Solar panels

[Don Y]

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?

[KevinJ93]

Post by Don Y
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.

Post by Don Y
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.

Post by Don Y
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.

Post by Don Y
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.

Post by Don Y
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

[Don Y]

Post by Don Y
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.

Post by Don Y
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)

Post by Don Y
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.

Post by Don Y
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.

[Don Y]

Post by KevinJ93

Post by Don Y
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.

[boB]

On Fri, 31 May 2024 13:50:41 -0700, Don Y

Post by Don Y

Post by KevinJ93

Post by Don Y
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

[Don Y]

Post by boB
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)

Post by boB
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)

[KevinJ93]

Post by KevinJ93

Post by Don Y
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

[KevinJ93]

Post by KevinJ93

Post by Don Y
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.

Post by KevinJ93
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.

Post by KevinJ93

Post by Don Y
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)

Post by KevinJ93

Post by Don Y
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.

Post by KevinJ93
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.

Post by KevinJ93
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.

Post by KevinJ93
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.

Post by KevinJ93
In the case of DC systems this may require rapid-shutdown mid-circuit
interrupters to meet these requirement.

Yes.

Post by KevinJ93
Commercial solar farms don't have to meet these rules so they can go
to higher voltages and avoid the expense of additional interrupters.

Post by Don Y
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".

Post by KevinJ93
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

[Don Y]

Post by KevinJ93

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.

Post by KevinJ93
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.

Post by Don Y
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/.

Post by KevinJ93

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 %

Post by KevinJ93

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.

Post by KevinJ93
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.

[boB]

On Fri, 31 May 2024 22:42:59 -0700, Don Y

Post by Don Y

Post by KevinJ93

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.

Post by KevinJ93
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.

Post by Don Y
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/.

Post by KevinJ93

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 %

Post by KevinJ93

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.

Post by KevinJ93
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

[Don Y]

Post by boB

Post by Don Y

Post by KevinJ93
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.

[KevinJ93]

Post by Don Y

Post by boB

Post by Don Y

Post by KevinJ93
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

[Don Y]

Post by KevinJ93

Post by Don Y

Post by boB

Post by Don Y

Post by KevinJ93
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.

Post by KevinJ93
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?

Post by KevinJ93
Maybe you could add a controllable dump for when solar generation significantly
exceeds your load consumption?
kw

[KevinJ93]

Post by Don Y

Post by KevinJ93

Post by Don Y

Post by boB

Post by Don Y

Post by KevinJ93
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.

Post by KevinJ93
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?

Post by KevinJ93
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

[Don Y]

Post by KevinJ93
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).

Post by KevinJ93
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.