Off grid solar system design help?

[Cord]

We have a off grid cabin and I'd like to use a solar panel to power some low voltage lights. My thinking is to buy some 400 watt, 40 volt solar panels and use them to charge some semi truck batteries. I can get these batteries super cheap used. Because the batteries would not be matched, I was thinking there's be one solar panel and controller per battery. I'm guessing two setups would be enough to power the led lights. I only want to power lighting, any other power demands would be on the generator. Does anybody have experience with a system like this? I want to confirm my approach before buying any parts. These are the panels I was considering: Solar panels

 

[Skagit]

We live off grid and our house is run off 120w (x6) solar panels. I wouldn't do a split system like you're describing... If you have a source for used group 31 batteries then finding a matched set shouldn't be an issue, highway trucks run sets of 3 to 6 depending on the application and they're always replaced in sets.

 

[Cord]

The panels that I was considering makes 40 volts, can this panel be used on 12v batteries that are in parallel?

 

[AndyMA]

You don't want to connect the panels directly to the battery. You connect the panels to a Charge Controller which controls how the batteries are charged. A good charge controller is the Midnght Solar Kid MidNite Solar Products

 

[Grumpycat]

The panels that I was considering makes 40 volts, can this panel be used on 12v batteries that are in parallel?

A solar panel needs a purpose-made inverter/controller to optimally function. Your PV panel does not "make 40 volts", that is just marketing telling you numbers to make you think you understand. The actual voltage for optimal electric production depends on brightness of the sun and temperature. Optimizing the voltage is best for getting the most power and for life of the panel.

400W are super premium panels these days. 315W is the best value. I think your best bet would be to purchase several panels and a matching off-grid inverter which is designed for battery storage. The same inverter will charge your batteries and provide 120VAC and probably 240VAC too, all day and night if you have enough battery.

 

[LittleBill21]

if your sole purpose is lighting and low voltage, you can skip an inverter. just need panels and a solar controller.

 

[Williy]

You need batteries that are the same voltage and amps buy your solar panels in 3's and the panels usually are 30 volts, 7 to 8 amps and they don't produce like the panel says 400 watts don't expect they will produce 400 watts maybe about 250 to 300 watts would be more realistic. Midnite solar makes very good products. Your solar panels you want in groups of 3 so you can set up your controller. You would
also need a dc circuit breaker box that you will hook
up all you solar panels and can shut them off if need be. Think its a state law?? Check this web site out:

DIY OFF GRID SOLAR SYSTEM

DIY OFF GRID SOLAR SYSTEM: Day by day the price of the solar panel falls gradually. But still, installation of a complete off-grid solar system is costly. So I write this instructable to get all the components of your solar system separately and assemble it all by yourself. C…

www.instructables.com

willy

 

[Grumpycat]

if your sole purpose is lighting and low voltage, you can skip an inverter. just need panels and a solar controller.

You do not understand electricity. You think everything is explained by “voltage”.

Solar panels are silicon solid state devices and being such are current devices. A proper PV inverter is constantly searching for the optimal voltage to transfer energy from the panel.

Download a PV panel data sheet. The open circuit voltage is commonly around 40. But the maximum power voltage is around 34 and will vary several volts depending on how bright the sun and temperature.

So one spends $300-$500 for a premium 400W panel and you recommend skipping the inverter or battery controller?

This isn’t a particularly good data sheet, but ine I found quickly.

https://documents.unboundsolar.com/media/9434325__black_mono_perc_1621295931.pdf?_ga=2.46697447.1325783907.1622500938-1744675150.1622500938

With no more knowledge than demonstrated the O.P. should plan on spending money to get a working package rather than buy the most expensive PV panel, the cheapest battery, and pray to find a means to put them together. This is $2616

https://documents.unboundsolar.com/media/9434325__black_mono_perc_1621295931.pdf?_ga=2.46697447.1325783907.1622500938-1744675150.1622500938

 

[LittleBill21]

You do not understand electricity. You think everything is explained by “voltage”.

Solar panels are silicon solid state devices and being such are current devices. A proper PV inverter is constantly searching for the optimal voltage to transfer energy from the panel.

Download a PV panel data sheet. The open circuit voltage is commonly around 40. But the maximum power voltage is around 34 and will vary several volts depending on how bright the sun and temperature.

