Two panels on one enphase?

Has anyone got info on combining two like panels either in series or parallel to a single enphase? Assuming, that together, the panels would be within or near the spec ranges. And which spec ranges would be most tolerant of slight deviations?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    Re: Two panels on one enphase?

    Functionally, any 72 cell string of solar panels (mono or poly crystalline) should work fine. Amorphous panels with similar Vmp/Voc should be fine too.

    Legally/regulatory, the UL Listing may be tied to specific approved panels/parameters.

    For testing/class demos, smaller or larger panels (within the correct Voc/Vmp range) should be OK too.

    You can try contacting Enphase--but they probably would not tell you anything else than follow the manual/approved panel list.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Two panels on one enphase?

    Enphase gave me the bum's rush (as you suspected) some time ago when I asked similar questions...
    Right now I have panels that are very close to the specs due to age/degradation.
    I am looking to find out where i might be risking the performance loss or even inverter damage by my peak current or voltage spikes?
  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    Re: Two panels on one enphase?

    How risk-adverse are you?

    Personally, I don't believe you will damage the inverter as long as the panel's Voc/Vmp do not significantly exceed the inverter ratings (less than 5-10% over). I would not (personally) be too concerned about having an excess of Panel Watt Rating (over 200 watts). The inverter should limit its output to 200 watts as part of normal operation. The bigger GT units (such as Xantrex) do this as part of their normal specifications (and, at times, just programmed a lower Pmax output to add "step" pricing to their model line without needing a separate hardware line). If you add, for example, 400 watts of panels to a 200 watt inverter--you could add a series fuse (1.25 rated input DC current to the Enphase inverter) to limit possible problems (will not "save" the inverter, but will limit risk of fire due to wiring failure--if this is even an issue).

    If you damage the inverter--is $200 going to hurt you?

    I believe, assuming the AC wiring and circuit breaker are to code--the chance of any "dangerous" failures are remote.

    Basically, if you are trying to do a test/demo system--you should be OK (if you know what you are doing).

    If you are going to install this permanently on your roof (and therefore need to meet code)--don't do it. In the end, if there is a problem (and even if it is not your fault)--you could end up with canceled insurance and civil/legal liability (the chances of this happening are remote--but is it worth the savings of not purchasing the correct solar panels).

    People, in general, seem to be getting good prices when selling panels on EBay or Craig's list... Use that money to buy the listed panels for permanent installations.

    Note, the above is all interesting (or, perhaps boring) musings on my part... You must have a good understanding of what you are doing before playing. This can be dangerous if done wrong. The NEC and building codes are there to make systems "generically" and "legally" safe.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Two panels on one enphase?

    Thanks
    This is good info
    More specifically, is it better(performance and/or inverter durability wise) to take two old panels(43v oc/ 5amp oc) in series on the ENPHASE M200-32-240-S
    Or put the two panels in parallel on the ENPHASE M175-24-240-S
    Risk issue is low...
  • boisblancboyboisblancboy Solar Expert Posts: 131 ✭✭✭✭✭
    Re: Two panels on one enphase?

    Does anyone have any good information or pictures that show how the enphase is wired in to the panels and into the grid? I havent been able to find anything that was detailed. Also is the Enphase inverter alone the only piece of equipment that you need to start connecting to the grid, besides of course the panels and such?

    Mods if you dont think this was a good question for this thread please move, I dont want to hijack his questions.
  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    Re: Two panels on one enphase?

    I don't know brand/model of your panel... But if you go and look at the "approved" list... For example the BP 4175 is a Voc=44v, and Imp=4.9 amps (175 watt panel).

    Would seem to be right in the ball park for what they define. An Enphase 175 watt (if you can get it cheaper) would probably be just fine.

    Series/Parallel of your existing panels--I don't know what their detail are (is the Voc=43v two panel in series with Imp=5amp the panel ratings?).

    The -24 volt and -32 volt are the "nominal solar panel Vmp" voltages for the inverter. The -32 does support higher maximum voltage rating--so may be better for you if you are going to play around. (Download the Enphase manuals from WindSun/NAWS' site)

    From the Enphase FAQ:
    Can Enphase be used in both Residential and Commercial solar deployments?Yes. Enphase Micro-inverters are designed for 240VAC residential, as well as 208VAC three-phase service.With which solar modules is the Enphase Micro-inverter compatible?Please view the Module Compatibility List for a list of all modules that work with the Enphase Micro-inverter. The Model M175 240V and Model M175 208V work with 72-cell modules (24V nominal) up to 210-215Wstc. The Model M190 208V and Model M190 240V work with 60- and 72-cell modules up to 230Wstc. The Model M200 208V and Model M200 240V work with 96-cell modules 32V nominal) up to 240Wstc.Configuration How many Enphase Micro-inverters can be on a single branch circuit?Following are the maximum Micro-inverters per branch circuit:
    • 240V split-phase power - 16 Micro-inverters per branch circuit
    • 208V three-phase power - 24 Micro-inverters per branch circuit
    There can be an unlimited number of branch circuits per installation.

    The above seems to provide a bit more information on how to configure the "proper" array voltage/current/power ratings.

    One big issue I have with Enphase is that their internal logging appears to only be accessible using their hardware (and--possibly) only after you have it connected to the Internet and signed up for their web-based monitoring service. And there is a yearly service charge for the website (to your data).

    This does not appear to be practical/cost effective on a small system level--the "EMU" costs ~$430 by itself (every other major GT inverter company appears to at least have a minimal LCD interface on the inverter itself)... So, you would need to install a meter/watt meter/watt*hour meter on small/demo/lab installations if you want to see how everything is going.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    Re: Two panels on one enphase?

    WindSun has a "sample invoice" that lists the major parts need to install an Enphase system on their website (PDF Download).

    I have not seen any detailed photos... Perhaps our host (WindSun) can post some.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Two panels on one enphase?
    Does anyone have any good information or pictures that show how the enphase is wired in to the panels and into the grid? I havent been able to find anything that was detailed. Also is the Enphase inverter alone the only piece of equipment that you need to start connecting to the grid, besides of course the panels and such?

    Mods if you dont think this was a good question for this thread please move, I dont want to hijack his questions.

    Don't forget permits, utility permission, and inspections.

    Tony

    Ps I do restate my opinion that enphase could capture a lot of people who want to build a system slowly over time,, and those who are interested in sort of proof of concept ideas. Or those whose spouses say,, "'m not going to let you spend $30k on some weird stuff on our roof, unless you can prove to me that it works,,,"

    T
  • boisblancboyboisblancboy Solar Expert Posts: 131 ✭✭✭✭✭
    Re: Two panels on one enphase?
    icarus wrote: »
    Don't forget permits, utility permission, and inspections.

    Tony

    Ps I do restate my opinion that enphase could capture a lot of people who want to build a system slowly over time,, and those who are interested in sort of proof of concept ideas. Or those whose spouses say,, "'m not going to let you spend $30k on some weird stuff on our roof, unless you can prove to me that it works,,,"

    T

    Absolutely if I did this I would for sure do it by the book. I also like the idea of being able to work into a bigger system instead of jumping into spending a ton right out of the box.

    Is the Envoy - Energy Management Unit with one year data service a required device?
  • shastaronshastaron Registered Users Posts: 24
    Re: Two panels on one enphase?

    Not to highjack the thread but is there a practical application to this for us Off-grid? Since we have to store at DC is there any benefit?
  • solarteksolartek Solar Expert Posts: 69 ✭✭✭✭
    Re: Two panels on one enphase?
    Absolutely if I did this I would for sure do it by the book. I also like the idea of being able to work into a bigger system instead of jumping into spending a ton right out of the box.

    Is the Envoy - Energy Management Unit with one year data service a required device?

    The EMU is not required. You just won't get all the fancy data logging.
  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    Re: Two panels on one enphase?

    Without the EMU (and a required Internet connection / subscription back to the hosting website?)--I don't believe you will get any information at all... Have 20 units setup and one fails--you would probably never see it with plain monitoring (5% loss of power)... Weather variability would probably swamp putting a kWHr meter on the array output.

    In California, I believe for the larger installations (over 5-10kW?), phone home energy logging is required for the rebates.

