# full time trailer solar system sizing

Registered Users Posts: 439 ✭✭
I recently had a battery bank sulfate in 10 months. So Ive been evaluating my loads. Disconnected my 300 watt inverter. Using 1 group 24 12 volt sli battery.  Testing  loads for 28 days. Radio, dometic fridge water pump leds charging 2 phones,  and on cool 40f mornings a 15 min furnace blast. Results were lowest usage 12 ah highest 20 per day.  28 days 475. (17 ah per day average) Highest amp peak 16.   I have 4 100 watt 18.9 x 5.29 mono panels. During the test it rained for 3 days complete cloud cover and I still made 17 ah avg per day without sun. My Question is in dec battery reduction at 20f,   and 4 avg peak hrs sun, what size mppt controller. And how many watts and amp hr battery  would I need to go 3 days with out running a generator. And fully charge on the 4th day with just solar?
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion

• Registered Users Posts: 439 ✭✭
Forgot to add the panels are not on top of the travel trailer they are pole mount adjustable.
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
• Registered Users Posts: 4,496 ✭✭✭✭✭
Using 20ah/day for consumption, 20ah x 3 days = 60ah. At 20°F, capacity might be ~ 2/3 of rated, so 60 ÷ .66 = 91ah rated capacity needed. To keep DOD to under 50%, a roughly 200ah@12v bank is indicated. A pair of 6v GC deep cycle batteries in series for ~200ah at 12v would be a good choice.

To recharge in one day - assuming 90% overall charging efficiency, to put 60ah back is 60÷.9= 67ah x 12v = 804w ÷4 hrs= ~200w ÷ .75 temp adj = roughly 250w min panel. I would increase that to at least a 10% of capacity rate of charge, so 225 x .1 = 22.5a x 15v charging = 330w, so your 400w of panels should work.

400w panel ÷ 11v charging very low SOC batteries = 36a min controller size, but I'd go a bit bigger to give some headroom.

All this assumes 12vDC loads. If using the inverter, inverter losses and AC loads would need to be added, and sizing recalculated.
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Solar Expert Posts: 3,854 ✭✭✭✭✭✭
One load stands out above all, that is the refrigerator, please tell us exactly what it is, because a refrigerator is a very high demand load, which is often underestimated,
1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS
Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
• Registered Users Posts: 4,496 ✭✭✭✭✭
The dometic fridge would have to be a propane/12v model.

To cool with electricity, it would have to be extremely well insulated to cool in a normal indoor temp environment and stay under 20ah. Dometics aren't particularly well insulated AFAIK. My top load home made version can do it in fridge mode, but it has 6"+ of rigid foam insulation.
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Registered Users Posts: 439 ✭✭
Just my Fridge on lp was 12 ah in 24 hrs by my meter.  I see .3 on standby. 8 running .I'll check the dometics model numbers when I get back.
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
• Registered Users Posts: 439 ✭✭
Yes estragon on propane. So a 40 amp controller? Would that be 2 in series 2 parelled panels? And why doesnt the ahs from cloudy days enter in the calculation?
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
• Registered Users Posts: 4,496 ✭✭✭✭✭
I based amp rating of the controller on the output. With an mppt controller, you could do a 2s2p panel wiring. If the array is close by, you could use a cheaper pwm controller with them all in parallel. If far away, the cost of heavier wire gets prohibitive, so higher voltage series strings can make more sense.

I normally assume a cloudy day means no power, but obviously this varies. Could be less than zero on a really gloomy day (because the controller takes power just being on) to getting to float on a lightly overcast day.
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Solar Expert Posts: 6,006 ✭✭✭✭✭
Yes estragon on propane. So a 40 amp controller? Would that be 2 in series 2 parelled panels? And why doesnt the ahs from cloudy days enter in the calculation?

Bright, but no direct sunshine is typically <10% of expected output (7-8% of panel rating) If you have distict shadows, but high overcast, you might get closer to 20-30%, but generally it's unreliable to calculate much of anything on over cast days.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Registered Users Posts: 439 ✭✭
With 4 panels in parallel and a 30 amp basic pwm.  I'm far  away from the panels 70 feet in nc 8awg on pwm. So mppt it is. My tt in virginia i spend the summer there full sun is 125 ft away mountains blocking. I take my solar with me there I seem to have had enough power. 11 months off grid  I see now winters are a whole different story. Mm
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
• Registered Users Posts: 439 ✭✭
My next project because of the 125 distance in virginia I want to build a solar shed in the sun and run ac for the distance. According to my killowatt i need 800 watt hrs per day (I want 1 day reserve) All are inverter loads tv and e blanket.  I have a 24volt  300 watt psw,  4 225 trogens in series. BUT WHAT DO I NEED? How many watts, controller battery etc I am leaning towards grid tie panels. any suggestions? Tv is 22 watts 14 hrs a day  e blanket 300 watts 10 hrs on medium. So is this do able? Thanks for all your help guys
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
• Registered Users Posts: 439 ✭✭
I can  get 7 hrs full sun on the panels 11 to 530 in summer there. At 3500 feet
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
• Registered Users Posts: 4,496 ✭✭✭✭✭
So 800w x 2 for reserve day =1600wh ÷.50 to not draw batteries down by more than 50% = 3200wh. 3200 ÷24v = 133ah, ÷ .85 inverter efficiency = 156ah. 4x225ah@24v string should work, but not a ton of wiggle room with the blanket potentially pulling 13-14adc.

For full time use, I'd shoot for a 10% charge rate, so say 20-25adc. 20a x 29v charging ÷.75 = 773w array.

For "full sun equivalent" (ie 1000w/sq.meter) hours in your locations for various times of year, you might want to check out pvwatts.nrel.gov
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Registered Users Posts: 439 ✭✭
So around  800 watt array and 30 amp mppt or pwm?     About  the king blanket amps it pulls 80 watt peak  both sides on high. I tested  A full size  single control 160 watts on high ???
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
• Registered Users Posts: 439 ✭✭
The months in va are June 5.24 July 4.58 Aug 4.95 sept 4.29.
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
• Solar Expert Posts: 175 ✭✭✭
We do fine with 500 watts, 200 watts roof mounted and tiltable; 300 watts portable. We have a 45 amp PWM CC and our daily usage is slightly higher then yours. 210 aH battery bank. This works well in most CG's in VA, WV, TN, and NC. Only place we had to run the ginny was Cataloochee in the Smokey MTNS. That was the last week of Sept and first week of Oct 2017.
• Registered Users Posts: 439 ✭✭
Hi scrubjaysnest good to here from someone living it. My system except for Im using 30 amp pwm is just like estragon recommended 208 ah gc battery 400 watt array. Im trying to figure my battery issue. are your batteries exposed to the cold on the tongue? And what do you use for generator charging.
2kw array 6 345 q cells  make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
• Solar Expert Posts: 175 ✭✭✭
Hi scrubjaysnest good to here from someone living it. My system except for Im using 30 amp pwm is just like estragon recommended 208 ah gc battery 400 watt array. Im trying to figure my battery issue. are your batteries exposed to the cold on the tongue? And what do you use for generator charging.
The RV came with an Onan 4kw ginny, really hate it for the noise.
House batteries are below the steps and fully exposed to the elements. While in NM in Jan at 7500 feet with 3 inches of snow and 12 degrees got the low voltage alarm twice while running the heater. After cleaning snow and ice off the portable panels it took two days to get the batteries back to 100 %. Heat is set at 55 degrees and in the above conditions cycles about 4 times per hour.