24V System Check

[NordicNerd]

Hi all, I am installing an off grid system for my bunkie at the lake (a few years off from the main cabin build and I am tired of running a generator). I would appreciate any feedback / comments regarding the schematic attached. I will not have a generator back up / transfer switch. I wasn't going to build it this year but I ended up with 2x 345 watt qcell panels that were only a couple of years old a two battle born batteries. The total build will be less than $2200 Canadian (about $1600 USD). I tested the panels and batteries and both check out perfect (total cost was $1000 for panels and batteries).

Also, I realize I could put the combiner box at the panels, but it is much less expensive to use 2 runs of 10 awg instead of 6 awg due to voltage drop. Other notes:

- I do not have room for an AIO wall mount
- all components will be inside in a 12 inch high storage area (60" x 80" wide)

Thank and I appreciate the feedback.

 

[Rednecktek]

If you get a MPPT controller with 100v+ PV input you can throw those panels in series and just do 1 run of wire and skip the combiner box completely. Even with 2 strings you can just use branch connectors at the panels and go single run with no combiner. Saves a lot of work digging through roots.

Other than that it looks good to go. You might want to plan in a way to get your existing genny to feed a battery charger for those cloudy rainy weeks when you just aren't getting enough sun.

 

[Craig]

Im wondering if 10 GA wire is enough for 9 amps at 100 ft?

 

[NordicNerd]

Thank you! With the temperature correction up here in Canada a 94 VOC can turn into a 110 VOC at -20 Celsius. So I would need to go bigger on the charge controller for 15O VOC or more with another panel going in eventually. That would increase my cost by about $350 - 400. I was thinking using parallel charge controller for another set of panels in the future if I need them.

Also, It's all sand where I am so digging is not hard.

 

[NordicNerd]

Im wondering if 10 GA wire is enough for 9 amps at 100 ft?

I could go 8 ga. You are correct. I have about a 5% voltage drop with 10 ga wires. I loose 17W per panel (34 watts total) with 10 ga. With 8 ga there is a 3.1% voltage drop (1.18 volts or 10W per panel 20 Watts total). So I would gain about 14 W total if I use 8 ga. I look at the cost difference, but I'm not sure its worth it to me. Thank You!

 

[Rednecktek]

Thank you! With the temperature correction up here in Canada a 94 VOC can turn into a 110 VOC at -20 Celsius. So I would need to go bigger on the charge controller for 15O VOC or more with another panel going in eventually. That would increase my cost by about $350 - 400. I was thinking using parallel charge controller for another set of panels in the future if I need them.

Also, It's all sand where I am so digging is not hard.

OK, that makes sense for paralleling. You can still save yourself a lot of work and money by putting your branch connections at the panels and run a single wire back to the MPPT.

10awg should be more than enough copper at a mere 9a.

 

[Craig]

I could go 8 ga. You are correct. I have about a 5% voltage drop with 10 ga wires. I loose 17W per panel (34 watts total) with 10 ga. With 8 ga there is a 3.1% voltage drop (1.18 volts or 10W per panel 20 Watts total). So I would gain about 14 W total if I use 8 ga. I look at the cost difference, but I'm not sure its worth it to me. Thank You!

Makes sense

 

[NordicNerd]

OK, that makes sense for paralleling. You can still save yourself a lot of work and money by putting your branch connections at the panels and run a single wire back to the MPPT.

10awg should be more than enough copper at a mere 9a.

Thanks again. Yeah, I'm going to run weeping tile for my cabling and install a pull cable for future if needed. It is a bit more work for sure - people always told me you don't buy a cabin you buy a project . . . .

 

[NordicNerd]

Decided I will use a T-fuse : 300amp. I took a look at some ratings on 3000 W inverters. Any thoughts?