Tesla fires, Amphenol connector

[boB]

On Wed, 28 Aug 2019 20:31:52 -0700 (PDT), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

On Wednesday, August 28, 2019 at 9:30:10 PM UTC-4, Winfield Hill wrote:
Rick C wrote...

Perhaps you can explain what you think optimizers do ...

Every panel has its own optimizer (OK, now they
have dual optimizer boxes, four wires, two panels
each.) Current must be the same in all optimizers
in series. The optimizers control their output
voltage, to match their panel's available MPPT
power: low power low voltage, high power, higher
voltage. An additional trick is that SolarEdge
optimizers somehow control all the optimizers,
so total series voltage is fixed, e.g., 400V. I
wonder a) how they do that, and b) failure modes.

If the current in all panels in series is equal, how can each panel be "optimized" separately??? I guess I've been thinking the current through the string to the inverter would pass through all the cells. But the reality is the optimizer isolates the cells of a panel from the output current so panels in series run at the same current, but the cells of each panel run at different current from other panels?

Originally, per module MPPT was to mitigate against partial shading
where a partially shaded module would go completely out of circuit
through its bypass diode(s). National Semiconductor had its "Solar
Magic" units that it tried to sell for like, $60 each per module. It
worked and they had a neat golf cart like example of it but it was too
expensive.

Then others like TIGO (partially owned by SMA) got into it. It is very
arguable that these optimizers actually help much in that regard but
they also tout that they help with unmatched solar panels.
The real way to mitigate partial shading is with a chain-saw and not
to have any, but there are places you just have shading at least part
of the day or in winter.

Solar Edge's modules evidently also limit the highest voltage that the
PV string can see.

Another thing that can be done wihen multiple PV strings are in
parallel and there is partial shading on say, one panel in one string
is to just boost the voltage of the shaded string up a bit so that
both strings are contributing their available power at the same
voltage....

A shaded module in a string of several panels can really reduce the
power output of the combined system because the entire PV array's MPPT
voltage that the inverter finds is a compromise. It's a better
compromise if both or more strings are all putting out maximum power
at the same voltage.

Of course, an MPPT box (optimizer) on every module can typically also
double as a rapid shutdown switch. BTW it is the SunSpec
specification that tries to require that 1V residual across a panel
that is OFF so that they can supposedly tell that it is working or
not.

So, just as solar PV was starting to get inexpensive, along comes some
fireman with their great ideas (and some with self interests) PLUS
tariffs to bring the price of solar back up again.

 

[Winfield Hill]

Rick C wrote...

On Wednesday, August 28, 2019, Winfield Hill wrote:
Rick C wrote...

Perhaps you can explain what you think optimizers do ...

Every panel has its own optimizer (OK, now they
have dual optimizer boxes, four wires, two panels
each.) Current must be the same in all optimizers
in series. The optimizers control their output
voltage, to match their panel's available MPPT
power: low power low voltage, high power, higher
voltage. An additional trick is that SolarEdge
optimizers somehow control all the optimizers,
so total series voltage is fixed, e.g., 400V. I
wonder a) how they do that, and b) failure modes.

If the current in all panels in series is equal,
how can each panel be "optimized" separately???

It's the optimizer outputs that are in series, and
of course each MUST be operating at the same current,
regulating its series voltage to determine how much
power it's contributing. The solar panel is the
input to the optimizer, which works as a buck-boost
converter between the panel and the optimizer output
to the string. The ratio setting of the buck-boost
converter determines its MPPT characteristic, where
the panel sees a current load that's just right to
pull its voltage down, from its open-circuit value,
to the maximum output power point. It determines
the optimum load current and voltage by continually
moving the buck-boost ratio up and down, calculating
the power output as it does so. It's fair to assert
optimizers earn their keep, making a huge improvement
over a simple series string of solar panels.

SolarEdge claims their optimizers run with over 98%
efficiency, which is something one can achieve if
a buck-boost ratio is close to unity. Think of the
job the buck-boost is doing as adding or subtracting
a little bit between the input and the output. The
little bit comes from the input voltage, stepped down
and applied as needed. If the little bit is 10%, and
that aspect is 90% efficient, that's only a 1% loss.


--
Thanks,
- Win

 

[Rick C]

On Thursday, August 29, 2019 at 6:00:04 AM UTC-4, Winfield Hill wrote:

Rick C wrote...

