Shed solar battery set up

[Modenacart]

I just installed a 100 watt solar panel in my shed to power a 35 watt light. I would like to be able to power the light for four hours a day though most days it will be less than an hour. The system is set up for 12 volts. I calculated the following battery requirement.

35Wx4hr/12V= 11 amp hr

Using 50% as utilization and I got about a 20 amp hour battery. The following two seem to be cost effective and should be more than I need but I don’t know the brand and the differences between the batteries.

ML35-12 - 12V 35AH DC DEEP CYCLE SLA SOLAR ENERGY STORAGE BATTERY - Mighty Max Battery brand product https://www.amazon.com/dp/B00K8E4LR6/?tag=hearthamazon-20

12V 35AH GEL Replacement Battery for Deep Cycle Solar 33Ah, 34Ah, 36Ah - Mighty Max Battery brand product https://www.amazon.com/dp/B01HC5B6JY/?tag=hearthamazon-20


I don’t mind spending a little more if it is worth it but I don’t see myself adding much more demand to my system.

Thanks.




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[begreen]

For a shed I would switch to a 9w LED light, unless the 35w light is special purpose.

 

[Modenacart]

For a shed I would switch to a 9w LED light, unless the 35w light is special purpose.

The shed is 16 by 14 so I don’t think the 9 watt light would be enough.


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[jebatty]

A 9W LED has the light output close to that of a 100W incandescent or an 18W CFL. What about going with two 9W LEDs, separately switched, so you can get the amount of light full or 1/2, depending on what you need? What charge controller did you get?

 

[Modenacart]

I already have light so I plan on using it.

I have this charge controller.

http://www.renogy.com/template/file...er-30A-PWM-Solar-Charge-Controller-Manual.pdf



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[peakbagger]

AGMs are pretty abuse resistant as long as long as you trust the charge controller to do what its supposed to do and not overcharge the battery(which is definitely not always true with some of the cheap Chinese junk on the web).

Just realize they aren't forever batteries, 3 to 5 years is about it (talk to anyone with a motorcycle, lawn tractor or snowmobile).

If you haven't bought the charge controller yet, a controller with a low voltage disconnect can keep a battery from a premature death. The LVD is no substitute for making sure the battery is charged fully on a frequent basis but far better than the alternative which is draining the battery until its dead. I have used the Morningstar sun savers in the past.

 

[begreen]

The shed is 16 by 14 so I don’t think the 9 watt light would be enough.

I light our 12x 20 greenhouse with one for general purposes. Two 9w LED lights would be quite adequate for full task lighting. That is half the wattage draw.

 

[Modenacart]

AGMs are pretty abuse resistant as long as long as you trust the charge controller to do what its supposed to do and not overcharge the battery(which is definitely not always true with some of the cheap Chinese junk on the web).

Just realize they aren't forever batteries, 3 to 5 years is about it (talk to anyone with a motorcycle, lawn tractor or snowmobile).

If you haven't bought the charge controller yet, a controller with a low voltage disconnect can keep a battery from a premature death. The LVD is no substitute for making sure the battery is charged fully on a frequent basis but far better than the alternative which is draining the battery until its dead. I have used the Morningstar sun savers in the past.

What is AMG? I don’t mind getting a different controller if it makes sense.


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[peakbagger]

Absorbed Glass Mat batteries , Gell cells are a minor variation of AGMs.

If you want another look at this by pros (who can be a bit brutal) solarpaneltalk.com is the place to go.

 

[Modenacart]

Absorbed Glass Mat batteries , Gell cells are a minor variation of AGMs.

If you want another look at this by pros (who can be a bit brutal) solarpaneltalk.com is the place to go.

I tried there but I can’t get anyone to approve my account so I can post.


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[peakbagger]

That is odd. Moderator must be on vacation or running behind.

 

[Modenacart]

I light our 12x 20 greenhouse with one for general purposes. Two 9w LED lights would be quite adequate for full task lighting. That is half the wattage draw.

I appreciate the commend but I already have the light. I would rather make any new purchases in battery capacity. From my calculations I should have quite a bit more capacity I need with a 35 amp hour battery.


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[georgepds]

Ok, you're willing to buy batteries, but not a light

Your light is 35w... bgreen suggests a 9 w led,. Your light draws four times the power, and for an equal use time 4 times the energy

Consider the light switch as 4 batteries for the price of 1

In solar applications the first rule is to minimize power draw.

Or not... just buy the other 3 batteries for similar utility

 

[Modenacart]

I just got some advice on solar talk and they recommended one marine battery. Price about $70.

Four batteries not needed.


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[Modenacart]

Also, the other thing that is not being considered when blindly recommending a lower load light to size the battery is the size of the panel. If the load on the system is low the size of the panel becomes the dominating factor in sizing the battery. If I size my battery on an 18 watt load the panel will fry the battery and it will dead in less than a year.


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[georgepds]

Most people use a controller to avoid frying the battery.

.Not sure what you're trying to do... connect the panel directly to the battery?



On a sunny day a 100w 24v panel will put out 4 amps.. This is more than a trickle charge. You should be able to hear the electrolyte boiling away once you reach full charge

 

[georgepds]

Also, the other thing that is not being considered when blindly recommending a lower load light to size the battery is the size of the panel. If the load on the system is low the size of the panel becomes the dominating factor in sizing the battery. If I size my battery on an 18 watt load the panel will fry the battery and it will dead in less than a year.


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Oppps.. just saw that you have a controller... in which case the above makes no sense . The controller protects the battery, no mater how many panels

The light discharges the battery... worse case.. it runs it down

Good thing you're starting small, it's a great chance to learn about these thingies

 

[woodgeek]

I have a hobby solar system that I have been using for close to ten years now.

The unknowns are how many hours do you want to run the light, and do you want illumination (not much light) or task lighting (a lot more light).

I would say that a 100W panel will give that rating times ~600-800 hours of output per year, or 60-80 kWh max/year. The hours of sun are a lot longer than 600, but the PWM controller and battery have a lot of losses, which add up.

So, a 35W load can run maybe 2000 hours per year. If this is a tool shed, I would think this is plenty of hours. If this is a writing (retreat) shed, then it probably isn't.

I find that my system really wilts in December-February due to persistent cloud cover. Usable power is maybe 1/3 what it is in the spring in summer. If the OP isn't going to use the shed much in the winter, this is no problem.

Keep in mind that a charged lead acid battery will NOT freeze in NC winter, but a deeply discharged one will (the 'acid' turns to distilled water when discharged). So, if you are using a lot of power in the winter, you are likely to run the battery down in February. This is not only bad for it (in terms of reducing life) but with below freezing temps it can kill the battery immediately.

So, if you don't need the light in the winter, I would bring the battery in in the winter and store it on a trickle charger in a cool place that is above freezing. OR, I would leave it on the solar panel and controller, and disconnect the load wires.

 

[Dobish]

I have recently been looking into solar systems for our popup, and one of the things that I have noticed is that a lot of people are going with 6v batteries wired together for a 12v system. Another is that a lot of the controllers will show full power on the battery but it is only at 14.4v, not 14.8v. This is not fully charging the battery, which means you aren't getting a true full charge.