• Solar panels

    From Don Y@21:1/5 to All on Thu May 30 22:00:22 2024
    My understanding is that solar panels are typically series wired
    as many as 10 high -- 500VDC into inverter.

    But, the individual wafers (on a panel) are probably wired in a
    series-parallel configuration with a nominal 48VDC output.

    To increase the ampacity from an array of such panels, I assume
    simply wiring in parallel would not be as effective as installing
    an MPPT controller on each and then combining to a 48VDC output?
    I.e., absorbing the cost of the conversion inefficiency in return
    for being able to eek a bit of extra power out of an underperforming
    panel?

    And, that this would be preferable to stacking them and then
    down-regulating to 48VDC?

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  • From KevinJ93@21:1/5 to Don Y on Fri May 31 12:56:32 2024
    On 5/30/24 10:00 PM, Don Y wrote:
    My understanding is that solar panels are typically series wired
    as many as 10 high -- 500VDC into inverter.

    The maximum voltage is usually limited by inverters available and
    various electrical codes. As you say around 500V is common.

    Note that the voltage increases as the temperature reduces so strong
    sunlight in the winter can give much higher voltages than on a hot
    summer day.

    But, the individual wafers (on a panel) are probably wired in a series-parallel configuration with a nominal 48VDC output.

    Not usually true - I don't know of any panels where there is a
    series-parallel configuration. As wafer sizes increase the panel current increases.

    It is common for the panel to be divided electrically into three series sections with a reverse diode across each so that if one section is
    shaded or damaged the panel will still give output at reduced voltage
    and the MPPT controller will adapt.

    To increase the ampacity from an array of such panels, I assume
    simply wiring in parallel would not be as effective as installing
    an MPPT controller on each and then combining to a 48VDC output?

    Wiring panels in parallel would require heavier gauge wiring - it is
    usually more cost effective to go with a higher voltage.

    I.e., absorbing the cost of the conversion inefficiency in return
    for being able to eek a bit of extra power out of an underperforming
    panel?

    Residential installations commonly use micro-inverters with one per
    panel. This minimizes issues with individual panels being shaded or
    being placed on different facets of a roof.

    Having each panel dealt with separately also avoids a problem with
    having high voltages on the roof where it could endanger emergency
    personnel in the case of fire.

    Electrical code in the US requires that where panels are placed on a
    residence that there be no more than 80V DC present when disabled.

    Micro-inverters usually have a anti-islanding protection so that when
    the grid is not-present they stop producing leaving the roof safe.

    In the case of DC systems this may require rapid-shutdown mid-circuit interrupters to meet these requirement.

    Commercial solar farms don't have to meet these rules so they can go to
    higher voltages and avoid the expense of additional interrupters.

    And, that this would be preferable to stacking them and then
    down-regulating to 48VDC?


    Why the conversion to 48V? Residential applications usually convert to
    direct to 240V AC.

    Even batteries for residential are commonly AC-in/AC-out with their own bidirectional inverters. (eg Tesla Powerwall and Enphase)

    kw

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  • From Don Y@21:1/5 to Don Y on Fri May 31 13:50:41 2024
    On 5/31/2024 1:43 PM, Don Y wrote:
    On 5/31/2024 12:56 PM, KevinJ93 wrote:
    On 5/30/24 10:00 PM, Don Y wrote:
    But, the individual wafers (on a panel) are probably wired in a
    series-parallel configuration with a nominal 48VDC output.

    Not usually true - I don't know of any panels where there is a
    series-parallel configuration. As wafer sizes increase the panel current
    increases.

    I count ~72 wafers on a panel I have here.  How does *it* get to a 48V nominal output?

    Ah! Each *wafer* is a *single* PV cell? The metalization layers led me
    to think each was *three* cells (~2V output) series connected.

    --- SoupGate-Win32 v1.05
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  • From Don Y@21:1/5 to All on Fri May 31 13:43:12 2024
    On 5/31/2024 12:56 PM, KevinJ93 wrote:
    On 5/30/24 10:00 PM, Don Y wrote:
    But, the individual wafers (on a panel) are probably wired in a
    series-parallel configuration with a nominal 48VDC output.

