solar system for shed

[Xplode]

I see some batteries that are really big usually with ropes tied to either side of them for easy lifting. I checked one out on a website and it was around $600. What are your thought on them? Are they specifically made for solar systems? And wouldn't a bunch of deep cycles battery's be much better for $600?

Do some digging in the off grid and battery forums here. Take a look at what others are using. The physical size of the battery isn't enough for us to go on. There are batteries made specifically for renewable energy, and will be marketed as such. But they are going to be more money than you need to spend right now for this system.

Go to an actual battery shop of you can and talk to the staff there. And i don't mean a Napa. I mean a battery distributor where that's pretty much all they do.

[Freeesun]

Ya once this one dies I'll spend some time reading and talking to people about batteries. Based off of my small solar panel I should be looking at golf cart batteries which only have 30-35ah which will still be plenty for me.

im confused about something. Amps= watts%volts
if I have leds connected straight to the charge controller and they use 9watts%12 volts= .75ah
now my tv will be plugged into the inverter and be roughly 80watts%120 volts = .66ah

i know I'm mistaken here somewhere but how does one led light bulb use more power than a tv?

If i multiply the light bulb .75 by 10 to make it the same as 120volts it's 7.5ah and I know that's not right for a light bulb

[SunEagle]

Ya once this one dies I'll spend some time reading and talking to people about batteries. Based off of my small solar panel I should be looking at golf cart batteries which only have 30-35ah which will still be plenty for me.

im confused about something. Amps= watts%volts
if I have leds connected straight to the charge controller and they use 9watts%12 volts= .75ah
now my tv will be plugged into the inverter and be roughly 80watts%120 volts = .66ah

i know I'm mistaken here somewhere but how does one led light bulb use more power than a tv?

If i multiply the light bulb .75 by 10 to make it the same as 120volts it's 7.5ah and I know that's not right for a light bulb

Actually your math should be in amps not ah.

The problem is while the 9 watt DC LED has a higher amp rating it will consume less Watt Hours then the 80 watt tv. Don't look at the amount of Ah consumption on the load because that causes all kinds of confusion when you figure in the voltage of the load. Use Watt hours as a usage value and calculate back as to how many Ah the battery will use based on it's voltage rating.

9 watt LED x 8 hours = 72 watt hours / 12V = 6ah
80 watt TV x 8 hours = 640 watt hours / 12V = 53ah.

[Xplode]

Yup. What SunEagle said.

Amps X Volts = Watts (not actually but let's not go down that rabbit hole just yet)

Watts x duration (in hours) = Watt hours (Wh)

Now, since you're calculating battery capacity, and you're generating the 120v from an inverter, there will be some inefficiency of the electronics. So assume 80% (the brochure will tell you 97% but that only applies in very specific load configurations).

So take your TV's Wh total (640Wh from SunEagle example) and divide by 0.8 to get a note accurate estimation.

640Wh / 0.8eff = 800Wh

Which from a 12v battery is (800Wh/12) about 67Ah

Efficiency will probably be better than this, but your battery will degrade over time so this helps build in a little buffer room.


If you're curious to learn about the power consumption of your devices, buy a "kill-a-watt" off Amazon. It'll tell you how much energy you're going to need.

[Freeesun]

My final step here is fuses and I'm ready to setup my system once my inverter comes in. I've read that I need s fuse from my battery to inverter and also charge controller to battery. The manufacture for my inverter said to get a 40amp fuse between my battery and inverter but now I'm wondering what should I put between my cc and battery. Considering my output will be max 2.8 amp (according to my panel box) I think I should use a 4amp fuse for that because I figured 2.8x 125%= 3.5 so get a 4

also I have no idea how the manufacture came up with a 40 amp fuse rating for me?

Earier in this forum someone said i aid I can get one fuse for both of these and be done with it? Should I get a single 50 amp fuse and connect both to the positive terminal of the battery?

my final question for this forum (for now at least) would be I found fuses on amazon that are 40amp 32v I believe but I need 12v.. could I use these or should I look for 12v ones?

[Xplode]

Fuse ratings are the max that they will handle, so a 32v (or even a 1000v) rated fuse is fine. You just make sure the rating is higher than your application.

