Solar power while stationary, not driving


#1

Hello everyone. I’m new to the forum and I have a question I haven’t seen here or anywhere else.

I am considering a solar setup that would include mounted solar panels (not portable or removable) BUT the panels would not be exposed to the sun and charging while driving. I expect to be charging off the alternator while driving, which is far more efficient (I understand). But once I stop driving, or if I am stationary for a few days or longer, I expect to charge off the solar panels.

The panels would be mounted either on the back of the vehicle, and pulled up and out on a bracket mechanism, or mounted on the roof underneath kayaks, and pulled out to the side when parked.

The primary question is: Does it make sense to think about solar charging as being a stationary function IF you are charging off the engine/alternator while driving?

A second question: Has anyone else done something like this? I think portable setups are similar (in concept they are the same… charging only while stationary), but has anyone mounted solar panels as I am describing?

Thanks!


#2

Greetings!

A cheapie generator and a regular battery charger are much cheaper and much more efficient than solar panels.

Solar panels have too many negatives, they’re expensive, they don’t charge the batteries correctly and kill them quickly, they don’t work well in the winter when you really need the power, they don’t work at night, and parking in the sun during the summer is cruel and unusual punishment.

I’m pretty frugal with my power usage, no power hog 12v fridge, no powered roof vents, no powered furnace, etc. I charge up all my rechargeables while driving, and only recharge them while parked if necessary. I don’t use an inverter for anything. My house battery will last up to a week, and so will my starting battery.

My starting battery is also a deep cycle battery, and I have low voltage cut offs on both my house battery and my starting battery. This makes sure you never drain your battery too deeply, and in the case of my starting battery, still leaves me plenty of power to start my van.

Don’t get me wrong, I have more than enough power for anything I need, I just don’t waste power on foolishness. I still run many things on my batteries.

Even with solar, no system is complete without charging while driving, and a generator. Deleting the solar added years to my batteries life span, and I still mainly charge while driving and only use my generator if I’m boondocking for over two weeks, or need shore power to run power tools or something. I actually use my generator more to charge other people’s batteries than I do my own. People relying only on solar always have dead batteries.

I also have been buying my deep cycle batteries from junk yards now. You can get practically new ones dirt cheap, and sometimes they have a rather impressive collection to choose from because people with cars usually don’t use deep cycle batteries. They have dates on them, so you can tell how old they are. I got two, 3 week old, $300+ batteries for under $20 each! That was over 6 years ago, and they’re still going strong. How’s that for bang for your buck!?!?!

Cheers!


"I can live like a king because I work like a dog." ~ An anonymous vandweller



#3

Thanks for the excellent, thoughtful reply. I’m now looking into the generator/charger option - at least as an additional backup to solar.

Maybe I’m naive (please feel free to say so) but I just like the idea of quiet, passive, effortless battery charging from a couple of solar panels (say, 350W). And if I can stow those panels such that they are not on the roof creating drag while I drive (very counter productive I would think) and easy to clean before I start a charging session… I just like the whole idea.

A few thoughts in direct response to your comments…

–On your “cheap” generator + charger comment, maybe I am looking at the high end of products but it looks like a decent 1000W generator/charger combo is at least $1000. A full solar setup to charge a 100Ah LiFePO4 12 Volt Deep Cycle Battery is about the same cost - maybe a little less.

–On solar panel negatives, let me comment… I am not worried about expense (I consider all cost differences to be de minimis when spread out over the time I expect to use the stuff). I am not worried about winter for various reasons. I am not worried about the need to charge at night (although the “winter” and “night” issues are good reasons for the backup option you are presenting). I am a little worried about parking either in the sun (“punishment”) or in a spot where I don’t have sun (like every ideal camping spot on the planet - at least in summer). But I am worried about the idea that solar panels won’t charge batteries properly, and they will kill battery life. Can you expand on that or point me to a good reference?

When you charge your batteries with a generator/charger combo, how long does that typically take? Do you know the math on this? I’d love to see how a 1000W generator and a matching charger bring a 100Ah battery to full power in X hours with Y gallons of gas. I’ll Google this, too.

Oh… and maybe I need to look at a different battery setup. $20 for a deep cycle battery… holy cow!

Thanks for your advice!!!


#4

Greetings!

Over the summer, helping others, we were buying cheap chinese generators for $99 each, and the battery chargers were $29 each. That was in south Florida. Now I’m in Minneapolis, and there don’t seem to be any of those around. The cheapest I can find locally are $299. We also added better mufflers to them for under $20 each, which made them super quiet.

