Where is best location for solar controller

[rich85704]

I'm putting together a new solar system for use with my Class C. I had a Renogy 100W solar suitcase which I had extended with a second 100W panel... this worked great until it was stolen this week 😞

I know from my previous system that I'll want a longer cable from the PV panel to the rig's battery bank. I'd also like something more like 200W of PV. I'm scanning solar posts on here, and I see three possibilities:

1. Mount the controller on the solar suitcase and run a cable from the controller to the batteries. This is what I had before: I replaced the stock Renogy 12AWG cable with a longer run of 10AWG cable and it worked pretty good.

2. I'm seeing suggestions to mount an MPPT controller right near the batteries, run two 100W panels (available from Renogy on eBay only) in series, run 24VDC back to the batteries and controller.

Is there less loss by putting the controller nearer the batteries? If I want 200W, what about running them in parallel and running 12V to a PWM controller, located at the suicase OR near the batteries? Are there other possibilities I should consider?

Rich

[rich85704]

OP again, here:

Folks, I'm getting closer. I'm grateful for the info and your patience with a noob.

I'm going with 2 100W panels, each with Voc of about 20 VDC. I intend to run these in parallel, outside of the rig, to optimize solar exposure, and run a cable from the panels to the controller, which will be mounted in the rig, as close to the 12V dep-cycle batteries as possible. My original idea was that this would require an MPPT controller. But after talking and reading, it seems like that was wrong. The panels would be electrically identical. So am I now right that I can use a PWM controller? The one I'm considering right now is a 30A Renogy Adventurer; the manual says that the combined Voc of the panels should not exceed 50 VDC.

It looks like I'd be OK unless I decided to add a third panel, which would take the Voc over the max. That's not in the picture right now.

Given all this, is there a reason to go with a more expensive MPPT controller?

Is there some other factor I'm not taking into account?

Thanks, again. Happy Saturday!

Rich

[Almot]

westend wrote:

Though I couldn't figure out what Westend said about 24V panel being more efficient

More efficient as to installation costs and roof real estate/watts harvested.

x2.

[westend]

Though I couldn't figure out what Westend said about 24V panel being more efficient

More efficient as to installation costs and roof real estate/watts harvested.

[rich85704]

Single 24V is easier to install on the roof than 2*100W, but in a portable this will be more pain yet than 2*100W. You don't want to handle 5x3ft sheet that weighs 40 lbs.
2*100W is not something that I would want to handle, either. But I'm mostly parked in the open, so my panels are on the roof.

OP here ... I'm not thrilled about lugging around 100W panels, but they're more awkward than heavy. About 16 pounds each. I often camp in an area with mixed sun and shade, which would make roof mounting less desirable. Fortunately, the 100W panels stow easily in the over-cab space in my Class C.

[Almot]

24V panels are cheaper per watt than 12V, but shipping is costly. People normally pick up 24V at the closest warehouse.

Though I couldn't figure out what Westend said about 24V panel being more efficient (with MPPT) than 2*12V.
Panels that OP is considering, 2*100W, have ~38Vmp in series.
Single 200W panel at 24V is a rarity, a common size is 230W and higher. 230-240W panel would have Voc ~37V, but in MPPT it's Vmp that counts, typically ~31V.

20% more wattage (of 240W panel) will eventually result in more solar harvest, but this is not because of different efficiency of MPPT at 31V vs 38V. Wattage is the king 🙂

Single 24V is easier to install on the roof than 2*100W, but in a portable this will be more pain yet than 2*100W. You don't want to handle 5x3ft sheet that weighs 40 lbs.
2*100W is not something that I would want to handle, either. But I'm mostly parked in the open, so my panels are on the roof.

[Unyalli]

westend wrote:
If you are considering an MPPT controller, there is better efficiency by using a larger, nominal 24V solar panel, than 2 X 100W panels. For the smaller, nominal 12V panels, you won't gain much buying a more expensive MPPT charge controller. Nominal 24V panels typically operate at 36V or so. To get the most out of the harvest, an MPPT charge controller is warranted.
FWIW, I have a 235W panel and a Morningstar MPPT-15 charge controller. It harvests 15 amps on a bright, sunny day when the batteries are not full.

Charge controllers are more efficient when mounted as close to the batteries as possible.

I'm sorry westend but I have to pipe in here. Depending on where you live is the difference. The best prices I find on solar panels is solarblvd.com. Shipping 2 140 watt panels (FedEx) is way cheaper than 1 280 watt panel (Truck Freight). 2 140's "in series" equal 1 280 and easier to handle.

By the way, #2 is best choice. Here is a suggestion Morningstar SS-MPPT-15L
Mount in the bottom of your properly vented battery box and hydrogen is not a problem.

- Jeff

[Almot]

In case if subtle message by time2roll didn't get through - it is correct voltage that will be affected, by placing controller far from batteries. Controller will "see" lower voltage than really is, in this case.

I would skip MC4, if you plan on frequent connecting/disconnecting. Get Anderson connectors.

[westend]

If you are considering an MPPT controller, there is better efficiency by using a larger, nominal 24V solar panel, than 2 X 100W panels. For the smaller, nominal 12V panels, you won't gain much buying a more expensive MPPT charge controller. Nominal 24V panels typically operate at 36V or so. To get the most out of the harvest, an MPPT charge controller is warranted.
FWIW, I have a 235W panel and a Morningstar MPPT-15 charge controller. It harvests 15 amps on a bright, sunny day when the batteries are not full.

Charge controllers are more efficient when mounted as close to the batteries as possible.

[Ava]

I have mine mounted in the battery compartment and wired directly to the coach batteries, so the cable is right there ready to plug in the panels.

[time2roll]

Close to the battery is best for superior voltage regulation.

[mbopp]

I plan on doing #2 myself. Controller will be mounted in the pass-through. Our son works for a solar company so MP4 connectors & crimping won't be an issue.

[DrewE]

#2 will have less loss because the connection through the long wire is at a lower current level (and higher voltage), so the ohmic loss in the wire will be lower. It's the same basic reason that the power lines on the poles to a house are usually operating at 7500 volts or so, rather than 240 volts.

[Boon_Docker]

Your best choice is #2.

[2oldman]

rich85704 wrote:
2. I'm seeing suggestions to mount an MPPT controller right near the batteries, run two 100W panels (available from Renogy on eBay only) in series, run 24VDC back to the batteries and controller.

Is there less loss by putting the controller nearer the batteries?

Yes, I like #2. Yes, less loss both in 24v and controller near batteries.