Solar Panels (why are people going small?)

[Mrrrkva]

I read thru the forums, and it looks like every one is buying 4 100 watt panels............ Why not just get 300 watt panels? I have a 40 foot RV............. Is it possibly to go COmpletely off grid with 2 roof top AC's? Can I line the whole roof with them, now that the panels are less than 70 cents a watt. I have an american tradition that is already rigged with a huge sine invertor, and a controller..... What am I missing? Whats it going to take for me NOT to use my generator, other than tripling my batteries?

[Tntman]

I installed two 100w, 5.5 amp solar panels, just to keep my batteries topped off. Can't run an AC unit, but I use the gen-set a lot less.

[time2roll]

40' MH? you could put 10x 320 watts up there if you build a scaffold to cover the roof. Tip to tip might get 12 panels.

3.2 kW will run one air conditioner in the day time but how long it continues at night will depend on how much it cycles off to charge the battery. Seen a few posts over 1000w and maybe one close to 1800 watts IIRC.

Speaking of battery you would probably want 12x L16 2 volt in series to make 24 volts or go lithium for such a setup. You do not want to run that much power at 12 volt, just as likely to go 48+.

Panels will also keep the heat off the roof :B

[Jim]

Can't hardly beat this high efficiency RV swamp cooler. But stay in the desert west.

Turbo Cool thingy.

[Searching_Ut]

edm3rd wrote:
Slightly off topic, but does anyone "out west" use a swamp cooler on an RV?

I haven't seen one in ages, but used to have an old TT about 35 years ago that had one mounted on the roof. As I recall the swamp cooler carried a coleman logo, ran off 12vdc and had a fairly low profile much like the regular ac units. biggest downside was that you had to fill the reservoir on it manually. Worked reasonably well on the small tt that was maybe 18 foot.

[edm3rd]

Slightly off topic, but does anyone "out west" use a swamp cooler on an RV?

[MrWizard]

Solar is not practical for roof top A/C units
To run two roof top units you need at about 2000 watts of solar, minimum
Each unit uses 12 amps 120vac or 1440 watts running
Unless you use the low power high efficiency polar cubs at about 10 amps each
And you only have full power during full sun
And if you run them in the evening you are on battery, lots of battery
Which has to be recharged the next day while you are trying to run the a/C some more, which means even more solar
So now you are at 3000 watts solar or more, plus batteries plus a large 4000w inverter

We have a couple of members that can run a small window a/C during the peak of the day, for solar assisting the batteries, for an afternoon cool down of the living area of a smaller RV
Even a 6 amp window unit needs 60 amps battery power into the inverter, which needs at least 800w of solar to generate it in full sun

That's about it

Now if you forget the a/c There is a lot you can do with the correct solar and battery setup

[pianotuna]

Hi,

The 300 watt panel may not be nominally 12 volt. That would require a more expensive charge controller.

I am hoping to put on six panels in the next 12 month period. I'll probably go with 265 watt poly panels.

[Effy]

off the grid solar ac

back of the napkin calculations for this setup is about $13k. That's to run one AC at 900ah. Day and night you likely want about 2000ah.

Begs the question, why? You have an on board generator you can run off gas you already have. For free. Solar is NOT a cheap solution to getting off the grid, or more pointedly to the OP's question of running AC off the grid.

Technically you already have all the equipment you need to be off the grid and run everything in your coach - infinitely as long as you have fuel. Converting it all to solar however is pretty pricey, that won't really save you much other than about 1/2 gal of fuel per hour.

You could also argue that it's greener, but is it? The waste and ecological impact of manufacturing solar panels and batteries can be worse than the fuel you would burn and it's exhaust running your gen.

There are reasons why they don't make totally solar Rv's. it's not cost effective and I'm not sold that it's more green either. Just because the power comes from the sun does not mean that all the products and manufacturing methods of the equipment used to capture that power are green. Fabricating the panels requires caustic chemicals such as sodium hydroxide and hydrofluoric acid, and the process uses water as well as electricity, the production of which emits greenhouse gases. It also creates waste. So while Solar is green, the production of solar products really isn't. Kind of ironic that you need to use the same method to manufacture solar that you are trying to avoid.

[Colo_Native]

I put 510 w on mine the panels were a good price and I had the room, it's a 35' FW.

[Searching_Ut]

To a very large extent, it all depends on your expected usage, and what sorts of compromises are going to have to be made. Unfortunately, solar is also one of those areas where accurate information tends to be hard to come by as many make some pretty wild statements as to how much energy harvest you can expect etc. Sort of like figuring out how good of gas mileage you can expect based on forum responses. Some will have you thinking you can get 20mpg with a certain chip etc...

Higher wattage panels tend to be physically larger. Finding the space to position it on your roof might be an issue, keeping in mind that shading even a very small amount of the panel reduces the output significantly. My RV roof has 2 full profile Air Conditioning units, a couple vents, TV antenna etc that cause issues over much of the roof at different times of the day, sun angles etc.

You'll also want to research different types of controllers and parallel vs series configurations. Larger panels require mppt controllers which can add some benefit in a series configuration but have some downfalls in certain parallel configs. Picking the right tool for how you want to configure your system involves compromises that you have to work out for your situation.

[Effy]

I am not sure solar is the answer to power large draws like multiple AC's. I just don't think the power is there. More to the point, solar doesn't really supply the power, it charges the batteries which supply the power. Large high end coaches like MM's Prevost have HUGE battery banks and can run AC's off of them but these banks are EXPENSIVE, and heavy and take up a lot of space. I am also not sure lining your entire roof with solar panels is a good idea. How will you get on the roof to fix anything or the annual check and caulk? I like solar, don't get me wrong, it's a cheap way to get power, but it takes a lot of panels to produce a lot of power.

[bluwtr49]

I suspect that how much electricity you need to generate depends on how you want to live and how much battery capacity you wish to add. More panels would necessitate more batteries to store the power. First thing would be to make an energy budget for your lifestyle that add panels and batteries to make that happen. AC units are particularly power hogs..figure 140 amps DC each so 280 amps or roughly 1700 AH.

I have 300 W of solar and 6 batteries. On a bight sunny day with nothing running I have a constant draw of 13 amps just powering the inverter and electronics in sleep mode. 20 odd amps when the fridge kicks on. If I shut off the inverter I see a net positive charge of a few amps.

To me, going off the grid would also mean I would have to find a way to handle waste products, no or minimal propane use and etc. In other words pretty much a tent camping lifestyle....not what I bought a MH for. So settling for the solar panels to extend the time between gen set operation is all I hope for.

[Ductape]

We've got two 315w panels on the roof of a 30 foot rig, and space to walk around. It all depends on the layout of your existing roof penetrations. I've seen plenty of larger roofs where small panels would be necessary.

[Ivylog]

What you are missing is about 5000 watts. Why did they put a 7.5 KW generator in it.