Harbor Freight online has these on sale right now for $89.99 : https://www.harborfreight.com/900-Max-Starting700-Running-Watts-2-HP-63cc-2-Cycle-Gas-Generator-EPACARB-63025.html?ccdenc=eyJjb2RlIjoiMzYxMzU2NzQiLCJza3UiOiI2MzAyNSIsImlzIjoiODkuOTkiLCJwcm9kdWN0X2lk IjoiMTE5NDIifQ%3D%3D

They also have battery chargers for under $50. So combined, you’re still under $150.

I’m not at all convinced that LiFePO4 batteries are a good deal. According to these guys, life expectancy is no longer than lead acid, at only 5-7 years. I get that much out of under $20 junkyard batteries. https://www.batterystuff.com/kb/articles/battery-articles/lithium-battery-overview.html

According to these guys, here’s what good deep cycle battery charging looks like:

"Deep-cycle batteries have special needs when it comes to recharging and maintaining. They last longer and charge faster if they are charged according to a temperature-dependent and battery chemistry-dependent schedule.

Under ideal circumstances an example schedule for a 200 amp-hour battery might be a Bulk Phase where charging proceeds at about 15 volts and 50 amps to approximately 75% charge followed by an Acceptance Phase where the battery is maintained at about 15 volts while reducing the amperage and charging the battery the remaining 25 percent capacity at a declining rate.

Deep Cycle Battery Charger CTEK MUS 4.3 Cables ViewOnce charged, the battery should be maintained using a Maintenance Float Phase where the voltage is reduced to around 13.4 volts to maintain the battery without losing electrolyte."


That’s pretty close to what I’ve read in multiple places. Basically they want a high amp charge to begin with, not the trickle charge that solar provides. This can be overcome somewhat with enough solar.

According to these guys: http://www.batteriesinaflash.com/deep-cycle-battery-faq here’s the typical life span of different types of deep cycle batteries.

General expectations for batteries if deep cycled (these are just approximate guidelines):

Starting battery (Automotive battery etc) : 3-13 months
Marine Battery : 1-6 years
AGM Deep cycle: 4-7 years
Gel Cell Deep Cycle: 2-5 years
Flooded Lead Acid Deep Cycle Battery (L16-RE etc): 4-8 years

It goes on to say that those life spans require proper charging algorithms, something solar isn’'t known for.

LifePo4 seems to be rated at about a 10 year life span, but at 10x the cost of lead acid (new), I just can’t justify it.


Decisions - decisions - decisions… For me, the cheapest route has also proven to be the best, and not because of the price being cheaper.

All that being said, everybody’s usage is different. I’m mainly a city dweller these days, and drive a little around town several times a week. Out to eat, groceries, laundromat, etc. Charging while driving keeps my house battery charged up. Before charging while driving, I had solar, and I also had roof vents with fans, and a power hog 12v compressor fridge. I ran out of power almost every night. I added a generator and needed to run it for about an hour every 3-4 days. The solar got stolen, and the generator usage didn’t change. When the fridge died, I only needed to run the generator for about half an hour every 6-7 days, sometimes a little longer or a little less depending on how much power I’d used.

I’d charge until the charger said the battery was fully charged. Some surf bum I met who was supposedly an expert on some forum or another claimed I was killing my battery by constantly undercharging it, and tried to sell me on solar panels. He claimed the battery charger cut off too quickly. I don’t know if he was right about that, but unlike with solar, I never ran out of power, and my under $20 junkyard batteries last for years. He was against junkyard batteries too, and wanted me to buy $350+ batteries. My philosophy is “If it ain’t broke, don’t fix it.” and my system works just fine for me. I’m approaching year 7 on my junkyard batteries. When I had solar, my expensive batteries died in about a year. My guess is that it was the solar that wasn’t charging my batteries fully or correctly.

Cheers!


"I can live like a king because I work like a dog." ~ An anonymous vandweller



#5

A cheapie generator and a regular battery charger are much cheaper and much more efficient than solar panels.

My 570w solar install cost less than a generator. And “regular battery chargers” are not designed for our purposes. Few have staged charging.

they don’t charge the batteries correctly and kill them quickly,

That is so bizarrely wrong I don’t know where to begin. All but the very cheapest solar charge controllers are smart chargers, and from the mid-range up most have user-configurable setpoints for ideal charging.

What most often [kills batteries] in 'dwelling scenarios is chronic Partial State of Charge (PSoC), which is common with an unassisted isolator or generator.
A isolator [or] alternator charging + solar (even small amounts) works very well, each strong where the other is weakest. Generator + solar also works, but the genny costs about 10x what an isolator setup does.

they don’t work well in the winter when you really need the power,

They actually work better in the cold. I agree that there is less insolation in the winter.

they don’t work at night,

True. And a generator doesn’t work when it’s not running.

and parking in the sun during the summer is cruel and unusual punishment.

