My Solar Questions

[DaveP]

I am looking to supplement my battery charging with some solar. I want to make sure I am thinking through this correctly, so I want to pass a few questions by you guys (the Airforum Experts ), one question at a time.

My first question is on capacity needs. I have 4 newish GPL-4CT batteries which are rated for 440 AHrs. With my BMS, I know I typically use 10% of my capacity during an average night/early morning (heater, misc. DC draw, coffee pot, microwave, etc.). That means I have drawn the battery bank down by approximately 44 Ahrs and that is what I need to add back in to the batteries during the day if I want to start the next night at 99-100% SOC.

I am thinking a 200-watt solar array, like the Renogy 200 Watt Solar Suitcase, will take care of my needs most sunny days here in Colorado. My calculations are as follows: a 200 W array delivers approximately 10.2 Ahrs at 92% efficiency with an MPPT controller. If I get 4-5 hours of sunlight, keep the panels out of the shade and align them properly, I will fully charge the batteries most days. If it is cloudy, I can always run my Honda 2000.

So, have I calculated this correctly?

Thanks in advance!

[Shermy1987]

You're on the money. But. Given all the weather variables, possibility of shade, especially due to the fact they're going to be close to the ground etc etc. 60-70℅ is probably going to be a more realistic figure to work with. Most people who calculate the minimum requirements for solar end up wishing they had more.

[alano]

The Renogy 200 Watt Solar Suitcase comes with a PWM controller, not a MPPT controller, so efficiencies will be less.

Why not add four 100W panels to the roof of your Classic in a series/parallel arrangement like I did, reuse the pre-wiring, add an MPPT controller and be done with it?

[DaveP]

Thanks for your inputs, guys.

Shermy – I agree the actual charging efficiency will probably be more around the numbers you quoted. Thank you for verifying the calculations are correct (if not a little too optimistic).

Alano – You can purchase the Renogy suitcase without the controller for a lower cost and then add your own MPPT. I also may buy the Renogy light-weight panels and make my own suitcase… For a variety of reasons, I do not want to mount the panels on the trailer.

This is a solar system to supplement my charging system, not be my primary charging system. I do not need it to get me to a full charge every night. I just want to minimize the use of my generators for the sake my fellow campers and myself. And, I want to keep the project as simple as possible.

My next question will be on the system design and integration. I will lay it out this weekend and post it for everyone’s inputs.

Thanks again for checking my "math".

[DaveP]

I found the attached diagram on the web. This is pretty much exactly how I plan to layout my system. I am going to make or buy a 200-watt solar suitcase. I will use two 50-amp inline breakers to protect the solar MPPT controller plus a battery switch so that I can isolate the solar. The rest of the charging system is already installed. I plan to run the wiring through the floor under the couch and terminate them to MC4 connectors in the old battery box behind the propane tanks to plug the panels into.

My question is, will I have to do something further to isolate the two charging systems, that is, isolate the Magnum charger from the solar charger when both systems are operating?

Thanks in advance!

[DaveP]

Not seeing any posts that could answer my question, I contacted Magnum technical support. They said no further separation is required. The Magnum will know to only put in any additional power required to maintain the charging profile (whether bulk, absorb or float) while on a generator, so it will share the charging/inverting energy input requirements with the Victron solar controller. That is what I thought would happen, but it was good to get a confirmation from an expert.

[alano]

Originally Posted by DaveP

I found the attached diagram on the web. This is pretty much exactly how I plan to layout my system. I am going to make or buy a 200-watt solar suitcase. I will use two 50-amp inline breakers to protect the solar MPPT controller plus a battery switch so that I can isolate the solar. The rest of the charging system is already installed. I plan to run the wiring through the floor under the couch and terminate them to MC4 connectors in the old battery box behind the propane tanks to plug the panels into.

My question is, will I have to do something further to isolate the two charging systems, that is, isolate the Magnum charger from the solar charger when both systems are operating?

