EnPhase on batteries?

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Comments

  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: EnPhase on batteries?
    BB. wrote: »
    Other thing to look into... 36 VDC battery banks are a bit odd ball these days for solar PV systems. It might be difficult to find mass market inverters, battery chargers and DC direct loads (pumps, etc.) that run at 36 volts nominal.

    -Bill


    I have a Tristar ts-45 charge controller, and I was pleased to see it could be used with a 36v bank.
    I guess they didn't want to miss out on the 36v golf kart market.?.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: EnPhase on batteries?
    solarix wrote: »
    All MPPT devices are basically variable impedance loads which can adjust their input resistance to match the optimum impedance of the source.
    (study the subject of impedance matching sometime - maximum power transfer is only achieved when the impedance of a source and load is matched)
    This is why you have transmission gearing in your car.

    When fed by a low impedance source (battery), the Emphase will ramp up its current until it sees the battery voltage droop too much (which won't happen) and will only stop when it hits its current limit, which it does have. The common size of Emphase has been the 190 watt size which they allow using on panels larger than that, so this overcurrent possiblility already happens. All inverters and charge controllers have current limiting inherently as a result of their MPPT capability.

    Now, why you would want to do this I don't know, as the only time you need battery backing is if the grid is down and the Emphase won't work then.


    I think the recommended PV (for the M-190) is 230w. Some installations are using 230w panels.
    With cloud edge boost, those panels might put out 250w plus a bit..

    But, the original question was, what happens with a battery connected? (or four 230w panels in parallel).
    Will the enphase run at full output and survive? Or, will it try to put out too much power and melt?



    Now, why you would want to do this I don't know, as the only time you need battery backing is if the grid is down and the Emphase won't work then.



    Because, the Enphase won't work then.. :roll:

    Getting the Enphase units to start up during a power failure (or at night) is another topic.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: EnPhase on batteries?

    Fuse/circuit breaker.
    The Enphase is meant to draw no more than the Isc of a single compatible panel. If you want to experiment with powering one from a battery put circuit protection in. If the current goes over the normally expected maximum draw the CP should blow before the inverter does.

    Note the cautionary "should". :roll:

    It is doubtful they put any other sort of current-limiting circuitry inside a unit that isn't meant to have more than Vmp * Imp available to it (i.e. the panel's output is self-limiting).

    Synching the output so it will even run with no grid is another issue that has been explored here before. Doesn't seem to be worth the effort & hassle.

    That 25 year warranty will be instantly voided, btw.

    If you want a hybrid GT system, buy a hybrid GT system. Alternatives include using a generator, a small, independent battery back-up system for essential needs, temporary rewiring of panels to support a charge controller, or the Xantrex 600 Volt controller on a central GT system.

    Shortcuts in electrical systems usually only lead to quicker failure.
  • Brianellul
    Brianellul Solar Expert Posts: 95 ✭✭
    Re: EnPhase on batteries?

    Here is the reply from Enphase.... :cry:

    My Email....
    Basically, I would like to know if I can power the Enphase inverter from batteries and fed the grid, i.e. instead of having a direct solar panel as a source, I'll have solar panels charging batteries and when the voltage is high enough the Enphase inverters will take excess DC power from the batteries and export to the grid.
    The Enphase inverter will still be configured to work in a normal grid-tie mode however sourcing power from the batteries. Also, the specifications read that the MIN start voltage is 28v. Is that that below this voltage the inverter is in sleep-mode i.e. not inverting?
    Regards
    Brian


    Reply...
    What you have described below has not been tested by Enphase Energy and is an application that we would not support. The Enphase Energy Microinverters are only to be used specified in the manuals and any deviation would void any Enphase Energy warranties.
    As for the minimum voltage, the answer is yes. The Enphase Microinverters must get to 28v for them to turn on. Once the units turn on, they can drop below this voltage and still work in bursts, but they must turn on first. Enphase Energy Microinverters use electrolytic caps in the dc input to filter and regulate changes in voltage, but only Enphase has added the logic to control the discharge of these caps to the utility during low light conditions, which causes the Microinverter to pulse or burst energy out.


    I was really under the impression that these Enphase inverters were similar to those cheap Chinese Grid-Tie Inverters you find on ebay but obviously built to a much higher standard.... Well I can always go for one of those to experiment!
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: EnPhase on batteries?