It doesn’t have to be. My insulated/ventilated white van stays at ambient temps well over 100F.

Note: I tried to link to more info on these subjects but “new users can’t post links”.


#6

a question I haven’t seen here or anywhere else.

The reason you are not seeing it anywhere is there is no upside to it. You can charge from the alt and solar at the same time. The one with the highest voltage will “win”, automatically and with no input required.

Alternator charging is not more efficient in any sense; it consumes engine horsepower, uses gasoline, and imposes additional loads on the alt. It does have it’s place: early morning driving to do your errands or commute will cram lots of current into the bank when you need it most. What it can’t do, excepting DC-DC chargers, is run at a voltage high enough to complete Absorption charging. And unless one is on a road trip of multiple hours even a DC-DC charger won’t have time to finish Absorption.


#7

And if I can stow those panels such that they are not on the roof creating drag while I drive (very counter productive I would think)

It is common for folks to put little air dams on the front of their racks to guide airflow, as one sees on bike/ski racks. In my case (Promaster), I set the panels back a bit on the roof where there is no direct windblast. My mileage was unaffected.

The downside of stowing is you have to unstow. With mounted panels they are always collecting sunlight no matter the crappiness of the local weather or short duration of your stop. I get ~10% yield in rain or dark cloud cover, but wouldn’t want to go outside to set up the panels.

A full solar setup to charge a 100Ah LiFePO4 12 Volt Deep Cycle Battery is about the same cost - maybe a little less.

Check craigslist for used/pulled panels. I got 3x 190w 24v mono panels for $120 each. The 40a epsolar charge controller w/monitor was $200.

75A voltage sensing isolator was $60.

That’s $580 for solar and alternator charging. Remember to budget for wiring and fuse expenses.

2x 6v actual deep cycle FLA batteries in series was about $230. So we have a complete self-operating system with copious power for less than $1000. Zero interaction from me. I never hit 50% depth of discharge and I run a compressor fridge, a laptop, phone, 12v water pump, roof vent, LED lighting, wifi minirouter to repeat wifi when I find it, a tiny litecoin miner, a raspberry pi, Roku, etc. There is enough untapped power that I put a power donation station just inside my sliding door so underpowered folks can plug in USB or 12v cigarette lighter devices.

It is 11am where I am. The controller is holding absorption voltage (Vabs, 14.7v in my case) and shunt-measured acceptance is ~6A and dropping appropriately. At this rate absorption will be complete (batteries actually fully charged to battery manufacturer specs) by 12:45p or so. As the [in]famous Handy Bob says, perhaps unkindly, “if you want solar advice don’t ask the guy running a generator half the morning”.

As soon as I’m allowed to post links I will provide more in-depth info with references.

That was almost certainly insufficient.

Some surf bum I met who was supposedly an expert on some forum or another

Sounds like Sternwake, who knows more about vanlife 12v systems than most of the rest of us put together.

claimed I was killing my battery by constantly undercharging it,

Almost certainly true.

He claimed the battery charger cut off too quickly.

He was right. Lead-acid chemistries take hours to charge completely from 50% DoD, and non-staged chargers usualy don’t hold Vabs long enough, leading to hard sulfation and “battery murder”.

Carbon-foam SLA batteries are an apparent exception; they only require a full charge every couple of weeks. And of course Li chemistries don’t have an Absorption requirement in the usual sense.

… my under $20 junkyard batteries last for years.

Agreed; I have bought used FLA deep cycles before and coaxed years out of them. Real deep cycle batts are incredibly resilient.


#8

OK… so this is super interesting and somewhat game changing (at least design changing) for me. I’ll need to research the stages of charging a battery to better understand this.

Thanks.


#9

So… this is your full setup?


#10

I’ll need to research the stages of charging a battery to better understand this.

If I can post links now, here is some info I’ve collected on staged charging and multipoint charging. Not claiming it is gospel, but it is footnoted so you can check context and decide for yourself.

Note: still can’t post links. Will strip off the protocol to see if this works:
rvwiki.mousetrap.net/doku.php?id=electrical:12v:charging
rvwiki.mousetrap.net/doku.php?id=electrical:12v:multipoint_charging

Note to site owner: this appears to be a work-around that spammers could use on your site. As a reward for finding this bug you could take me off newbie status so I can post regular links. :slight_smile:

this is your full setup?

