My first small off grid solar power system quesetions

silverstreamersilverstreamer Registered Users Posts: 10
Bill-
Thank you first and foremost for sharing your wealth of knowledge. I have read your many posts and am at an impasse on my RV set up.
I Currently have a Kyocera 175W panel, with a Go-Power GP-PWM-25 Amp controller and 3 Fall River DC105-12 AGM batteries.
I hope i am in the right spot- please move my thread if I have made a newbie error- tks;)


My objective is to gain maximum storage of the sun to my batteries.
I am having some difficulty in usage ( we boondock) on grey days- We are all LED, no TV, Water pump and brain board on the refrig( it is LP, as is H2O)
The most usage comes from the laptop, water pump when required.

Here is my dilemma, I was told that my controller may not be "harvesting " the max output of my PV.
I have a few options,
1. buy a MPPT controller -Perhaps a Blue Sky or morning Star
2. Add another PV - looking at a Kyocera 150W to add

If I opt to add a second 150W panel that would bring me to 325 W....that said if I am not "harvesting " all my PV's ability now,
would adding a second PV be the best option in addition to adding a new controller?

Many thanks for your time and assistance with this-

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,717 admin
    Welcome to the forum Silverstreamer!

    And thank you for the kind words--Every one here is volunteering their time and knowledge to help answer these types of discussions.

    I have moved your post to its own thread... It will make it easier for people to follow your discussion and answer your questions without confusing others.
    My objective is to gain maximum storage of the sun to my batteries.
    I am having some difficulty in usage ( we boondock) on grey days- We are all LED, no TV, Water pump and brain board on the refrig( it is LP, as is H2O)
    The most usage comes from the laptop, water pump when required.

    You have done the first step really well... You have reduced your electrical loads to the minimum needed, and chosen appliances that are designed to use very little electrical energy.

    One thing that is missing--Is the daily electrical load for your devices and if they are are 12 VDC or if you have an AC inverter and 120 VAC loads too.

    Basically, looking for something like:

    30 Watts average power * 5 hours per day * 1/0.85 typical AC inverter efficiency = 176 Watt*Hours at 120 VAC for laptop (12 VDC load equivalent)
    8 amps * 1/2 hour per day * 12 volts = 48 Watt*Hours for water pump
    1 amp * 3 hours per day * 12 volts = 36 Watt*Hours for LED lighting
    ===========================================================
    260 Watt*Hours per day (at 12 volts)

    Say you have 4 hours of sun minimum when you are dry camping:

    260 Watt*hours * 1/0.61 typical DC off grid system eff * 1/4 hours of sun per day = 107 Watt solar panel minimum

    And then there is the 5% to 13% typical charging current for the solar system we recommend for lead acid battery banks. You have 3x 105 AH @ 12 volt AGM batteries (I think). The typical solar array would be something like:
    • 3 * 105 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 295 Watt array minimum (seasonal/weekend usage)
    • 3 * 105 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 589 Watt array nominal (full time off grid)
    • 3 * 105 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.15 rate of charge = 766 Watt array "cost effective" maximum
    Now--I really do not know how much power you use daily... If you use 500 WH per day, and design for 2 days of storage and 50% maximum discharge (longer battery life), your "optimum" battery bank would be something like:
    • 500 WH per day * 1/0.61 DC off grid system eff * 1/12 volt battery bank * 2 days of storage * 1/0.50 maximum discharge = 273 AH @ 12 volt battery bank
    Of course, that would depend on your actual daily usage (500 Watt*Hours or ~42 AH per day is not a lot of power--Count yourself as doing good if that is your daily usage (or less)).
    Here is my dilemma, I was told that my controller may not be "harvesting " the max output of my PV.
    I have a few options,
    1. buy a MPPT controller -Perhaps a Blue Sky or morning Star
    2. Add another PV - looking at a Kyocera 150W to add

    I would like to know (roughly) when and where you camp (desert southwest, summer or winter/etc.). That helps us know how much sun you get and how hot/cold the area is.

    In general, I would not suggest you buy a MPPT charge controller to "get more harvest" from your solar array. Especially if much of your camping is not done during winter. An MPPT controller in sub freezing weather may harvest another 10-15% or so additional energy vs a PWM controller (all things being equal--which they rarely are).

