Solar Power-interesting read

  • HTML tutorial

Mark D

Rank V
Launch Member

Pathfinder II

2,467
Whittier CA
First Name
Mark
Last Name
Dickens
Member #

2100

I have been seeing videos on YouTube of people out on the trail setting up small solar systems when they park. I looks to me like there is a lot of misunderstanding of how much power is produced by a solar panel. I found this article very informative. The author also covers things that effect batteries. It is written for RV people but the thing I like is how he gets into the actual energy that you can expect out of a solar system.

https://www.thefitrv.com/rv-tips/how-much-solar-do-i-need-on-my-rv/
 

Mark D

Rank V
Launch Member

Pathfinder II

2,467
Whittier CA
First Name
Mark
Last Name
Dickens
Member #

2100

The chart about battery “level” was great. I had no idea that a battery at 12volts is sitting at less than 50%.
 

smritte

Rank V
Launch Member

Member III

2,827
Ontario California
First Name
Scott
Last Name
SMR
Member #

8846

Ham/GMRS Callsign
KO6BI
Nice read. He did leave a couple of things off but, the article puts things into perspective. The charts are nice for showing you how much things draw. He hit it spot on with the amp hours too.

He mentioned adding in a second alternator. What I think he should have mentioned was how much a low battery draw's. This is a key point in setting up a battery and charging system.

A dead or really low battery will draw around 40 amp's. Most modern vehicles run a 100-120 amp alternator. Your vehicle just driving down the road during the day will draw 20-30 amps. Lights and other things around 10 ish.

I like to say your stock system draws a max of 80 amps including the battery. Add in a second battery and your at 120 amp draw.

Your battery will draw less as its charged. What that means is 40 amp draw is when its low. Without doing the math, a battery with 80-90% charge draws around half that. I pulled those percentages off my head so they will be close only.

Putting this into English. It can take you 8 hours of driving to charge a low battery. If you run your alternator over 70% for that time, most likely, you will burn it out. Newer alternators do a better job and older are worse when it comes to what they can handle. If you take a deep cycle battery down to 20-30% (11.5-11.75 volts) It shortens it life. Dipping it down there occasionally is ok, all the time is not a good idea. Running your batteries almost dead really shortens their life.

My camper has 2 house batteries. I run 3 120 watt panels. My alternator is 160 amp. Before I got solar and LED's, I was good for 7-8 days with firing up the generator for the microwave and coffee pot. When I got home, depending on how far I drove, my batteries would be 80%-90%. If I camp in the forest with my panels shaded, they do very little. Some is better than none. Desert keeps them topped off and I don't have to depend on alternator. As I travel the highway, the panels charge. They average 30-35 amps. This takes load off the alternator. I almost never drive at night.

Alternators are not free power. The bigger the power draw the more horsepower they draw. Nothing is free.
My off road trailer has a single 120 watt panel. The little bit my lights and fridge take are put back in a couple of hours. I have not upgraded my landcruiser alternator yet. Charging that battery from low would not make my alternator happy.

Figure out what you draw and that will determine what you need. My little trailer would be fine with a smaller panel. I got a deal on it. The panels on my camper work out well. Because of forest camping, I could probably use another. No room though.

Scott

EDIT: I don't remember if the article mentioned this, when checking battery voltage, let the battery sit for two hours after charging. It needs to settle. Otherwise your reading will be high. This includes driving.
 
Last edited:

Mark D

Rank V
Launch Member

Pathfinder II

2,467
Whittier CA
First Name
Mark
Last Name
Dickens
Member #

2100

Nice read. He did leave a couple of things off but, the article puts things into perspective. The charts are nice for showing you how much things draw. He hit it spot on with the amp hours too.

He mentioned adding in a second alternator. What I think he should have mentioned was how much a low battery draw's. This is a key point in setting up a battery and charging system.

A dead or really low battery will draw around 40 amp's. Most modern vehicles run a 100-120 amp alternator. Your vehicle just driving down the road during the day will draw 20-30 amps. Lights and other things around 10 ish.

I like to say your stock system draws a max of 80 amps including the battery. Add in a second battery and your at 120 amp draw.

