FYI Solar 101 - A General Guide to Solar in your RV or Motorhome

[Chuggs]

Scissor lift? In my dreams!!! Getting the panels up on the roof was the biggest hurdl.

The 6AWG works great. Early adopters were heck bent on parallel wiring of a bunch of 12v 100w panels. If I am not mistaken...AMSolar and Marvin Braun (PrecisionRV.com) were fans...and added thick cables from the roof to the basement. They have each diversifield since.

Yes...the 6AWG has it’s limitations, and as you point out...setting the panels in a series-parallel configuration will keep you within the amperage limits. I do not know the exact cutoff point..but at some voltage you go into “high voltage” category. In the solar industry...high voltage requires additional safety labels and manual shutoff switches...so I didn’t want to go there either.

Here’s a link that shows different configurations and formulas for calculating the theoretical voltage and amperage for choosing wires and fuses...

http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/technical-literature/bus-ele-an-10191-pv-app-guide.pdf

In a perfect world/perfect day...1,000 watts per meter sq. sun intensity...I would yield 1,440 watts (8 x 180watt panels). The math worked out nicely...if your batteries absorb setting is around 14.4v...1,440watts will give you 100A of current. My Interstate batteries recommend just a bit below that... ( C/10, or 92.8A). I wired my panels in four strings of two... So, each pair are wired in series...and each string of two are combined in parallel. It’s a balance. MPPT controllers love voltage...they wake up much faster with two panels in series...and can start working. The controller will have a recommended minimum voltage for best power point tracking. I advised another friend...he went with the Magnum PT-100 controller. I used the then current guidance in the Magnum Manual. They later found out the minimum voltage for their controller is higher than they originally thought. The controller works...but throws out an error code...which basically says the voltage is too low to compute maximum power point. I would recommend three panels in series for that controller based on the latest guidance...vs. two in series. During a high output point...I see somewhere around 1,200 watts...and the PV voltage is around 42v...and around 28A going down the 6AWG solar prep wire. The same gauge used in your cord reel to carry up to 50A. I believe the insulation they used on this solar prep wire is rated much higher than 50A...can’t remember what the amperage was that I found..but needless to say it is leaps and bounds more than 28A.

The way we use our coach...we have the minimum I would recommend. The atmosphere doesn’t always give you a full count of wattage. Having a residential refrigerator, microwave, espresso machine....we LIKE power. Seems a few of the high end installs lately have been closer to 2000watts and parallel charge controllers. Might fit on a 45’ coach nicely ?...

I do like not worrying about power outages, or being able to boondock and not running the Generator a huge amount. I also never worry about coming out to dead batteries. I‘m sure you are already onboard as to the advantages.

The 6AWG is great for what I have. If you were designing a system for 2,000 watts and parallel controllers...then two sets of 6AWG would have been my choice for solar prep.

The BMV-712 that you purchased can pair with certain SmartSolar charge controllers. They use proprietary VE.Smart (BLE) communication. With an optional temperature sensor designed for the BMV-712...the sampled voltage and temperature are relayed to the SmartSolar charge controller. If using Lead Acid chemistry...this is most beneficial as it give you more precise compensation of charge parameters based on battery temperature. LiFePO4...I gather uses no such temperature compensation...but can use the temperature in other ways....such as cutting off solar charge if the batteries get too cold.

I am a big fan of Victron solar products...

 

[Kevin D Pem]

The 6AWG is great for what I have. If you were designing a system for 2,000 watts and parallel controllers...then two sets of 6AWG would have been my choice for solar prep.

There is only to small a wire. The larger the better. If your wire is much above ambient temp you would better have been served with larger wire. Heat is lost power. use your IR thermometer. I have 4 wires coming from the roof, two for each controller in the rig. My MPP is 55 volts.

High voltage according to the NEC2017 is 100+ volts. under that is low voltage. The call of NEC2017 is for an E-shutoff switch that emergency responders have access to. In the past 48 volts was the limit at that voltage NEC had a say if the state adopted it. There is still the "preexisting work " for older systems.

 

[Chuggs]

There is only to small a wire. The larger the better. If your wire is much above ambient temp you would better have been served with larger wire. Heat is lost power. use your IR thermometer. I have 4 wires coming from the roof, two for each controller in the rig. My MPP is 55 volts.

High voltage according to the NEC2017 is 100+ volts. under that is low voltage. The call of NEC2017 is for an E-shutoff switch that emergency responders have access to. In the past 48 volts was the limit at that voltage NEC had a say if the state adopted it. There is still the "preexisting work " for older systems.

Thank you for those details. I couldn’t remember what the voltage and safety cutoff requirements were/are...and haven’t stayed abreast of the latest.