    MPPT controllers are good for matching "GT Solar panels" to DC battery banks (i.e., "cheap" solar panels and "expensive" MPPT charge controllers). PWM controllers (cheaper) use solar panels with Vmp~18 volts (36 cell panels--today, these panels are more expensive) for charging a 12 volt battery bank.

    So, cold weather camping with a 175 Watt array, a good MPPT controller gives you another ~20 watts for ~$100-400 more money. Vs buying a second 140 Watt panel for ~$300.

    Go with adding more solar panels.

    There are other good reasons for MPPT type charge controllers (on very hot days, solar panel output voltage Vmp (voltage maximum power) does fall, and can reduce charging current for the battery bank if the day is very hot with PWM controllers).

    Anyway... We need to talk some more about your power needs, where/when you camp (and how many days at time you dry camp), and about your existing system. There are "rules" about mixing/matching solar panels and MPPT/PWM charge controllers. And it is less confusing if we talk about your specific system and needs, instead of trying to give you all the generic design rules (confusing as heck).

    Note that it is difficult to "cost effectively" grow an off grid solar power system. Not everything "plays nicely" together. And if you make the system larger, you may need to go to 24 or 48 volt battery bus (new inverter, new batteries, possibly a new charge controller, etc.).--I think you should be fine with a 12 volt battery bank and your existing loads--But just be warned that you need to plan out your system to avoid (costly) mistakes.
    If I opt to add a second 150W panel that would bring me to 325 W....that said if I am not "harvesting " all my PV's ability now,
    would adding a second PV be the best option in addition to adding a new controller?

    Lets talk some more first. You will probably get several suggestions on what you can do--And you should pencil out several paper designs and cost them out--Figure out which is most cost effective for your needs. Don't get too wrapped up in what is "most efficient" piece of hardware--It is how the system functions overall (at what cost) to meet your needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • silverstreamersilverstreamer Registered Users Posts: 10
    Good Evening Bill,
    I will do my best to give you more information on the specifics. Kindly forgive my “technical” verbiage, as to be humorous, you lost me at hello. I have a very solid mechanical background, however leave the electronic loads to the experts such as yourself ;)
    Here are some further details:
    1. We are retired, and “full-timers with 2 govn’t pensions, so we tend to follow the sun.
    2. We tend to reside in the national forests in MT from June to October 1- fully off grid.
    3. In the winter, we tend to roam NM, AZ, TX, lower UT ( at times) as well as NV.
    99.99% of the time we we are off grid.

    Grey Day problems- We don’t operate in ‘cold weather” , but do operate in hot weather in the winter…That stated, it is the grey days in MT that will bring us down to 55% or so in the evening on the laptop usage. ( hiking in the day- a bit of admin work at night)

    For usage: please help me out on this a bit, as again this is above my pay scale ;)
    Here is some baseline operational information:
    1. We ONLY run on DC, operated via the current 175W panel.
    2. Our 12V to 110 inverter is NOT sine- it is a 3000 to peak 6000, hate to say it - china model- perhaps this is a problem?
    3. That 175W panel is tied to the Go-power PWM-25 AMP controller
    4. We do NOT run a furnace or microwave- we operate on LP for the stove and Hot water.
    5. We charge our cell phones in the Truck, as it is a 3500 HD with two 12volt 900cold crank batteries
    6. We are avid readers and …don’t laugh- Do not own or operate a TV….ok – you can chuckle a bit ;)
    Normal electric usage generated from Solar Panel
    1. We use 1 or 2 LED lights in the evening, at 2.7 watts for perhaps 3hrs tops
    2. We are mandated to use the “brain board” on the refrigerator, to operate the electronics- it runs on LP for the coolant properties. The label in the door states 0.8amps @ 10 watts 12V DV for the brain board.
    3. We operate a whisper king water pump perhaps 6 times per week for “short navy showers” We operate the same for limited dish water into a dish pan to conserve water & power.
      1. Water pump information: 12 VDC, 2.0 GPM, 30 PSI, and 5.5 Amps
    4. The Laptop cord states: 100-240v1.5A (50-60 hz)
    5. Propane CO2 hardwire alarm 0.24Amps 24 hours a day
    We try to err on the side of an extreme conservative approach.
    Our heaviest usage comes from the charging of the laptop. , we operate it 4-5 hours or so a day for email- etc. The power cord states “ 100V 1.5Amps (50-60hz)

    We noticed that the 150W panel will not fit on our roof, and will need to go with a 100W to give us a total of 275W …The original 175W Kyocera +100W ( Renogy- is it a decent brand?)