Thanks in advance!

Dave,

Not sure why you're planning to add two 50-amp breakers. Only one is required on the positive connection from the batteries to the controller. Also, I don't see why you need a battery switch to isolate the solar. Normally folks directly connect their solar chargers directly to the battery.

[DaveP]

Hi Alano,

It is a bit of over-kill, but this layout (including the breakers and shut-off) makes it compliant with the ABYC standards for marine installations. The breakers protect the solar controller from both directions and the switch allows you to work on the system easily (or shut it down in an emergency). Lewster, a well-known (to this forum) solar system installer complies with these standards on all of his RV installs. But you are right, this is not required, just prudent IMHO.

Thanks.

[billrector]

Originally Posted by DaveP

Hi Alano,

It is a bit of over-kill, but this layout (including the breakers and shut-off) makes it compliant with the ABYC standards for marine installations. The breakers protect the solar controller from both directions and the switch allows you to work on the system easily (or shut it down in an emergency). Lewster, a well-known (to this forum) solar system installer complies with these standards on all of his RV installs. But you are right, this is not required, just prudent IMHO.

Thanks.

I think what Alano is saying is that for a permanently mounted set of panels you need a disconnect switch so that you can safely work on the system. For portable systems, no switch is needed as you simply disconnect the panel if you need to work on it. I'm curious....why do you have so much battery capacity if you only use 10% per night?

[DaveP]

Hi Billrector,

I have already installed the system. I ended up eliminating the marine switch as it was redundant since I used 30 amp breakers which have switches on them. I do like, however, being able to isolate each end of the system (the battery side and the panel side) and it does completely protect the $230 Victron 100/30.

Good question on the 10%. I wanted to be able to camp for five days without recharging the batteries and that is what I calculated I needed. We prefer the smaller campgrounds around CO and the West that usually have no services (we are fly fisher persons). We also have a 3000 watt inverter, so that we can run the microwave, coffee pot, etc. in the morning without firing up the generator (and disturbing the peace ). That accounts for about half of our energy consumption each day (about 45 Ah total). And really, 220 Ah usable capacity is not all that much (four 6v Lifeline batteries), but it allows us to go 5 days or more, if we want to and conserve, without any battery charging. The solar charging is just to supplement our electrical capacity and extend our ability not the use generators when possible. It was an add-on to the original system I installed, so was not part of my calculation. With solar in the equation, I could have gone for less battery capacity.

Cheers!

Originally Posted by billrector

I think what Alano is saying is that for a permanently mounted set of panels you need a disconnect switch so that you can safely work on the system. For portable systems, no switch is needed as you simply disconnect the panel if you need to work on it. I'm curious....why do you have so much battery capacity if you only use 10% per night?

[DaveP]

Hi Billrector,

To clarify the 10%, it is 10% of my total battery capacity of 440 Ah measured by the BMS state of charge (SOC). Since I can only use 50% of the total battery capacity, my actual usage is 20% of the usable capacity each day. Sorry I did not fully define that.

[billrector]

Originally Posted by DaveP

Hi Billrector,

To clarify the 10%, it is 10% of my total battery capacity of 440 Ah measured by the BMS state of charge (SOC). Since I can only use 50% of the total battery capacity, my actual usage is 20% of the usable capacity each day. Sorry I did not fully define that.

If you are doing the install yourself, adding 400W vs. 200W would be more typical with the battery capacity you have. The incremental cost is minimal.....I just picked up 100W Renogy Eclipse panels for $119 ea. On Amazon. At that price you can add 200W more for less than $500 including upgrading your controller, wiring everything, and the panels. Something to consider!

[DaveP]

Originally Posted by billrector

If you are doing the install yourself, adding 400W vs. 200W would be more typical with the battery capacity you have.

And I may do just that. I want to try the system as is to see if it does what I would like it to do. I did size the components so that I can add an addition 200 watts in the future. At this point, it will not get its first real field test until next April.