Thoughts On System Design - Assistance Appreciated

[rkwolfe]

I have a 12 x 20 off grid cabin I have been building on and off for about a year. Very excited about solar power and ready to make the investment in batteries, panels, charge controller, etc. Been studying Will's videos and projects for a couple of years now. Amazing and inspiring. I am a Mechanical Engineer in the power industry with basic knowledge of wiring and power generation. I have done some home wiring with 120V AC but I have never done DC. Would like to get some thoughts on compatibility between the major components before I make the investment.

I plan to run a DC air conditioning unit once in a while in the summer. Other than that just charging a computer, small electronics, and a few lights the rest of the time for load. Have a wood burning stove for heat. I am looking at the Hot Spot Energy DC48 Unit. The direct DC unit is very efficient. Curious if anyone knows of a different model. This is the only one I can find.

Running some basic numbers for charge per day based on 6 hours I was thinking of two strings of 4 panels 440W / 50 VOC / 11A (each string) in (two strings) parallel for a total output of around 200VOC at 22A. I think that would be a good fit for a Victron 250V, 100A MPPT. For batteries I like the SOK server style units 48V 5kW. I was thinking two in parallel for about 10kW storage.

With the cabin being off grid I am concerned about the inverter running a lot while I am not there – hence the DC air conditioning unit. I would like to set up the system so it can charge and the air conditioning unit can run a little to control humidity and keep the cabin temp at or below 90F to preserve the batteries. That would require a bus in the 48V range to power the air conditioner and an inverter for 120V AC loads.

I like the Victron setup with the Lynx shunt 1000 and Distributor 1000. I don't have the fusing or breakers laid out yet but I have a diagram with the major components.

Looking at the spec sheets the air conditioner operating range is 46-59VDC, the battery charging voltage is 57.6-58.4VDC, and the Victron inverters show an input voltage of 38-66 VCD. Not sure how sensitive the air conditioning unit is or what type of fluctuations come out of the MPPT. My only concern looking at the specs is that the battery charging range is within 1 VDC of the top end of the air conditioning unit. I don’t have any practical experience to know how much the system voltages fluctuate.

Any thoughts would be greatly appreciated. Layout and spec sheets attached.

 

[12VoltInstalls]

One thing jumps out just reading: It says it removes a quart per hour of water.

Is that sufficient?

Also think you’ll need more panels to utilize this 24x7 unattended.

 

[MichaelK]

You pay a price premium for anything DC powered, so I think you would be better off just scaling the system up a bit, and then going with a straight AC only power system. That's the way I did it, and everything functions very well for me. I have 5500W of panels online as we speak, and I leave my inverter on 24/7 to power the refrigerator, router, and other stuff.

I would say that 10kW of storage is too small for a cabin system that will be powering what you want to power. I would go at least 150% on both the batteries, and the solar input.

 

[rkwolfe]

You pay a price premium for anything DC powered, so I think you would be better off just scaling the system up a bit, and then going with a straight AC only power system. That's the way I did it, and everything functions very well for me. I have 5500W of panels online as we speak, and I leave my inverter on 24/7 to power the refrigerator, router, and other stuff.

I would say that 10kW of storage is too small for a cabin system that will be powering what you want to power. I would go at least 150% on both the batteries, and the solar input.

Thank you for the feedback! I agree on the DC power premium and I have been on the fence with that. It is also a concern that the top end DC input for the air conditioner is 1V from the bottom end voltage input for battery charging. If they don't work well together then I just wasted $2k on an air conditioner. I figured the overall system would be a little under powered for continuous operation during the summer. I rarely use it more than 2 days in a row over the summer so I was thinking it might get me by for a day or two in a row with time in between to charge. On the other hand a cheaper system with more panels and another battery would cost about the same and give me more output. If you don't mind me asking what type of inverter and charge controller configuration do you have and how many square feet to air condition? I would rather go with an all in one like the Growatt to make the wiring simpler but I was concerned with the stand by voltage required. In summary I don't have any experience with the systems and I don't know if the premium cost for a Victron or similar system is worth the investment. My concern (maybe unwarranted) with the all in one units was the waste heat with a lower efficiency. Also not sure the failure rate on those units compared to the Victron type of equipment and I am a little concerned since it will operate most of the time un-attended.

 

[MichaelK]

I have an Schneider XW+6848 mated to a Midnight200 charge controller charging Rolls-Surrette batteries. I included a Midnight power center in my installation, which holds all the AC/DC breakers that control the whole system. Following Midnight's wiring scheme, I wired it all up in an hour or two. I would not concern myself with saving a bit of time wiring a system that will be running for decades. An extra hour or two of very well-spent time, I think.

I'm just running a single 8000BTU wall air-conditioner upstairs, that consumes ~750W. After about 3 hours of cooling of so, it reaches the set point and starts cycling on and off, with the average power consumption dropping from that point forward. I installed a 1000W array facing due West to supply the power the air-con needs in the late afternoon, so I can keep it running without any battery depletion till about 6pm.

Keep in mind that there appears to be a LOT of disinformation concerning background power consumption with the inverter just staying on. I keep seeing claims that low frequency inverters have far higher background consumption then the AiO units have. I suspect that it's purposeful disinformation created by the AiO companies themselves. All the major tier-1 companies like Magnum, Outback, Schneider, and SMA all have background consumption in the 20something to 30something Watt range. All the AiO units I've seen all have consumption in the 100+Watt range. So, I think it's intentional.

 

[12VoltInstalls]

a

gree on the DC power premium and I have been on the fence with that. It is also a concern that the top end DC input for the air conditioner is 1V from the bottom end voltage input for battery charging. If they don't work well together then I just wasted $2k on an air conditioner.

I run a 5CF mini fridge 120VAC 24x7. Both the current 1012LV and for like 3 years on a Giandel 1200W.

The efficiency ‘penalty’ is such that I ran all last summer on just 400W. So it isn’t always a problem in the kilowattsosphere.