    You'll loose efficiency going that route. Much better to do a standard grid-tie configuration and then use the Xantrex high-voltage charge controller to supply your batteries when the grid is down (and a standard AC charger normally).
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    Re: EnPhase on batteries?
    XRinger wrote: »
    I think the recommended PV (for the M-190) is 230w. Some installations are using 230w panels.
    With cloud edge boost, those panels might put out 250w plus a bit..

    But, the original question was, what happens with a battery connected? (or four 230w panels in parallel).
    Will the enphase run at full output and survive? Or, will it try to put out too much power and melt?
    The Enphase M190 will limit it's AC power output to 199W maximum regardless of how much power is available on the DC side. DC input will be about 210W since the inverter is about 95% efficient.

    Even though Enphase doesn't recommend it, I don't see any reason why it wouldn't work.

    One can sometimes find Enphase inverters for cheap on eBay. Would be perfect for an experiment like this.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: EnPhase on batteries?
    drees wrote: »
    The Enphase M190 will limit it's AC power output to 199W maximum regardless of how much power is available on the DC side. DC input will be about 210W since the inverter is about 95% efficient.

    Even though Enphase doesn't recommend it, I don't see any reason why it wouldn't work.

    One can sometimes find Enphase inverters for cheap on eBay. Would be perfect for an experiment like this.


    To do this experiment, I would want to try the M210, since it's voltage range is 38 to 62 volts.
    62 volts seems to say it would work on a 48v battery bank. (If not in Equalize mode) :)

    I would have to use a real grid, (and not a PSW inverter) for sync up & run.
    So, to keep any of the M210 power from sneaking into the neighbors TV sets,
    I would need to be using at least 400 watts @ 240vac during the experiment.
    By keeping my 240vac 400w load* turned on, none of the power from the M210 could find it's way out into the world.. :roll:

    * Four tons of Sanyo Mini-Split ASHP systems using 240vac

    I have just the gizmo to instantly switch off the M210, when the 400w load started to drop off.
    It's a very accurate current sensor/switch connected to SSRs.
    http://ecorenovator.org/forum/appliances-gadgets/1490-diy-230vac-adjustable-power-limiter.html

    But, in this world of Zero tolerance, I would have to test this system on a private grid.. :p

    Cheers,
    Rich
  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    Re: EnPhase on batteries?
    XRinger wrote: »
    ... I have just the gizmo to instantly switch off the M210, when the 400w load started to drop off.
    It's a very accurate current sensor/switch connected to SSRs.
    http://ecorenovator.org/forum/appliances-gadgets/1490-diy-230vac-adjustable-power-limiter.html

    I like your gizmo. Where did you get the current sensor with the NO contacts and adjustable setting?
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: EnPhase on batteries?
    I like your gizmo. Where did you get the current sensor with the NO contacts and adjustable setting?

    95% of my parts comes from Ebay.. :)

    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360401446811

    This one has no moving parts, since the "relay" contacts are actually a solid state switch.

    The newer unit I just got has the extra contacts, which aren't really needed
    in my applications, but maybe. They don't hurt anything, if the price is right.
  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    Re: EnPhase on batteries?

    Was reading the Enphase Community forum, there's a huge thread there regarding how to hook up Enphase to an off-grid inverter.

    http://community.enphaseenergy.com/enphase_energy_community/topics/are_enphase_microinverters_grid_tie_only

    In the last couple weeks, it's been confirmed that Enphase will work with a Magnum Inverter setup.

    If the solar is producing too much power and the battery back reaches full, it will adjust the AC frequency out of range so the inverters will go offline.

    Tough to get the required info out of the Enphase forum, but it should work and Enphase has said it won't void warranty.
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: EnPhase on batteries?
    drees wrote: »
    Was reading the Enphase Community forum, there's a huge thread there regarding how to hook up Enphase to an off-grid inverter.

    http://community.enphaseenergy.com/enphase_energy_community/topics/are_enphase_microinverters_grid_tie_only

    In the last couple weeks, it's been confirmed that Enphase will work with a Magnum Inverter setup.

    If the solar is producing too much power and the battery back reaches full, it will adjust the AC frequency out of range so the inverters will go offline.

    Tough to get the required info out of the Enphase forum, but it should work and Enphase has said it won't void warranty.


    Thanks for posting the link. Looks like it might be an interesting read..
    X
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: EnPhase on batteries?

