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Comments for Solar Basics – Know how to determine your solar system

  • We’ve got three 125 watt panels on the roof of our trailer, and they power our two 6 volt Trojan T-145’s. For the most part they do a fine job. We don’t watch TV much and basically we just need power for the Dish box (so we can listen to the Dish music), use our LED lights, and the fridge and water heater electrical needs (minimal). I have an older Cobra 5000 watt modified sine wave inverter which runs all our AC needs. I know “they say” modified sine wave doesn’t work for some electronics but we have been charging ‘goodie’ batteries for years and years with no apparent problems. Oh, and wifey runs her hair dryer off this system, and if wifey is happy, everyone is happy . . . .

  • On running hair dryer (and microwave, same power need), a) a robust system will permit this, and b) it DEFINITELY makes my wife (and me) happy.

    As for modified sine-wave inverters, here’s some tech background:
    Once upon a time, 120VAC power was used via transformers in appliances, to achieve necessary power levels. These transformers didn’t work well with modified sine waves. But MODERN appliances use “switching” electronics in their power supply sections, solid-state power transforming designs that are much more tolerant of ‘chunky’ input waveforms. YMMV, and you always risk damage — but I also have never had problems with modified sine wave power.

  • i’m unusual.. perhaps one of a kind. 48v, 100ah Li battery pack, 4kw PSW inverter, 835w solar. I got tired of 12v systems with their fat wires and things getting hot under heavy loads.

    • What charge controller are you using?

      I’m not averse to higher voltage banks, but the specifics of my use case argued against it. I wanted to keep the ability to charge from coach alternator, and wanted to be able to “donate” 12v power to needy campers nearby.

      Otherwise I might have gone 24v.

  • Chris, not THAT unusual. Here’s my numbers:

    406W panels, 360AH LFP batts, 2500/5000 Cobra inverter. All 12V.

    I too dislike the heavy gauges needed, but I wasn’t looking to make sweeping wiring retrofits. The 360AH was needed because we do a LOT of microwave heating.

    Lithiums RULE!!

    • Hey Greg.

      I thought you might have been running LFP because otherwise the panel/battery balance didn’t make sense. Might want to edit that into the article.

  • Jason,

    Great response, and accurate in some regards — although I do have some disagreements. Suffice it to say that I made some simplifying assumptions/statements, not intended for deep-knowledge individuals (like yourself) to dissect. 12V instead of 13 will work fairly well, for example, without having to explain to a neophyte that he/she doesn’t actually have EXACTLY a 12V battery.
    Longer interchange would have to leave the text realm and go to verbal — not enough bandwidth here .
    Thanks for all the work and thought.

  • When you speak of running your fridge, are you running it on 120v?
    Because my (residential style) fridge and a few odds and ends sucks my 8 Trojans dry overnight.

    • Roy, no, I haven’t taken the plunge on a 120V fridge. Mine is the normal 12V/chemical style (Norcold). I don’t think my style (extended boondocking) is compatible with a 120V fridge. Not until they make one far more efficient.

      • There is a better option. Try a waeco upright fridge 190 to 220ltrs. Can be run on 12 volt or 24 volt. They run the same compressor as the portable fridges. They are a little expensive but far superior to 3 way fridge

        • Diana,

          Those are quite interesting — but when I looked up the power consumption, the 190 was rated at 3AH/hr, or 75AH per day. Such power draw would drain my entire battery bank in 3-4 days of overcast or heavy shade. But for BIG battery bank installations (or of course hookups and generators), it could be interesting. Pricey though.

  • Thanks for the basic solar overview. There will always be some readers who will poke holes in any solar article, as here. I have always suspected that potential solar rv users just want someone to point them in the correct direction of buying either a basic or midrange system without all the technical jargon.

  • Great article, I noticed you are using 12V to get your amps, in a 12V system. I have a GoPower system & they use a different measuring system. I have 3@ 160W = 480W, but only have 25.8A. In your measurements using 12V I would have 40A. Well I like yours better, but mine is what it is. I suppose each controller manufacture has it specs. I noticed you didn’t get into the L16 size batteries, is that for a future article? I do regret somewhat on not using a 24V system, actually I didn’t know it was available. I do remember that my Dad’s 49 Dodge had a 6V system & the huge battery wires needed compared to next generation of 12V car systems. Ya using a smaller gage wire would also same a grip of cash just on the wires!
    Thanks
    Dave

  • Dave,
    Most folks (me included) just aren’t prepared for the complexities and difficulties of running a 24V or 48V system. Unless you have two separate busses, how would you find a 24V fridge? Or a cabin full of 24V LED bulbs?

    Batteries are indeed a whole separate article. I have switched to Lithium (LFP) and will never go back, but they are complicated and relatively fragile — not for everyone. Lead batteries, for most folks, would be either flooded or AGM golf-cart style. Why? Good efficiency (space/weight/capacity), and easy to find replacements when (not if) they croak. Also, for wimpy guys like me, a 65-pound battery is about all I can muscle in and out of my compartment. Those big 120-pound monsters are beyond me.
    G.

  • Thank you, Greg, for your article. For me it was very informative. My next plan of action for my RV is to add a solar system so I’ve been doing a lot of reading and research. It’s very hard to find trusted information when the exchange of money is involved.

  • Why not use enphase inverters and feed 220 volt ac which will feed the inverter the same as a generator and then charge the batteries, smaller wire less cost less heat

  • Bill,

    I don’t know what an “enphase” inverter is, so I can’t answer. As for 220 (vs 120 I presume), the wire gauges for these voltages are relatively small and easy to deal with. It’s the 12/24 difference in gauges that can make a difference. Also, the generator should never drive the inverter; this is not a standard configuration. Heat-wise, the inverter doesn’t charge the batteries (the converter does this), and the inverters are all in the 90%+ range anyway, so here again I don’t think I can answer. [Some folks use the term “inverter” for the power converter that supplies 12V to the coach and charges the batteries. I avoid this, and use the term “converter” so as to avoid confusion with the power-inverter used to make 120VAC from the batteries’ 12V.)

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