    Your thoughts are greatly appreciated-
    Something on a curiosity-
    1. The Go Power 25Amp unit ( discontinued) we noticed that the Specs stated
    Max solar volts is 56V, with a max battery voltage range of 6-31V
    http://gpelectric.com/files/gpelectr...-PWM-25_vB.pdf


    2. On the 30Amp unit now in production it is stating max solar Volts is 28 with a max battery voltage range of 6-15.5V
    http://gpelectric.com/files/gpelectr...M-30_boost.pdf

    We are running the 3 FallRiver AGM 12V 105h batteries, and were told that the closer the max solar volts to the actual battery volts, the more efficient…( I have NO clue on this) any information on it would be appreciated- meaning that the Go Power 30 A controller with a max solar Volts at 28 is closer to the 12V battery than the Go power 25A controller with a max solar Volts at 56V being less efficient.

    What say you gurus?

    Again many thanks for assisting me in the right direction, I just hate to through good money after bad-
    Respectfully-
    Stan
  • silverstreamersilverstreamer Registered Users Posts: 10
    Battery information:
    Fullriver FR27 (DC105-12) Specifications:



    Nominal Voltage: 12V
    Amp Hour Capacity @ 20 hr rate: 105 a/h
    Reserve Capacity @ 25 amp discharge rate: 175 mins
    BCI Group Size: 27
    Marine Cranking Amps @ 32* F: 1080 amps
    Cold Cranking Amps @ 0* F: 900 amps
    Weight: 66.5 lbs
    Length: 12.09 in.
    Width: 6.65 in.
    Height: 8.46 in.
    Terminal Type: heavy duty bronze marine terminals
    Hardware: brass bolts and washers



  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    99.99% of the time we we are off grid.

    Impressive on 175Wp !
    it is the grey days in MT that will bring us down to 55% or so in the evening

    This from a battery monitor? Just be careful with those can catch you out, as the battery ages, capacity reduces at 55% might be 40 or 30 or ? Then battery ages even faster, as you uniwttingly take it lower and lower.
    Our 12V to 110 inverter is NOT sine- it is a 3000 to peak 6000, hate to say it - china model- perhaps this is a problem?

    Whole kettle of issues there.
    1. Big China inverters, avoid them like the plague. Too many quality/safety issues observed here. Also sine wave inverters are now the norm. The price difference has evaporated. Yes, i know brand name inverters cost like a wounded bull, thats just a fact of life with inverters, buy peanuts get monkeys.
    2. Big inverter, small battery. As a rule of thumb you need 400Ah of battery per kW of inverter (at 12V), thats so that the inverter can draw the kind of surge current it needs with out losing everything on heating losses.
    3. Big inverter,small system. Your small (tiny) system doesnt have the resources to support any significant inverter idle tare, so be sure to switch it off after use. Or get something like a 300W suresine, which has super low tare.
    That 175W panel is tied to the Go-power PWM-25 AMP controller

    Gopower are one of those brands with uncertain perhaps variable quality. So you might want to re evaluate your reliance on it. Being in the sticks you are at the mercy of your gear. SO get decent stuff. Midnite now makes a neat little PWM unit called the MNBRAT.
    [*]We use 1 or 2 LED lights in the evening, at 2.7 watts for perhaps 3hrs tops - the “brain board” on the refrigerator, .... The label in the door states 0.8amps @ 10 watts 12V DV for the brain board. We operate a whisper king water pump perhaps 6 times per week for “short navy showers” We operate the same for limited dish water into a dish pan to conserve water & power.

