Stand alone 12V solar system

D

darekelec

Senior Member
Location
nyc
Good morning/evening.

Can you recommend a stand alone solar setup for barn lights?
20-50 W of lights at 12V for 4-6 h 3x a week. Preferably with replaceable aged car battery. A relative has a shop in the woods without electrical service and it would be great to run some lights there.
Setup that can be used in winter too.
 
darekelec said:
Good morning/evening.

Can you recommend a stand alone solar setup for barn lights?
20-50 W of lights at 12V for 4-6 h 3x a week. Preferably with replaceable aged car battery. A relative has a shop in the woods without electrical service and it would be great to run some lights there.
Setup that can be used in winter too.
Click to expand...
Car batteries are generally not a good choice for applications like this. They are designed to deliver large amounts of current for short periods of time, not low current for long periods.
 
darekelec said:
All right. Let’s scrap the idea of using car battery.
Can you recommend a stand alone system to run 20-50 W of LEDs
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Marine batteries are a better choice for your application, and relatively affordable. Check out products that are targeted for boats and/or RV's, they're usually plug-and-play, affordable, and scalable.
1762534418705.png
 
darekelec said:
All right. Let’s scrap the idea of using car battery.
Can you recommend a stand alone system to run 20-50 W of LEDs
Click to expand...
50W @ 12VDC is only 0.24A. How many hours per day do you want to run the lights? How many days of autonomy (days with insufficient or no solar) do you want to plan for? 0.24A X hours per day X days of autonomy will yield the approximate minimum ampere-hours of 12V usable battery capacity you will need, keeping in mind that with lead acid batteries you never want to draw them down to less than 50% full..
 
darekelec said:
20-50 W of lights at 12V for 4-6 h 3x a week
50% autonomy.
Click to expand...
You will want to assume highest usage so you won't run short, so say 50W. Likewise 6 hrs/day, 3 days /week

So for a week you will need (0.24A)(6hr/day)(3days/week) = 4.32 Ampere hours (A-h). Figure in never going below 50% state of charge and 50% autonomy, that gets you to 17.3A-h, which would be a pretty small battery. If it were me, I would get a significantly larger battery because stuff happens.

CAVEAT: It has been several years since I have done anything with off grid DC systems, so verify my numbers and assumptions.
 
For a bare bones functional system here, you really just need PV panel(s), charger controller, batterie(s), and overcurrent protection for the batteries and load. I think for this application you might as well look for the best deals on those components separately. Extra battery and/or willingness to replace battery if over-discharged are recommended.
 
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jaggedben said:
For a bare bones functional system here, you really just need PV panel(s), charger controller, batterie(s), and overcurrent protection for the batteries and load. I think for this application you might as well look for the best deals on those components separately. Extra battery and/or willingness to replace battery if over-discharged are recommended.
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Forgot to say I second the Morningstar recommendation, or similar company with a good track record. The charge controller is the component of this system where I wouldn't pinch pennies.
 
electrofelon said:
Did your power triangle wrong gunny. Battery isnt so small anymore is it?
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You are correct, sir; I had a nagging feeling that something was not right.

P = VI
I = P/V = 50W/12V = 4.16A, not 0.24A. That's what I get for trying to do simple algebra in my head.

So for a week you will need (4.16A)(6hr/day)(3days/week) = 74.9 Ampere hours (A-h). Figure in never going below 50% state of charge and 50% autonomy, that gets you to about 300A-h. Sorry about that.
 
ggunn said:
You are correct, sir; I had a nagging feeling that something was not right.

P = VI
I = P/V = 50W/12V = 4.16A, not 0.24A. That's what I get for trying to do simple algebra in my head.

So for a week you will need (4.16A)(6hr/day)(3days/week) = 74.9 Ampere hours (A-h). Figure in never going below 50% state of charge and 50% autonomy, that gets you to about 300A-h. Sorry about that.
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4 posts and no one corrected it, very rare for this forum. You could probably post on this forum "the Riemann hypotheseis is true" and someone would post a counterexample within a few minutes. So I had to quadruple check myself, was very paranoid I was the one that messed up :ROFLMAO:
 
electrofelon said:
4 posts and no one corrected it, very rare for this forum. You could probably post on this forum "the Riemann hypotheseis is true" and someone would post a counterexample within a few minutes. So I had to quadruple check myself, was very paranoid I was the one that messed up :ROFLMAO:
Click to expand...
That is what everyone gets for assuming that I always know what I am talking about. :D
 
darekelec said:
Good morning/evening.

Can you recommend a stand alone solar setup for barn lights?
20-50 W of lights at 12V for 4-6 h 3x a week. Preferably with replaceable aged car battery. A relative has a shop in the woods without electrical service and it would be great to run some lights there.
Setup that can be used in winter too.
Click to expand...
Using Gunny's figure of a 300AH battery, (2) L-16 type batteries would be about right. you could just get a small charge controller like a Schneider XW MPPT-60-150. This is a great little inverter with very low standby losses:

www.morningstarcorp.com

300 Watt Off-Grid Inverter | SureSine Classic

Morningstar's Suresine Classic is a highly reliable 300 watt pure sine wave off-grid solar inverter.
www.morningstarcorp.com www.morningstarcorp.com
 
electrofelon said:
Using Gunny's figure of a 300AH battery, (2) L-16 type batteries would be about right. you could just get a small charge controller like a Schneider XW MPPT-60-150. This is a great little inverter with very low standby losses:

www.morningstarcorp.com

300 Watt Off-Grid Inverter | SureSine Classic

Morningstar's Suresine Classic is a highly reliable 300 watt pure sine wave off-grid solar inverter.
www.morningstarcorp.com www.morningstarcorp.com
Click to expand...
Did the OP not say that the LEDs would run on 12VDC?
 
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