Your battery will draw less as its charged. What that means is 40 amp draw is when its low. Without doing the math, a battery with 80-90% charge draws around half that. I pulled those percentages off my head so they will be close only.

Putting this into English. It can take you 8 hours of driving to charge a low battery. If you run your alternator over 70% for that time, most likely, you will burn it out. Newer alternators do a better job and older are worse when it comes to what they can handle. If you take a deep cycle battery down to 20-30% (11.5-11.75 volts) It shortens it life. Dipping it down there occasionally is ok, all the time is not a good idea. Running your batteries almost dead really shortens their life.

My camper has 2 house batteries. I run 3 120 watt panels. My alternator is 160 amp. Before I got solar and LED's, I was good for 7-8 days with firing up the generator for the microwave and coffee pot. When I got home, depending on how far I drove, my batteries would be 80%-90%. If I camp in the forest with my panels shaded, they do very little. Some is better than none. Desert keeps them topped off and I don't have to depend on alternator. As I travel the highway, the panels charge. They average 30-35 amps. This takes load off the alternator. I almost never drive at night.

Alternators are not free power. The bigger the power draw the more horsepower they draw. Nothing is free.
My off road trailer has a single 120 watt panel. The little bit my lights and fridge take are put back in a couple of hours. I have not upgraded my landcruiser alternator yet. Charging that battery from low would not make my alternator happy.

Figure out what you draw and that will determine what you need. My little trailer would be fine with a smaller panel. I got a deal on it. The panels on my camper work out well. Because of forest camping, I could probably use another. No room though.

Scott

EDIT: I don't remember if the article mentioned this, when checking battery voltage, let the battery sit for two hours after charging. It needs to settle. Otherwise your reading will be high. This includes driving.
You bring up some very good points. I think there is a lot of misunderstanding out there about how batteries work. Maybe you could write an article for OB?
 

smritte

Rank V
Launch Member

Member III

2,827
Ontario California
First Name
Scott
Last Name
SMR
Member #

8846

Ham/GMRS Callsign
KO6BI
You bring up some very good points. I think there is a lot of misunderstanding out there about how batteries work. Maybe you could write an article for OB?
I totally agree with you on that. It's not only batteries but, vehicle electrical systems as a whole. Its like anything you customize. It has to fit your needs and all the pieces have to work together properly. What works for you may not be the best for me. I think that's where people get confused. There really is no off the shelf solution. Articles like what @Mark D posted give people a base understanding and then they can start to properly plan their system. Which means more research.


Scott
 

Dilldog

Rank V
Launch Member
Investor

Influencer I

2,358
Spokane, WA.
First Name
Dillon
Last Name
Wilke
Member #

20298

Ham/GMRS Callsign
KJ7LVO/ WRQL275
Service Branch
USAF
That article really put things into perspective. I had no idea solar was that bad at generating power.
For most people you would probably be better off to run an isolated battery system with a few group 31s and an HD second alternator. In on highway trucks you can run quite a few accessories and still start the truck after sitting for 10 hours on 4 group 31s. Then some of the new Delco alternators are not much bigger than a standard automotive type and will crank out 150amps. A few rigs I helped build ran 2 group 31 batteries with an isolator and a Leese Neville alternator modded to make 250amps, this was mostly to run on board welders, but worked really well for powering a camp too.
Only advantage I see to solar is maybe weight, but I would rather have a simpler cheaper system that should it ever go down would be easy to get parts for.
 

billiardspintail

Rank V
Launch Member

Traveler II

1,845
San Jose, CA
First Name
Bryce
Last Name
McNab
Member #

11911

Ham/GMRS Callsign
KN6GNT
I fell into the trap of using the online power calculators for figuring out the size of battery. My plan is to use one of those "Solar Generators" and use the 12v charger when driving and the panel when at the campsite. I think I have picked out what I want and am going to try it out before going for a bigger or custom built system. Thanks!
 

Cpol

Rank IX
Launch Member

World Traveler III

15,013
Jackson Heights, Queens, NY, USA
First Name
Chris
Last Name
Pol
Member #

14325

DDC040D3-46FB-401B-9D43-3AB3DC5CC6BC.jpeg 669148A0-FAD4-47F0-A1F1-43D9CF03581C.jpeg
I got a stainless steal electrical weather proof donation from legion lighting. Got a 12 volt lawn mower battery. A 120 watt solar panel from o solar. Looking at an duwalt inverter, and the project is on its way..
 
