar farm.

I have only run the fridge on inverter once due to the propane would not light as I was headed out on a trip. Next day had it fixed. I have no intention of running fridge on electric in normal conditions.

[pianotuna]

Hi CJW8,

Which MPPT controller will you use? I hope it has a temperature sensor.

[SkiSmuggs]

You can drive yourself nuts trying to figure it all out. I eventually just got a Renogy 200w kit and installed it. Optimally, I should have 400w, but the controller will support that when or if I get around to it.
I do have the Renogy 100w suitcase portable to supplement if needed.

[CJW8]

Well, I am going to go against the grain here and recommend MPPT Because:
1. Will only add 100 to 150 dollars to the system.
2. Typically has more features.
3. Allows for 24 volt nominal verses 12 volt nominal panels. Typically 24 volt panels are less expensive.
4. Gives more charge, granted it isn't much more.

I'd also run larger than #10 wire from panels to controller.

[pianotuna]

Hi SMK,

When my upgraded battery bank was new, I could run the fridge on 120 volt while trundling down the road and still have plenty of power for a week long trip. As the bank aged I had to eventually abandon running on the inverter while traveling.

Now that I'm full time, I tend to run the fridge on propane, because I don't have enough panels to support the fridge.

You may have better luck as you have a much larger solar farm.

[time2roll]

KE6IRJ wrote:
As for power draw, I would like the power to run the fridge on power, but will probably turn it to gas regularly.

My absorption fridge draws a solid 27 amps when running on inverter power.
That will chew up 400 watts of solar panels right there.
Might be workable while in motion and getting some power from the alternator.

[Almot]

You'll have to run fridge on gas.

System cost should be about $2 per watt of solar, including panels, controller and wiring. $3.50 per W in that kit is too much.

With LED lights, pumps, propane heater (no furnace), DC circuit of the fridge, some radio etc you need 200-400W system.

This 280W, $518 would work. Not the best components but it will do. I would discard the brackets and make my own of aluminum angles, and buy extra length of MC4 cable if needed ($20?). Plus, couple of DC breakers MNEPV ($10 ea?), 2 insulated terminals $7 ea, and Big Baby breakers box or Small Baby ($30?). Az Windsun aka Solarelectric will have all this - Baby box, breakers and terminals.

Or buy panels and controller separately. I would try and fit as much panel wattage on the roof as possible, there is no such thing as too much solar. Controller size will become clear after you've decided on the panels. Or buy that $500 kit and don't strain the brain.

You don't need hired help to decide on the components, people here will do this for you for free :). Wiring and installing is a different matter, some users have to pay, and it costs at least as much as the system parts.

[pianotuna]

Hi,

Absorption fridges are not too efficient. Mine, which is a small Dometic, uses 5.7 KWH per day on the 120 volt setting.

Given 5 "good" solar hours per day about 1140 watts of solar would be needed--plus a quite large battery bank to run it when the sun is not shining.

The drawing board starts with an energy audit.

KE6IRJ wrote:
As for power draw, I would like the power to run the fridge on power, but will probably turn it to gas regularly.

[KE6IRJ]

Okay, back to the drawing board.

As for power draw, I would like the power to run the fridge on power, but will probably turn it to gas regularly.

[red31]

KE6IRJ wrote:
Is there a chance of overcharging if the controller is PWT?

both mppt and pwm use switching to limit overcharging.

[rexlion]

A PWM controller will not overcharge, unless it's malfunctioning. You have to look at how many amps and volts your panels can put out, and buy a controller that is rated to handle more than those numbers.

No need to mess with your converter. No need for an inverter if you don't have AC devices to run.

If you are not running your furnace (a big power hog) and if you run the fridge on LP, that just leaves lights and water pump and fan... and some low-draw things that won't use much battery power. Camping alone, I kept my battery charged with just one 75W panel and a $25 Morningstar controller, all from solarblvd.com . Instead of mounting it on the roof, I kept the panel portable and plugged it into the trailer's 7-pin pigtail when charging. No problems or issues. Very simple and easy.

[Boon_Docker]

..

[Boon_Docker]

I purchased my system from this Ebay Seller 4 years ago and have been very pleased with it.