Off grid solar system design help?

[Cord]

Greatly appreciate the info. Well, the observations were correct, the panels were hail damaged. The search continues on.

I bought a 70v 15w controller, any suggestions on what I want to Target for panel watts? I figure that my angles will not be close to optimal and there might be some shading.

 

[Williy]

Never heard of this odd thing: 70v 15w controller,
controllers come in 12, 24 and 48 volts and some
have 36 volts

willy

 

[koshari]

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

i have precisely 3 setups pretty much as you describe. all my panels are recycled house 24v 250w panels.
all mine are 24v with 2 batteries in series and all 3 use cheap chinese pwm controllers ( all rated at 30A so i can have a common spare) . one is a pump controller for a 24v solar lift pump (2 x 7ah alarm batetries in series with 1 panel) , the other 2 are set up in shipping container (2 x 80ah sealed lead acids in series / 2 panels in paralell) and machinary shed (2 x z80 marine batteries / 2 panels in paralell) .

 

[sodamo]

Greatly appreciate the info. Well, the observations were correct, the panels were hail damaged. The search continues on.

I bought a 70v 15w controller, any suggestions on what I want to Target for panel watts? I figure that my angles will not be close to optimal and there might be some shading.

Buying individual pieces without an overall plan? What can you connect to a 15w controller? Can you provide a link?

I just bought this cheapy https://www.amazon.com/gp/product/B07FT7RRGT/ref=ppx_yo_dt_b_asin_title_o03_s01?ie=UTF8&psc=1, but I already know what it connects to.

 

[Cord]

Never heard of this odd thing: 70v 15w controller,
controllers come in 12, 24 and 48 volts and some
have 36 volts

willy

Here is the controller I purchased: SmartSolar MPPT 75/10, 75/15, 100/15 & 100/20 - Victron Energy

 

[sodamo]

The Victron site answers you pv question.
220watts @ 12 vdv
440watts @ 24 vdc

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-75-10,-75-15,-100-15,-100-20_48V-EN.pdf

Note:

Safety
EN/IEC 62109-1, UL 1741, CSA C22.2
1a) If more PV power is connected, the controller will limit input power. 1b) The PV voltage must exceed Vbat + 5V for the controller to start.
Thereafter the minimum PV voltage is Vbat + 1V
2) A PV array with a higher short circuit current may damage the controller.

 

[Cord]

Thanks for pointing out the wattage. Theoretically a 250w panel would be more than sufficient. However, I know that my installation won't be optimal. The install angles will be wrong and it's likely there will be shading. What I was trying to ask is; how much do I need to oversize the panels to maximize the potential of the controller?

 

[Phil Timmons]

if you would like some fairly exact numbers, maybe take a look at the NREL (National Renewable Energy Lab) online calculator program called PVWatts. The have a 30+ year database across the US and points beyond.

It uses your location, equipment type, install angles, direction, losses across inverters, etc., and gives you month-by-month estimates of production -- in practice, we find their model typically within 1%. Here is the link. You can change numbers, equipment, and mounting angles, directions, and see how that changes things. Or you can just use the model defaults. >> PVWatts

But for a shotgun number, if you take your total PV rated DC watts, with a typical US install, and go with 80% (PV x .8) that will give you rough AC Watts, and multiple the number of hours (typical US 6 or so) that will give you around the AVERAGE expected daily output.

 

[sodamo]

Me, I’d get as close to 440 watt, nominal 24v pv to charge a 12 v battery.
I would NOT risk hooking up more than the manufacturer maximum and hope for inefficiency. Should you blow the CC I doubt warranty would cover.

 

[ArlyA]

Don't feel bad. I just wanted to charge lawn mower and atv batteries in our unpowered garage. Started out with a 75w which did something but not enough, so now I'm adding another 100w panel. Trees and snow are not your solar power friends.