So one spends $300-$500 for a premium 400W panel and you recommend skipping the inverter or battery controller?

This isn’t a particularly good data sheet, but ine I found quickly.

https://documents.unboundsolar.com/media/9434325__black_mono_perc_1621295931.pdf?_ga=2.46697447.1325783907.1622500938-1744675150.1622500938

With no more knowledge than demonstrated the O.P. should plan on spending money to get a working package rather than buy the most expensive PV panel, the cheapest battery, and pray to find a means to put them together. This is $2616

https://documents.unboundsolar.com/media/9434325__black_mono_perc_1621295931.pdf?_ga=2.46697447.1325783907.1622500938-1744675150.1622500938

LOL

Dude... he said he needed low voltage lighting. that's all he said, that tells me he's looking at some form of 12v lighting like an rv setup. he needs a solar panel and a solar controller, to charge the battery, the 12v lights will have their own buck/boost controller, or are old school and just a regular bulb, use all the fancy words you want but at the end of the day, he needs a battery a panel and a controller and a light and he's done. if he actually provide more then 2 words for what he wanted, maybe we could give him a better design.

I don't care what panel he's quoted, if he knows nothing about solar, then he knows nothing about solar panels, so why should I base my comments off that.

LOL maybe you should look at what he quoted. he's looking at 65 dollar used panels, and used truck battery's, yea i think he wants to go cheap...... most controllers can easily handle a 40v OC panel with ease. so yea, he doesn't need a inverter, can always add one down the road if need be

 

[ning]

We have a off grid cabin and I'd like to use a solar panel to power some low voltage lights. My thinking is to buy some 400 watt, 40 volt solar panels and use them to charge some semi truck batteries. I can get these batteries super cheap used. Because the batteries would not be matched, I was thinking there's be one solar panel and controller per battery. I'm guessing two setups would be enough to power the led lights. I only want to power lighting, any other power demands would be on the generator. Does anybody have experience with a system like this? I want to confirm my approach before buying any parts. These are the panels I was considering: Solar panels

These panels look like they've been through an intense hail storm or were damaged by some other means.

*If* they work at all, they're going to be missing a lot of cells and certainly will never come anywhere near 400W.

 

[Cord]

I noticed that shading you pointed out. I was hoping it was just dirt, but if it's damage then I'll pass. There are other options out there.

How can I test the panels for function?

 

[Cord]

LOL

Dude... he said he needed low voltage lighting. that's all he said, that tells me he's looking at some form of 12v lighting like an rv setup. he needs a solar panel and a solar controller, to charge the battery, the 12v lights will have their own buck/boost controller, or are old school and just a regular bulb, use all the fancy words you want but at the end of the day, he needs a battery a panel and a controller and a light and he's done. if he actually provide more then 2 words for what he wanted, maybe we could give him a better design.

I don't care what panel he's quoted, if he knows nothing about solar, then he knows nothing about solar panels, so why should I base my comments off that.

LOL maybe you should look at what he quoted. he's looking at 65 dollar used panels, and used truck battery's, yea i think he wants to go cheap...... most controllers can easily handle a 40v OC panel with ease. so yea, he doesn't need a inverter, can always add one down the road if need be

Yes, I'm trying to work with a budget. I think I'll steer myself away from the truck batteries and go with some AGMs instead. According to some calculators I'd be looking for a battery between 100-160aH. Thoughts on going with a single large battery vs a pair of smaller ones?

You are correct, low voltage only. Any 120/240v needs to be handled with the generator.

Since the first post, I've purchased a Victron 75/15 controller.

 

[LittleBill21]

Yes, I'm trying to work with a budget. I think I'll steer myself away from the truck batteries and go with some AGMs instead. According to some calculators I'd be looking for a battery between 100-160aH. Thoughts on going with a single large battery vs a pair of smaller ones?

You are correct, low voltage only. Any 120/240v needs to be handled with the generator.

Since the first post, I've purchased a Victron 75/15 controller.

agm's are more money, but don't require watering, nor needed to be vented, see if that is important to you. single battery is better if doing dual 12v, as you don't have to worry about balancing battery loads, if you wire in series 6v's then its a non issue. gc2 from sams club is considered a pretty solid option.

 

[Phil Timmons]

Are you doing good on your design, now? Need some more review?

