Basic but good quality and reliable solar system design

[Mwilliamshs]

I have a Fullsize Ford Extended Body Penthouse camper van build underway (think big westfalia) and when finished I plan to hit the PanAm Hwy for a year or so. I'm beginning to ponder solar solutions and come here seeking advice. If anything I say or my math is questionable please let me know. I do not want a system that requires constant monitoring or maintenance and I want quality components I can trust far into foreign lands. I also don't want to waste money on useless features or components I don't need.

Loads will be a TF65 fridge at about 25AH/day, a 12v water pump I'm guessing to be 20 minutes at 4 amps so ~1.33AH/day, Fantastic vent for cooking (minimally) sleeping, venting etc and I don't sleep well hot so I'm budgeting 10 hours at 3 amps so 30AH/day, plus LED lighting, DC-DC laptop and smartphone charging, a DC tv, etc. Not set on all my appliances yet but not planning to rough it too extremely and I plan to keep the van a GOOD long while and will transfer appliances to the next one when the time to move on comes (van's a 1989 so minimal value other than its SMB PH top and what I build in). I anticipate about 85AH/day on the high-side. All the numbers above are rough estimates fudged up slightly to not be underpowered in the end.

Taking overplanning a step further, let's fudge 85 to 105AH/day. My female companion isn't likely to conserve well, especially initially. Add 20% for solar system inefficiency and I'm looking to have 130AH of solar charging completed in 4 hours of sunlight. Average peak sunlight hour info for Central America appears in short supply but Mexico is about 5ish most places and I'll likely be on beaches and mountains and further south obviously so this is another conservative guess. 130AH/4H = 32.5 amps of solar panel current to meet my goals. 32.5 amps/100 watt panels = 4 (8.33 amps each [100/12]) while 125w panels (10.42 amps[125/12]) theoretically do it with just 3. I like 3 better than 4.

I will likely NOT make all my solar purchases from Solar Boulevard but their site is easy to use and they sell everything I want so I'll share a shopping list I've compiled from there. Again, if you know more about this stuff than I do please speak up.

Solar Cynergy PV-SC140J12 140wp panels are ~40"x40"x1.5" so 3 of them should fit easily on my EB PH I think. They're rated for 21 Voc @ 8.4 Isc and 17 Vmp @ 8 Imp. I'd connect 3 of them to a Morningstar Tristar 45 amp PWM charger. Chosen for good reviews (read: rave), and its ability to bulk charge to 14.8v, as Trojan recommends. I'll use it with temp and volt sensing connected and do my monitoring with its optional remote display (so I can put it closer to the batteries but still check on it easily) and also use a Bogart Eng. Trimetric 2020.

Total cost at current prices = $800

I do not feel I'd benefit sufficiently from a MPPT controller. Am I wrong?

All this gets connected to 2 Golf Cart batteries, 6v each, 225AH. $250 total, give or take.

So $1,200 should buy panels, controller, monitor, batteries, cabling, etc without much haggling or bargain hunting. (I'll do lots of both)

I expect to add an inverter but likely won't need it much, as everything I plan to add will be DC unless there's a very good reason not to. I'm open to suggestions on inverters. I doubt a full sine wave model gets put in.

 

[Joe917]

How long will you drive each day? Will you be driving most days or will you stay in one spot boondocking for more than two days at a time often? Your battery bank size and type looks spot on.Solar looks more than enough. You can't go wrong with Morningstar charge controllers. you don't need MPPT for a system as small as yours.

 

[Mwilliamshs]

Driving will likely vary from 8+ hours a day to only firing the engine as needed for hot showers (heat exchanger/coolant loop). I want to be able to park in partial sun, leave the fridge running (but nothing else) and hike away from the van for a couple nights, worry free.

 

[dwh]

Nice job on roughing out the math.

Only thing I see missing, is that it's normal when estimating to also derate the solar - they put out less when hot, and being black and glass, they are usually hot. So figure you need 100ah + 20% to top off the battery - and also figure that your solar will only put out 80% of its rated output on average.