Yes, that is my off-grid setup. During the build I also installed a shore power port and made a DIY converter out of a 24v power supply and small, configurable MPPT controller. This allowed me to have power and keep the bank properly charged while installing the solar. The last time I used it was 3 months ago, when I was in a driveway.

rvwiki.mousetrap.net/doku.php?id=electrical:converter


#11

Secessus,

Oh goody… A follower of Sternwake, one of the poster boys of inaccurate, bad, and dangerous advice. He regularly tells people to overcharge their batteries, causing them permanent damage, and the risk of fire and/or explosions. Every battery has specific specs, it’s not one size fits all. With many batteries, anything over 13.8-14.0v is entering into dangerous territory.

Vehicle charging, and battery chargers are designed to charge your batteries correctly, fully, and without damaging them. Thinking you know more than the battery manufacturers or charger manufacturers is just plain stupidity. People need to check the spec sheets for their specific batteries, PERIOD!!! Not take some self proclaimed expert’s loony tune advise.

One of the biggest problems with the internet is that bad, incorrect, or inaccurate advice outnumbers factual information by at least 100:1. That’s why I tell everybody to do their homework, but even then it can be very difficult separating fact from fiction. In this particular case, thankfully, spec sheets are usually available.

Nobody should follow anybody’s advice without first verifying the facts.

Now you are perpetuating Sternwake’s bad advice, and the cycle continues… Even though most of his advice has been proven wrong by multiple people on multiple occasions, and with accurate references, the garbage that he has posted is still out here, and still harming more people than it’s ever helped.

In my case, batteries that have lasted almost 7 years, providing plenty of power, and still going strong, must be getting charged adequately, and without the need of solar.

As for your challenges to my statements of facts, the majority of off grid full timers do exactly or similar to what I do, and we all do it successfully. Challenging the most popular and successful methods people have been using for many years shows a major misunderstanding of how this stuff actually works. Maybe we’re all nuts and doing everything totally wrong, but if it works for us, then nothing else matters. Following the successes of the majority is usually the best choice. Not solar, and certainly not screwing with battery charging algorithms.

Cheers!


"I can live like a king because I work like a dog." ~ An anonymous vandweller



#12

Oh goody… A follower of Sternwake,

Good morning. A few thoughts here:

  • I am hardly a follower of Sternwake. I have taken issue with his statements several times, on forums and in blog articles.
  • I see now your “surf bum” comment earler was an ad hominem attack, rather than a case of not knowing someone’s name.
  • where did you meet this person?

one of the poster boys of inaccurate, bad, and dangerous advice. He regularly tells people to overcharge their batteries,

His general position is for folks to hold manufacturer’s Vabs until acceptance falls to manufacturer’s stated rate, usually C/100 - C/200, then drop to manufacturer’s Vfloat.

causing them permanent damage, and the risk of fire and/or explosions.

Manufacturer’s Vabs specs do not cause the results you give.

Every battery has specific specs, it’s not one size fits all.

Indeed, that’s why we charge to spec with configurable controllers.

With many batteries, anything over 13.8-14.0v is entering into dangerous territory.

Popular RV/Van house batteries and manufacturer’s Vabs spec:

  • Trojan T-105 FLA - 14.82v
  • Trojan T-105 AGM - 14.1v to 14.7v, finishing at 14.7v
  • EP/Deka rebrands (duracell, etc, as found in warehouse clubs and B+) 14.4v to 14.7v
  • Renogy AGM12/100 - 14.4v to 15v
  • cheap Chinese Universal UB121000-45978 - 14.5v to 14.9v

Those were the first 5 that came to mind and I looked up the specs. Still can’t post links or I’d provided references.

Vehicle charging, and battery chargers are designed to charge your batteries correctly, fully, and without damaging them.

Those chargers are designed to charge starting batteries (ie, non deep-cycle) batteries. They are typically charged at mid-to-high Vfloat. That is insufficient for actual deep cycle batteries.

the garbage that he has posted is still out here, and still harming more people than it’s ever helped.

To the OP: when you are doing your homework it may be productive to discount the opinions of people who resort to name-calling and make broad, hyperbolic statements without evidence.

Thinking you know more than the battery manufacturers or charger manufacturers is just plain stupidity. People need to check the spec sheets for their specific batteries, PERIOD!!!

Agreed. The specs for my bank are:
Vabs==14.4v to 14.7v
Vfloat==13.8v to 14.1v when cycled
Max current == C/3
3mv/cell/°C from 25°C temperature compensation

I have configured my solar charge controller setpoints within those specs. I also have inlined a HVD to ensure the insolator never passes voltage > Vabs in either direction.

Real question, not being a wise guy: what are the charging specs for your bank? How are you keeping to those specs?

Not take some self proclaimed expert’s loony tune advise.

More ad hominem.