    You are truly doing well on the whole voluntary simplicity thing. So cool. However if you have the roof space, PV is now real real cheap and a couple extra panels could increase your power secuity and comfort by a good bit.
    The Laptop cord states: 100-240v1.5A (50-60 hz)

    Laptops are a bit deceptive, what they actually use depends on whether the laptop is running, whether its charging, and how hard its working. Save yourself some agrivation and go measure the actual use (Killawatt). If the laptop is the only reason you run the inverter, then my advice is to power it/them off of DC instead. Theres two ways to do this. Shop around for a "car laptop adapter" suuitable for your voltage and wattage. Or, buy a suitable DC to DC converter and solder the right laptop plug on it. This is what i do, i power 3 laptops off one of these: http://www.ebay.com/sch/i.html?_odkw...+190W&_sacat=0
    One other thought is if the thing is a power gobbler (certain large older laptops with large power bricks), you might want to compare costs of upgrading it, as current generation laptops tend to have much smaller adapters (40Watts ish), and more aggressive power managment. Just a thought sometimes the cheapest way to save cost on power system design is to spend the money on more efficient loads.
    Propane CO2 hardwire alarm 0.24Amps 24 hours a day

    While that doesnt sound much, things that run 24/7 are often the big total average power users. In this case its 70Wh/day. Again measure it, it might actually be lower.
    We noticed that the 150W panel will not fit on our roof, and will need to go with a 100W to give us a total of 275W …The original 175W Kyocera +100W ( Renogy- is it a decent brand?)

    Theres a trick to mixing and matching panels. The important things are:
    - same "chemistry", ie all mono or all poly
    - Vmp within 5% of each other
    -If stringing panels Isc must also be within 5%.

    If that all sounds like goblegook, holler and we'll decrypt.
    We are running the 3 FallRiver AGM 12V 105h batteries,

    Those batterys have a good reputation amongst the RV crowd. Make sure they are wired right http://www.smartgauge.co.uk/batt_con.html
    and were told that the closer the max solar volts to the actual battery volts, the more efficient…

    Is it actually a pwm controller or mppt controller. For PWM there is a narrow band of voltages that work. Using 36 cell panels, gives a Vmp of around 17 or 18V, Thats about optimum for a 12V bank on PWM. Go lower (or lose too much in cable losses) and it wont charge right , go higher and you just throw away the power from the extra volts.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • silverstreamersilverstreamer Registered Users Posts: 10
    Morning ZoneBlue-

    Thanks for the cudos- We are trying our part to be green- heck, my wife even re-uses the grey water for her small flower pots!

    Ok- for most all of your feedback I am still in my pay scale ;)
    I DO need an interpretation on the matching of PV cells, I understand the same "chemistry" per se

    Reference: the 55% is from the charge controller, as opposed to a battery monitor- or is that one of the same?)



    It is the statement
    - Vmp within 5% of each other
    -If stringing panels Isc must also be within 5%.

    That is giving me the translation headache or need to reach for the life boat!


    On the rest of the story.......
    As a side note the laptop is not old- a year perhaps- 17" Toshiba-
    However- I do run it often, and it does use the juice-

    On that note about inverters......
    we ALWAYS turn it off when not in direct use

    I will take a look at that control charger-
    my thoughts after this discussion with you are as follows:
    1. New panel
    2. Update the controller
    3. Update to a sine inverter

    I would appreciate anyone weighing in on the above order of priority- many thanks
    Im looking to keep this little upgrade to <1K


    We are pretty self reliant, the idea is to see and enjoy the beauty of the west, NOT be plugged into
    what we call a parking lot (KOA ...etc)
    Many thanks for your feedback- Will post a photo of the "rig" when i get a moment
    Kind Regards-
    Stan
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    zoneblue wrote: »
    ...

    Theres a trick to mixing and matching panels. The important things are:
    - same "chemistry", ie all mono or all poly
    - Vmp within 5% of each other
    -If stringing panels Isc must also be within 5%.

    If that all sounds like goblegook, holler and we'll decrypt.
    ...
    Is it actually a pwm controller or mppt controller. For PWM there is a narrow band of voltages that work. Using 36 cell panels, gives a Vmp of around 17 or 18V, Thats about optimum for a 12V bank on PWM. Go lower (or lose too much in cable losses) and it wont charge right , go higher and you just throw away the power from the extra volts.
    The rules of thumb are both simpler and more complex than the way that you stated them.
    The way I like to look at it is:
    When using an MPPT DC input,
    For a series string, all panels in the string should have Imp within a 5% range. In general if Imp is within 5% the Isc is within 5% and vice versa. There is no need to match voltage from panel to panel in this case.
    For a parallel arrangement (of individual panels or of series strings) the total voltage (Voc or Vmp) needs to be within the 5% range . The current match between strings does not matter. If you want to stretch that 5% some, be very sure that you do not let Vmp of one string go above Voc of the other. If that happens the MPPT input may not try to use the lower voltage string at all, depending on just how it does its search for the Maximum Power Point.