For "lite" 120 / 240 Volt Loads -- like say a notebook computer, or a wifi for internet -- various little inverters, typical small portable car and truck types, generally work pretty well. That way you can keep down the Generator Run Time.

 

[Cord]

For the moment I'm ok with the design. I would like some advice on how to evaluate the panels for condition and proper function.

 

[ArlyA]

We have a "off the grid" garage we store a mower and boss atv in which I'm in the process of adding panels to so I can charge there batteries. Its not been hassle free job and I'm adding a second 100w panel now. Just ask if anyone cares to see the panels and there mounts.

 

[Snobdds]

Start with buying a solar generator. These take all the guess work out of the equation. Hook up a couple of panels and your hooked up. There is no need to build your own system anymore. These things are great.

 

[Newby first timer]

I started building my own system
It is a lot larger than the system you want
I started with (2) 200amp Lithium Increased two (6)
I purchase (2) Flamezum 4000w/8000w Inverters and they were named right
I flamed one of them out. They are not as advertised and you get absolutely no customer service from these thieves
I purchased (3) Renogy Rover Elite 20A/40A Charge Controllers.
I already had a bunch of Harbor Freight Solar Panels and I purchased (10) 100A 12V panels to add to them.
I hooked up all of my Harbor Freight Panels to one Controller and the (10) 100A panels to one of the other controllers.
The Controllers are hooked up to a Buss Bar that the Batteries are hooked up in series for a 24V system.
The Imbalance between the Harbor Freight Panels and the New 100A Panels Freaked the controllers out Even though they were not directly connected. and Cooked one of the Controllers.
So I went back to the drawing board and called the altE Store that I found on the internet
I have talked to them a few times and have watched the videos that they have on their site several times over to learn about what I am doing.
When I get my order from altE
I will be set up with a Magnum 4024 Inverter which has (2) 30 Amp poles and (1) 220 Amp pole all built into one unit.
I purchased the Magnum Panel which has all of the breakers ,switches and other stuff to make a legal ,safe connection of everything.
And Today I added their Magnum 100Amp Charge Controller.
Adam their Rep has been very very helpful and informative in getting me set up with what I am needing
I am taking the Harbor Freight panels off of my system and I am going to purchase more 12V 100Amp Panels for my system so that it will be a balanced system.
I am learning as I go and the learning curve has bit me a bit with lower grade items that what I need for my system.
All of these extra items will not go to waist as I am looking to build a smaller system for a smaller demand.
If you are planing on building your own system I highly recommend that you check out altE and watch some of their videos.
And
Do not cheep out just to get by with your system. It will not be cheep in the end.
Good luck with what you end up with.

 

[sodamo]

Interesting thread.
I know several members on solar forums that own tractors, but I ask my tractor questions here and stick to solar issues there.
I have been truly off grid since 2004, have had several systems, still have a traditional 120/240 vac house system as well as a 48vdc purposed system (and building a 12 vdc purposed system) and wouldn’t begin to sort out the previous posts.

ETA:
For the curious
My current house system is 52 PV (14.2kw) connected to 4 Outback Charge Controllers charging 12 SimpliPhi 3.8 lithium batteries driving 2 Outback Radian Inverters with the appropriate breakers and connections and backed up by a 14kw Kohler LP generator and a 10kw MEP diesel.
My purposed system is 6 12v panels directly connected in series to 48 vdc pump controller.
My being built system is 2 235w PV panels (used but look new compared to OP post) connected to 12/24v charge controller to a 12v FLA battery to power 12v fan, pump, and lights for my hydroponics.

 

[Phil Timmons]

For the moment I'm ok with the design. I would like some advice on how to evaluate the panels for condition and proper function.

mkay. Usually we look for 3 things:

+ Open Circuit Voltage -- point at Sun and measure Volts across the leads.
+ Short Circuit Current -- (we do this, but only a maybe for you) -- make sure the Amp Rating and connections on your meter can handle the current -- many have a fuse and Max of 10 Amps. You can do this in a dark area, for less Amps.
+ MPP -- Max Power Point. This usually takes an inverter, or micro-inverter that acts as a load, and optimizes the combination of Volts and Amps (Volts X Amps = Watts) to get max combination from each panel. This tells you what it will really produce in the optimized system.