I don't know off the top of my head what your inverter is for wattage, but the fuse is to protect the wire. So if you're using #8awg or larger and your Inverter is less than 450W, 40A seems appropriate.

For the cc, 4A is probably good.

[Freeesun]

For grounding I'm going to put a pipe down into the ground and I'm wondering how do I go about grounding the system?

Im thinking I should buy a bus bar and connect the cc. Battery and inverter to it and connect the bus bar to the pole in the ground?

[Sunking]

For grounding I'm going to put a pipe down into the ground and I'm wondering how do I go about grounding the system?

Why? Grounding does nothing for your application

[Freeesun]

I thought you have to ground everything

[Mike90250]

I thought you have to ground everything

Well, it depends. If you are putting a panel on your garage and keeping a battery charged, what's grounding going to do ? no appliances, sinks, plumbing,

many small inverters don;t have a ground lug. Inverters for RV & cars don't have ground lugs.

If you have lightning storms, you would want to ground the metal mounting gear

[Sunking]

No there is no requirement to ground a 12 volt system. Only applies if system voltage is 50 volts or higher in an occupied structure with permanent wiring system. You would just be throwing more of your money away, and trust me every penny you have spent is lost money. You just do not know it yet.

Wished I could help you, but I cannot. So far you have taken one bit of advice, what little has been given, and throwing all known design concepts and practices out the window. All your issues revolve around not having any plan or objectives. All pieces of equipment must be matched in order to work with each other. Here are two examples.

With a 12-volt 300 watt Inverter like you have using a Pb battery requires a minimum 12 volt 200 AH battery along with a 20 Amp Controller and a 240 to 360 watt panel depending on what type CC you use or MPPT or PWM.

With a 50 Watt Panel like you have can only support a 25 to 35 AH battery depending on the controller type being MPPT ot PWM and a 50 to 60 watt Inverter.

Honestly no one can help you with what you have. To go off-grid solar you must do two things or forget it.

1. Determine Watt Hour needs as that determines all the equipment requirements.
2. No budget, sky is the limit because you decided to use the most expensive power source known to man and must be willing to pay 5 to 10 times more for power just in battery cost alone. . Smaller the scale, the more it cost.

So not much I or anyone can do for you. For $500 to $1000 you could run a 50-amp circuit from your home and run lights, fridge, lighting, heater, small air conditioner, and anything you want for as long as you want. $1000 in solar might run a small fridge and $500 or that in a battery you replace every few years supplies you with $100 worth of electricity. Bottom line here is a 50 watt panel makes a good USB charger to charge 4 or 5 cell phone sin a day. In a year will generate 20 to 50-cents worth of electricity. But hey the Sun is Free when it shines,

[Freeesun]

the inverter size shouldnt matter because the power will just drain the battery quicker. i wont be using the shed all the time so charge discharge time should be fine. my cc is the cheapest amazon pwm and the battery i have is a regular car battery that i got for free but will end up getting a gold cart battery when it dies.

i think that when i use this system that itll be fine especially when i downsize the battery to the proper size for the panel.

[Sunking]

the inverter size shouldnt matter because the power will just drain the battery quicker.

Right you are and with your grossly over sized Inverter will drain and kill the battery very fast.

[Freeesun]

it was the smallest pure sign wave i could find and i would like to run a tv and a radio every once and a while. i almost bought a 600 watt and im happy now that i didnt. i didnt know that inverter size matters with battery size. i just figured it would drain the battery quicker while using more load.

so for ground now im guessing i connect my cc negative to battery negative and battery negative to inverter negative? any fuses in between?

[Tecnodave]

Freesun,

An automobile starting battery's job is to start the car, it's job I'd done in 15 seconds or less, then it's going along for the ride, on the other hand a golf cart battery is charged at nite then when you go out on the course it's all on its own! (Unless you like pushing) That is the minimum battery to be considered useful for solar use. Almost all newcomers to off grid murder their first set of batteries. Consider 2 ea. "GC-2" golf cart batteries as a start, then find a MPPT controller than can charge that set, you will need something like 20 amps output. More and battery will be cooked, less and you will be undercharging. Keep the inverter small, big inverters need bigger batteries and use more power, electric heater .......forgettaboutit! stick with small and efficient.....LED lites, occasional small power tools, read a lot, you have a lot to learn.....