    The exception, which zoneblue called attention to, is that for a PWM CC the voltage match of parallel panels does not matter as long as all of the Vmp values are above the required input voltage of the CC for full charging including equalize voltage out. The higher the Vmp above that figure, the more power you will waste from that panel, but putting them in parallel will not make it any worse than just using the high voltage panel by itself.
    SMA SB 3000, old BP panels.
  • silverstreamersilverstreamer Registered Users Posts: 10
    INETDOG-
    Ok- I know know that I need to take my degree, dust off all the old age and send it back to the university !!
    You lost me at hello-

    My concern is do i need a MPPT CC or will the 25A PWm work ok- or should I upgrade to a 30A PWM CC?
    to handle the following:
    I currently have a Kyrocera 175W panel, will be adding another (same chemistry 100W panel)-
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    INETDOG-
    Ok- I know know that I need to take my degree, dust off all the old age and send it back to the university !!
    You lost me at hello-

    My concern is do i need a MPPT CC or will the 25A PWm work ok- or should I upgrade to a 30A PWM CC?
    to handle the following:
    I currently have a Kyrocera 175W panel, will be adding another (same chemistry 100W panel)-

    Odd, because I never said Hello. ;)

    If your panels are the ones I looked up, the maximum power voltage is 23.4V. Since a PWM CC cannot change the current passing through it you are getting 7.5A times 12V instead of 7.5A times 23.4V. You are losing about half of the panel power by not using MPPT.

    Which would cost you less to get twice your current charging power? To buy another panel or to buy an MPPT CC and get rid of our PWM?

    Long term I would certainly go with MPPT. But you say you would add a 100W panel instead. We would need to know the Vmp and Imp for that panel to decide. If the panel is a low voltage "12V battery" panel, you could put it in parallel with your existing panel into your PWM CC and get at least 2/3 of that 100W added to your total. You would still be getting half power from the 175W panel.
    But if you go to MPPT, there may not be any good way to combine the panels. That is why we need the numbers.
    SMA SB 3000, old BP panels.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    ok putting this much simpler. Heres the terms you need. A solar panel is a 'module'. Each module is comprised of 'cell's. (Historically, most modules comprised 36 cells. "12 volt" panels). However these days there is a wide variety of module configurations and its this that makes matching panels tricky. Heres a typical range of panels we come across
    - 36 cell vmp around 18V
    - 60 cell vmp around 30V
    - 72 cell vmp around 36V.

    Each module has a 'nameplate' sticker. On it will be the following 4 important specs (plus some).

    Voc = volts open circuit (no load)
    Vmp= volts max power (where it operates best)
    Imp= amsp max power
    Isc= amps short circuit

    For a '100Wp' (watts peak=max power) panel this means Vmp x Imp = 100W (at some pretermined set of test conditions called STC) (In the real world output will vary and usually be somewhat less).

    Now for the matching, Inet explained it right. But first we have to go back to PWM or MPPT. I tend to go the other way. Panels are now cheaper than Mppt controllers and last a lot longer. 3-4 times longer. So a better investment generally for systems that arent 'large'. This is a sea change that is currently still gestating, as the price drop in PV has caught the industry somewhat by surprise. But the fact that the likes of mdnite have just released a new PWM controller is a sign of the times. (See also for instance electrodacus's forthcoming 3kW PWM controller targeted specifically at Lithium banks.) However given the legacy, ie all current good quality larger controllers are MPPT, and given long cables, and/or 60cell panels (which tend to be cheap but funny voltage) for larger systems (>1kW) MPPT is still the right choice.

    Other advantages of PWM is:
    - lower tare. 30amp MNBRAT is 0.2W idle, my little 10A morningstar is half that again. Compared with 30amp MNKID at 0.5W.
    - physically small, can make a difference in an RV.

