Solar power - how many watts do I really need? ???

[pmsherman]

I have a remote building that's solar powered with everything in the building running on 12V. A few lessons that have been learned are:
1. MPPT controllers can provide 30% more power to recharge the battery than PWM controllers. This becomes more apparent when you have more than one panel (see #2).

2. If you have 12V panels, wire them in series to feed the MPPT controller. Two 120W panels will provide 20A at 12V or 10A at 24V. The 10A circuit will have 1/4 the power loss (vs the 20A circuit) in the wiring between the panels and the controller if both arrangements are using the same sized wire.

3. Most solar panels are wired with the individual cells in series. If one cell receives no sunlight, caused by a shadow from a vent or air conditioner, the entire panel will have no output. This could be a reason to install panels wired in parallel instead of series. Don't forget that parallel wiring of panels increases current which should mean using a larger wire size from the panels to the controller.

In my research on solar panels, I found that there are panels that are wired with internal diodes that allow bypassing a cell that's shaded. These will produce power at a lower voltage when a cell is covered. The ones I found were wired for 24V output and would be compatible with an MPPT controller.

Phil

[Tom48]

Originally Posted by bikendan

I also find solar too expensive and complicated.
Especially when I only have to run my Honda 2000i for 2-3 hours, every 3-4 days.
Plus we usually camp in forested campgrounds.

If you are at all crafty and can "put things together " you ought to try a portable system. A 200 watt system can be delivered ups in the us from windynation.com for about $325 us. Probable a bit more for shipping to ca. Build some legs to "aim them" directly to the sun and use a plain old 16 or 14 GA extension cord to bring the solar power back to the charge controller in or near your battery compartment.

You will significantly reduce or eliminate your generator usage and enjoy the quiet, convenience and economy.

Yes less powerfull in winter, but in southern us during spring through summer 200 flat on our roof which is only half as powerful as it would be if aimed at the Sun supports all of our needs completely, except of course air conditioning

[Skyliner]

Solar discussions are almost as bad as oil type/brand discussions on automotive forums.

To the original poster, you stated shore power hookups in your original post. In that case, solar isn't for you.

While others may disagree, the solar purchase is best for those who camp away from places with shore power and prefer the convenience of solar.

Some personal solar observations:

I hate unloading generators, installing cable 20-30 feet away from camper for noise reasons, and then securing said generator to a tree for theft protection. Its a PITA. I hate refueling generators every two days while camping. I hate going outside to start/shutoff a generator. I have an old Boliy and understand new gennies have remote start/shutdown now.

Solar doesn't save money for 99.9% of campers. Almost all of the time, a Champion or Boliy generator is more economical.

Solar is about paying for convenience but at reduced capability of a generator.

Solar is more economical if you do it yourself. Labor is about 50% of cost of an install. A little self-study on the internet and mechanical ability is all you need. Understanding of electricity helps.

Most people who want solar are clueless about cost and capabilities. As an installer of solar RV systems on the side as a hobby to earn extra money, I am extremely frustrated by the average buyer who wants solar to power their ac unit with a budget of $2,000. Ain't gonnna happen! I don't bother wasting my time with these people anymore. I am very selective in picking my customers to ensure they understand solar's limitations and capabilities.

I steer many potential customers to an inverter generator in lieu of solar.

I wouldn't waste my time by installing anything less than a 400 watt panel system, with 4 golf cart batteries, and a 1500 watt inverter system.

A $6,000 solar system is worthless in my opinion if the wiring to the panels is 10 gauge wiring and batteries are not wired together with cable length/thickness to minimize voltage drop less than 3%-My goal is .5% voltage loss or less and I overbuild to achieve this goal.

I am available to provide free consultation on solar designs/installs. Folks are free to visit me in Colorado to copy my fifth wheel solar design setup.

I do not have the best setup. I have the best setup for me based on my needs and budget. I am very happy with it because it WORKS...300 days of sunshine in CO doesn't hurt either.

[SidecarFlip]

One thin g for sure and that is, I can buy numerous Bolly's or Honda's or Champions or Wens or Yamaha's and gallons of gasoline and quarts of oil... and even hire a flunky to unload the generator and set it up and keep in running for what I'd pay for a modest output solar sysyem. I'd much rather be comfortable on cloudy days and in the rain than be 'green'. Just me.

[Fiddler Dan]

Be sure that your RV has beams in the roof to firmly attach solar Panels. I have a Rockwood Mini-lite and the roof is sturdy to walk on but it is thick styrofoam and drilling holes is not an option. I checked with Forest River and they said no way.
I have 2 new ZAMP 160 Panels, controller, remote panel & Battery temp sensor for sale cheap. I went with a 200 Watt Portable Unit, 2000 Watt Inverter and 2 Golf Cart Batteries.

