How big of a solar battery do I need?

[Van on 66]

Hello everyone,

I am looking into beefing up my power supply setup for my van and wanted some information as to how to determine just how much of a batter that I need.  

Up to this point I have been using a 100-watt solar panel, but decided to move up to a 200-watt panel just this week.  My latest laptop is a very powerful editing station that requires 170 watts as opposed to the 65 watts I have been used to and when I am using it the readout from the solar panel really drops.  

Up to this point I have also been using a Duracell AGM battery aimed at the Mazda Miata which is rated at 82 amp hours, at least that is what I remember it being when I bought it.  Now I can't seem to find the specs for it.  I only use just the battery power in the evenings to watch a movie or check emails so it has been enough power for me.  The readout from the solar panel is 13.6 when I shut it all down at night and they typically at around 12.5 when I set it all up in the mornings.  Sill, I am wondering if I should move into a battery with more amp hours or if that is really necessary at this point.

Does anyone have any input on this?

 

[PlethoraOfGuns]

What are all the loads from the battery? Just the laptop? How many amp hours would you use in a 24hr period without the solar panels?

 

[jacqueg]

What are all the loads from the battery? Just the laptop? How many amp hours would you use in a 24hr period without the solar panels?

Since High Desert Ranger is no longer with us, I'll repeat his mantra -

1) figure out what your total load is
2) size your battery to fit your load
3) size your battery charging system - solar or otherwise - to fit your battery

There's more than one way to meet your needs, but going through it step by step is the best way to proceed.

 

[Van on 66]

What are all the loads from the battery? Just the laptop? How many amp hours would you use in a 24hr period without the solar panels?

 
I run and charge my laptop primarily and also charge my cell phone and things such as standard batteries, etc.  It is how to calculate all the usage that I am not sure of how to do and what I was looking for direction with.  Any formulas, etc.?

 

[Van on 66]

Since High Desert Ranger is no longer with us, I'll repeat his mantra -

1) figure out what your total load is
2) size your battery to fit your load
3) size your battery charging system - solar or otherwise - to fit your battery

There's more than one way to meet your needs, but going through it step by step is the best way to proceed.

Thanks for the reply.  BTW I didn't know that High Desert Ranger is no longer around.  He was always a lot of help for me.  I hope that he is okay and just doing other things now.

I understand the basic idea about all this, I just don't know how to calculate it all.  I did some internet searching this morning and I didn't find anything to help.

 

[Freelander]

One thing I might add, don't go big enough, you need to make sure you have a little extra. You will find a need for it soon enough. Its better to have to much instead of just enough.

 

[PlethoraOfGuns]

HDR would have definetely chimed in on this. So you use inverter for laptop and cellphone. Your loads are small, you shouldn't need much. How many hours per day do you plug your laptop in to use/charge it?

 

[Camper]

Here's an easy to use solar calculator:

https://www.parkedinparadise.com/solar-calculator/

 

[Van on 66]

One thing I might add, don't go big enough, you need to make sure you have a little extra. You will find a need for it soon enough. Its better to have to much instead of just enough.

And that is very wise advise too.  I had to start out small due to finances, but am now able to build on what I have, hence asking the questions I am asking.

 

[Van on 66]

HDR would have definetely chimed in on this. So you use inverter for laptop and cellphone. Your loads are small, you shouldn't need much. How many hours per day do you plug your laptop in to use/charge it?

,
I would imagine that I am using my laptop anywhere from 6-8 hours a day.  I do a lot of writing, photo editing, etc. and I stay pretty busy.  And, as you know, there are those cloudy days when I don't generate enough power via my solar panels.  On those days I rely on portable batter power banks and a small power station.  And then, of course, those need to be charged back up.  

I have been doing the solar thing now in my van for nearly two years so I am pretty familiar with what my needs are and at this point I basically keep up with it hence me looking into getting into bigger panels and also an additional battery.

 

[Van on 66]

Here's an easy to use solar calculator:

https://www.parkedinparadise.com/solar-calculator/

Thanks.  I actually worked all this out a couple of years ago when I first went solar, but now I don't remember how I figured it all out.

 

[PlethoraOfGuns]

Hmmm, actually that computer is quite the draw. At the minimum, I'd say you need at least 250ah of AGM battery. Remember, you only get half the battery capacity at your disposal, unless you go LiFePo4. So if you have a cloudy day and aren't taking in any solar power, you're gonna use up 125ah, which is 50% of a 250ah battery bank. Like others said, it wouldn't hurt to go a bit bigger to give you some wiggle room. And how much solar do you need? Generally, I think it's good to go twice the solar panel watts as you have in useable ah battery capacity. So if you run 250ah of AGM with 125ah of useable capacity, I'd say you'd need at least 250 watts of solar. But those are under perfect sun conditions. Again, give yourself some wiggle room. Maybe get a 350 watt solar setup.

I'd get 2 more of the 82ah AGM batteries, tie them in parallel. Get another 200 watt panel and a MPPT charge controller big enough for 400 watts, run them in series. If you decide to just do one 200 watt panel and supplement the charge with the vehicle alternator, still get a charge controller for 400 watts in case you upgrade later. Charge controllers can get pricey. Best to buy them once.

