PV for a 30ft 5th wheel (photovoltaic solar panels on RV)
 

I am looking at various components for a 400W array to put on my trailer. Unless I am missing something it appears I have three options:

1. Buy a kit that is either overpriced and/or does not have the components I want.

2. Buy somebody's book that will tell me how to build a system ten years ago.

3. Seek answers on a solar forum from people that have trouble with Ohm's law.

OK, I'm being cynical, but the freely available information I am finding does not instill me with confidence. Can someone point me to a non-dealer forum where I can get basics and perhaps a little inside advice on products? I want four 100W panels with room for expansion, MPPT, and enough information on panel connectors so I don't end up having to hack things just so I can use my own wire.

Thanks;
Doug

First rule with solar is decide what you want to run and know how much energy it uses and how long you plan to use it.. Then we can help..

One microwave (1200W) for heating coffee, five or ten 4W LED bulbs, one computer hooked to a 32" flat screen TV two hours a day, 80W heater circulation pump (not OEM), a Dometic ammonia absorption refrigerator at 300W with unknown duty cycle. Power supplemented with a genset as needed. No air conditioning required.

400W is not optimal, it's what will fit on my roof. Our RV campground membership includes free electricity. The amount of solar/genset required will depend on how much time we spend boondocking.

12 or 24v batteries?

Four Trojan T105's in series parallel for 12V at 450AH. 24V wasn't an option due to existing equipment and the availability of 12V from the vehicle alternator. The inverter is a Xantrex SW2000

Solar 12v assist - EcoModder

There is a link for installing solar on a camper.

Use MC4 connectors. Any panel you likely buy will have MC4 connector ends.

Do you have a large battery charger for use with the generator?

Mine is 40 years old and not regulated. Do you have a recommendation? I've had good luck with most Harbor Freight stuff. Don't know much about their electrical devices though.

When I needed a larger battery charger I decided to go with 220 volt power and just built my own out of junk I had in my stash.
To control my home made battery charger and keep it from frying the battery I wired it into my 30 amp Morningstar PWM solar charge controller. (which the manual says not to do).

If you want to charge batteries that size in a reasonable amount of time you need a charger that will put out at least a good 20 to 30 amps.

Iota makes some nice chargers. They have an IQ version that is a 4 stage charger for running off of 120 or 240v. As far as charge controllers for your panels go I would stick with a small name brand charge controller. They are responsibly priced and will give you great performance. Some even have dumb load controllers so if your batteries get topped off by the sun it will switch the pv to a load of your choice ie a 12v heating element in a water heater if you have one. If you don't have panels yet renogy has 100 watt panels for 120$ shipped and that's one of the better deals I have seen for a name brand panel

Renogy has a few MPPT controllers as reasonable cost, though I did not find the $120 panels you mentioned. The Grape Solar panels sold by Home depot are a little more at $135 but I can get a replacement shipped to any store in the country if I have a problem on the road.

To help offset the system cost I was thinking of installing a preheat tank for DHW in my house and powering it with the solar array when the trailer isn't in use. DHW is a big expense for us, even in summer.

The trailer (2002) has a built-in charger though I have no idea how good it is. RV charge units seem to have a bad reputation among RV'ers for cooking batteries.

Buy the time you get any 100 watt panel shipped to you, I think you will be looking at spending at least $130 to $140.

This is almost exactly what I do with my suburbans solar roof top.
See:
Vehicle solar panels to grid - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

Home Depot doesn't charge shipping if you pick them up at a store. They had them for about $120 a while back but I procrastinated. Now they are $134 - still not bad. I would rather refuse a broken panel at the store than have a three way fight involving UPS or Fedex.

Oil Pan 4:
I like your thinking. Put the excess PV energy into vampire, or in my case, continuous loads. Around my house there is always water to heat. I will look for an MPPT with the ability to divert the PV energy when the batteries are in float mode.

With a few more panels I could even run a window shaker once the DHW reaches setpoint.