On Wednesday, August 28, 2019, Winfield Hill wrote:
Rick C wrote...

Perhaps you can explain what you think optimizers do ...

Every panel has its own optimizer (OK, now they
have dual optimizer boxes, four wires, two panels
each.) Current must be the same in all optimizers
in series. The optimizers control their output
voltage, to match their panel's available MPPT
power: low power low voltage, high power, higher
voltage. An additional trick is that SolarEdge
optimizers somehow control all the optimizers,
so total series voltage is fixed, e.g., 400V. I
wonder a) how they do that, and b) failure modes.

If the current in all panels in series is equal,
how can each panel be "optimized" separately???

It's the optimizer outputs that are in series, and
of course each MUST be operating at the same current,
regulating its series voltage to determine how much
power it's contributing. The solar panel is the
input to the optimizer, which works as a buck-boost
converter between the panel and the optimizer output
to the string. The ratio setting of the buck-boost
converter determines its MPPT characteristic, where
the panel sees a current load that's just right to
pull its voltage down, from its open-circuit value,
to the maximum output power point. It determines
the optimum load current and voltage by continually
moving the buck-boost ratio up and down, calculating
the power output as it does so. It's fair to assert
optimizers earn their keep, making a huge improvement
over a simple series string of solar panels.

SolarEdge claims their optimizers run with over 98%
efficiency, which is something one can achieve if
a buck-boost ratio is close to unity. Think of the
job the buck-boost is doing as adding or subtracting
a little bit between the input and the output. The
little bit comes from the input voltage, stepped down
and applied as needed. If the little bit is 10%, and
that aspect is 90% efficient, that's only a 1% loss.

The part I'm not getting is that the optimizer is designed to set the current drawn from the solar panel to set the voltage so the power is at a maximum. It is then not clear to me what happens at the output.

In a typical buck voltage regulator, when the input switch is closed the input current is pretty close to the output current. The only variation is current from the output cap which is there to smooth the voltage and the circuit will still operate without it. When the switch opens the input current stops, but the coil supplies current to the output. The on/off time ratio defines the ratio of the input to output voltage. It also defines the input to output current ratio even though the currents are the same, but because the input current is duty cycle modulated.

Applying this same circuit to the solar panel optimizer, now there has to be a large input cap so the input current is relatively constant. The switch current still pulses and the duty cycle is managed to adjust the current flowing from the panel to find the MPP. The duty cycle will set the ratio of the input current and output current. The input voltage will vary with the panel illumination and the output voltage will vary along, but also factoring in the duty cycle multiplier.

This is an easy circuit to imagine when driving current into a battery. The battery is nearly a constant voltage load so all the output variation will be in current. How does the optimizer work when the output is in a string of equal current optimizers? Do all the voltages just float? Seems to me the multiple optimizers would interact and could be unstable. What actually sets the output current? Is that the inverter?

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

On Wed, 28 Aug 2019 16:01:56 -0700 (PDT), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

On Wednesday, August 28, 2019 at 11:30:38 AM UTC-4, Winfield Hill wrote:
Robert Baer wrote...

"Amphenol Industrial Solar Technologies (tm) H4
PV Connector is the premiere solar connector in
the market today. Carries more amps ...

The M4-type connectors generally come pre-molded
from the PV panel companies and the optimizer /
micro-inverter companies, so installers simply
plug them together. A special tool is required
to unplug them. They look and feel quite rugged.
But images of the contacts look very wimpy.

Supposedly optimizers shut off panel output, if
the inverter is off or disconnected. However
there are stories of shut-off cables sparking.

A series string of panels with M4 connectors
is simply one wire, carrying DC current, yet
supposedly the inverter somehow controls all
the optimizers. I couldn't find out how it
does that, or how reliable that scheme is.
There may be an issue of shorted MOSFETs.

In the case of the micro-inverters on my roof,
one per panel, they require 230Vac to run, so
disconnection is a good on/off control method.
But micro-inverter systems cost about $50 to
$100 more per panel than optimizer systems.

Perhaps you can explain what you think optimizers do and how they are used in the system. I'm not following what you seem to be saying. Are you suggesting there is more than one optimizer per inverter? I'm surprised there are separate optimizers and inverters.

If you are going to connect multiple MPPTs in parallel e.g. for
charging a battery, each MPPT must have a constant voltage but
variable current output.

If you are going to connect multiple MPPTs in series, each MPPT must
be floating constant current but variable output voltage type.

