Roof solar panels, go 2 50w or 100w

paranoid56

Adventurer
so with all this talk about shade on a panel and all that jazz, what does everybody think?

do 2 50w panels or a single 100w. I have limited space on my roof rack so cant go much larger.

currently i am finishing up my dual battery setup then next up is the 100w of solar with a Victron BlueSolar 75/15 MPPT Charge Controller.
 

spikemd

Explorer
More wattage means more chance of getting more power at any solar level. Always go higher power than you think you need. Just understand that any shade with mono-crystalline panels will drop output tremendously. Better to have panels you can move around to capture the sun all day than hard mounted. Also depends on your house battery to be able to run appliances overnight or multiple days with shady conditions.
 

rayra

Expedition Leader
You could transport-mount a double stack of 100w and fit them with adjustable legs to use them as ground-deployed panels. Or even hinge them together like a portable 100w, but with the panel faces together. Then unfold the top one for a roof mounted double 100w
 

john61ct

Adventurer
Fewer higher-power panels is better than many.

But make sure they're 24V nominal, ideally 40+Voc, can go up to 65.

ideal is one per controller

unless hinging two together for portability, then keep from any shade and wire 2x 20+Voc in series
 

paranoid56

Adventurer
I agree more watts the better, but I have a limited amount of roof space. Will not be doing any portable panels either. so what fits on the roof is what will go in. i may add a way to tilt, but not sure yet. My alt will charge the house battery when driving and the solar when sitting. only charging a H8 AGM 900CCA, 1000CA, 160 Reserve cap, 95amp hrs battery. on that battery it will just be a ARB fridge. I dont normally stay in one place for over a night, but every once and a while i do. This panel is more to help augment the alt charging.
 

rayra

Expedition Leader
Don't see the point of doing solar if it's just going to be a fixed flat mount, because a 1 to 2A trickle is all you'll get, most of the year. Barely one-third of their rated output.
Angling and aiming your panel at the sun makes a huge difference in power collection levels. Same for being able to set them somewhere in full sun, while your vehicle is in the shade or unavoidably partially shaded.


/lol 'connection issues' seriously? A basic parallel wiring diagram and maybe a couple diodes are terra incognito / 'here be dragons' for you?
 

john61ct

Adventurer
Even low amps better than none. Carrying a genny and say 40-60A charger lets you get a bank up to 80-85% quickly (with a high-CAR chemistry) in the morning, but it still needs 4-5 hours to get to 100% Full, which is needed for longevity.

The combination works better than either alone.
 

WOODY2

Adventurer
Don't see the point of doing solar if it's just going to be a fixed flat mount, because a 1 to 2A trickle is all you'll get, most of the year. Barely one-third of their rated output.
Angling and aiming your panel at the sun makes a huge difference in power collection levels. Same for being able to set them somewhere in full sun, while your vehicle is in the shade or unavoidably partially shaded.


/lol 'connection issues' seriously? A basic parallel wiring diagram and maybe a couple diodes are terra incognito / 'here be dragons' for you?
Yeah seriously. Please educate me why having multiple connections would be better, if that be the case use 5 20 watt panels? Wiring diagram and diodes ********** of making a simple task not so simple?
 

dwh

Tail-End Charlie
2 x 50w or 1 x 100w?

Depends on how the panels are made and how many bypass diodes in each panel. Everything else being equal, more bypass diodes is better, so if the 50w each have 2 bypass diodes, then you get a total of 4 and shade causing a single bypass will cut out 25w, wheras if the 100w panel is made with 2 bypass diodes you get a total of 2 and shade causing a single bypass will cut out 50w.


But it also depends on panel voltage and how you rig the panels.

Two 18v 50w, each with 2 bypass diodes, rigged in series and fed through an MPPT controller will have better shade tolerance than a single 18v 100w with 2 bypass diodes, or the two 50s in parallel.


With the 2 18v 50s in series, you get 36v. Shade causing a single bypass drops that to 27v. A 25% loss in power output, but still a high enough voltage to charge a 12v battery. A second bypass and the voltage drops to 18v. A 50% loss in power output, but still a high enough voltage to charge a 12v battery. A third bypass and the voltage drops to 9v, and since that is too low to charge a 12v battery, you've just effectively achieved a 100% loss in power output.


With a single 18v 100w panel with two bypass diodes, shade causing a single bypass drops the voltage to 9v and you've hit 100% loss in power output.


With the two 50s rigged in parallel, a single bypass will drop that one panel to 9v, so a 100% loss in power from that panel, but the second panel still has a high enough voltage, so it's only a 50% loss for the array. A second bypass on that same panel would be irrelevant, but if the second bypass happened on the other panel, then both panels would be at 9v, which would be a 100% loss from the array.

So...