    In any event small systems have never justifyed mppt. One of the moderators here rule was the 400Wp limit. Below that you are better off with PWM. From a cost point of view. Small systems tend to be on small structures like RVs. Hence cable losses and cable cost is not a factor (justifying higher string voltages for smaller cables).

    So, for you, MNBRAT or one of the little morningstars is perfect. However we have to come back to your actual panels. If inet is right and your Vmp is as high as 24V, then thats not ideal. But before we go too far, find the panel (or its datasheet on line) and get the actual specs. (Failing that, take a multimeter and measure the Voc, and Isc. (For the former disconnect everything from the panel and measure the voltage across it during a clear day. For the latter put the meter on teh 10A range and measure the short circuit current.) (Dont worry nothing will blow up. Small spark is all)

    Until we have those we are just guessing. Also remember that perserving with a old panel (say 10+yrs) maybe folly, and one option is to just flog it on ebay, and get a matched set, that exactly fits your roof space, and voltage requirements. The side benefit there is that you can now get 22% efficinent panels, and for an RV that is a real boon, more output for less roof space.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    One more thing. For small systems that arent micro (<100W), always consider a system voltage of 24V. Heres why:
    - you can avoid parallel batterys more easily.
    - you can use DC down converters to power DC loads more easily, rather than trying to boost 12 up to 19 etc
    - smaller cable, less heat, less loss.
    - dc appliances still available in 24v, eg waterpumps.
    - smaller charge controller required (CCs are sold by the amp).
    - bigger solar panels are cheaper than smaller ones. 60 or 72 cell panels are cheaper than 36 cell per watt.

    On our motorhome we have a single 300W 72 cell mono panel. Left over from the house build. But it fits perfect, and saved me a whole bunch of brackets and holes and gunk for several small panels. 72cell panel plus 4mm2 cable plus PWM 24v controller= happy, happy happy.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • silverstreamersilverstreamer Registered Users Posts: 10
    PLEASE FORGIVE ME- I misspoke on the Panel- it is a 185W- specs below

    Ok- This is a cut and paste on the specs for the Kyocera KD185GX-LPU
    185W Polycrystalline Module High Efficiency, Kyocera Solar KD185GX-LPU



    Maximum Power (Pmax)

    185W (+5W/-0W)


    Maximum Power Voltage (Vmpp)

    23.6V


    Maximum Power Current (Impp)

    7.84A


    Open Circuit Voltage (Voc)

    29.5V


    Short Circuit Current (Isc)

    8.58A


    Max System Voltage

    600V


    Temperature Coefficient of Voc

    -1.06x10-1 V/°C


    Temperature Coefficient of Isc

    5.15x10-3A/°C


    *STC: Irradiance 1000W/m2, AM1.5 spectrum, cell temperature 25°C



    Electrical Performance at 800W/m2, *NOCT, AM1.5



    Maximum Power

    131W


    Maximum Power Voltage (Vmpp)

    21.0V


    Maximum Power Current (Impp)

    6.27A


    Open Circuit Voltage (Voc)

    26.7V


    Short Circuit Voltage (Isc)

    6.96A


    *NOCT (Nominal Operating Cell Temperature): 47.9°C









    Cells



    Number per Module

    48





  • silverstreamersilverstreamer Registered Users Posts: 10
    The following is a hyperlink on the 100W that i would like to add:
    http://renogy.com/wp-content/uploads...evised0805.jpg

    ONE thing I do notice is that my original Kyocera has 48 cells , as opposed to the new "proposed " cell of 36.( is this a concern?)
    BOTH units are Polycrystalline units though

    I ask as it is the only "size that will fit in my available roof space-
    I can say one thing for sure, I have a deeper appreciation for you guys that have this knowledge, as I would be lost
    without your assistance- again I appreciate the time and insight of all of you that are "guiding me" -
    many Thanks
    Stan
  • silverstreamersilverstreamer Registered Users Posts: 10
    INETDOG-
    Quick question on your last post
    "Which would cost you less to get twice your current charging power? To buy another panel or to buy an MPPT CC and get rid of our PWM?"

