Will the panel below require a 48 volt mppt charge controller for use in a travel trailer? Yingli Solar YL295p-35b Electrical Characteristics System Rating: 295 Watts Watts (PTC): 266.1 Watts Max Power Voltage (Vmpp): 36.3 Volts Max Power Current (Impp): 8.12 Amps Open Circuit Voltage (Voc): 45.4 Volts Short Circuit Current (Isc): 8.63 Amps Max System Voltage: 600 Volts Series Fuse Rating: 15Amps Module Efficiency: 15.1%

Do you plan to get more in the future? If you do plan to get more in the future, you will need to get panels that are very close in open circuit voltage (45.4) to inter-operate.

You might get away with the Rogue 20a MPPT controller and some clipping at peak. My 245w's are good for 17a at peak.

OK thanks

Only question I've got is why you want to use panels that physical (and electrical) size? I went with mono 100 watt, 12v panels that were the size I could place on my roof the way I wanted to ensure they wouldn't be shaded by anything. That meant I also didn't have to spend the extra $200 for MPPT and got a Morningstar Tristar 45 - $145 delivered. Big panels mean you've less flexibility in placement and they almost always will require MPPT since they usually put out way over 12v.

A friend is putting it on his trailer and he is getting the panel practically free.

High voltage panels produce more power early in the morning and late in the evening hours, when the sun is weak, and on overcast days. I've even heard of them producing some power under bright artificial light, such as bright, sodium street lights or parking lot lights.

Also a higher voltage system allows smaller gauge wires going to the controller, saving both weight and money. Their cost per watt, weight per watt, and surface area per watt is usually much lower too. If you are building a large system (1,500 watts+) larger, high voltage panels make this possible, such as this 4ft x 7.7 ft. 395 watt (82v) panel: sunelec.com/solar-panels/sun-395-watt-monocrystalline-solar-panel.html Here's some 435 watt panels that produce even more power from a slightly smaller footprint: sunelec.com/sunpower-435w-modules-grade-b.html though at 68 cents/watt (in lots of 20) they are a little more pricy than the former 395 watt panels at only 58 cents/watt (in lots of 15). Most 100 watt 12v panels run over $1/watt. These high wattage panels could be mounted with the long axis going cross ways (side-to-side) on your roof, taking up only 4 ft. of roof length (or less). Find room for just 4-5 of those on your roof and you will have all the power you need for a large battery bank and even supplemental solar air conditioning and heating when boondocking.

It would take 16-20, 100 watt 12v panels to produce the same power. Where would you mount all these panels? Plus the mess and complexity of wiring 20 panels on your roof (if you could find the space) would be immense. With this much current at only 12v, (over 100 amps) your drop down cable would need to be 000 or larger (depending on the run) costing $$$. With these high voltage panels, a 1975 watt system would only produce 24 amps, (at 82 v) requiring a much smaller wire size going to the charge controller. I will be using a 48v battery bank (probably 8 GC-2 golf cart batteries to start, as a cheap "learning bank" better ones when these die) - drawing off 12v to run any 12v appliance, lights, etc. as needed (using something like this www.amazon.com/GOLF-CART-voltage-reducer-converter/dp/B008CM4WZ2 or this www.axiomatic.com/48dc-converter.html on each 12v circuit as needed.) The 48v battery bank would then power this 48v DC powered heat pump (HSAC- 12A/C) www.geinnovations.net/Specifications.html which produces 12,000 BTU's of cooling using only 11.5A (560watts) and 12,500 BTUs of heat from 12.1 amps (600 watts - as long as the temp remains above 38 degrees) reducing propane use for heating while boondocking in milder weather too. This super high-efficiency heat pump (21.43 EER) is a mini-split design which doesn't require a hole in the roof, allowing even more roof space for mounting solar panels. A 48v to 120vac inverter would also be used to power ac appliances - either a full featured whole house inverter like this www.wholesalesolar.com/products.folder/inverter-folder/outbackfx3048T.html or a couple smaller, less expensive ones for increased efficiency - say a 1,500 watt one dedicated for kitchen use and a 1,000 watt inverter for entertainment center use.

Chip

Good description, Chip, and right on the money.

I'll be interested in your airconditioning experiment. I've used high SEER mini splits in semi trucks before - driven by solar - but not in an RV. Mainly because of the tonnage cooling requirements. So I'll be real interested in how this works out for you. I'm designing a semi-trailer-based towable that will have a flat roof and nothing protruding other than some vents (and maybe not even them - they might come out the side). Cooling will be high SEER mini-splits or a basement air unit. Right now a basement unit. But given that I would have 8'x45' of available roof space there could be "significant" solar harvest from it. It will be stored in LiFePo4 batteries. On the order of 2000 Ah, most of which is usable. If mini-split I think it will take three units to provide the cooling. Maybe only two.

Thanks Jack,

That means a lot coming from someone "in the know" about RV solar systems like you. Yes, 12,000 Btus is a little small for primary cooling at peak weather, (though it's not much smaller than a standard 13,500 BTU roof air unit standard on most TT. I will have a back-up 15,000 Btu factory AC unit available for use during peak summer daytime heat, if occasionally needed. I would run this primarily in RV parks (with hook-ups) but could also use this as supplemental cooling when boondocking powered by a pair of EU2000 Hondas. I mainly plan on using the solar AC for cooling only the bedroom at night, so it wouldn't have to run at max load, but its variable speed compressor would scale back quite a bit, consuming only the amount of battery power needed for a comfortable sleep. I intend to move to higher elevations to reduce the outside temp. and thus the heat load on this smallish ac. Another benefit of these largish panels mounted 2-3" off the roof of the 30+ ft. TT I have planned is it will block a most of the sunlight striking the roof and reduce its heat load as much as parking in the shade would. I have a lot of experience using Reflectix in my small Aliner's generous windows, as an effective way to reduce the heat load too, as my Aliner only has a 5,000 BTU ac. The square footage of this little camper is about the same as that of a typical RV bedroom, so I'm thinking 12,000 Btus should be more than adequate to cool a single room, if not just lower the temps and humidity 10 degrees or so inside the entire TT making it at least livable, if not optimally cooled.

Since the original subject was about charge controllers, I'm planning on using either a Morningstar MPPT Tri-Star 45 amp controller which is rated at 2,400 watts of solar power (at 48volts). Their 60 amp model will give me a little more headroom, though I doubt I'd have enough roof space available for more than 2,400 watts of panels. 5 - 435 watt panels = 2175 watts, more power than I can envision ever needing, even after their power output degrades somewhat after a decade of use. Plus the closer I get to its capacity, the closer to that 99% rated peak efficiency I will get. I think properly sizing a charge controller will yield similar results to properly sizing an inverter, in terms of operating at near peak efficiency. I'd love to be able to afford LiFePo4 batteries for their many advantages over lead acid, but I'll have to wait till the price drops some more before I'll be able to afford to take the plunge. Right now the s-550 Rolls/Surrettes are still the most affordable choice as far as available AH/$, but at a huge weight penalty. They can stand a much greater charge/discharge rate than your standard GC-2 too, but of course still not nearly as well as Lithium ions can - though this will not be a factor with the charge/discharge rates I have planned.

For your planned 8x45 trailer, mini-splits do come in larger sizes, though at higher cooling levels their efficiency drops significantly. If it were insulated like a reefer with 3-4" of foam insulation then 2 -12k Btu units would suffice.

Chip

Wow

And here I was all happy that we could run a 5000 BTU window shaker.