(assuming two bypass diodes per panel)

2 x 50w in series takes three bypasses to hit 100% loss

2 x 50w in parallel takes two bypasses (one on each panel) to hit 100% loss

1 x 100w takes one bypass to hit 100% loss
 

dwh

Tail-End Charlie
Also...

2 x 50 in series a single bypass is a 25% loss

2 x 50 in parallel a single bypass is a 50% loss

1 x 100 a single bypass is a 100% loss
 

calicamper

Expedition Leader
2 x 50w or 1 x 100w?

Depends on how the panels are made and how many bypass diodes in each panel. Everything else being equal, more bypass diodes is better, so if the 50w each have 2 bypass diodes, then you get a total of 4 and shade causing a single bypass will cut out 25w, wheras if the 100w panel is made with 2 bypass diodes you get a total of 2 and shade causing a single bypass will cut out 50w.


But it also depends on panel voltage and how you rig the panels.

Two 18v 50w, each with 2 bypass diodes, rigged in series and fed through an MPPT controller will have better shade tolerance than a single 18v 100w with 2 bypass diodes, or the two 50s in parallel.


With the 2 18v 50s in series, you get 36v. Shade causing a single bypass drops that to 27v. A 25% loss in power output, but still a high enough voltage to charge a 12v battery. A second bypass and the voltage drops to 18v. A 50% loss in power output, but still a high enough voltage to charge a 12v battery. A third bypass and the voltage drops to 9v, and since that is too low to charge a 12v battery, you've just effectively achieved a 100% loss in power output.


With a single 18v 100w panel with two bypass diodes, shade causing a single bypass drops the voltage to 9v and you've hit 100% loss in power output.


With the two 50s rigged in parallel, a single bypass will drop that one panel to 9v, so a 100% loss in power from that panel, but the second panel still has a high enough voltage, so it's only a 50% loss for the array. A second bypass on that same panel would be irrelevant, but if the second bypass happened on the other panel, then both panels would be at 9v, which would be a 100% loss from the array.

So...

(assuming two bypass diodes per panel)

2 x 50w in series takes three bypasses to hit 100% loss

2 x 50w in parallel takes two bypasses (one on each panel) to hit 100% loss

1 x 100w takes one bypass to hit 100% loss
This is what I was thinking. Better shade tolerance with two 50's. The commentery about wiring two vs one is just silly talk. I run two 10watt panels and I'm pretty happy with the set up.
 

dwh

Tail-End Charlie
Thanks for the enlightenment.
No worries. And it doesn't mean rayra was right either. He was talking about external diodes, which is wrong; the diodes are inside the solar panel's connection box and have nothing to do with wiring up the system. :)

Also, if you count the connections, series has less.
 

JCDriller

Adventurer
2 x 50w or 1 x 100w?

Depends on how the panels are made and how many bypass diodes in each panel. Everything else being equal, more bypass diodes is better, so if the 50w each have 2 bypass diodes, then you get a total of 4 and shade causing a single bypass will cut out 25w, wheras if the 100w panel is made with 2 bypass diodes you get a total of 2 and shade causing a single bypass will cut out 50w.


But it also depends on panel voltage and how you rig the panels.

Two 18v 50w, each with 2 bypass diodes, rigged in series and fed through an MPPT controller will have better shade tolerance than a single 18v 100w with 2 bypass diodes, or the two 50s in parallel.


With the 2 18v 50s in series, you get 36v. Shade causing a single bypass drops that to 27v. A 25% loss in power output, but still a high enough voltage to charge a 12v battery. A second bypass and the voltage drops to 18v. A 50% loss in power output, but still a high enough voltage to charge a 12v battery. A third bypass and the voltage drops to 9v, and since that is too low to charge a 12v battery, you've just effectively achieved a 100% loss in power output.


With a single 18v 100w panel with two bypass diodes, shade causing a single bypass drops the voltage to 9v and you've hit 100% loss in power output.


With the two 50s rigged in parallel, a single bypass will drop that one panel to 9v, so a 100% loss in power from that panel, but the second panel still has a high enough voltage, so it's only a 50% loss for the array. A second bypass on that same panel would be irrelevant, but if the second bypass happened on the other panel, then both panels would be at 9v, which would be a 100% loss from the array.

So...

(assuming two bypass diodes per panel)

2 x 50w in series takes three bypasses to hit 100% loss

2 x 50w in parallel takes two bypasses (one on each panel) to hit 100% loss

1 x 100w takes one bypass to hit 100% loss
I'm in the process of setting up 200w on the roof rack of my 4R and am currently waiting on the 100w Renogy Eclipse panels to come back in stock so my backorder will ship. These panels will be on a slide out under my roof rack, it will slide out using a linear actuator when the engine is turned off. I will have them set up so they can be removed and used remotely when needed. However, after reading your explanation, I'm considering canceling that order and going with 4 50w Renogy Eclipse panels wired in series. I didn't realize the difference smaller panels in series could make when exposed to shade. Thank you so much for the explanation!
 
Top