Solar Array Size

[Rescuebox]

I am very new to using solar. I have been studying it for a while but I can’t seem to find my answer. I am sure this has already been discussed but I have not been able to find it.

I am building an off grid system for my Rescue Camper. I plan to have a 24 volt battery system. I plan to use four 24 volt 200 ah batteries.

All of my lights and water pumps will be run on 12 volts. I will run my refrigerator, Air conditioner and occasionally a microwave on 110 volts. I may eventually swap my A/C to a 12/24 volt Mini Split A/C.

If I have it calculated correctly I will need 800 ah of Lithium Ion batteries to run my A/C for up to 10 hours at night. The trouble I am having is figuring out how many watts of solar that I need to recharge my 800 ah of batteries and run my A/C in the daytime.

Could someone tell me if this will work and how to calculate my solar array size?

Thanks

 

[sunshine_eggo]

I am very new to using solar. I have been studying it for a while but I can’t seem to find my answer. I am sure this has already been discussed but I have not been able to find it.

I am building an off grid system for my Rescue Camper. I plan to have a 24 volt battery system. I plan to use four 24 volt 200 ah batteries.

So 800Ah of 24V (25.6V LFP) is 20,480Wh.

All of my lights and water pumps will be run on 12 volts. I will run my refrigerator, Air conditioner and occasionally a microwave on 110 volts. I may eventually swap my A/C to a 12/24 volt Mini Split A/C.

I would look hard at a simple 110VAC unit and compare the cost to a DC unit. IMHO, the efficiency gains rarely justify the increased price.

If I have it calculated correctly I will need 800 ah of Lithium Ion batteries to run my A/C for up to 10 hours at night.

If we're talking typical rooftop RV A/C, then those burn as much as 1500W.

20480/1500 = 13.65h (you'll lose some in efficiencies)

You either need a soft start or an inverter capable of dealing with the compressor surge current, which can be 5X run current.

The trouble I am having is figuring out how many watts of solar that I need to recharge my 800 ah of batteries and run my A/C in the daytime.

Could someone tell me if this will work and how to calculate my solar array size?

Depends on your available insolation, but we'll assume 5 hours (5 hours of equivalent full power output from solar exposure from sunrise to sunset - no shading). Let's assume you want to be able to use loads beyond just the A/C, and you want to be able to fully charge your battery in a day with no other loads.

20,480Wh / 5h = 4100W solar. Likely more than you have roof space for. That's about 220 square feet of panels assuming 20% efficiency.

Lastly, panels mounted flat on a roof rarely produce anything near full power. In the heat of summer, the hot cell temperature will actually decrease your panel output, so don't count on more than about 80% of your rated array power.

See link #1 in my signature.

 

[Rescuebox]

So 800Ah of 24V (25.6V LFP) is 20,480Wh.



I would look hard at a simple 110VAC unit and compare the cost to a DC unit. IMHO, the efficiency gains rarely justify the increased price.



If we're talking typical rooftop RV A/C, then those burn as much as 1500W.

20480/1500 = 13.65h (you'll lose some in efficiencies)

You either need a soft start or an inverter capable of dealing with the compressor surge current, which can be 5X run current.



Depends on your available insolation, but we'll assume 5 hours (5 hours of equivalent full power output from solar exposure from sunrise to sunset - no shading). Let's assume you want to be able to use loads beyond just the A/C, and you want to be able to fully charge your battery in a day with no other loads.

20,480Wh / 5h = 4100W solar. Likely more than you have roof space for. That's about 220 square feet of panels assuming 20% efficiency.

Lastly, panels mounted flat on a roof rarely produce anything near full power. In the heat of summer, the hot cell temperature will actually decrease your panel output, so don't count on more than about 80% of your rated array power.

See link #1 in my signature.

Right now I am using a 6000btu LG a/c which is very energy efficient.

Thanks for your imput

 

[Zwy]

Right now I am using a 6000btu LG a/c which is very energy efficient.

Thanks for your imput

If it isn't inverter based like a mini split, then it can't be that energy efficient. Looks to be cheap window air conditioner unless you have the portable unit.

I can run the roof air on my truck camper using my 24V 3000W Growatt inverter but it takes about 1200W so run time on my 280Ah bank would be about 4.5 hours and I wouldn't be able to run the compressor fridge/freezer. With an inverter 120V mini split drawing 400W on average non stop, that jumps to 16 hours on battery alone.

Get yourself a Killowatt meter and measure the wattage your current air conditioner draws.

For array size on any RV, you put the maximum PV that will fit on the roof. Measure the roof size, then look for panels that work well with the dimensions of the roof. It seems an RV never has enough PV. The advantage of fully covering the roof is less heat load due to the air gap between panels and roof, plus enough PV to not only run AC but also charge the battery bank to maximum for the day.

 

[sunshine_eggo]

Right now I am using a 6000btu LG a/c which is very energy efficient.

Thanks for your imput

Got specs?

Good news is that the 1500W number is for your typical 13,500-15,000 BTU RV rooftop A/C, so you should be notably lower than that. Let's just say half.

20480Wh/750W = 27 hours.

If you only want to run it 10 hours per day total, you'll need.

10 * 750W = 7500Wh

PV estimate:

7500Wh/5h = 1500W - of course you can't run anything else without dipping into your battery capacity.