    Could I do both- upgrade to a MPPT CC, and add the 100W Panel?
    Also, I like the function of the PMW, as I can see the charge rate and current status- do the MPPT CC offer this , or do you need the extra gauges?
    I like this "Midnite Kidd":

    http://www.ebay.com/itm/Midnite-Solar-Kid-MPPT-Charge-Controller-Regulator-150V-30A-Made-in-USA-US-/261944001190?pt=LH_DefaultDomain_0&hash=item3cfd1442a6

    Am I asking too much by looking for a "small" MPPT CC that is an all in one gauges & CC with a lower end price tage- My gut tells me that the MPPT is designed more for the higher end systems, accordingly, the analogue gauges are and additional part of that system per se-
    Thanks-
    Stan
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    You may not be able to go to MPPT and add the mismatched 100W panel. I know that the voltage will not be compatible for parallel connection to an MPPT input, but the 36 cell panel is an 18 volt Vmp "battery" panel, and is itself more suited to your PWM CC than that higher voltage 48 cell panel.
    And the current of the two panels is likely not be within 5%, so you could not run them in a series string into an MPPT input. But check the rated Imp of the 100W panel and compare it to your current panel just to confirm that. Even though it will not be efficient in a series string, you might still lose less power than you do with the PWM CC.
    SMA SB 3000, old BP panels.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    ONE thing I do notice is that my original Kyocera has 48 cells , as opposed to the new "proposed " cell of 36.( is this a concern?)
    BOTH units are Polycrystalline units though

    48 cells huh. Well thats an odd duck. The thing you have to realise is that mppt isnt magic. It introduces ineffciencys of its own, the internal buck converter is only ever going to be 90% effcient, and this combined with higher tare loss reduces the gain they get from your average panel to battery voltage differential. Also MPPT controllers need quite a bit of voltage headroom. You cant use a 36cell panel on a 12v mppt controller, you need something like twice the battery voltage to give it some room to down convert. That 48cell panel might be enough, but unles you can still find them for sale, trying to match any current generation panels with it is going to be an unhappy experience.

    You really have to decide which of the engineering requirements are highest priority (cost/space/functionality/reliability). Generally arround here the last one is a given, no one has time to mess about with unreliable gear, not when its mission critical. The Kid is a good controller, and good for 500W of solar.

    If its price thats making you cling to that funny panel then fine, we can look at the best way to move forward. But as i said with the availability of the more efficient mono panels hand picking 2-3 matched panels has merit for your application. If its that the existing one is already mounted and your loathe to mess with it then, well. Maybe. Or, sometimes you have to break eggs to make an omlette.
    Could I do both- upgrade to a MPPT CC, and add the 100W Panel?

    PV is a current source, so with PWM you can put pretty much anything together in parelle and itll drag what it can out of them at the battery voltage. However for mppt to work it needs to be able to 'sweep' the array to locate the max power voltage. Mismatched panels confuse this and result in unhappiness. So my suggestion is to forget mppt if you want to retain that odd panel and cant find a match for it. (actually my suggestion was to forget mppt but hey)
    Am I asking too much by looking for a "small" MPPT CC that is an all in one gauges & CC with a lower end price tage-

    Yes, i think youve fallen for the marketing hype. See above, theres no magic. Mppt controllers are all without exception exensive, and you ideally want to run them at optimum conditions to get your moneys worth. (And dont go prowling ebay looking for a cheap mppt controller, all youll find is lies and tears. Its common to see (poor) pwm controllers labelled mppt by unscrupoulous vendors.)

    So summarising:
    - that panel has a Vmp of 23.6V. A PWM controller will waste about (24-17)/24 of the energy from it.
    - its too small a system to justify mppt, both from a cost and effiency point of view.
    - that 48 cell panel is worth what about $100 to replace, and your contemplating spending $330 on a mppt controller to fix its foibles?
    - thus, that panel is a liability.

    I know what RV roofs are like, all sorts of junk up there. I would be doing a drawing and seeing what will fit in the way of matched panels.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    inetdog wrote: »
    And the current of the two panels is likely not be within 5%, so you could not run them in a series string into an MPPT input.

    This is a good point inetdog. Silverstreamer, if you can find another poly panel (of no particular voltage) that has an Imp within 5% of 7.84A, then you could run those two panels in series into the kid. Just make sure that the sum of the Vmps doesnt get too high. That will make the controller run less efficiently. And also introduces shock level voltages into your design.

