Budget-friendly solar setup for a weekend cabin

[Q-Dog]

The OP wants to keep an ice chest cold, power a couple of led lights and charge his phone, and you guys are trying to get him to install a whole house system.

The original plan is adequate for what they want to do. Install the cabin system, learn how it works, then start planning solar for your house.

 

[ksmithaz1]

Jeeze, you want to roll 12v solar might as well not limit yourself to a bunch of low voltage stuff. They have 2KW stuff for 24V systems.

 

[12VoltInstalls]

The question is if it is wise to plan putting them into parallel connection. If they are in series, the voltage will go from max. 39V to 80V which is fine with Victron 150/35

Higher voltage gives you less % resistance loss over distance, lets you use smaller gauge wire, and ‘sometimes’ gives you a tiny bit of earlier and later charge potential.

In any case, heating consums energy. I would put heating pads but not sure about fire safety.

In a locale not 100% monitored and if the batteries go dead there is no heating and then it tries to charge when the sun comes up. I don’t have faith in Murphy not showing up in these mornings.

 

[12VoltInstalls]

View attachment 276472

Jeeze, you want to roll 12v solar might as well not limit yourself to a bunch of low voltage stuff. They have 2KW stuff for 24V systems.

Did I miss the OP locale being European?
OP also posted

• Camping fridge: ~200W per day
• Lights: ~100W per day (4 hours of use)
• Phone charging: ~50W per day
  Total: ~350W per day, while our battery stores 1200W. 1200Wh

So it does not appear that 220V was mentioned?

 

[blackarrow]

• Total: ~350W per day, while our battery stores 1200W. 1200Wh

Is this important? I mean the amount of energy in the battery is 1200W, right? Not sure if I understand correctly.

 

[CaliSunHarvester]

Is this important? I mean the amount of energy in the battery is 1200W, right? Not sure if I understand correctly.

1200W is what a device may pull at a given moment from the battery. Or perhaps 200W.

If your fridge pulls 200W for 6 hours, then it consumed 1200 Watt Hours = 1200Wh

amount of energy in the battery is 1200W, right

NOT correct. The amount of energy is 1200Wh.

 

[blackarrow]

The third panel idea is a waste because of the limit on charging current to the battery at 12v
Two panels are just fine and in the sweet spot of a 150/35

I am not sure I understand this right.
Lets say I would put 150/45 controller that can handle 3x440W panels (that is 3x42V=126V + 3x13.4V=40.2V).
Of course, in that case I would probably but additional battery to store more energy.

And then the controller transforms everything to 12V and puts it into the battery. Or am I getting something wrong here?

 

[Drunkin Solar]

I am not sure I understand this right.
Lets say I would put 150/45 controller that can handle 3x440W panels (that is 3x42V=126V + 3x13.4V=40.2V).
Of course, in that case I would probably but additional battery to store more energy.

And then the controller transforms everything to 12V and puts it into the battery. Or am I getting something wrong here?

You would be correct with the the panels you cited earlier in your post.
You have to pay attention to charging current
Thanks for learning here
It's a great place to understand

 

[blackarrow]

So this is what I came up and I think this system could support some modifications in the future if it turns out that the system need to support 2 additional panels as well as one additional battery.
Not sure why I do not need fuse between MPPT and solar panels.

 

[blackarrow]

I guess I made a mistake related to the number of solar panels. There is no way I can put 3x440W on 150/35 controller. What I could do is maybe put 150/35 now, put additional panel to have 2x440W and put additional battery in parallel and have 28.8 V. But for now with only one battery at 12V, one 440W is all I can do safely.

For 3x440W it seems to me that I have to go to at least 250/70 with two batteries in parallel.

 

[Drunkin Solar]

Two panels makes you over paneled with that controller at 12v and is a good thing for sub-optimal days to still get some charge in the battery.
You don't need a fuse between the panels and MPPT, you can put one in in if it makes you feel better but not necessary.

 

[Q-Dog]

Not sure why I do not need fuse between MPPT and solar panels.

Because a solar panel is a current limited device. If it shorts it can't deliver more power than it can make. You can put a fuse if you want to, but if you have a short it won't do anything.

 

[blackarrow]

Two panels makes you over paneled with that controller at 12v and is a good thing for sub-optimal days to still get some charge in the battery.
You don't need a fuse between the panels and MPPT, you can put one in in if it makes you feel better but not necessary.

Wouldn't that damage the controller on long run? I mean, I should have around 70A controller but with 35A it will be often on its limit with 2x440W solar panels.

 

[blackarrow]

Because a solar panel is a current limited device. If it shorts it can't deliver more power than it can make. You can put a fuse if you want to, but if you have a short it won't do anything.

Thanks, now I understand.

 

[Drunkin Solar]

Wouldn't that damage the controller on long run? I mean, I should have around 70A controller but with 35A it will be often on its limit with 2x440W solar panels.

Like I said you would be over paneled meaning that during clear skies your controller will not be able to use all the power available from the panels.
The benefit is on cloudy days most times the two panels will likely produce enough to recharge a 100 amp hour battery.
35 amp charging current will charge that battery from empty to full in around three hours on a good day. That is a nice balanced system.

 

[blackarrow]

That is also nice option. The first step is I think to try with one panel and see how it goes for a year.

 

[blackarrow]

What is still not clear to me is grounding the whole system. Although the cabin is very small (3 m high) and there are higher buildings left and right in vicinity of 30-50 m, I guess I should do the proper grounding. For now, only DC is planned, no inverter.

 

[12VoltInstalls]

What is still not clear to me is grounding the whole system

If you wish to ground the load side, take an 8ga (10ga would work for present config in your drawing) and crimp a ring terminal to it, connect to BlueSea neg(-) bus bar. Clamp other end of that to a driven ground rod.

To ground the panel frames (not the panel(s) electrical neg(-)!!! ) you can run a 6ga using a biting clamp on the panel frames homerun to the driven ground rod.
•I like to use 6ga THHN(THWN) in green for this as it is clear what it is AND if there ever is a panel “leakage” or whatever the wire is less contactable by mine or someone else’s elbow (or whatever) but that’s pickyuni OCD on my part responding to an essentially nonexistent problem I made up in my paranoid head.

The first step is I think to try with one panel and see how it goes for a year

Use two panels is my advice

Not sure why I do not need fuse between MPPT and solar panels

because one string does not exceed the maximum fuse rating listed on your panel label

 

[blackarrow]

Hello, thank you for your help. I hope I managed to make the setup as simple as possible. There are some modifications with fuses but I think this is something that could work fine.
I am not sure about fuses and wire sizes, especially the connection to the several 12V outlets for charging laptops.

 

[12VoltInstalls]

not sure about fuses and wire sizes

2.5mm wire is “like” ~15A so ten amp fuse does protect the wire.

connection to the several 12V outlets for charging laptops

What do the laptop AC chargers have printed on them for output volts and output amps? That is what you need to exceed /meet for charging the laptops from your solar.

 

[blackarrow]

It says up to 20 V (which in my case can not go above 12V) and up to 3.25 A. So The charger is rated to 65W but I guess with 12V and 3.25A I will reach only around 40W.

 

[12VoltInstalls]

It says up to 20 V (which in my case can not go above 12V) and up to 3.25 A. So The charger is rated to 65W but I guess with 12V and 3.25A I will reach only around 40W.

Up to? So that is what the obligatory labeling says for rated output voltage? Odd.

Here is one ‘somewhat inefficient’ solution.

Here is another potentially slightly more efficient solution. That’ll be 8.x-10A draw to produce up to 90W of charging.