And that's on PV that is tilted toward the sun...for flat mount it could be worse. This is partially offset by the fact that you will get some amps before and after the peak 4 hours. Figuring 80% average output puts you in the ballpark.

A bunch of solar engineers over on the NAWS forum a few years ago hashed out the cost/benefit of MPPT to the penny - the consensus was it wasn't worth the extra expense for an array of less than 200w, but over 200w and the extra harvest would cover the extra cost. Morningstar, Midnite Solar and Rogue are all TOP quality.

Morningstar SureSine inverter is awesome, and all solid-state, but only 300w continuous rating (though it can do 600 if you can keep it cool enough). It can also use Morningstar's RM-1 remote.

Depending on how the PV module (solar panel) is constructed - ANY shade, even only on a couple of cells, could cut the module's output by 1/3, 1/2, 2/3 or even 2/2 or 3/3 (i.e., to nothing). DON'T *plan* on getting ANYTHING in partial shade. You might, you might not.

Driving is good, but your vehicular voltage regulator likely does not go to 14.8v - so you might consider a DC-DC charger, though if you are driving in good sun, the solar will push it up to 14.8v anyway so it might not be needed.

 

[Mwilliamshs]

Nice job on roughing out the math.

Only thing I see missing, is that it's normal when estimating to also derate the solar - they put out less when hot, and being black and glass, they are usually hot. So figure you need 100ah + 20% to top off the battery - and also figure that your solar will only put out 80% of its rated output on average.


Depending on how the PV module (solar panel) is constructed - ANY shade, even only on a couple of cells, could cut the module's output by 1/3, 1/2, 2/3 or even 2/2 or 3/3 (i.e., to nothing). DON'T *plan* on getting ANYTHING in partial shade. You might, you might not.

I did derate the solar 20%. Uh, twice, kinda. In my opinion an exaggeration of load is a reduction in generation. So: 85 -> 105 (85/105 = .80) and 105 -> 130 (105/130 = .80)

Taking overplanning a step further, let's fudge 85 to 105AH/day....Add 20% for solar system inefficiency and I'm looking to have 130AH of solar charging completed in 4 hours of sunlight.

How would you expect shade to impact the panels listed? Here: http://www.solarblvd.com/Solar-Pane...40-Watt-12-Volt-Solar-Panel/product_info.html How could I identify panels of a superior construction, with regard to partial shading?

I mention parking in partial shade and walking away only as a worst case scenario and yet with fridge-only-loads, 25AH, even with NO sun/full shade, that 225AH battery bank should be good for over 7 days before 80% maximum discharge (absolutely would never go that low intentionally, but Trojan says it's not fatal) considering it maths out to 7.2 days (225 x .08 = 180, and 180/25 = 7.2) and the fridge door won't be opening at all in an unoccupied van (so actually <25AH/day consumption). Thanks for input tho and please share info on panel types and shading impact :drool:

 

[lysol]

My Monocrystalline panel drops by about 90% in any type of shade. Amorphous does better in partial to full shade than monocrystalline/polycrystalline panels. Amorphous panels however come with the cost of greater size per watt which isn't so great when you don't have a lot of roof realistate.

Do you know the "Solar Irradiance" for the area's you wish to travel with the solar panel flat?

 

[Mwilliamshs]

My Monocrystalline panel drops by about 90% in any type of shade. Amorphous does better in partial to full shade than monocrystalline/polycrystalline panels. Amorphous panels however come with the cost of greater size per watt which isn't so great when you don't have a lot of roof realistate.

Thanks. I would also expect the potential for large performance differences in the way the cells themselves were connected to one another within the panels. If, for example a 4 cell x 9 cell panel were wired as 4 rows of 9 in series it'd be better to shade a long side, 9 cells, (disabling 1 row) than a narrow end, 4 cells, (disabling all rows). Is this accurate? Are the cells of all panels interconnected the same way?

Do you know the "Solar Irradiance" for the area's you wish to travel with the solar panel flat?