    Not usually true - I don't know of any panels where there is a series-parallel
    configuration. As wafer sizes increase the panel current increases.

    I count ~72 wafers on a panel I have here. How does *it* get to a 48V
    nominal output?

    It is common for the panel to be divided electrically into three series sections with a reverse diode across each so that if one section is shaded or damaged the panel will still give output at reduced voltage and the MPPT controller will adapt.

    Yes.

    To increase the ampacity from an array of such panels, I assume
    simply wiring in parallel would not be as effective as installing
    an MPPT controller on each and then combining to a 48VDC output?

    Wiring panels in parallel would require heavier gauge wiring - it is usually more cost effective to go with a higher voltage.

    Yes. But, if your goal is 48VDC, you then need to regulate that ~500VDC
    back down to 48VDC.

    It then boils down to where the various components are located (long,
    high amperage runs suffering higher IR drops; conversion losses for
    long high VOLTAGE runs)

    I.e., absorbing the cost of the conversion inefficiency in return
    for being able to eek a bit of extra power out of an underperforming
    panel?

    Residential installations commonly use micro-inverters with one per panel. This
    minimizes issues with individual panels being shaded or being placed on different facets of a roof.

    Yes. Or "power optimizers" in lieu of inverters.

    Having each panel dealt with separately also avoids a problem with having high
    voltages on the roof where it could endanger emergency personnel in the case of
    fire.

    Thus arguing against a high string voltage.

    Electrical code in the US requires that where panels are placed on a residence
    that there be no more than 80V DC present when disabled.

    Local electronics at the panel ensure that -- whether microinverter or power optimizer.

    Micro-inverters usually have a anti-islanding protection so that when the grid
    is not-present they stop producing leaving the roof safe.

    I'm not looking for grid connection. So, the grid is never present.

    In the case of DC systems this may require rapid-shutdown mid-circuit interrupters to meet these requirement.

    Yes.

    Commercial solar farms don't have to meet these rules so they can go to higher
    voltages and avoid the expense of additional interrupters.

    And, that this would be preferable to stacking them and then
    down-regulating to 48VDC?

    Why the conversion to 48V? Residential applications usually convert to direct to 240V AC.

    The straight forward approach is to AC then BACK to a lower voltage DC
    that can then be used, as is, and directly backed up with a low voltage
    (48) battery pack to carry over through periods of cloud cover.

    When "dark", I expect nothing from the array, having *consumed* all
    available power during the illuminated period.

    I'm not trying to power AC loads. So, going to AC means an inverter
    followed by a BIG "power supply".

    Even batteries for residential are commonly AC-in/AC-out with their own bidirectional inverters. (eg Tesla Powerwall and Enphase)

    But, those try to back up the entire array's capability. Give me 3-4KW
    during daylight and I can get by on < 100W for the rest of the day (night).
    So, a modest battery can carry the dark load and act to bridge small
    variations in output during full illumination. Adjusting the load
    accomplishes the rest.

    --- SoupGate-Win32 v1.05
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  • From boB@21:1/5 to blockedofcourse@foo.invalid on Fri May 31 14:15:40 2024
    On Fri, 31 May 2024 13:50:41 -0700, Don Y
    <blockedofcourse@foo.invalid> wrote:

    On 5/31/2024 1:43 PM, Don Y wrote:
    On 5/31/2024 12:56 PM, KevinJ93 wrote:
    On 5/30/24 10:00 PM, Don Y wrote:
    But, the individual wafers (on a panel) are probably wired in a
    series-parallel configuration with a nominal 48VDC output.

    Not usually true - I don't know of any panels where there is a
    series-parallel configuration. As wafer sizes increase the panel current >>> increases.

    I count ~72 wafers on a panel I have here.  How does *it* get to a 48V
    nominal output?

    Ah! Each *wafer* is a *single* PV cell? The metalization layers led me
    to think each was *three* cells (~2V output) series connected.



    72 cells is a common PV module (panel) configuration.

    So is 60 cells.

