Solar Sizing

[BumpsAcre]

I’m trying to understand the numbers better on solar. Much appreciated if one of you experts can check my thinking. I’ve got standard 2020 Classic set up: three 90 watts panels on roof and two 100 amp-hr AGMs. I see that each panel can generate about 15 volts. 90 / 15 = 6 amps per hour times 3 panels = 18 amps per hour charging. If I’ve got my batteries down to 50% I need 100 amp-hrs to fully charge. 100 / 18 = 5.5 hours of good charging needed to refill batteries. Say I’m using 5 amps per hour while charging. Now I’m up to nearly 8 hours to fully charge.

I realize the solar voltage output varies. Where I’m going is that I could well utilize 200 watts of additional solar panels to ensure I fully charge batteries. Portables that can be angled would be a bonus. Where I’m going is ability to offshore for multiple days, with minimal generator use. Make it through eves and early morn on batteries. No AC, fridge on gas, mainly just lights, TV, water pump. Many thanks to anyone’s feedback on my numbers.

[dznf0g]

I think you have some volt and amp terminology mix-ups in your post. Most panels fall into the 18 - 21 volt raw output range. It will vary with sun intensity, but generally speaking you will have some net amp output to your coach down to around 15V raw panel output.
A quality MPPT solar controller takes that raw excess voltage and scavenges amperage out of it...in addition to the amperage output from the cells.
A 90 watt panel, in conjunction with an MPPT controller will put out around 5 amps, realistically. Solar noon...maybe 6 amps.
3 X 5 = 15 Ah on a good day.

IMO, a solar suitcase to supplement, as well as chase the sun around on a shady site is a good idea.

I have 200 watts on the roof and a 160 watt suitcase. That is enough for our consumption lifestyle on 90% of off grid days. Successive mostly cloudy to cloudy days...out comes the generator for a couple hours to boost my starting point for solar.

It all really depends on your "true" consumption, site configuration and weather.

[SilverWind]

Mine is a short and simple answer. I had A&M Solar in Springfield, OR install as many panels that would fit on my last two Airstreams. My current 2017 25 FB has 500 watts. I very rarely need to draw lower than 80 percent of the two AGMs' capacity. They will charge well in a variety of conditions, shade, clouds etc. As long as you have the correct wiring size and controller, go for the max.

[dznf0g]

Too late to edit: That should be 15Ah/hr...but that's at a solar noon rate. I'd figure 3.5 to 4Ah/hr net overall on a fully sunshine day (per panel).
Other factors: Parallel or series or series/parallel system? Wire gauge? number of physical connections in circuit? Efficiency of controller?

[dznf0g]

I'll share my consumption numbers with you, but I suspect that a 2020 Classic has A LOT more parasitic load on it than my now antique 2007 Classic. If I am really conserving, I have LED lighting, fridge board, water pump cycles, Hydraulic brake actuator keep alive circuit, propane detector, water heater board, occasional bathroom fan operating, battery monitor, interior fridge fan, trio of exterior fridge compartment fans, ARP fridge temp protector.
I pull the radio faceplate off, turn off thermostat.

In this max conservation mode, I consume 38 to 40Ah/day.

[TouringDan]

I believe getting a 200 watt solar suitcase is a no brainer. It allows you to be better able to find the sun particularly in the winter when you can angle the panels. I can usually figure on about 25-30 Ah per day from my 200 watts of portable panels.

You really can never have too much in terms of solar panels.

Dan

[BumpsAcre]

Many thanks for feedback. Very helpful. I have a plug in for an extra panel near the battery box and so I guessing my wiring and Blue Solar controller will handle another panel. I’ll have to check the specs. I believe the panels all operate in parallel from the diagram in the manual, all connecting to roof top junction box and breaker.