No. I've looked and only found solar irradiance numbers for parts of Mexico, and what I've found are very similar to, but better than, Texas. Given that I'll be getting steadily closer to the equator for half the trip and since beaches are typically fairly flat and offer parking as you please (you can turn 90° to the sun, in a spot without obstructions, for example) I expect the figures to be quite good, but simply assume they'll be no worse than at home (Arkansas), roughly 4.5 kwh/m2/day. Not willing to count those eggs till they hatch, so to speak, but think I've got good odds of a productive hen.

 

[DiploStrat]

Short and Long Answers

For the short answer, I would shoot an e-mail to these folks as they have just done the route you want to take and have a rather modest solar set: http://songoftheroad.com

The long answers follow. I have 5x100w panels connected to 4x300Ah 6v batteries, charged with a Blue Sky MPPT controller and 2x125A alternators using the stock GM regulator/controller.

-- My panels, which I believe are fairly typical modern panels, consist of 32 cells wired in series. The five panels themselves are wired in parallel. Grossly, lose one cell and you have lost most of a panel. Lose one panel and the other four are unaffected. http://www.amsolar.com/home/amr/page_13_20/gs100_solar_panel.html

-- 5x100w panels will peak at about 30A of charge in full sun, multiplied by the number of hours you can get it. In the southwest of the US, that easily exceeds 100Ah per day. In the summer, in the east, with leaves on the trees, you can easily drop to between 1 and 5A of charge.

-- Properly wired, the alternators can easily deliver over 150A of charge, but the trick is that they will not do so all day. Batteries will take the greatest charge when they are about 50% discharged and the charge rate drops when they exceed 80% charged. It can be a real bear to get the last 10%. Alternators are probably essential for bulk/boost charging, but you will rarely, if ever, drive long enough to get a big (200+Ah) battery bank through the absorb stage all the way to float.

The good news is that 3-6 hours of driving will probably get you to 80+% charged without difficulty. Thereafter, it is a matter of time, lots of time. (Read up on the absorb/accept stage of charging.) Of your solar kit will give you5 to 10A for the last six hours of the day, you may be fine. If not, you are looking for shore power at least once a week if you want to get your batteries to a true 100%. (And, for a variety of reasons, you do.) Lifeline, for example, specs two hours of absorb AFTER you reach full charge. Most of us double that time in the real world.

I go through 125Ah per day, running a 5 cu. ft. Nova Kool refrigerator, a composting toilet, diesel heat, electric cooking, and various fans, computers, etc. Take away the electric cooking and 75 - 100 Ah seems reasonable. I typically see 2 - 5Ah as "background noise" discharge.

Remember, M. Peukert loves to play havoc with small battery banks and big discharges. So my free advice is this:

-- Optimize your alternator charging. Trojan open cell batteries want some of the highest charging voltages around. This means an alternator system that will run at about 15v and big wires, over 100mm2 to connect your camper batteries to your starter batteries.

-- More, rather than less, solar. I favor more, smaller panels to limit the impact of shading. (And, I assume, that you have designed your roof to be as "clean" as possible. Watch the positioning of antennae, etc.)

-- More, rather than less, battery capacity. Peukert rules and the common battery rating is for a 20 HOUR discharge rate. I routinely pull 150A, so the impact on the batteries is proportionately larger.

-- Make sure you have a decent shore power charger somewhere. My truck is designed to never need shore power, but I wouldn't want to be without it in an emergency.

Hope this is useful and have a great trip.

 

[dwh]

I did derate the solar 20%. Uh, twice, kinda. In my opinion an exaggeration of load is a reduction in generation. So: 85 -> 105 (85/105 = .80) and 105 -> 130 (105/130 = .80)

It's normal to A) add 20% when figuring out how much you'll need to top off the battery (battery inefficiency), and B) add another 20% when figuring how much your solar will supply (solar inefficiency). If you've covered both, then how you got there doesn't much matter.