    An MPPT charger is usually a buck converter so that's how it gets
    there. A nominal 48V PV array will need to have a higher Vmp than the
    battery voltage to charge that battery bank.

    Sounds like Kevin knows his stuff regarding this and you aren't far
    off, if at all.

    Rapid Shutdown requires the array at the string (HV) inverter or
    charge controller input to be at or below 30V in 30 seconds after its
    clear to go signal is removed. At least those who are being inspected
    to NEC.

    boB

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  • From Don Y@21:1/5 to boB on Fri May 31 15:48:35 2024
    On 5/31/2024 2:15 PM, boB wrote:
    72 cells is a common PV module (panel) configuration.

    So is 60 cells.

    An MPPT charger is usually a buck converter so that's how it gets
    there. A nominal 48V PV array will need to have a higher Vmp than the battery voltage to charge that battery bank.

    Not intended to "charge" the battery but, rather, for the battery
    to look like an ideal capacitor.

    I can "charge" it from the mains, after hours (as well as supplement
    any load that I feel needs to be powered in the absence of sunlight)

    Sounds like Kevin knows his stuff regarding this and you aren't far
    off, if at all.

    Rapid Shutdown requires the array at the string (HV) inverter or
    charge controller input to be at or below 30V in 30 seconds after its
    clear to go signal is removed. At least those who are being inspected
    to NEC.

    If I can let the array look like a single 48V panel (a bunch of them,
    each contributing some amount of current to a single/shared load),
    I figure it simplifies the deployment by distributing the electronics
    among multiple relatively low power (300-400W) sources.

    Otherwise, you have to reengineer a solution for each deployment -- 3KW,
    5KW, 6KW, etc. each requiring a bigger "power supply" (to produce the
    48V from the AC generated by microinverters or a string inverter)

    E.g., I can use a single panel, by itself -- as long as my solar load
    is ~300W (supplementing with mains-derived power if it exceeds this
    on the short term or if the sun hides)

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  • From KevinJ93@21:1/5 to Don Y on Fri May 31 18:31:54 2024
    On 5/31/24 1:50 PM, Don Y wrote:
    On 5/31/2024 1:43 PM, Don Y wrote:
    On 5/31/2024 12:56 PM, KevinJ93 wrote:
    On 5/30/24 10:00 PM, Don Y wrote:
    But, the individual wafers (on a panel) are probably wired in a
    series-parallel configuration with a nominal 48VDC output.

    Not usually true - I don't know of any panels where there is a
    series-parallel configuration. As wafer sizes increase the panel
    current increases.

    I count ~72 wafers on a panel I have here.  How does *it* get to a 48V
    nominal output?

    I don't think it is 48V nominal output - it is probably 48V open-circuit
    with a maximum power voltage of ~41V.

    Ah!  Each *wafer* is a *single* PV cell?  The metalization layers led me
    to think each was *three* cells (~2V output) series connected.

    I don't think they do that - normally they use the substrate connection
    from the back as one of the terminals - putting multiple cells on a
    wafer would be more difficult requiring some form of device isolation as
    is used in integrated circuits. The metalization on the front forms the
    current collector for the front contact.

    kw

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From KevinJ93@21:1/5 to Don Y on Fri May 31 18:18:51 2024
    On 5/31/24 1:43 PM, Don Y wrote:
    On 5/31/2024 12:56 PM, KevinJ93 wrote:
    On 5/30/24 10:00 PM, Don Y wrote:
    But, the individual wafers (on a panel) are probably wired in a
    series-parallel configuration with a nominal 48VDC output.

    Not usually true - I don't know of any panels where there is a
    series-parallel configuration. As wafer sizes increase the panel
    current increases.

    I count ~72 wafers on a panel I have here.  How does *it* get to a 48V nominal output?

    Are you sure that isn't the open-circuit voltage(Voc)?

    For the couple of 72 cell panels I looked Voc is 49.0V +/-

    The peak power voltage is about 41.0V.

    Each cell has a peak voltage of ~0.7V and a peak power voltage of ~0.56V.

    That voltage is not enough to charge a nominal 48V battery which
    probably needs up to ~54V.

    Interestingly I did find out that the 400W Q-Cell panels are in fact 144
    cell. They look they are configured as two 72 cell strings in parallel.
    There isn't any provision for reconfiguring as far as I could see.

    It is common for the panel to be divided electrically into three
    series sections with a reverse diode across each so that if one
    section is shaded or damaged the panel will still give output at
    reduced voltage and the MPPT controller will adapt.

    Yes.

    To increase the ampacity from an array of such panels, I assume
    simply wiring in parallel would not be as effective as installing
    an MPPT controller on each and then combining to a 48VDC output?

    Wiring panels in parallel would require heavier gauge wiring - it is
    usually more cost effective to go with a higher voltage.

    Yes.  But, if your goal is 48VDC, you then need to regulate that ~500VDC back down to 48VDC.

    It then boils down to where the various components are located (long,
    high amperage runs suffering higher IR drops; conversion losses for
    long high VOLTAGE runs)

    I.e., absorbing the cost of the conversion inefficiency in return
    for being able to eek a bit of extra power out of an underperforming
    panel?

    Residential installations commonly use micro-inverters with one per
    panel. This minimizes issues with individual panels being shaded or
    being placed on different facets of a roof.

    Yes.  Or "power optimizers" in lieu of inverters.

    Some inverter vendors (in particular SolarEdge) use optimizers with each
    panel - to perform part of the MPPT function. As far as I know they only
    work with the same vendor's inverter.

    Having each panel dealt with separately also avoids a problem with
    having high voltages on the roof where it could endanger emergency
    personnel in the case of fire.

    Thus arguing against a high string voltage.

    Electrical code in the US requires that where panels are placed on a
    residence that there be no more than 80V DC present when disabled.

    Local electronics at the panel ensure that -- whether microinverter or
    power optimizer.

    Or a Mid-Circuit Interrupter (MCI) as in the case of systems such as Tesla.

    Micro-inverters usually have a anti-islanding protection so that when
    the grid is not-present they stop producing leaving the roof safe.

    I'm not looking for grid connection.  So, the grid is never present.

    In the case of DC systems this may require rapid-shutdown mid-circuit
    interrupters to meet these requirement.

    Yes.

    Commercial solar farms don't have to meet these rules so they can go
    to higher voltages and avoid the expense of additional interrupters.

    And, that this would be preferable to stacking them and then
    down-regulating to 48VDC?

    Why the conversion to 48V? Residential applications usually convert to
    direct to 240V AC.

    The straight forward approach is to AC then BACK to a lower voltage DC
    that can then be used, as is, and directly backed up with a low voltage
    (48) battery pack to carry over through periods of cloud cove > When "dark", I expect nothing from the array, having *consumed* all
    available power during the illuminated period.

    I'm not trying to power AC loads.  So, going to AC means an inverter followed by a BIG "power supply".

    Even batteries for residential are commonly AC-in/AC-out with their
    own bidirectional inverters. (eg Tesla Powerwall and Enphase)

    But, those try to back up the entire array's capability.  Give me 3-4KW during daylight and I can get by on < 100W for the rest of the day (night). So, a modest battery can carry the dark load and act to bridge small variations in output during full illumination.  Adjusting the load accomplishes the rest.

    There are many "Solar Charge Controllers" on Amazon that could do the
    voltage conversion and MPPT to charge a 48V battery at up to 60A (~3kW).

    They seem to want a string voltage of up to 100V or 150V which would
    equate to 2-3 panels in series. Provided all panels have the same aspect
    and sun exposure you could put strings in parallel to get the power
    level you need.

    Not sure how to avoid excessive charge currents into the battery if it
    can't take the full solar output.

    https://www.amazon.com/dp/B0D2KRL34V/ref=sspa_dk_detail_0?pd_rd_i=B0D2KRL34V&pd_rd_w=3xPB3&content-id=amzn1.sym.386c274b-4bfe-4421-9052-a1a56db557ab&pf_rd_p=386c274b-4bfe-4421-9052-a1a56db557ab&pf_rd_r=TKMP47AV732XMSDXGQRM&pd_rd_wg=bRMca&pd_rd_r=4b973d61-
    537b-40d4-8e1c-560122e38f7d&s=sporting-goods&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWM&th=1

    kw

    --- SoupGate-Win32 v1.05
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  • From Don Y@21:1/5 to All on Fri May 31 22:42:59 2024
    On 5/31/2024 6:18 PM, KevinJ93 wrote:
    I count ~72 wafers on a panel I have here.  How does *it* get to a 48V
    nominal output?

    Are you sure that isn't the open-circuit voltage(Voc)?

    For the couple of 72 cell panels I looked Voc is 49.0V +/-

    The peak power voltage is about 41.0V.

    Each cell has a peak voltage of ~0.7V and a peak power voltage of ~0.56V.

    That voltage is not enough to charge a nominal 48V battery which probably needs
    up to ~54V.

    Actual voltages don't matter. Its the design topology that's important. Delivering an output that can be simply summed among panels and avoiding
    a many kilowatt "low voltage power supply" following that.

    Interestingly I did find out that the 400W Q-Cell panels are in fact 144 cell.
    They look they are configured as two 72 cell strings in parallel. There isn't any provision for reconfiguring as far as I could see.

    I.e., absorbing the cost of the conversion inefficiency in return
    for being able to eek a bit of extra power out of an underperforming
    panel?

    Residential installations commonly use micro-inverters with one per panel. >>> This minimizes issues with individual panels being shaded or being placed on
    different facets of a roof.

    Yes.  Or "power optimizers" in lieu of inverters.

    Some inverter vendors (in particular SolarEdge) use optimizers with each panel
    - to perform part of the MPPT function. As far as I know they only work with the same vendor's inverter.

    Yes, but, again, you're assuming a "domestic power" application. If all you want it for the panel to track all the other panels that it is in parallel with, you don't care about an inverter.

    Get the panel to operate at its maximum power point. Then, follow that with a "48V" converter. The panel just contributes whatever current it can, at that voltage, /while operating at its MPP/.

    Electrical code in the US requires that where panels are placed on a
    residence that there be no more than 80V DC present when disabled.

    Local electronics at the panel ensure that -- whether microinverter or power >> optimizer.

    Or a Mid-Circuit Interrupter (MCI) as in the case of systems such as Tesla.

    Output During Standby (when disconnected from inverter or inverter off): 1 Vdc

    (read that as "when load disconnected", in my case)

    Absolute Maximum Input Voltage (Voc): 75 Vdc
    MPPT Operating Range: 5 - 75 Vdc
    Maximum Input Current: 10 Adc
    Maximum Output Current: 15 Adc
    Operating Output Voltage: 5 - 60 Vdc
    Maximum Efficiency: 99.5 %
    European Weighted Efficiency: 98.8 %

    Even batteries for residential are commonly AC-in/AC-out with their own
    bidirectional inverters. (eg Tesla Powerwall and Enphase)

    But, those try to back up the entire array's capability.  Give me 3-4KW
    during daylight and I can get by on < 100W for the rest of the day (night). >> So, a modest battery can carry the dark load and act to bridge small
    variations in output during full illumination.  Adjusting the load
    accomplishes the rest.

    There are many "Solar Charge Controllers" on Amazon that could do the voltage conversion and MPPT to charge a 48V battery at up to 60A (~3kW).

    They seem to want a string voltage of up to 100V or 150V which would equate to
    2-3 panels in series. Provided all panels have the same aspect and sun exposure
    you could put strings in parallel to get the power level you need.

    Yes, but now you're up at those "lethal" voltages, again. If you think of it as a ~48V source, then it contributes just a few amps (~6). You rely on having many of them working alongside each other to get the ampacity needed.

    Not sure how to avoid excessive charge currents into the battery if it can't take the full solar output.

    I think you have to be able to "talk" to the module to tell it how you would like it to behave, NOW.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From boB@21:1/5 to blockedofcourse@foo.invalid on Sat Jun 1 18:29:20 2024
    On Fri, 31 May 2024 22:42:59 -0700, Don Y
    <blockedofcourse@foo.invalid> wrote:

    On 5/31/2024 6:18 PM, KevinJ93 wrote:
    I count ~72 wafers on a panel I have here.  How does *it* get to a 48V
    nominal output?

