How I'm approaching acquiring a solar system for the old boy…

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This topic contains 9 replies, has 6 voices, and was last updated by Eddie & Aileen 3 months, 2 weeks ago.

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  • #50043

    I’ve looked at a lot of the “kits,” offered to American consumers and I just shake my head. Not good enough, not powerful enough, too spendy for what you get.

    Welp, couple things:

    1. I want more power than most of those kits provide.

    2. I want to spend the same money on my 500-watt system as others do on a 200 watt Renogy system. Renogy is a Chinese company, in case anyone was wondering. What, you thought you were buying American? You’re so silly.

    In listening to Pippi Peterson’s four-part discussion of solar, I learned it’s better to put more than 12vdc into the controller because all “12-volt” batteries (car batteries included) like to be charged at 13.6-14.2 volts. Voltage slows as full charge nears but the batteries will be *fully* charged. I don’t see how a 12v panel can fully charge a 12v battery, when we know they crank at 13-14 amps.

    Unlike many, mine will not be attached to the roof of the coach, and that was an idea I got, believe it or not, from Carolyn’s RV life (don’t much care for her but she’s right about this). I want the panels on the ground so I can move them as the day progresses, or set them up for best charging during the hottest (solar energy speaking) part of the day.

    I can get, directly from China, for $100 each, two 250-watt 36v panels. So, $200 for panels. Maybe $250 with shipping. Charge controller: Nice, beefy. Again, more than the system will really need, but why not overbuild and reap the benefits of extra juice to the inverter? MPPT, of course. About $150. TWO, 12V 200ah li-ion batteries: $1000. That’s right, two big boys for a grand. Sounding better?

    Totally overbuilt system but scalable and more than enough for our power needs. She needs  her HAIR DRYER!!! =:-O

    Feel free to ping me about this. I can give you links and even a few contact names.

    #50046

    Ray
    Admin

    Hi Old Man, So-called 12V panels actually are 18 volts or more. There are different panels, mobile panels usually smaller and so-called 12 volt and large fixed grid-tie panels designed for mounting on a house or cabin but not a mobile structure like an RV. You may be taking a chance with the large panels as they aren’t as robustly built. Many people will take the chance as the grid tie panels are much cheaper. Also, it’s harder it mount a really large panel versus several smaller ones.

    Renogy is an American company they are based in LA and the lady CEO went to the University of Louisiana where she started Renogy. They have some stuff made in China and some made in Thailand, not unlike many companies that proclaim to be Made in the Good old USA. China is actually a world leader in solar, they many times make better stuff than America which unfortunately is lagging behind.

    If you have a lot of time to read Handy Bob’s blog is great primer for real-world boondocking solar on the cheap – https://handybobsolar.wordpress.com/

    Our current 500 watts, 4 golf cart battery 1000 watt inverter system serves ours needs fine. Total cost around $2500, I did all the labor.  – http://www.loveyourrv.com/diy-rv-boondocking-power-system/

    Cheers, Ray

    PS. BTW Everything isn’t as black and white as some make out MPPT vs PWM controllers.

    Here is an explanation from Ralph of Bogart Engineering who is an engineer. – http://www.bogartengineering.com/

    A very good question! They BOTH have good and bad. Plenty of hype has been written already. Here’s my (Ralph’s) view:

    The “good” for PWM: It is simpler and lower cost technology. Under some common circumstances–it can actually deliver more amps to the battery. That could be when:

    (1)days are moderate or warm, with few clouds.

    (2) batteries are charging at over 13 volts, (in a 12 battery system) which they almost always are when actually CHARGING.

    (3) Panel voltage is properly matched to the battery voltage, for example “12V” panels are being used with a 12V system.

    PWM is actually more “power efficient” than MPPT–which means less total power loss in the controller itself. So heat sinks in the design can be smaller (and less expensive). Missing in most analysis of MPPT is that there is always a conversion loss with MPPT, which tends to be higher the greater the voltage difference between battery and panels. That’s why PWM can actually beat MPPT under circumstances described above.