Of course, the string voltage varies which may cause problems with
some loads. You can't directly connect multiple strings in parallel.
If you are going to feed the mains, you need a variable DC / constant
AC voltage inverter. This should not be a problem, as long as the
string minimum voltage is greater than the mains peak-to-peak voltage,
just a simple PWM.

It would also be beneficial to have a parallel control voltage to set
the constant current for each series connected MPPT, if the average
output power may drop significantly (> 50 %) below peak output power.

 

[Jasen Betts]

On 2019-08-29, Rick C <gnuarm.deletethisbit@gmail.com> wrote:

On Wednesday, August 28, 2019 at 9:30:10 PM UTC-4, Winfield Hill wrote:
Rick C wrote...

Perhaps you can explain what you think optimizers do ...

Every panel has its own optimizer (OK, now they
have dual optimizer boxes, four wires, two panels
each.) Current must be the same in all optimizers
in series. The optimizers control their output
voltage, to match their panel's available MPPT
power: low power low voltage, high power, higher
voltage. An additional trick is that SolarEdge
optimizers somehow control all the optimizers,
so total series voltage is fixed, e.g., 400V. I
wonder a) how they do that, and b) failure modes.

If the current in all panels in series is equal, how can each panel be "optimized" separately??? I guess I've been thinking the current through the string to the inverter would pass through all the cells. But the reality is the optimizer isolates the cells of a panel from the output current so panels in series run at the same current, but the cells of each panel run at different current from other panels?

Suppose the inverter is a 400V voltage sink... and the optimisers just
put as much current on the line as they can. That'd work wouldn't it.

--
When I tried casting out nines I made a hash of it.

 

On Fri, 30 Aug 2019 07:20:33 +0300, upsidedown@downunder.com wrote:

On Wed, 28 Aug 2019 16:01:56 -0700 (PDT), Rick C
gnuarm.deletethisbit@gmail.com> wrote:

On Wednesday, August 28, 2019 at 11:30:38 AM UTC-4, Winfield Hill wrote:
Robert Baer wrote...

"Amphenol Industrial Solar Technologies (tm) H4
PV Connector is the premiere solar connector in
the market today. Carries more amps ...

The M4-type connectors generally come pre-molded
from the PV panel companies and the optimizer /
micro-inverter companies, so installers simply
plug them together. A special tool is required
to unplug them. They look and feel quite rugged.
But images of the contacts look very wimpy.

Supposedly optimizers shut off panel output, if
the inverter is off or disconnected. However
there are stories of shut-off cables sparking.

A series string of panels with M4 connectors
is simply one wire, carrying DC current, yet
supposedly the inverter somehow controls all
the optimizers. I couldn't find out how it
does that, or how reliable that scheme is.
There may be an issue of shorted MOSFETs.

In the case of the micro-inverters on my roof,
one per panel, they require 230Vac to run, so
disconnection is a good on/off control method.
But micro-inverter systems cost about $50 to
$100 more per panel than optimizer systems.

Perhaps you can explain what you think optimizers do and how they are used in the system. I'm not following what you seem to be saying. Are you suggesting there is more than one optimizer per inverter? I'm surprised there are separate optimizers and inverters.

If you are going to connect multiple MPPTs in parallel e.g. for
charging a battery, each MPPT must have a constant voltage but
variable current output.

If you are going to connect multiple MPPTs in series, each MPPT must
be floating constant current but variable output voltage type.

Of course, the string voltage varies which may cause problems with
some loads. You can't directly connect multiple strings in parallel.
If you are going to feed the mains, you need a variable DC / constant
AC voltage inverter. This should not be a problem, as long as the
string minimum voltage is greater than the mains peak-to-peak voltage,
just a simple PWM.

Assuming 1 m^2 panels with individual constant current MPPT, the
maximum output power is 150 W. A constant loop current of 10 A could
be used, thus the maximum output voltage from each panel could be 15
V. Make two strings with 50 panels each in series. Connect these
strings in series and connect the midpoint to neutral/ground, thus the
maximum output voltage between the ends of the strings is +/- 750 V
relatively to neutral, still fitting inside the Low Voltage Directive
(LVD 1500 V).

From this it easy to make AC with PWMing without needing any
transformers.

With reduced solar radiation, the string voltage can drop to +/-350 V
(7 V/panel) and it is still possible to produce clean sine wave for
230/400 V three phase. If modified sine wave or square wave is
allowed, the string voltage could drop to +/- 250 V (3 V/50 W per
panel).