    Are you sure that isn't the open-circuit voltage(Voc)?

    For the couple of 72 cell panels I looked Voc is 49.0V +/-

    The peak power voltage is about 41.0V.

    Each cell has a peak voltage of ~0.7V and a peak power voltage of ~0.56V.

    That voltage is not enough to charge a nominal 48V battery which probably needs
    up to ~54V.

    Actual voltages don't matter. Its the design topology that's important. >Delivering an output that can be simply summed among panels and avoiding
    a many kilowatt "low voltage power supply" following that.

    Interestingly I did find out that the 400W Q-Cell panels are in fact 144 cell.
    They look they are configured as two 72 cell strings in parallel. There isn't
    any provision for reconfiguring as far as I could see.

    I.e., absorbing the cost of the conversion inefficiency in return
    for being able to eek a bit of extra power out of an underperforming >>>>> panel?

    Residential installations commonly use micro-inverters with one per panel. >>>> This minimizes issues with individual panels being shaded or being placed on
    different facets of a roof.

    Yes.  Or "power optimizers" in lieu of inverters.

    Some inverter vendors (in particular SolarEdge) use optimizers with each panel
    - to perform part of the MPPT function. As far as I know they only work with >> the same vendor's inverter.

    Yes, but, again, you're assuming a "domestic power" application. If all you >want it for the panel to track all the other panels that it is in parallel >with, you don't care about an inverter.

    Get the panel to operate at its maximum power point. Then, follow that with a >"48V" converter. The panel just contributes whatever current it can, at that >voltage, /while operating at its MPP/.

    Electrical code in the US requires that where panels are placed on a
    residence that there be no more than 80V DC present when disabled.

    Local electronics at the panel ensure that -- whether microinverter or power
    optimizer.

    Or a Mid-Circuit Interrupter (MCI) as in the case of systems such as Tesla.

    Output During Standby (when disconnected from inverter or inverter off): 1 Vdc

    (read that as "when load disconnected", in my case)

    Absolute Maximum Input Voltage (Voc): 75 Vdc
    MPPT Operating Range: 5 - 75 Vdc
    Maximum Input Current: 10 Adc
    Maximum Output Current: 15 Adc
    Operating Output Voltage: 5 - 60 Vdc
    Maximum Efficiency: 99.5 %
    European Weighted Efficiency: 98.8 %

    Even batteries for residential are commonly AC-in/AC-out with their own >>>> bidirectional inverters. (eg Tesla Powerwall and Enphase)

    But, those try to back up the entire array's capability.  Give me 3-4KW
    during daylight and I can get by on < 100W for the rest of the day (night). >>> So, a modest battery can carry the dark load and act to bridge small
    variations in output during full illumination.  Adjusting the load
    accomplishes the rest.

    There are many "Solar Charge Controllers" on Amazon that could do the voltage
    conversion and MPPT to charge a 48V battery at up to 60A (~3kW).

    They seem to want a string voltage of up to 100V or 150V which would equate to
    2-3 panels in series. Provided all panels have the same aspect and sun exposure
    you could put strings in parallel to get the power level you need.

    Yes, but now you're up at those "lethal" voltages, again. If you think of it >as a ~48V source, then it contributes just a few amps (~6). You rely on having
    many of them working alongside each other to get the ampacity needed.

    Not sure how to avoid excessive charge currents into the battery if it can't >> take the full solar output.

    I think you have to be able to "talk" to the module to tell it how you would >like it to behave, NOW.



    The MPPT controller simply raises the PV operating voltage above
    Vmp... At Voc, the current becomes zero. Whatever Vpv gives the
    correct controller output voltage to the battery it is charging.

    boB

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  • From Don Y@21:1/5 to boB on Sat Jun 1 20:32:17 2024
    On 6/1/2024 6:29 PM, boB wrote:
    Not sure how to avoid excessive charge currents into the battery if it can't
    take the full solar output.