    Some places that analyze MPPT assume that panels with 30V open circuit voltage are being used in a 12V system. Any good MPPT system will easily provide better performance in that case. They also may assume batteries are charging at 12 or even 11 volts, which is unrealistic. Lead acid batteries are typically below 13 volts only when discharging, or perhaps charging with very little charging current–meaning the actual potential gain in amps is not great.

    The benefit for MPPT becomes apparent if you use panels not voltage matched for the battery. If they are not, MPPT will utilize more of the potential energy of the panels. For example, if you use 24 volt panels to charge a 12 volt battery system you must use MPPT, otherwise you would be using your panels very inefficiently. If you are trying to use PWM in that case, you are misusing the PWM technology.

    Another potential benefit with MPPT is that if distance between panels and batteries is far, smaller wire can be utilized by running panels at higher voltage to the batteries. Running at twice the voltage reduces wire size to 1/4, which for a long run can be a significant saving in copper wire.

    If temperatures are low enough, the slightly less power efficiency of MPPT will be compensated by the higher panel voltages, which will result in a little more battery current. But in actual measurements we made using a commonly sold MPPT solar controller, this would occur at temperatures less than 55 F degrees (in full sun, when charging at more than 13 volts), where there is a slight advantage to MPPT in my location (Boulder Creek, near the California coast). As temperature drops below that (in full sun) MPPT will get some advantage, such as could occur at high elevations in Colorado in the winter. Potentially this would be maximum about a 2.5% improvement in amps output for every 10 degrees F lower in temperature (or 4.6% per 10 degrees C colder. I’m using data from Kyocera KD-140 panels.)

    There can be theoretically optimal situations (that I don’t personally experience where I live) where MPPT could give some advantage: that is when solar current is present, but the batteries are quite low in charge–but because loads are high and even greater than the solar current the batteries are still discharging despite the solar current. Under these conditions the voltage COULD be at 12.5 volts, or even lower. Again, using data from Kyocera panels, (“Normal Operating Conditions”) there is a theoretical maximum gain over PWM of 20% current assuming NO MPPT conversion loss and no voltage drop in the wires to the panels, at 20C (68F). With PWM, the voltage drop in the wires in this case would not affect the charging current. Now if in addition you lower the temperature to below freezing at 28 degrees F (while sun is shining) you might actually get up to a THEORETICAL nearly 30% gain while the batteries are discharging.

    The only REALLY BAD part of MPPT, is all the hype surrounding it–for example one manufacturer advertises “UP TO 30% OR MORE” power harvested from you panels. If you are using solar panels properly matched to the batteries, 30% ain’t gonna happen unless it’s EXTREMELY cold. And your batteries have to be abnormally low in charging voltage–which tends not to happen when it’s cold (unless you assume the battery is still discharging while solar is happening). Virtually all the analyses I’ve seen touting MPPT on the Internet ignore the conversion loss, assume really cold temperatures, assume unreasonably low charging voltages, assume no voltage drop in the wires from panels to batteries, use STC conditions for the panels (that the marketing types prefer) rather than more realistic NOCT conditions, and in some cases assume panels not voltage matched to the batteries.

    The other thing that is misleading about MPPT, is that some manufacturers make meters that show both the solar current and the battery current. In almost all cases for a well designed MPPT type the battery current will be greater. The engineers making these know better, but it is implied (by marketing types?) that if you were NOT using MPPT you would be charging your batteries with only the SOLAR current that you read on their meters. That’s not true, because the PWM BATTERY current should always be higher than the MPPT SOLAR current. It is the nature of the MPPT that maximum power occurs when the current is lower than the maximum, so they must operate there to get the maximum power. So to properly compare the two you need to compare MPPT with an actual PWM controller in the same circumstances.

    Finally, the reason we went to PWM is that I was anticipating that panel prices were going to drop (which they certainly have over the last 5-10 years!) and that the small advantage of MPPT (under conditions where the correct panels are used for the batteries) would not justify their additional cost and complexity. So my thinking, for more total benefit per $, put your money in an extra panel rather than a more expensive and complex technology.