I know of no MPPT with a load dump. But I have really only looked at genasun and Morningstar.
It turns out the MPPT charger and grid tie work together rather well.
If the batteries are hungry for power the MPPT charger will gobble up almost all of the available PV power. Then when the batteries are full the MPPT charge controller will go into stand by mode where it draws almost no power and then the grid tie will start soaking up that excess power.

I suppose some variation of this idea is available in all but the least expensive controllers. Otherwise an off grid system would waste a lot of energy once the batteries are up. This is the kind of information I need before buying components.

Doug

I just run the MPPT charge controller and grid tie inverter together.
If the batteries in the camper sit idle then the solar panels and charge controller form the worlds most expensive battery maintainer.
I hooked the grid tie into the solar panels circuit.
The cool thing about the MPPT charger is it will soak up almost all the power and put it into the batteries when the battery needs power. While the battery is charging the grid tie puts out about 5 watts. Then once the battery's MPPT charge controller tops up the battery and goes into stand by mode it draws very little power, as that happens the grid tie output ramps up. No need to get your self another expensive MPPT charge controller with load dump.
Its almost as if I carefully selected components to do this, but in reality I just recombined old junk that was collecting dust into a new configuration for most of the build.
I also didn't just haphazardly throw all this stuff together. I do have an associates in applied sciences for wind and solar power generation, what I studied didn't exactly cover this application but, as I put it together I had a pretty good idea it was going to do exactly what I wanted. So when it worked, it really wasn't a big surprise.

I think what you have is just going to be a larger version of what I have.
Really the only major component you need to pick up is a 12 to 28 or 14 to 28 volt grid tie inverter.

I looked at the documentation on the Morningstar MPPT-45 this morning. It has four auxiliary relay control outputs (open collector, I presume) but I can't find much in the way of an explanation how they are programmed. The operator manual refers me to the website which refers me to a data sheet on the relay drivers which refers me to the manual. Morningstar has a good reputation but this is not comforting.

My guess is that an output could be programmed as a load dump. I just haven't found the information.

The Morningstar is about double the price of the Renogy MPPT-40A. This could be justified by the Morningstar's PC connectivity options. Perhaps the software interface manual will tell me more about the output programming features. I like the Modbus interface. If the software is any good it would replace the need for a separate battery monitor.

Grid tie seemed like a good way to utilize otherwise wasted energy. Then I read the power company's requirements. So much for that idea.

It turns out the relay driver is a $160 option. For a little less money one could instead use a brick PLC with six outputs instead of four and also have eight inputs. The Tri-Star Modbus interface is well documented and shows that it would be a simple matter to interface with a PLC to make a load dump.

I couldn't find a manual for MSView on Morningstar's website and there isn't one in the downloadable zip file. I didn't install the software but I suppose a help file is included in the executable.

OK, new problem. I have a converter/charger in the RV of the type known to destroy batteries. A new 4 stage Iota 45 amp converter is $187. Not bad but is it necessary?

The MPPT provides four stage charging when the sun is shining and becomes a brick when the sun goes away. Rather than buy the Iota would it not be simpler to provide a backup DC source for the MPPT in lieu of the PV array? A simple current limiting supply can be built for much less than the price of the Iota.

I can provide 120V to the supply from a generator or the pedestal at an RV park. Having one charging device means I only have to monitor one system.

That's what I did.
Took a PV charge controller and powered it with external non-PV power.
But I built my charger to mimic the output of a PV array, around 21 volts DC open current and then drops down to between 17 and 15 volts while under load.
Just like a solar panel.

supercaps
 

Buy blemished solar panels for about 50 cents a watt and get enough deep cycle batteries to handle the normal loads and use supercapacitors hooked in series to match the voltage of your solar panels. Most good panels are about 300 watts and 34-37 volts. The caps will handle the heavy loads for about 2 minutes and recharge very fast. By adding caps you do not need as much cranking amps in the batteries.