How would you expect shade to impact the panels listed? Here: http://www.solarblvd.com/Solar-Pane...40-Watt-12-Volt-Solar-Panel/product_info.html How could I identify panels of a superior construction, with regard to partial shading?

Don't have time at the moment to research the listed panels. Gotta run in a minute. If they have a single string of 32-36 cells with bypass diodes that cut out part of the string, then they'll have more loss with partial shading than panels with 2 or 3 strings of 32-36 cells with bypass diodes that cut out an entire string.

I mention parking in partial shade and walking away only as a worst case scenario and yet with fridge-only-loads, 25AH, even with NO sun/full shade, that 225AH battery bank should be good for over 7 days before 80% maximum discharge (absolutely would never go that low intentionally, but Trojan says it's not fatal) considering it maths out to 7.2 days (225 x .08 = 180, and 180/25 = 7.2) and the fridge door won't be opening at all in an unoccupied van (so actually <25AH/day consumption). Thanks for input tho and please share info on panel types and shading impact :drool:

180/25? There are 24 hours in a day, not 25. No, it's not fatal to go down to 80% DoD - but it cuts down the number of cycles in the battery's life. Most deep cycle batteries, if you take them down to 50% normally, will have a life of around 1000 cycles. The deeper you go, the less cycles you'll get.

 

[dwh]

Are the cells of all panels interconnected the same way?

Yes.

All cells put out around .5v under load so all panels are made of strings of cells wired in series. For a "12v nominal" panel they'll wire it to produce between 16v and 18v Vmp, depending on how many cells in the string (32, 34 or 36). Some panels are made with multiple strings of smaller cells, rather than a single string of larger cells.

Those are more shade tolerant because the bypass diode cuts out a string, thus not lowering the output voltage of the entire panel. With a single string and bypass diodes that cut out half the string, then a bypass on a diode will drop the panel voltage by half, if a single string with 3 diodes a bypass on 1/3 of the string will cut the panel voltage by 1/3.

If the panel voltage drops below 14v, then it won't contribute to battery charging.

 

[Mwilliamshs]

It's normal to A) add 20% when figuring out how much you'll need to top off the battery (battery inefficiency), and B) add another 20% when figuring how much your solar will supply (solar inefficiency). If you've covered both, then how you got there doesn't much matter.

To clarify, using your terms: A) 85 -> 105 and B) 105 -> 130

180/25? There are 24 hours in a day, not 25. No, it's not fatal to go down to 80% DoD - but it cuts down the number of cycles in the battery's life. Most deep cycle batteries, if you take them down to 50% normally, will have a life of around 1000 cycles. The deeper you go, the less cycles you'll get.

What I said was "(225 x .80 = 180, and 180/25 = 7.2)." What I meant was the battery bank total amp hours (225AH), x .80 to find 80% of that number = 180AH, which is 80% of battery bank total amp hours, which is the absolute lowest Trojan suggests these batteries can be drawn and survive and 180AH in batteries / 25, which is the anecdotal daily AH draw of my fridge = 7.2 days. Again, this is an extreme case and not something I'd ever allow intentionally but it does illustrate the van left without solar exposure should keep food cold and batteries alive for say 48 hours without worry.

To divide the total available AH, 180, by hours in a day, 24, would give...uhm, the number of AH you'd have to draw per hour to deplete the battery bank to 20% remaining power in a 24 hour period I guess...but I don't know why that number would be useful at all and it certainly isn't germane to my point of how long the batteries could theoretically power just the fridge without charging. This calculation is of course flawed because these are STC #s on the battery specs and anecdotal #s on the fridge and none of them include the "phantom" or "ghost" loads present in the system.

 

[dwh]

the common battery rating is for a 20A discharge rate

Typo - should say 20 hour discharge rate.