    RVHH Chief Cook and Bottle Washer - LoveYourRV.com

    • This reply was modified 4 months ago by Ray.
    1 user thanked author for this post.
    #50049

    I agree with what Ray is saying about RV solar systems. The so called 12 volt panels are for charging 12 volt systems, but they put out much more than 12 volts, optimally around 18 volts in full sun. I would be skeptical of Youtube experts, quite often they are repeating what they have been told by others and get some of their “facts” wrong.

     

     

    dave and nina lafontaine!

    #50053

    I tip my hat to you Ray!:good:

    Happy Trails!!!:bye:

    #50064

    Welp, we all have our way of doing things. I like mine. Nobody sold me on anything I’m spending money on and I like that. I don’t like being sold to, I’m old, kinda cranky and I like learning and doing for myself. I understood what you wrote about PWM controllers, and as they say, that’s why there’s more than one flavor. I like the advantages the MPPT controller provides. You did a great job of stating them. Thank you. Again, I’ll stick with what I know.

    I’ll have 400AH of 12v Lifepo4 batteries for $1000, instead of $3000. Call me weird.

    Beastly batteries for half price

    One mistake I made (that’s what I get for writing after a safety meeting) is the panels are 200 watt, not 250. They’re also designed for the RV, off-grid application. Prostar 200W panels

    Ever so glad I kept all of Alisa Huang’s emails. I apologize for my dumbassery.

    Controller is a 40A controller, configured a lot like the 40A Renogy MPPT unit. Less money by a good bit.

    Another mistake I made was thinking I couldn’t find a better deal for an inverter than I did on Amazon. BZZZZT. Found it last night. $240 instead of $380.

    I went back and checked the external dimensions of the frame. They’re not much bigger.

    4′ 3″ x 3′ 3″ x 2″ doesn’t seem massive to me. You?

    Anyway, I saved your explanation of the differences between PWM and MPPT to a text file. Far better analysis than I could have EVER come up with. Nicely done, sir. Again, thanks.

    P.S. FWIW, I’ll have a PWM controller on board as a backup. Also, Is it possible Renogy was bought out?

    • This reply was modified 4 months ago by Old_Man.
    • This reply was modified 4 months ago by Old_Man.
    • This reply was modified 4 months ago by Old_Man.
    #50317

    Eddie if you have any comments on these batteries can you call me. plz.

     

     

    We became FullTimers July !6th, 2016

    #50319

    Where did you buy those batteries Plz?

    We became FullTimers July !6th, 2016

    #50329

    Wow. I heard how one guy used lithium batteries, thought it was great, but one cold morning he could not get ANYTHING to power up.

    Beats me what happened. New technology I guess.

    Good luck with your system.

    -Kimberly, Wagon Master - LovetheRVlife.com
    "Let's Make a Point To Leave This Place Better Than When We Came, One Life at a Time."

    #50337

    lolaandrush I have never heard of these batteries. I cannot find any real world testing on them other than the company selling them, and for sure no long term use testing. You know me, I believe in using something that I can with no dough know what it will do in performance. It would be a bad deal to be deeply “Bushed” and a cold spell come in and your battery bank goes on a temp lock-down. As the guy said, to each is own. I’m a bit “Old-Timey” I like to make sure what I help some one install will work for the long haul. You know the funny thing with being on the “Cutting edge”, you will have to give up some “blood”.:scratch:

    Happy Trails My Friends!!!:bye:

    1 user thanked author for this post.
    #50339

    lolaandrush I have never heard of these batteries. I cannot find any real world testing on them other than the company selling them, and for sure no long term use testing. You know me, I believe in using something that I can with no dough know what it will do in performance. It would be a bad deal to be deeply “Bushed” and a cold spell come in and your battery bank goes on a temp lock-down. As the guy said, to each is own. I’m a bit “Old-Timey” I like to make sure what I help some one install will work for the long haul. You know the funny thing with being on the “Cutting edge”, you will have to give up some “blood”.:scratch:

    Happy Trails My Friends!!!:bye:

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