[ctdarcys]

Here is a good sizing utility I have used in the past

http://samlexsolar.com/calculator/index.aspx

[Craiginok]

Originally Posted by Fiddler Dan

I have 2 new ZAMP 160 Panels, controller, remote panel & Battery temp sensor for sale cheap. I went with a 200 Watt Portable Unit, 2000 Watt Inverter and 2 Golf Cart Batteries.

What part of the country are you in? Might be interested if close enough....

[Fiddler Dan]

I am in Nacogdoches, Texas. The Solar system is brand new. I have a Rockwood 2304S and the roof is one piece laminated foam. I didn't know that the factory does not recommend mounting panels on the roof until I had purchased the panels and other accessories.

[babock]

Originally Posted by Skyliner

voltage drop less than 3%-My goal is .5% voltage loss or less and I overbuild to achieve this goal.

Out of curiosity, why do you think it's necessary to go for a drop of 0.5% over less than 3%?

I am an electrical engineer and on the electronic chassis that we build that run over $50K, we are fine with 3% loss on power lines and these are low voltage power lines similar to the outputs of these PV arrays.

[Larry123]

Originally Posted by Fiddler Dan

I am in Nacogdoches, Texas. The Solar system is brand new. I have a Rockwood 2304S and the roof is one piece laminated foam. I didn't know that the factory does not recommend mounting panels on the roof until I had purchased the panels and other accessories.

I just now bought a palomino puma that is supposedly pre- wired for solar 20 amps. It has the little hook up in the front of the trailer. I was talked into a residential frig ! I'm kicking my rear as i type. I'm just trying to get something that will give me a little light inside & run my frig when we boon dock. I really don't know anything about solar !! Is the one you have for sale what I need??? I'm going to set it up on the ground. Thanks .

[babock]

Originally Posted by Fiddler Dan

I didn't know that the factory does not recommend mounting panels on the roof until I had purchased the panels and other accessories.

I am very surprised that this is true. You can walk on the roof right? At worst, you can locate the metal roof trusses and screw into them.

[SLOArmada]

Originally Posted by babock

I am very surprised that this is true. You can walk on the roof right? At worst, you can locate the metal roof trusses and screw into them.

I have a 2504s Mini Lite. The roof is walkable, but you can feel it flex and bend underfoot. I have also seen a cross-section of the roof (through the Air Conditioner cutout), and the roof is made of really thin plywood and foam.

I went with the thin semi-flexible solar panels (seven 100-W panels, and one 50-W panel) mounted flush to the roof using eternabond tape around the edges of the panels. Securely fastened, no holes, and no stress on the flimsy roof.

[babock]

On my Coachmen that I bought, It also has that thin plywood but has wood trusses. According to Forrest River I just have to locate the trusses and screw into those. Don't see any reason why you couldn't do the same with the aluminum ones as long as you can locate them.

I am working in getting a diagram of mine according to my VIN number.

[Skyliner]

Originally Posted by babock

Out of curiosity, why do you think it's necessary to go for a drop of 0.5% over less than 3%?

I am an electrical engineer and on the electronic chassis that we build that run over $50K, we are fine with 3% loss on power lines and these are low voltage power lines similar to the outputs of these PV arrays.

I want to extract as much power as possible from my system and using thicker wire initially gives me more flexibility in the future to add more panels without worries about losses exceeding 3%. I started out at 400 watts, now I'm 600 watts, next year I'll be at 800 watts, and the year after that I will upgrade to 1,000 watts of solar panel. The cost of using thicker wire to achieve very low losses is minimal for the wire length considered. An RV's solar system is very small so achieving such a stringent goal is not that expensive as compared to a much larger $50,000 system.

Truth be told many RV solar systems are poorly designed and rely on 10 AWG run long lengths resulting in unacceptable loses and a system that performs poorly. I have had folks want an extra solar panel or two on their RV's to get a better performing solar system and upgrading the wiring, moving stuff closer together accomplished the same thing at lower cost.

I'm pretty meticulous about everything I do. If I rebuild an engine, you betcha your butt that any clearances will be at the tighter end of the allowable range and engine is overbuilt to allow for future power upgrades and long term reliability. I don't like leaving horsepower on the table on an engine build and I take the same mentality with solar. My mentality probably is a result of being an engineer, a former military pilot (maintenance test pilot), a gear head and a perfectionist.

[babock]

Originally Posted by Skyliner

I want to extract as much power as possible from my system and using thicker wire initially gives me more flexibility in the future to add more panels without worries about losses exceeding 3%.

3% is plenty margin for wiring a panel. You were implying people should go to 0.5% where 3% is more than satisfactory.

Even the difference between 5% and 3% is in the noise.

You of course said NOTHING in your original post that the reason you went to 0.5% was that you were adding more panels and you wanted to reduce your overall drop after expansion. Anyone who is putting solar on their RV should be more than happy with a 3% drop.