    I'm wondering about DC to AC isolation within the Enphase modules. (like the M190-72-240-S12).

    piggybak.jpg
    (This rig seems like it would be keep the inverters online, when the clouds came over)!

    In a setup like this, will the common connection point in the middle of the battery bank cause any problems?
    Are the AC outputs (tied in parallel to the 230 line) isolated enough,
    not to feed any DC potential from the battery bank, out to the AC lines..
    Maybe causing some weird loading down of the inverters..?.

    Thanks,
    Rich
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: EnPhase on batteries?

    Two issues...

    First is, I don't know if the Enphase inverters have isolated DC inputs or not... Good chance they are isolated inputs, but it is certainly possible they are not, and you will fry the inverters with that DC connection scheme. You need to ask Enphase and/or do the smoke test.

    Second, pulling 24 volt power from a 48 volt battery bank. There is no guarantee that the two Enphase inverters will balance their power draw over time and temperature. There is a good chance of damaging the battery bank with unequal current draw (unless the battery are balanced with other methods).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: EnPhase on batteries?
    BB. wrote: »
    Two issues...

    First is, I don't know if the Enphase inverters have isolated DC inputs or not... Good chance they are isolated inputs, but it is certainly possible they are not, and you will fry the inverters with that DC connection scheme. You need to ask Enphase and/or do the smoke test.

    Second, pulling 24 volt power from a 48 volt battery bank. There is no guarantee that the two Enphase inverters will balance their power draw over time and temperature. There is a good chance of damaging the battery bank with unequal current draw (unless the battery are balanced with other methods).

    -Bill

    I've been thinking about it, and since the isolation cuts-both-ways, they would
    have have really good isolation. Otherwise, someone working on the PV DC
    (even at night) could possibly be electrocuted, right off his roof..
    Just look at almost any UL listed battery charger, AC-DC Isolation is a must.
    Allowing AC to back-feed into PV DC connections would leave Enphase wide open to law suits..


    If the batteries are only charged to 12.0 volts, it's questionable if the M190-72-240-S12 would even start up.
    But, if the sun was bright and the charger was pushing around 56v,
    a lot of the power to the inverters would be from the PV & charger..

    I can run my 48v MSW inverter with a light load (under 400w) and not discharge
    the 48v bank at all. (If the sun is bright)! 8)

    I'm pretty sure that automatically monitoring two 24v sources wouldn't be very hard.

    I have built a circuit that looks at just one 12V battery. which signals the general charge of the 48v bank(It turns off an SSR, disconnecting the inverter).

    Building two (48v) boards, with opto-isolators to control inverter disconnect would
    take very little effort. (I have the parts in stock). ;)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: EnPhase on batteries?

    The problem is that the new requirements do not required DC (galvantic) isolation between the AC and DC side of GT inverter.

    And solar panels for GT are rated at 600-1,000 volts--so they are perfectly OK to run at higher than local Voc/Vmp voltages.

    Again, I have no idea if the Enphase are isolated or not--Although, I would guess they probably are... But I would not want to do that test with my fingers.

    Regarding pulling power from 24 volts splits from a 48 volt bank... It is the chance that one battery bank is discharged further than the other. Because both are sharing one current source for charging... If they are not balanced, it is very possible for one battery bank to over charge and the other to under charge... And you would have to do some heavy equalization to balance them out.

    However, there are a few ways that I have seen where people use separate chargers, or special devices that bypass current around the "full battery", and you can even setup a DC to DC converter to balance the charge between two series connected batteries.

    Over all, it would seem better just to build out a 24 volt bank (or 36 volt) and you may have to get a second charge controller to handle the larger current that a 24 volt bank requires (vs the same number of batteries wired up as a 48 volt bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    Re: EnPhase on batteries?

    I was looking the dual 24v idea, only because I have a 48v back-up system.
    It's fully charged about 98% the time these days.

    It seems like GTIs should have good isolation, since you wouldn't want any
    of 240VAC dancing around on your roof, after a hail storm or other mishap..

    Thanks for your replies Bill.

    Cheers,
    Rich
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: EnPhase on batteries?

    With central GT inverter, I have >400 VDC if something were to break... Yes, the low voltage DC side on the roof is supposed to be an advantage with Enphase microinverters.

    I can certainly see the disadvantages with 300-500 VDC solar panels wired in series for a large central inverter...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset