Waving the little white flag

monicaj said:
I bought 4 of these solar panels (for $1,000 + 200 shipping = good deal huh?  I think it's 72 cells?), and I'm trying to put 2 of them over on a friend's property and set them up for him.  

• Sounds like a good price (I am not in the business).

My first question:  Am I right that these are 24v?

• I would prefer to call them Vmp~35.2 Volt panels. What you use them for (and behind what type of solar charge controller) is what matters. But, yes, this panels can (singly) charge a 24 volt Lead Acid Battery bank.
  

Second question:  Should I connect them in series for 48v?  I keep reading that increasing volts instead of amps will save money by using smaller wire.  The wire they mean is the one going from the panels to the charge controller?  (I'm picturing the panels being maybe 40 feet from the camper and the charge controller is in the camper.)

• What is your Battery Bank Voltage and what Brand/Model of solar charge controller (MPPT or PWM--Needs to be MPPT). Higher Vmp-array will let you use smaller AWG (light weight) cord. However, it will make the MPPT charge controller run a little less efficiently (controller will run a bit hotter)
  

More questions... 

Am I right that he should get an MPPT controller and use a 12v battery bank because he's going to be running 12v stuff (fans, lights, radio, maybe fridge...)?  and this question leads to the next...

• Fridge can be a big load (relative to all other loads)--It will probably define if you use a 12 or 24 volt battery bank (plus fans+lights+etc. can consume a lot of energy too). For RVs, there are a wide variety in refrigerator types/power usage. For example a Gas Absorption type (propane) fridge on 12 VDC or 120 VAC is very energy wasteful.
  
• really need to know how much power/energy you will use. For off grid and RV power from solar, you really need to conserve energy (LED lighting, small/energy efficient fans, turn stuff off when not used, etc.).
  

5th question:  IF he should use a 24v battery bank,  then does he have to get something to change the volt from 24v down to 12v for his 12v stuff, and is it an expensive piece?

• Yes, there are DC to DC converters... But if you can use a small/efficient AC inverter--Would that work for you?
  

For some reason, he's wanting to have 2 separate systems... in case one goes down.  But is that necessary?  Because wouldn't the charge controller be the only thing that may fail, and couldn't that be protected with an inline fuse or breaker or whatever it's called to protect the controller?  So if he's really worried about that, couldn't he just make sure to have a second controller on hand?

• Yes, things fail. Having backup parts is sometimes needed. Also, if full time off grid, will there be a genset available--That can be your backup energy source.
  
• If loss of power means loss of life (or loss of work)--Then the person should use the rule of three for backup. I.e., assume that the primary "thing" failed, and the secondary/backup failed too. The third backup is still available.
  

IF it's a better idea to have 2 systems, then he could put each panel on a charge controller, and both charge controllers can charge one battery bank right?

• It depends. Yes, you can have parallel power systems and if one fails, the second would be available. However, you now have 2x more parts and 2x more likely something will fail, and possibly it will be harder to debug/fix (more complexity, more confusion, more ways for things to fail).
• In general, for most people, keep it simple. And have some backup parts on the shelf, and one (or two) backup gensets.
  

And specifically, which charge controller/s should I get?  What specs should I be looking for?

• Lets talk about sizing your system first. There is no "one ideal" device that works in any size system.
  

A question about monitoring things... I saw something that can tell you exactly how much the panels are producing and how much juice is in the battery and a few other things... I think charge controllers can give you that info?  A cc that gives you all this info would probably be a lot more expensive so should he just spend a little less on the controller and get the gadget that monitors these things?   But if he has 2 systems, is there even a way to connect up that gadget so that it can read both charge controllers?  Or am I completely off base with how that works.

• There are many ways to monitor your system (locally, remote over the Internet, via charge controller/inverters themselves, separate monitoring devices, etc.). Cost and complexity are usually important. Are you somebody that wants the system "to work"--Or do you want hourly data to graph/put into a spread sheet? Do you want the system to email you if there are problems?
  

Lastly, how many amps should he have for his battery bank?

• Need to know your loads first (suggest you choose energy efficient devices--cheaper than building a larger solar system).
  

About inverters:  He does have an inverter but I think it's way to big.  He said it's 3,000 watts, but I haven't seen it yet or looked up the specs on it, so maybe it's not even an off grid inverter, but a grid tie one, but either way, wouldn't he do just fine with a smaller inverter, 1,000 watts maybe, and doesn't the big one use more juice to run?

• Yes--Especially for RV's, you are better off running small loads and small AC inverters. In some cases, you may want a second/large AC inverter to run a power tool for a few minutes, etc... I would humbly suggest a 300 Watt 12 VDC TSW Inverter should keep most RV folks happy (propane fridge, not large motor homes) and 2 to 4x 6 volt @ 220 AH "Golf Cart" batteries wired to a 12 volt @ 220 or 440 AH battery bank.
  

If you can please help me get clear on this, my beat up brain thanks you profusely.

• I also suggest that your next posts focus on one subject at a time (I suggest picking your loads and measuring/estimating your energy usage). That will drive much of the rest of the system design.
• If you do this a step at a time, you will better understand the entire solar power system at the end of the process. It is difficult to "understand everything" at one time--Like drinking from a fire hose.

-Bill