    Tricky, hey?
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • silverstreamersilverstreamer Registered Users Posts: 10
    Evening guys- or morning as it may be-
    to quote ZONEBLUE..." If its that the existing one is already mounted and your loathe to mess with it then, well. Maybe."
    Its mounted to an airstream....ahhhh need we say more- a serious bear to get it mounted, stable and secured...needing no less then something called SIX-TEN epoxy with a strength of 7200lbs per sq/in for the brackets into the ribs of this beast....so yip...Im married tho her ....at least for now.

    Given all the great input- here is what I am hearing and would like a nod from one ( or more of you)

    Buy the 100W panel, add it in parallel to the existing 175W PV
    Will keep the existing 25A PWM CC, unless there is a reason to upgrade to a 30A PWM CC ??
    Will toss the MPPT CC idea out the window...saving for the cold beer to assuage my mortification of the depth of
    knowledge required to get this "little project" right-
    Many thanks again for following me on this trail-
    Regards
    Stan

  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Sounds like your path of least resistance. That renogy is a 36 cell panel, so its excellent for 12V PWM. The combined current of 8A plus 6A still comfortably in the range of your controller.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • silverstreamersilverstreamer Registered Users Posts: 10
    ZoneBlue etal-
    Many thanks to all of you for your your time and effort in assisting me with your knowledge in these systems.
    Forever thankful am I to be able to turn to others when I am outside of my abilities-
    All the Best-
    Stan
  • ApplesApples Solar Expert Posts: 39 ✭✭
    zoneblue

    You cant use a 36cell panel on a 12v mppt controller...

    zone, thank you for all of the experienced info you've posted. But I have to ask you here regarding this quoted statement: Why not?

    I ask because I'm using, successfully, one or two, depending on cloud cover and/or how quickly I want the controller to finish bulk and get into absorption... Renogy monocrystalline 100W panels, 10ga stranded copper extensions to my small camp trailer, 8AWG to the controller then more 8AWG in a less-than 24" run to a 100Ah AGM Odyssey-made for Sears Die Hard Platinum. The battery is being sent almost 6 amps per panel in full sun during the charger's bulk phase, then 180 mins at constant voltage of 14.7 during absorption, ending with a 13.6 float.

    Silverstreamer, that is a fantastic rig! you roll down the road with. Amazing!
  • grizzzmangrizzzman Registered Users Posts: 18 ✭✭
    Bill-
    Thank you first and foremost for sharing your wealth of knowledge. I have read your many posts and am at an impasse on my RV set up.
    I Currently have a Kyocera 175W panel, with a Go-Power GP-PWM-25 Amp controller and 3 Fall River DC105-12 AGM batteries.
    I hope i am in the right spot- please move my thread if I have made a newbie error- tks;)


    My objective is to gain maximum storage of the sun to my batteries.
    I am having some difficulty in usage ( we boondock) on grey days- We are all LED, no TV, Water pump and brain board on the refrig( it is LP, as is H2O)
    The most usage comes from the laptop, water pump when required.

    Here is my dilemma, I was told that my controller may not be "harvesting " the max output of my PV.
    I have a few options,
    1. buy a MPPT controller -Perhaps a Blue Sky or morning Star
    2. Add another PV - looking at a Kyocera 150W to add

    If I opt to add a second 150W panel that would bring me to 325 W....that said if I am not "harvesting " all my PV's ability now,
    would adding a second PV be the best option in addition to adding a new controller?

    Many thanks for your time and assistance with this-

    I would like to ask what i feel is an important potential issue with your system. What is the size and length of the wires from the solar panel to the controller?
    Also what is the size and length of the wire from the controller to the batteries? Your trailer is long and my concern is voltage drop due to size/length.
    If voltage drop is an issue then watts are wasted heating wires but what is worse it fools the controller into believing that the batteries are at a higher state of
    charge causing chronic undercharging. If it is a problem then adding a panel (more amps through the same wiring) will just add to the problem.
    Boondocking is my game
    640 Watts Mono Bogart TM2030 and SC2030  Controller GC 6V 208 AH  Costco batteries  300 Watt Inverter and 2000 watt inverter 100AH LIFEPO4 2P4S
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