 

[dwh]

To clarify, using your terms: A) 85 -> 105 and B) 105 -> 130



What I said was "(225 x .08 = 180, and 180/25 = 7.2)." What I meant was the battery bank total amp hours (225AH), x .08 to find 80% of that number = 180AH, which is 80% of batter bank total amp hours, which is the absolute lowest Trojan suggests these batteries can be drawn and survive and 180AH in batteries / 25, which is the anecdotal daily AH draw of my fridge = 7.2 days. Again, this is an extreme case and not something I'd ever allow intentionally but it does illustrate the van left without solar exposure should keep food cold and batteries alive for say 48 hours without worry.

To divide the total available AH, 180, by hours in a day, 24, would give...uhm, the number of AH you'd have to draw per hour to deplete the battery bank to 20% remaining power in a 24 hour period I guess...but I don't know why that number would be useful at all and it certainly isn't germane to my point of how long the batteries could theoretically power just the fridge without charging. This calculation is of course flawed because these are STC #s on the battery specs and anecdotal #s on the fridge and none of them include the "phantom" or "ghost" loads present in the system.

Relax - I was in a hurry - AM in a hurry - and read it as you were calculating days. Days would be 24 hours. Gotta run, have fun.

 

[Mwilliamshs]

Super helpful and informative post, DiploStrat! THANKS

The long answers follow. I have 5x100w panels connected to 4x300Ah 6v batteries, charged with a Blue Sky MPPT controller and 2x125A alternators using the stock GM regulator/controller.

:drool:

-- My panels, which I believe are fairly typical modern panels, consist of 32 cells wired in series. The five panels themselves are wired in parallel. Grossly, lose one cell and you have lost most of a panel. Lose one panel and the other four are unaffected.

http://www.amsolar.com/home/amr/page_13_20/gs100_solar_panel.html

I thought most panels were 36 cells? Maybe I'm looking at old technology.

-- 5x100w panels will peak at about 30A of charge in full sun, multiplied by the number of hours you can get it. In the southwest of the US, that easily exceeds 100Ah per day. In the summer, in the east, with leaves on the trees, you can easily drop to between 1 and 5A of charge.

Adds up. 500w @ 14.8v = 33.x amps minus efficiency losses, ~30amps. What gauge wire connects your panels to controller and controller to batteries? How long are the runs? I ask because your losses are minimal and your cabling is probably worth copying.

-- Properly wired, the alternators can easily deliver over 150A of charge, but the trick is that they will not do so all day. Batteries will take the greatest charge when they are about 50% discharged and the charge rate drops when they exceed 80% charged. It can be a real bear to get the last 10%. Alternators are probably essential for bulk/boost charging, but you will rarely, if ever, drive long enough to get a big (200+Ah) battery bank through the absorb stage all the way to float.

True, alternators are a good charger for raising DoD's of 50% to 80% but it takes prolonged periods of 14.8 + substantial amps to get over bulk charging. Since alternators taper off amperage as voltage climbs, they are more effective at lower states of charge and not good at finishing the process.

The good news is that 3-6 hours of driving will probably get you to 80+% charged without difficulty. Thereafter, it is a matter of time, lots of time. (Read up on the absorb/accept stage of charging.) If your solar kit will give you 5 to 10 A for the last six hours of the day, you may be fine. If not, you are looking for shore power at least once a week if you want to get your batteries to a true 100%. (And, for a variety of reasons, you do.) Lifeline, for example, specs two hours of absorb AFTER you reach full charge. Most of us double that time in the real world.

Noted.

I go through 125Ah per day, running a 5 cu. ft. Nova Kool refrigerator, a composting toilet, diesel heat, electric cooking, and various fans, computers, etc. Take away the electric cooking and 75 - 100 Ah seems reasonable. I typically see 2 - 5Ah as "background noise" discharge.

You have more fridge for sure and gizmos than me I think. Does your diesel heat, as I suspect, have electric fuel pump(s), glow plug/ignition source, a blower motor, and electric thermostat? When the time comes to prepare for cold weather camping I'll likely use a 12v mattress warmer, heavy sleeping bag, and likely a propane catalytic heater, which uses no electricity but is less safe and less convenient than a forced-air furnace. The mattress warmer is surprisingly (IMO) efficient. I've read of ~5 amps (legit sources IMO, HandyBob, etc) when turned up enough to feel the heat but throttled for efficiency.