[smsasf]

FYI, The Zamp portable wiring plug is compatable with your Zamp port of course. I initially purchased a Zamp 230W portable but when I took it out of the case I found that at its almost 50 lb weigh, and given its length x width x thickness dimension, it was rather unwieldy. So I sent it back and got the 180W which is only around 35 lb and a bit smaller in length and width. Easier to handle. Also, after I took out the Atkinson charge controller and replaced with a Victron 100/30 I found that using the portable with its own charge control is not a problem (there has been lots debate on various threads about whether the two charge controllers work together). Working together might not be the best choice of words. When my 2 Zamp 90W rooftop panels were in partial shade I could read that my Victron 100/30 showed they were working at an “absorb” level, not at float. When I hooked up the Zamp portable, placed it in direct sun, its charge controller quickly showed it was pushing 14.4 volts. Then after a several minutes when I looked at the Victron readout it showed the charge had gone to float level. So my perception is they do “work” together, or at least the Victron recognizes the battery is getting charged from another source as well.

[BumpsAcre]

Originally Posted by smsasf

FYI, The Zamp portable wiring plug is compatable with your Zamp port of course. I initially purchased a Zamp 230W portable but when I took it out of the case I found that at its almost 50 lb weigh, and given its length x width x thickness dimension, it was rather unwieldy. So I sent it back and got the 180W which is only around 35 lb and a bit smaller in length and width. Easier to handle. Also, after I took out the Atkinson charge controller and replaced with a Victron 100/30 I found that using the portable with its own charge control is not a problem (there has been lots debate on various threads about whether the two charge controllers work together). Working together might not be the best choice of words. When my 2 Zamp 90W rooftop panels were in partial shade I could read that my Victron 100/30 showed they were working at an “absorb” level, not at float. When I hooked up the Zamp portable, placed it in direct sun, its charge controller quickly showed it was pushing 14.4 volts. Then after a several minutes when I looked at the Victron readout it showed the charge had gone to float level. So my perception is they do “work” together, or at least the Victron recognizes the battery is getting charged from another source as well.

Thanks I sent a note to Airstream on why the portable plug is not routed thru the Blue Solar controller(appears that way in the wiring diagram)? Will see what they say. Guessing it is because most portables have their own integrated controllers.

[gator.bigfoot]

Originally Posted by BumpsAcre

Thanks I sent a note to Airstream on why the portable plug is not routed thru the Blue Solar controller(appears that way in the wiring diagram)? Will see what they say. Guessing it is because most portables have their own integrated controllers.

I would hope so, since when you're adding other panels they will most likely be of different specs and then using the same controller would be an issue. Always use another controller when using mismatched solar panels. But make sure you get a decent controller. The ones that come prepackaged with portable solar panels are most likely junk. There's more junk out there in the low power solar world than good stuff.

Also, running down your batteries down to 50% on a regular basis is not good for them. Get more batteries.

[dznf0g]

Originally Posted by gator.bigfoot

I would hope so, since when you're adding other panels they will most likely be of different specs and then using the same controller would be an issue. Always use another controller when using mismatched solar panels. But make sure you get a decent controller. The ones that come prepackaged with portable solar panels are most likely junk. There's more junk out there in the low power solar world than good stuff.

Also, running down your batteries down to 50% on a regular basis is not good for them. Get more batteries.

A long time ago, Lewster (IIRC) stated that as long as the panels are of the same cell type and they are within 1V of each other with regard to the panel raw output, that they are fine to mix. I have two renogy 100 watt panels on the roof and a Zamp 160 watt suitcase. They play very well together utilizing one Victron controller.

[smsasf]

Originally Posted by BumpsAcre

Thanks I sent a note to Airstream on why the portable plug is not routed thru the Blue Solar controller(appears that way in the wiring diagram)? Will see what they say. Guessing it is because most portables have their own integrated controllers.