 

[jacqueg]

Thanks for the reply.  BTW I didn't know that High Desert Ranger is no longer around.  He was always a lot of help for me.  I hope that he is okay and just doing other things now.

 
HDR is now traveling in another dimension. There will be a memorial for him in QSite in January. There's a sticky about it here - https://vanlivingforum.com/showthread.php?tid=44411

For sizing, watch this video - 

 

[jonyjoe303]

get a bigger panel minimum 365 watts, its what I got. You need to have a panel thats going to charge that battery up every day, even when the weather isnt great.
Your 170 watt laptop won't be using the 170 watt all the time (only when its gaming or editing) , you might get away with the battery you got as long as its fully charge everyday.
If you get a bigger battery it won't do you any good with a 200 watt panel (especially in winter) .
With my 365 watt panel it charges at up to 15 amps in winter and 27 amps in summer. Thats with the panel lying flat on the roof. Its the best investment I made. I used to use a 240 watt panel and it was barely keeping my batteries charge in winter. The 365 watt panel produce more power in winter then the 240 watt produce in summer. Right now I have two battery banks a 220ah lifepo4 and a 312ah li-ion and both are at 100 percent everyday and all I use is solar to charge them. If you get another battery you need to keep them at 100 percent everyday.

 

[Van on 66]

Great information.  Thanks for the response!

 

[Van on 66]

Hmmm, actually that computer is quite the draw. At the minimum, I'd say you need at least 250ah of AGM battery. Remember, you only get half the battery capacity at your disposal, unless you go LiFePo4. So if you have a cloudy day and aren't taking in any solar power, you're gonna use up 125ah, which is 50% of a 250ah battery bank. Like others said, it wouldn't hurt to go a bit bigger to give you some wiggle room. And how much solar do you need? Generally, I think it's good to go twice the solar panel watts as you have in useable ah battery capacity. So if you run 250ah of AGM with 125ah of useable capacity, I'd say you'd need at least 250 watts of solar. But those are under perfect sun conditions. Again, give yourself some wiggle room. Maybe get a 350 watt solar setup.

I'd get 2 more of the 82ah AGM batteries, tie them in parallel. Get another 200 watt panel and a MPPT charge controller big enough for 400 watts, run them in series. If you decide to just do one 200 watt panel and supplement the charge with the vehicle alternator, still get a charge controller for 400 watts in case you upgrade later. Charge controllers can get pricey. Best to buy them once.

Thanks again for all the input.  I will put my mind to work on all this.

 

[Van on 66]

 
HDR is now traveling in another dimension. There will be a memorial for him in QSite in January. There's a sticky about it here - https://vanlivingforum.com/showthread.php?tid=44411

For sizing, watch this video - 

I am very sorry to hear that.  He and I were going to get together last winter and things got delayed.  That is definitely a loss for me as well as everyone else.

 

[frater secessus]

Others have already offered good input. I'd pay special attention to @jonyjoe303, who is both experienced and well-informed.

Here is my 2c.

Up to this point I have also been using a Duracell AGM battery aimed at the Mazda Miata which is rated at 82 amp hours, at least that is what I remember it being when I bought it.

If the big loads (laptop) are only being run in the daytime then IMO battery capacity is less of an issue.

The readout from the solar panel is 13.6 when I shut it all down at night and they typically at around 12.5 when I set it all up in the mornings.

Both of those look normal.

Longer answer: 13.6v battery voltage shown on the controller before sundown is a pretty normal float voltage. 12.5v in the morning suggests the overnight draw is being handled nicely by the battery.

Sill, I am wondering if I should move into a battery with more amp hours or if that is really necessary at this point.

Not necessary, and could even be counterproductive. Right now the 200w:82Ah panel-to-bank ratio is advantageous; adding more battery capacity would dilute that advantage.

If I wanted to run the big laptop offgrid* I'd consider these approaches:

• free: running thirsty laptop in the afternoon when excess solar power is most likely to be available. Maybe use the lower-powered laptop at other times when not editing?
• relatively cheap: if driving for errands fairly often, adding isolator charging. Alternator + solar together are one of those situations where the sum can be greater than the parts. 2+2 = 6. Examples.
• mo' money and effort: maxxing out roofspace with panel. To decrease costs one might source used panels off craigslist

---

* I really do run a thirsty laptop and other significant loads offgrid, so it's not entirely armchair speculation. Currently baking bread in the crockpot. My setup is described in this parts list.

 

[technerd88]

Ya know for laptops that use 19v in, especially ones that drink a lot of watts like my ryzen 7 one with a dedicated gpu you can use a voltage booster like the drok one I got from amazon. says 1500w which is only at max voltage out but it works great boosting the 12+ v I get from my lifepo4 battery bank to 19v at 17a which is what my laptop needs. Much more efficient this way than using the giant brick it came with. If yours has usb c you can get converters for that too. All you need if yours is like mine is a multimeter and a little patience unless its a dell which use a special wire for charging but it will still run just wont charge.