 

[flyboy013]

So I’ve been trying to figure out some of the basic specs for the panels and the controller.

While I need to procure and install the panels and controller, there are several components that I already have. Those being the AGM batteries, Xantrex SW3012 inverter, AND the 6 AWG solar prep wires from the roof to the basement compartment.

Here are some thoughts. I’m looking for feedback to see if I’m think about this correctly.

My thought is that I want to develop a plan on how I would max out the solar capability. Whether I implement it now or incrementally over time.

It would seem that one of the implementation limitations will be the 6 AWG wire. Looking online, I find that a 6 AWG wire is limited to 55 amps (various based on temperature). If I were to install 12V panels in parallel, the output would be limited to roughly 660 watts (55A * 12V). Obviously I would want more capability than this. If the 12V panels were installed in a series of two and then each series in parallel, the 6 AWG wires could support approximately 1320 watts. That’s much better and in line with numbers that I’ve read in various posts.

I suppose I could combine the panels in a series of four to yield 48 volts and the 6 AWG wire could support unto 2640 watts. That sounds really nice! Am I understanding this correctly?

Also, it seems like panels are available in various voltages to include 12V, 24V, and 48V. If the input to the controller is going to be 48V, would it best to installed 4 12V panels in series, 2 24V panels in series, or just 48V panels. My understanding is that these would be options.

I also have a questions on selecting a MPPT controller, but I’ll post that latter as this post is probably long enough.

 

[Chuggs]

You need to use the data plate numbers from your desired panels. They will have Isc (Short Circuit Current)...and Voc (Voltage Open Circuit)...a 12v panel isn't putting out 12v... It appears you were estimating wattage based on 55A x 12V...doesn't work that way. I believe I linked a source pdf which details the computations...and application of safety factors...

 

[Rich-MLsRV]

@Neal

When you installed the panels on the roof did you add fuses between the panels and the combiner box?

In your picture the fuse beside the MPPT solar controller - Is that a 100A fuse?

 

[Neal]

@Neal

When you installed the panels on the roof did you add fuses between the panels and the combiner box?

In your picture the fuse beside the MPPT solar controller - Is that a 100A fuse?

Yes I did and later removed them. You'll never know when one fails or in my case my crimps not being done good enough. AMSolar no longer uses them, I cut all of my out.

 

[mrbillr]

i have a 2002 Coachmen Class A motorhome. it currently has a 30amp shore power service with an Onan generator.
i want to add solar to be able to power the 120v service and charge the aux solar battery.
what inverter do i need to use and how do i tie it into the current coach inverter? can i still use the stock power panel and inverter?

i am doing this on the cheap. i have:
100w Harbor Freight solar panels and controller
Renogy Rover 30 Amp 12V/24V MPPT Solar Charge Controller
2 on/off toggle switches
a 3000w inverter
added 1 AGM battery

panels are mounted on the roof with the wires coming down the refrig vent.

 

[Richpatty]

Hard to say without knowing your setup, but why not just have your solar controller charge your house batteries. Solar is really just a battery charger….and then you use that stored power to run what you want (basically). You also did not say how much solar you have.

And why not use the inverter you have? 3000 watts is very adequate.

 

[Kevin D Pem]

i have a 2002 Coachmen Class A motorhome. it currently has a 30amp shore power service with an Onan generator.
i want to add solar to be able to power the 120v service and charge the aux solar battery.
what inverter do i need to use and how do i tie it into the current coach inverter? can i still use the stock power panel and inverter?

i am doing this on the cheap. i have:
100w Harbor Freight solar panels and controller
Renogy Rover 30 Amp 12V/24V MPPT Solar Charge Controller
2 on/off toggle switches
a 3000w inverter
added 1 AGM battery

panels are mounted on the roof with the wires coming down the refrig vent.

Your my kind of person (on the cheap). We do have a different opinion of "on the cheap" however.

First things first! I would not run wires in a plenum (hot air vent cavity).

What I think you are asking is:
What do I need to do to power my house circuit on the cheap?
So this is the answer.
Disconnect the 110 vac wires from the converter. (Having the converter in the 110 circuit creates a loop).
Either run the power cord directly to the inverter, or wire an outlet from the inverter to the rv cord storage location so you can plug the coach in at that location. .
Hook up the charging system as defined in the solar controller paperwork.
Oversized wires are standard for solar. The controller should be as close to the batteries as is possible, and share the same temperature, not the same compartment.

One final point! DO NOT MIX AND MATCH BATTERY TYPES, OR DIFFERENT BATTERY SIZES! ALSO ALL BATTERIES SHOULD HAVE MANUFACTURED DATES WITHIN 6 MONTHS OF EACH OTHER. The old will destroy the new.