Which 130w panel to buy for starting out?

I am just starting in PV and have a Xantrex C12, a 54 amp Deka AGM sealed deep cycle batt. I am searching for a (12v) 120-135 watt pv module and running into starters dilemma. For now one panel, next year another,etc. What I am looking at is what brand PV module/panel should I get and or stick with? Also is there universal sizing for wattage and mounting between brands when I try and buy a pv module 3 years down the road? For useage I just plan on using it lighting 12v cf bulbs, emergency lighting and 12v power tool recharging (infrequent).


  • BB.BB. Super Moderators, Administrators Posts: 32,804 admin
    Re: Which 130w panel to buy for starting out?

    More or less, any of the big names of poly or mono-crystalline solar panels will be of good quality and work well.

    The issue with larger panels (typically over 100 watts) is that they are usually "high voltage" panels--instead of being rated at "12 volts" (really around Vmp=17 volts), they will be rated at Vmp>20-30+ volts.

    So, right off at the beginning, you will need a MPPT solar charge controller. And they are not cheap (at least the good ones are not).

    Now, you have to ask the question of:

    1) how many solar panels (in watts) you will need in the end
    2) what battery bank voltage you will need
    3) mixing and matching of panels (in series, the panels should be within 10-20% of same Imp... In parallel, the panels should be within 10-20% of Vmp ratings).

    So, just looking at "class" of good MPPT controllers... For 200-400 max watt systems (12 volt / 24 volt)--The Morningstar SunSaver MPPT Solar Charge Controller is pretty hard to beat.

    If you are planning larger systems, then you would have to look at the Outback and Xantrex 60-80 amp MPPT charge controllers. They cost about 2-3 times the price of the MorningStar--and are not really that efficient on systems that are under 400 watts (the power to run the larger charge controllers eats into the power you are collecting with the smaller panels).

    The last major issue with adding parts to your system over the years is that you need, roughly 5%-13% of your battery bank's Amp*Hour rating in charging current... Below 5%, it is difficult to fully charge your bank and properly equalize your flooded cell batteries. Above 13%, and you can pump too much power into your batteries and cause them to overheat (and it is less efficient charging).

    And, if you add batteries to your bank, there are some issues with newer batteries accepting more of the load--and wearing down to where they match the old bank in life expectancy (and adding unmatched rated batteries is usually not recommended at all). If the bank is over a year old--probably not the best idea to add to the bank unless you have too.

    The above are rough rules of thumb... You can violate them and still be happy with your system's performance--especially when you understand where the weaknesses are (may have to use your generator to equalize your "under paneled/over sized" battery bank once a month, and/or use the genset very often in the first couple years until you can afford more panels, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Which 130w panel to buy for starting out?

    Panels have several rateings that need to be closely matched, or you are wasting efficiency of one of the panels. So buy one today, that will be in production a year from now !!

    What you need to match for parallel panels:
    Voltage at Max Power (Vmpp)

    For Series panels
    Current at Max Power (Impp)

    The closer the values match, the less losses.

    ** Note on connecting - All new panels are switching over to the MC latching cable connectors to meet the new UL/NEC standards. We expect that within a few months there will not be any panels over 80 watts or so available with junction boxes - only MC cables.

    **(PANELS WITH LATCHING CABLE CONNECTIONS ONLY) For more than 1 panel on a 12 Volt system you will need a latching MC extension cable (MC4) and branch connectors (PV-AZB4 and PV-AZS4) for parallel connections.

    This will complicate connecting things in the future.

    For your charge controller, decide how large your final system will be, and get an appropriately sized controller for that system. Otherwise, you will have a left-over controller that will not handle your array. If you look at a MPPT style controller, you can run higher array voltages, and use smaller wire, and let the converter down convert the array voltage to the battery bank voltage.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Which 130w panel to buy for starting out?

    actually a 130w pv will most likely be over 13% of your charge rate percentage using stc ratings and unless your battery will be fast charged i'd say adding another would be out of the question unless the manufacturer says it can take the higher rate of charge. i think it will take this higher rate of around 26-27%, but for your plans you have to know from the manufacturer if they say it's ok to do this.
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