Remember, M. Peukert loves to play havoc with small battery banks and big discharges. So my free advice is this:

-- Optimize your alternator charging. Trojan open cell batteries want some of the highest charging voltages around. This means an alternator system that will run at about 15v and big wires, over 100mm2 to connect your camper batteries to your starter batteries.

Yes, Peukert is a study-up subject. I've learned a lot but I'm sure there's more to go. Designing to require <7' of cable from start battery (passenger side, underhood) to house bank (as far forward as possible, considering frame rail boxes). This will be 2/0 or better. Haven't done the math on voltage drops but I generally calculate actual and go one size heavier. I only have 1 start battery (6 cyl engine) and will not oversize it. This is to keep its charging needs to a minimum and allow more alternator capacity to be dedicated to the house bank. Its loads will consist only of the van's OE systems whilst running (which will also be tailored for efficiency, LEDs, etc) so excess battery size there seems wasteful. There is space underhood for a second battery (would have to add a tray but there's a simple, established method for this era Ford van) but I'll likely not use the space for that. I'll have a single 130 amp alternator, Ford 3G.

-- More, rather than less, solar. I favor more, smaller panels to limit the impact of shading. (And, I assume, that you have designed your roof to be as "clean" as possible. Watch the positioning of antennae, etc.)

-- More, rather than less, battery capacity. Peukert rules and the common battery rating is for a 20A discharge rate. I routinely pull 150A, so the impact on the batteries is proportionately larger.

-- Make sure you have a decent shore power charger somewhere. My truck is designed to never need shore power, but I wouldn't want to be without it in an emergency.

Roof will have only solar and the Fantastic vent. Hoping to get the vent far back and the panels far forward so its shadow isn't an issue even when the sun is to the sides of the van. I'll pick a good quality shore power charger of the highest amp rating feasible. I've shopped these a bunch and think I've got a compact 60 amp industrial piece selected.

Hope this is useful and have a great trip.

Very useful and much appreciated. :Wow1:

 

[DiploStrat]

32 vs. 36? No idea, I simply went with what AM Solar sells. The core of my system is their SunRunner40 MPPT, the largest system they sell before going to a Morningstar controller. http://www.amsolar.com/home/amr/page_234_68/sunrunner_signature_40mppt4pro_core.html

I think that you will find that your alternator is the fastest charger that you have. As you noted, however, the charge rate tapers off and, as I stressed, the last 50Ah or so can be hard. 6v camper batteries are way too large to go under the hood. Mine are at the frame level, but rather further back than I would like. I run 2x1/0 cables which is grossly 200A over a 40 foot round trip. That is 100mm2 of copper. I would not go smaller.

I would not bother to upside my starter battery, in fact, If I could, I would reverse the common logic. That is, I would attach the alternators directly to the camper batteries and simply have a small branch circuit to the starter battery. (Even discharged 50% my camper battery is still twice the size of my starter battery.) Can't do this because of vehicle warranties, etc., so I do the next best thing. I also recommend an intelligent relay and a manual override switch.

-- The intelligent, bidirectional relay assures that, when you do have solar, it is shared with the starter battery.

-- The manual override can be handy when you find it hard to start your engine at 15,000 feet. Modern, fuel injected engines are better, but in the old days I had to take off the air cleaner and hold the automatic choke open or the beast would not start. (Had to use the clutch to stop it as well as it would diesel forever on near water octane levels.)

Based on years freezing my ankles off on the Altiplano, I would urge that you pack long undies and have a good heating system. This from someone who didn't and watched the water freeze inside his tent. The two classic errors of overlanding are:

-- Selling your sand ladders after the Sahara. You need them for Congo mud.

-- Thinking that South America is warm, after months on the beach in Central America.

The Altiplano is bone chillingly cold. Ironically, it can be worse in summer as it is cloudy and rainy. The winter tends to be dry and sunny. You will learn why people worship the Inti Raymi. :Wow1: