Any tips on my setup?

[sensij]

Two of your 300 watt panels wired in series exceeds the 100 Voc input of your controller. Hear that.

This is false if the temperature does not drop below -3 deg, and the panel performs as the data sheet says it will. The manual that *you* linked agrees that 2 panels in series can be acceptable for this configuration. Multiplying Voc by 1.25 is the safe thing to do when you don't have any more information, but the NEC agrees that if proper design temps and panel coefficients are used, a smaller Voc adjustment for a specific installation is valid.

You are applying rules of thumb to a system that is beyond that stage, and careful analysis shows that what the OP is proposing is totally viable, and an improvement over what he had. Is a 40 A CC going to outperform a 60 A? No. This aspect of the discussion is similar to the cost benefit analysis when choosing between an M250 and an S280 microinverter for an LG300 panel, for example. Yes, more power is available, but it might not be needed or worth the cost. Putting 900 W on a 40 A CC will produce more energy than if only 600 W are on that CC, and both configurations are well within this particular CC's specs. It is up to the OP to determine if optimizing beyond what he has now is worth it, but nothing he has suggested doing is fundamentally wrong and would result in system malfunction or failure.

[Wrybread]

First of all I never claimed to be an expert. I've been doing it for 20 years, but I'm very much still learning. And the fact that you don't know you're still learning is part of your problem.

And as I said over and over, I'm working with what I have. In my opinion that's extremely important to Rv solar system design. These things aren't pure theory. Sure things would be more efficient with a charge controller that costs $600 (or much more) instead of $150, but I don't want to spend that money on an RV installation. Especially when I don't need to.

Just as my battery bank would be more efficient at 24v, but that's another tradeoff I'm simply not willing to make for yet another massive increase in cost and inconvenience.

You keep insisting people don't understand you when they simply disagree with you. You might benefit from trying to understand people rather than calling everyone ignorant. And, worse, trying to scare the crap out of people. That didn't even come close to working on me thankfully, but I gather it's worked on others, costing them a massive amount of money and labor for questionable gain.

[-TX-]

Because you do not understand 10 hours day light does not equal 10 Sun Hours. Kwh / M^2 / Day = Sun Hours. Additionally you cannot compare a Grid Tied System with a Battery System. With a battery system you use December sun hours and a 66% efficiency with MPPT or 50% with PWM. Stick around, in 1 week here you have learned more in the last 20 years.

All I got to say about that is, if I sit myself up on my roof from 8am-9pm I'd be dead at 6pm from sun exposure. Come May, the sun is EVERYWHERE in W TX. It is brutal. If PV can't take advantage of that than we're all wasting our time until competent tech comes around.

[J.P.M.]

All I got to say about that is, if I sit myself up on my roof from 8am-9pm I'd be dead at 6pm from sun exposure. Come May, the sun is EVERYWHERE in W TX. It is brutal. If PV can't take advantage of that than we're all wasting our time until competent tech comes around.

Lots of places are like that, and PV can and does can take advantage of the available insolation in effective but limited ways. However, and in spite of what you may think, things need to be quantified a bit more than you describe. That's just the way the game is run. The ante to get in the game is a bit of technical education. Suit yourself.

[-TX-]

You just agreed with my comment about the tech being immature.

[Sunking]

All I got to say about that is, if I sit myself up on my roof from 8am-9pm I'd be dead at 6pm from sun exposure. Come May, the sun is EVERYWHERE in W TX. It is brutal. If PV can't take advantage of that than we're all wasting our time until competent tech comes around.

TX you are missing all of our points. Daylight hours does not equal sun Hours. A 100 wat panel only generates a maximum of 80 to 90 watts a few precious minutes around noon. So example in Lubbock TX in the months of June/July with optimum panel tilt and orientation is 6.5 Sun Hours despite 15 hours of day light. In December/January that drops to 2.75 Sun Hours. For a battery system you use worse case months the system is used in. So if you had a 100 watt panel used in December January the panel can only generate 100 watts x 2.75 Sun Hours = 275 watt hours. However that is at the panels output terminals and not all is usable, only 66% once you factor in all the system loses. So that 275 watt hours turns in .66 x 275 watt hours = 180 watt hours usable.

That is how you use Solar Insolation tables to design a system. Watt Hours = Watts x Hours. So if you need 1000 watt hours a day in Lubbock in December, you have to know Sun Hours so you can factor out the Wattage. So you look up the Sun Hours to find the panel wattage required. The formula that takes losses into effect is;

Panel Wattage = [Daily Watt Hours x 1.5] / Sun Hours. So let's run Lubbock to use 1000 watt hours and the system is use din Dec/Jan. [1000 watt hours] x 1.5 / 2.75 Sun Hours = 545 watts.

Lik eJPM said if you are going to play the game, you need to know the laws and rules. With energy it is the Law of Physics. Unlike man made laws, you cannot break or bend the Laws of Physics. If you could, you could jump over your house or flap your arms and fly.

Solar if a fully matured science and has not changed in 60 years. Does not matter if a 100 watt panel was made 50 years ago, today, or 100 years from now will still produce the exact same 180 watt hours usable in Lubbock.

[-TX-]

it's just hard to believe, Sunking, that's all. I'll bear witness to it soon.

[Sunking]

it's just hard to believe, Sunking, that's all. I'll bear witness to it soon.

What is so hard to understand? It is 5th grade math and science. No technology can change physics, Watt Hours will alway equal Watts x Hours.

[-TX-]

What is hard to believe is that my sun is downright dangerous come May, but apparently not dangerous enough to heat the same pot via PV, that if I placed on my roof its contents would boil within a (kW) hour.

edit: hyperbole alert but the point stands.
.

[Sunking]

What is hard to believe is that my sun is downright dangerous come May, but apparently not dangerous enough to heat the same pot via PV, that if I placed on my roof its contents would boil within a (kW) hour.

edit: hyperbole alert but the point stands.
.

OK you are now comparing Apples to Oranges. That is what is throwing you off track. A solar panel transforms photons to electrons, and when it is heated up produces less power. Additionally at best when the panel is at freezing temps is only 20% efficient, and goes down as it heats up. Exact opposite of thermal radiation. Just the nature of physics. The difference between winter and summer is Sun Hours and you cannot change that. In Summer you get around 7 Sun Hours, and in winter less than 3. Watt hours = Watts x Hours. Summer you have more hours, winter much less.

[Wrybread]

TX, I don't know the specs of your system, but all the systems we're describing here are way overkill for most RVs. Mine (600 - 900 watts!) is absolutely absurdly over powered for an RV for example. Most RVs have 100 or 200 watts of solar with panels wired for 12 volts. If they're lucky they'll have an MPPT charge controller but that's far from a given. A few more modern ones will have 250 watts of power and an MPPT, but I've seen very few with more than that. And assuming they convert their lights to LEDs, that's fine for most RVs.

That's not to say I think 200 watts is adequate, especially now that charge controllers and panels are so cheap. And that's not to say a knowledge of the theory behind solar isn't massively valuable. But the culture on this forum is to overthink it without enough understanding of the realities of RV installs. RVs are all about compromises (in more ways than just solar of course). And a little inefficiency in a massively over spec'd system isn't a dealbreaker, especially if it saves hundreds or thousands of dollars, and keeps the system simpler. And the reason I care at all is that this kind of thinking is the opposite of empowering for people who come here wanting to build a solar system on their camper, and ultimately fewer people will build a solar system, and (from an RV'er perspective) there's more people running their noisy and stinky generators even during sunny days.

Personally I think this is the correct assumption to start with:

All I got to say about that is, if I sit myself up on my roof from 8am-9pm I'd be dead at 6pm from sun exposure. Come May, the sun is EVERYWHERE in W TX. It is brutal. If PV can't take advantage of that than we're all wasting our time until competent tech comes around.

And not Sunking's! Who actually said:

Solar is just for show and tell or for extending long stays. You still need a generator or Isolator to get charged up dry camping for extended periods.

Mind boggling.

And unfortunately he chased away the person who built the best mobile solar rig I've ever seen:

https://www.solarpaneltalk.com/filedata/fetch?id=340644&d=1484320513

[jflorey2]

from reading this forum, I see that these 900 watts of solar panels are more like 693 watts (900 * .77).

That's a reasonable normal power on a 72F day.

my panels are all permanently flat mounted, so their output is probably a lot less than that. Is there some formula for determining the output of a flat mounted solar panel? I'm in Northern California (latitude 38) if that's a factor.

Cosine of the angle between insolation and panels. At latitude 38, at the equinox, at noon, you'd be at a 38 degree angle - so that's 79% of max. That will vary about 23 degrees from there to summer or winter.

my battery bank is 4 Trojan T105s wired for 12 volt. From reading this forum, I gather that's 450 amp hours, which is 5400 watt hours.

And 2700 watt hours usable.

my charge controller is the Tracer 40 amp. I've read conflicting reports of what that amp rating means, but I think it means a maximum of 40 amps on either the PV or battery side?

Max 40 amps battery side. Input current will be the same or less.

- If I got a full 693 watts output from my charge controller, that would be 50 amps @ 14 volts. Should I worry about going that high? I'm thinking I'm not likely to get that much power from flat mounted solar panels, am I right?

The charge controller will limit its output to protect itself if your power goes that high (unlikely.)

[J.P.M.]

You just agreed with my comment about the tech being immature.

If that comment was directed to me: I did not and do not agree that "tech is immature". Immature is probably a poor choice to describe the evolution of science and technology or, for that matter, the acquisition of knowledge in general, in this case as it may relate to solar energy utilization. The discovery process is never ending (thank goodness), as is product improvement. The basics of the solar resource are pretty well developed. PV process improvements and improvements in batteries and support electronics will continue.

FWIW, what may look immature, to me anyway, is your level of understanding and attitude toward learning and understanding the basics. Almost like you've got a chip on your shoulder about it. Like I wrote - suit yourself, but my guess is you're not doing yourself as much good as if you'd take what's been shared here, crack a book or two, and learn some things. You've been given a lot of valuable information here from very experienced folks - for free. If you'd follow up on that and try to understand what's been presented, you'd probably do things in a more efficient way.

Good luck in your future endeavors.

[-TX-]

My RV is my office away from home.

My situation is that it could mean money, time and convenience if I could service an off-grid site in my 'office'. So for me, no matter that I have not read of a single 2k solar setup on an RV, I measured space availability for 2k of panels, then went nuts fitting them into a system that would work. So this isn't a weekender where, you're correct, 200w would suffice, mine is a different beast.

I agree with Sunking about the MPPT

[Wrybread]

2k, awesome! What are you doing for a battery bank?

That indeed is a massive system and I'd go 24 volt for that too.

I agree with some things Sunking said about MPPT. Don't get me wrong, I'm not advocating PWM. Where I disagree with him is a) that the Tracer 4210A controller is a POS (I don't think he's updated his thinking since the early Chinese "MPPT" controllers on ebay that were fakes; these are very well reviewed), and b) that its inadequate for my setup to the point that it justifies spending another $600+.

And is there a thread where you're discussing why you think you need 2k of panels? My RV is an office too (as well as coastal surf buggy), I run a laptop all day every day (I'm a programmer), and I'm typing on it now in fact. And I have a ton of lights and music, and I currently only have a single 300 watt panel. But I don't power my fridge or water heater off electric though, yet. And I don't watch TV or use the furnace blower often, since I've found Buddy style heaters to be great. And I don't run a desktop computer, just laptops.