The trailer A-frame Zamp port typically is wired straight to the battery. Is on my 2020 Bambi 20’. And most portables, and certainly the Zamp, have their own charge controller. My wiring diagram only shows rooftop solar panel hub being wired internally. But as I said, at least for the Victron 100/30 it at least seems to see what is going on with the battery when you hook up the portable solar. Whether that can be construed as the two charge comtrollers “working together” has been debated in older posts.

[gator.bigfoot]

Originally Posted by dznf0g

A long time ago, Lewster (IIRC) stated that as long as the panels are of the same cell type and they are within 1V of each other with regard to the panel raw output, that they are fine to mix. I have two renogy 100 watt panels on the roof and a Zamp 160 watt suitcase. They play very well together utilizing one Victron controller.

That's because they are closely matched. I was talking about panels that are not that closely matched. One volt is a very acceptable mismatch. I also have mismatched panels that are within 1 volt. Of course if you hook in parallel you want to watch your voltage, but in series you need to look at current.

[biznitch15]

The victron is an MPPT controller as you all know. But the portable zamp Controller is PWM. Seems to me that “working” together is more like saying that they recognize each other but still independently charge the batteries in their own respects. I’m not an electrician but I would assume that there can be a way to re-wire the front zamp port through the MPPT controller so that it’s a better charging system. I would also assume you Would need to keep the panel sizing the same as to the roof panels.

[lewster]

When ever folks want a portable solar option added to the systems I install, I remove the Zamp plug-in option and replace it with a couple of input plugs and a switch that run directly to the Victron solar controller. They then purchase their portable panels with no controller (cheaper). A better option!

[ASWinos]

Originally Posted by lewster

When ever folks want a portable solar option added to the systems I install, I remove the Zamp plug-in option and replace it with a couple of input plugs and a switch that run directly to the Victron solar controller. They then purchase their portable panels with no controller (cheaper). A better option!

Thanks, Lewster. Going through one charge controller means you don't have multiple charge controllers trying to do different things. I assume you are connecting these portables in parallel which means it would be best if the voltages of the portable panels are closely matched to the rooftop panels strings, correct? You would also want to have the switch be off until you plug in the portable and then turn the switch on?

[lewster]

Originally Posted by ASWinos

Thanks, Lewster. Going through one charge controller means you don't have multiple charge controllers trying to do different things. I assume you are connecting these portables in parallel which means it would be best if the voltages of the portable panels are closely matched to the rooftop panels strings, correct? You would also want to have the switch be off until you plug in the portable and then turn the switch on?

Yep, sounds about right!

[fiftysafari]

I am also trying to get a handle on solar sizing.

Looking at the Trojan battery site, I see a recommendation to have the amps from the panels to be 10 to 20% of the battery amp hour rating.

I have purchased a Newpowa monocrystalline 210W panel kit that puts out 12.48 amps, and I was considering a 225 Ah battery which according to Trojan should be supplied with at least 22.5 amps from the panels.

Does this mean I should have an additional 210W panel putting out an additional 12.48 amps?

Do I add the amperage from the two panels, so 12.48 + 12.48 = 24.96 amp output?

I was hoping to get by with one panel.

[ROBERT CROSS]

Originally Posted by TouringDan

I believe getting a 200 watt solar suitcase is a no brainer. It allows you to be better able to find the sun particularly in the winter when you can angle the panels. I can usually figure on about 25-30 Ah per day from my 200 watts of portable panels.

You really can never have too much in terms of solar panels.

Dan

^
X2

We have three Seasons with two 180w Zamp Suitcase panels charging thru the 7pin umbilical...KISS werks well for us.

Bob
🇺🇸

[Shiny16]

Originally Posted by TouringDan

I believe getting a 200 watt solar suitcase is a no brainer. It allows you to be better able to find the sun particularly in the winter when you can angle the panels. I can usually figure on about 25-30 Ah per day from my 200 watts of portable panels.

You really can never have too much in terms of solar panels.

Dan

Just remember that a 200 watt portable is about the same weight as a Honda eu2000. Just a consideration that depends on different setups.