    I think you have to be able to "talk" to the module to tell it how you would >> like it to behave, NOW.

    The MPPT controller simply raises the PV operating voltage above
    Vmp... At Voc, the current becomes zero. Whatever Vpv gives the
    correct controller output voltage to the battery it is charging.

    You have to signal to the controller that the battery is charged;
    that it can't (shouldn't) continue to accept charge.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From KevinJ93@21:1/5 to Don Y on Sun Jun 2 10:21:17 2024
    On 6/1/24 8:32 PM, Don Y wrote:
    On 6/1/2024 6:29 PM, boB wrote:
    Not sure how to avoid excessive charge currents into the battery if
    it can't
    take the full solar output.

    I think you have to be able to "talk" to the module to tell it how
    you would
    like it to behave, NOW.

    The MPPT controller simply raises the PV operating voltage above
    Vmp...  At Voc, the current becomes zero. Whatever Vpv gives the
    correct controller output voltage to the battery it is charging.

    You have to signal to the controller that the battery is charged;
    that it can't (shouldn't) continue to accept charge.


    That will happen automatically when the battery reaches the set voltage.

    Some of the charge controllers allow configuration for various
    parameters such as 100% charge voltage so that it will work with
    different chemistries.

    In your case your load could be directly across the battery.

    The one thing that is not obvious to me is how to limit the charge
    current if you use a small battery where the solar available could
    exceed the allowable battery charging current.

    Maybe you could add a controllable dump for when solar generation
    significantly exceeds your load consumption?

    kw

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  • From Don Y@21:1/5 to All on Sun Jun 2 11:06:32 2024
    On 6/2/2024 10:21 AM, KevinJ93 wrote:
    On 6/1/24 8:32 PM, Don Y wrote:
    On 6/1/2024 6:29 PM, boB wrote:
    Not sure how to avoid excessive charge currents into the battery if it can't
    take the full solar output.

    I think you have to be able to "talk" to the module to tell it how you would
    like it to behave, NOW.

    The MPPT controller simply raises the PV operating voltage above
    Vmp...  At Voc, the current becomes zero. Whatever Vpv gives the
    correct controller output voltage to the battery it is charging.

    You have to signal to the controller that the battery is charged;
    that it can't (shouldn't) continue to accept charge.

    That will happen automatically when the battery reaches the set voltage.

    *If* you have a charge controller for the battery, the controller limits
    what will flow into the *battery*.

    But, I use loads in much the same way that one would use a battery; if
    there is excess capacity available, then I will bring more loads on line. There's no other "storage" for that excess capacity -- use it or lose it.

    Some of the charge controllers allow configuration for various parameters such
    as 100% charge voltage so that it will work with different chemistries.

    In your case your load could be directly across the battery.

    The one thing that is not obvious to me is how to limit the charge current if you use a small battery where the solar available could exceed the allowable battery charging current.

    See above. Unlike a typical application where you would "store" the excess produced into the grid, I am avoiding that complication. I'll just "do extra work" with it, storing the results of that "work" instead of the electrons themselves.

    That's why I need more intimate control and knowledge of what the available power, battery reserves and loads are.

    Power FROM the grid is always available to supplement my needs -- but, that doesn't want to be the main source of power. E.g., I could find it advantageous to charge the battery at C/100 (!) in preparation for darkness
    if I can make use of all of the available solar power to "do real work"
    (cuz that won't be possible, later).

    Likewise, if the battery doesn't have sufficient reserves to bridge the dark period, rely on mains-sourced power -- but, as a temporary stopgap.

    I.e., you continuously are making supply and demand decisions trying to minimize the expected cost of your usage: "Is it better for me to delay
    this 'work' until tomorrow when I *expect* to have a surplus of solar power available? Or, have I already 'borrowed' to heavily from that future
    source?"

    It's just a resource management issue: should I wash the dishes, laundry, irrigate the yard AND take a shower now? Or, can I distribute those
    loads to better use the available water (and hot water) to eliminate
    the need to up-size my supply?