    Regarding off-grid systems... I would guess that you could hook up a TSW inverter + battery bank system, and have the Enphase back drive the TSW inverter to charge the batteries (or share the load).

    This has been done with larger installations (one around 10kW or so--Solar Guppy's lab/home--as I recall). Should work with the smaller setups too.

    However, there are drawbacks... 1. No "off the shelf" regulation of GT inverter power backfed through TSW inverter/charging the battery--could overcharge/damage/worse the battery bank.

    2. Enphase does not seem to offer off-grid monitoring solutions (need real bi-directional Internet acess). Also, for a small system I would wonder if the "EMU" would be a significant power hog (if it worked off-net).

    3. Given that you can wire up a regular MPPT Solar Charge Controller to any reasonable size of panels and charge the battery bank directly--why do it for Off-Grid applications?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shastaronshastaron Registered Users Posts: 24
    Re: Two panels on one enphase?

    That makes sense. I couldn't see how it would help off-grid but just wanted to check. Still is a neat concept for grid tie.
  • System2System2 Posts: 6,290 admin
    Re: Two panels on one enphase?

    I've been thinking about trying an EnPhase unit on my off-grid installation. I should probably talk to them first, but my thinking is this ...

    I just built an 8X8 chicken coup with perfect southern exposure, with a perfectly pitched roof. I plan to run AC power to it. It seems like a cool idea to plop some panels on the roof and tie into the (off)grid, if possible.

    The shed is some distance from the rest of the solar system, batteries, etc., and the supplemental panel installation and wiring would be far easier at the shed than at or near the existing array (AC vs DC installation).

    My house could easily absorb the power from one EnPhase unit (on one leg). With an EnPhase inverter tied in to my (off)grid, would the existing inverter simply draw less current from my battery bank/charge controller? Please excuse my ignorance of how a grid-tie inverter works, but how does the grid-tie inverter ensure that any loads draw power from it vice the grid (in my case, a Trace/Xantrex SW5548)?

    DDDD
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Two panels on one enphase?

    now don't get me wrong here as i'm sure there would be a point at which an enphase would work in conjunction with a large offgrid load, but what that point would be is unknown to me. it isn't how large of an inverter (or generator for those that have wondered) you have as much as how large of an ac load you have to absorb the higher voltage introduced by the enphase inverter. loads absorb this ac power and not inverters or generators. would i believe that you would be using that many kilowatts at the time and everytime (daylight) the enphase is to always be engaged? not likely. either expand your present system to allow for the new loads and run the appropriate wire to the coup or get yourself another system to handle the coup.
  • System2System2 Posts: 6,290 admin
    Re: Two panels on one enphase?
    niel wrote: »
    now don't get me wrong here as i'm sure there would be a point at which an enphase would work in conjunction with a large offgrid load, but what that point would be is unknown to me. it isn't how large of an inverter (or generator for those that have wondered) you have as much as how large of an ac load you have to absorb the higher voltage introduced by the enphase inverter. loads absorb this ac power and not inverters or generators. would i believe that you would be using that many kilowatts at the time and everytime (daylight) the enphase is to always be engaged? not likely. either expand your present system to allow for the new loads and run the appropriate wire to the coup or get yourself another system to handle the coup.

    Thank you for your response. Definitely food for thought. I guess I need to learn how grid-tie inverters work.

    However, in the model I'm exploring, if the house loads amounted to less than the capacity of the enphase system, I would think it would simply be underutilized, much like the solar panels are underutilized once the battery bank is charged. This is not the most efficient model to be sure, but neither are most solar off-grid systems (lacking an infinitely large battery).
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Two panels on one enphase?

    you aren't using the utility grid system as a battery, but are using batteries as batteries. sending the enphase power into the inverter ac system will not store any power, which you have acknowledged, that you can reap back making this underutillization of power at the time a throwing away of the power you could be sending to more batteries that can utilize it when it's needed and not so dependent upon the time the power is used. also underutillized power from the enphase will cause a rise in the ac voltage levels and one must be aware of this as higher voltages can damage things plugged into it. you just won't have the grid there that would load down and be large enough to absorb the rise in voltage the enphase would introduce.
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