One of the biggest problems with the internet is that bad, incorrect, or inaccurate advice outnumbers factual information by at least 100:1.

Another problem is folks mistaking their biases and opinions for facts. I agree that doing the homework is critical. That homework is not made easier by people making ad hominem attacks and regarding their opinions as facts.

Nobody should follow anybody’s advice without first verifying the facts.

Agreed.

Now you are perpetuating Sternwake’s bad advice, and the cycle continues

I am following my manufacturer’s spec sheets. I assume you are doing the same.

In my case, batteries that have lasted almost 7 years, providing plenty of power, and still going strong, must be getting charged adequately, and without the need of solar.

I am pleased to hear it.

the majority of off grid full timers do exactly or similar to what I do,

I don’t think that has been true over the past several years.

Challenging the most popular and successful methods people have been using for many years shows a major misunderstanding of how this stuff actually works.

Critical examination of popular methods reveals exactly how stuff actually works, not how we think it works, claim it works, or how we want it to work.

A meter, shunt, and hydrometer tell me precisely how my bank is doing. I am not guessing or hoping. It is 9:30am and my bank is in Bulk, 14.2v, accepting 237w/6.3A from solar alone. The controller is putting out 269w. Panel Vmp is 36.2v. Bank temperature is 23c. Those empirical measurements are facts. If I were to claim “my system works awesome and you should get one like mine” that would be opinion, and misguided opinion at that.

Maybe we’re all nuts and doing everything totally wrong, but if it works for us, then nothing else matters. of the majority

Ii am not claiming anyone is nuts. I agree that if something works for someone then it works for them, at least in the short term.

The dangers of issuing opinions/“fact” based on observed success are misunderstanding causality (post hoc) or more commonly assuming that a similar setup would work for others (hasty generalization). Anecdote is useful as a datapoint but it is not “fact” or evidence.

What I disagree with is the propagation of biases and opinions as if they are facts. Opinions like “solar panels… don’t charge the batteries correctly and kill them quickly”. That can badly mislead folks doing their homework.

following the successes of the majority is usually the best choice.

Following the succeses of the majority results in average results. Understanding the outcomes the majority experiences can lead to greater success.

Not solar,

I’d wager the majority of off-grid folks are running solar nowadays.

and certainly not screwing with battery charging algorithms.

The manufacturer spec sheets for deep cycle batteries (which we both hold to be gospel) indicate Vabs and Vfloat setpoints, and sometimes terminal acceptance current. We ignore those charging stages at our bank’s peril.


#13

Greetings Secessus!

No, I actually don’t know who that surf bum was, only that he rudely and unnecessarily got into my business. He claimed to be an expert, and rattled off some websites as a reference, none of which I paid attention too. I believe he wanted me to hire him, and he named a specific solar company, claiming they had the best products and prices. I still wasn’t paying attention and was hoping either he would leave, or I could drive off. It was in Florida, somewhere between Daytona and Miami.

I regard Sternwake as a hack. His advice is frequently erroneous, as well as overly complicated, and his hacks are laughable, when proper repairs would be just as easy, and possibly cheaper. He suggests hacks, even though the people aren’t stranded somewhere, and if you follow his ramblings, he can’t even keep his own stuff working, yet suggests others follow in his footsteps.

For the rest, it’s probably best if we just agree to disagree. We each have our own experiences, and people we choose to follow, and would be willing to bet that both of us could come up with accurate references to back up our views, and neither of us is likely to change the other person’s mind. At this point we have both presented our views, so readers will have valid choices to consider.

Cheers!


"I can live like a king because I work like a dog." ~ An anonymous vandweller



#14

Peace brothers! I’ve learned a lot!!


#15

I always change my views when presented with new evidence. To do otherwise would be operating on faith rather than reason.

I do agree we have both made our cases, and I appreciate your input. [edited to add: I am sorry to hear of your experience with the rude surfer/salesdroid. That sounds deeply unpleasant.] Yaz, let us know what you decide and how it works out.


#16

I will! Thanks to all for your valuable input.


#17

Greetings!

That’s the way I’ve always been too, always in search of better ways. The problem lies in the fact that sometimes those supposedly better ways can be terribly expensive and wind up worse than what you had to begin with.

Choices are always a good thing!

I don’t know why, but sometimes I feel like I attract more than my share of weirdo’s. Usually at big box stores or restaurants. From panhandlers to bums asking if they can bunk with me, to people trying to sell me stuff or hire them. Maybe that’s the price I pay for usually having a smile on face and acknowledging others… I don’t know… But both of those things make ME feel good. hehe

Cheers!


"I can live like a king because I work like a dog." ~ An anonymous vandweller