  • Like
Reactions: amenges45

Mark D

Rank V
Launch Member

Pathfinder II

2,467
Whittier CA
First Name
Mark
Last Name
Dickens
Member #

2100

I totally agree with you on that. It's not only batteries but, vehicle electrical systems as a whole. Its like anything you customize. It has to fit your needs and all the pieces have to work together properly. What works for you may not be the best for me. I think that's where people get confused. There really is no off the shelf solution. Articles like what @Mark D posted give people a base understanding and then they can start to properly plan their system. Which means more research.


Scott
Hey Scott,
Does this look like a good controller? The specs look good to me but I would like a second set of eyes

 

smritte

Rank V
Launch Member

Member III

2,827
Ontario California
First Name
Scott
Last Name
SMR
Member #

8846

Ham/GMRS Callsign
KO6BI
Hey Scott,
Does this look like a good controller? The specs look good to me but I would like a second set of eyes
Haven't seen that one. It didn't say if its a PWM or MPPT. Im going to assume its a PWM due to the price. amperage is good for 2 -100 watt and it has a USB outlet. Looks like it got good reviews. Worse thing is you wont like it.
Not sure if you noticed, its a panel mount. If you don't have a spot to set it into, you will need to get a box for it.
I get my solar stuff from from solar blvd. Great prices, real good stuff and it's close to me.

Scott
 

Mark D

Rank V
Launch Member

Pathfinder II

2,467
Whittier CA
First Name
Mark
Last Name
Dickens
Member #

2100

Thanks Scott, they have really good prices! I ordered two of those controllers. I will let you know how they work.
 

Lindenwood

Rank V
Launch Member

Member III

2,779
New Mexico
First Name
Jay
Last Name
M
Member #

2636

Great article! It really puts into perspective the true role of batteries, especially when considering momentary or non-continuous loads.

For example, after reading this article, I revisited the whole "air conditioner" question. The 13500 BTU unit in a 30ft Airstream might take 2700w or so at startup, so most folks recommend a >3000w generator to run it.

However, it only uses about 1250w continuous, and realistically is probably only running maybe 50% of the time on a hot day at a readonable setting. So really, we're looking at 700-800 watt-hours. Thus, a 2000w generator should easily keep the batteries charged throughout the day, with the batteries themselves actually handling the intermittently-higher loads of AC startup or toasters or whatever.

That means instead of 100+ pounds of 3000+ watt generator, one can get a <50lb (and quieter) 2000w model.

Of course, such a setup might be a bit custom since I don't think the system is actually wired to be used like that from the factory. But, it makes a lot of sense!
 
Last edited:

Enthusiast III

1,212
Grand Falls-Windsor, NL, Canada
First Name
Steve
Last Name
Adams
Some good reading there. I am currently working on an off grid solution for our boondocking camper. I do have a 2000w honda generator that will be going with us, but I want a solar solution to have power most of the time. I was going to run two golf cart batteries in a case on the front of the camper. Should have enough juice for our needs of a small LCD tv, video games/computers and DVD, plus a few LED lights.

I also want a pure sinewave inverter installed (not sure if the current one is) to use an induction cook top at times. Our fridge runs on propane when needed so that's "cool" as does our cook top. But it would be nice just to stop, plug in our induction unit and whip up a quick meal.
 

billiardspintail

Rank V
Launch Member

Traveler II

1,845
San Jose, CA
First Name
Bryce
Last Name
McNab
Member #

11911

Ham/GMRS Callsign
KN6GNT
My power needs are simple: Charge a phone, run a fan and some LEDs. I've been looking at this battery and this solar panel, which I think should do the trick. Any thoughts? It has an inverter in case I want to do something wild like bring a laptop or run a power tool, but the idea is that the battery is big enough for my needs alone and then some, and the panel should be enough to charge it with my limited use. There may be a fridge in the future, but I'm iffy on that and I'm not building out for that.