    Maybe you could add a controllable dump for when solar generation significantly
    exceeds your load consumption?

    kw

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    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From KevinJ93@21:1/5 to Don Y on Sun Jun 2 19:07:30 2024
    On 6/2/24 11:06 AM, Don Y wrote:
    On 6/2/2024 10:21 AM, KevinJ93 wrote:
    On 6/1/24 8:32 PM, Don Y wrote:
    On 6/1/2024 6:29 PM, boB wrote:
    Not sure how to avoid excessive charge currents into the battery
    if it can't
    take the full solar output.

    I think you have to be able to "talk" to the module to tell it how
    you would
    like it to behave, NOW.

    The MPPT controller simply raises the PV operating voltage above
    Vmp...  At Voc, the current becomes zero. Whatever Vpv gives the
    correct controller output voltage to the battery it is charging.

    You have to signal to the controller that the battery is charged;
    that it can't (shouldn't) continue to accept charge.

    That will happen automatically when the battery reaches the set voltage.

    *If* you have a charge controller for the battery, the controller limits
    what will flow into the *battery*.
    But, I use loads in much the same way that one would use a battery; if
    there is excess capacity available, then I will bring more loads on line. There's no other "storage" for that excess capacity -- use it or lose it.

    Some of the charge controllers allow configuration for various
    parameters such as 100% charge voltage so that it will work with
    different chemistries.

    In your case your load could be directly across the battery.

    The one thing that is not obvious to me is how to limit the charge
    current if you use a small battery where the solar available could
    exceed the allowable battery charging current.

    See above.  Unlike a typical application where you would "store" the excess produced into the grid, I am avoiding that complication.  I'll just "do extra
    work" with it, storing the results of that "work" instead of the electrons themselves.

    That's why I need more intimate control and  knowledge of what the
    available
    power, battery reserves and loads are.

    Power FROM the grid is always available to supplement my needs -- but, that doesn't want to be the main source of power.  E.g., I could find it advantageous to charge the battery at C/100 (!) in preparation for darkness if I can make use of all of the available solar power to "do real work"
    (cuz that won't be possible, later).

    Likewise, if the battery doesn't have sufficient reserves to bridge the
    dark
    period, rely on mains-sourced power -- but, as a temporary stopgap.

    I.e., you continuously are making supply and demand decisions trying to minimize the expected cost of your usage:  "Is it better for me to delay this 'work' until tomorrow when I *expect* to have a surplus of solar power available?  Or, have I already 'borrowed' to heavily from that future source?"

    It's just a resource management issue:  should I wash the dishes, laundry, irrigate the yard AND take a shower now?  Or, can I distribute those
    loads to better use the available water (and hot water) to eliminate
    the need to up-size my supply?

    Maybe you could add a controllable dump for when solar generation
    significantly exceeds your load consumption?

    kw


    I understand what you are wishing to do.

    Just putting the load across the battery that is being fed from a MPPT
    charge controller may be all that you need.

    By monitoring the state of charge you can then make decisions about how
    to control the load to make best use of the available energy.

    The only thing that is unusual about your application is that the
    battery would be sized to be smaller than normal.

    kw

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  • From Don Y@21:1/5 to All on Sun Jun 2 20:56:18 2024
    On 6/2/2024 7:07 PM, KevinJ93 wrote:
    I understand what you are wishing to do.

    Just putting the load across the battery that is being fed from a MPPT charge controller may be all that you need.

    The problem will be ensuring the battery voltage remains where I would like it regardless of where I am sourcing (and sinking) power. I.e., would I rather use power to top off the battery -- or, feed a bigger load. And, would that power want to come from the mains (which has a price associated) or the PV array (which has no such charge).

    By monitoring the state of charge you can then make decisions about how to control the load to make best use of the available energy.

    The only thing that is unusual about your application is that the battery would
    be sized to be smaller than normal.

    And the grid is never back fed *from* the array. I.e., this just looks
    like a regular electrical device that happens to use less power from
    the grid than it actually uses.

    One would typically size an array and its backup to handle arbitrary loads
    as determined by occupants. In my case, a machine determines the loading
    so can better tolerate the variation in power availability.

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