For US, the string voltage could drop to +/-200 V and still deliver
clean 2 x 120 Vac.

It would also be beneficial to have a parallel control voltage to set
the constant current for each series connected MPPT, if the average
output power may drop significantly (> 50 %) below peak output power.

Switching all MPPTs to a lower constant loop current, say 3 or 5 A
would make sense for early morning and late evening and also during
partly cloudy conditions.

 

[Rick C]

On Saturday, August 31, 2019 at 4:31:29 AM UTC-4, Jasen Betts wrote:

On 2019-08-29, Rick C <gnuarm.deletethisbit@gmail.com> wrote:
On Wednesday, August 28, 2019 at 9:30:10 PM UTC-4, Winfield Hill wrote:
Rick C wrote...

Perhaps you can explain what you think optimizers do ...

Every panel has its own optimizer (OK, now they
have dual optimizer boxes, four wires, two panels
each.) Current must be the same in all optimizers
in series. The optimizers control their output
voltage, to match their panel's available MPPT
power: low power low voltage, high power, higher
voltage. An additional trick is that SolarEdge
optimizers somehow control all the optimizers,
so total series voltage is fixed, e.g., 400V. I
wonder a) how they do that, and b) failure modes.

If the current in all panels in series is equal, how can each panel be "optimized" separately??? I guess I've been thinking the current through the string to the inverter would pass through all the cells. But the reality is the optimizer isolates the cells of a panel from the output current so panels in series run at the same current, but the cells of each panel run at different current from other panels?


Suppose the inverter is a 400V voltage sink... and the optimisers just
put as much current on the line as they can. That'd work wouldn't it.

--
When I tried casting out nines I made a hash of it.

That's what I'm having trouble wrapping my head around. If the optimizer is duty cycling to get the input current to the MPP, the output current will be in the proportion of the duty cycle. Then the output voltage will have to be in proportion to the input voltage so the input and output power are the same. I guess this is not in opposition to the idea of the output voltage being set externally. Then it just gets reflected back to the input voltage by the duty cycle with the input current also being reflected to the output current since the load is current compliant.

I guess I'm hung up on the idea that in a fixed voltage output the the duty cycle is controlled to maintain the output voltage. Here that is not true.. If a buck converter is operated to a fixed duty cycle a change in the output load will result in varying output voltage and current as well as an input current variation. So that makes sense.

Ultimately the input power is being controlled and the output will adapt to whatever sort of load is attached.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[boB]

On Sat, 31 Aug 2019 19:59:36 -0700 (PDT), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

On Saturday, August 31, 2019 at 4:31:29 AM UTC-4, Jasen Betts wrote:
On 2019-08-29, Rick C <gnuarm.deletethisbit@gmail.com> wrote:
On Wednesday, August 28, 2019 at 9:30:10 PM UTC-4, Winfield Hill wrote:
Rick C wrote...

Perhaps you can explain what you think optimizers do ...

Every panel has its own optimizer (OK, now they
have dual optimizer boxes, four wires, two panels
each.) Current must be the same in all optimizers
in series. The optimizers control their output
voltage, to match their panel's available MPPT
power: low power low voltage, high power, higher
voltage. An additional trick is that SolarEdge
optimizers somehow control all the optimizers,
so total series voltage is fixed, e.g., 400V. I
wonder a) how they do that, and b) failure modes.

If the current in all panels in series is equal, how can each panel be "optimized" separately??? I guess I've been thinking the current through the string to the inverter would pass through all the cells. But the reality is the optimizer isolates the cells of a panel from the output current so panels in series run at the same current, but the cells of each panel run at different current from other panels?


Suppose the inverter is a 400V voltage sink... and the optimisers just
put as much current on the line as they can. That'd work wouldn't it.

--
When I tried casting out nines I made a hash of it.

That's what I'm having trouble wrapping my head around. If the optimizer is duty cycling to get the input current to the MPP, the output current will be in the proportion of the duty cycle. Then the output voltage will have to be in proportion to the input voltage so the input and output power are the same. I guess this is not in opposition to the idea of the output voltage being set externally. Then it just gets reflected back to the input voltage by the duty cycle with the input current also being reflected to the output current since the load is current compliant.

I guess I'm hung up on the idea that in a fixed voltage output the the duty cycle is controlled to maintain the output voltage. Here that is not true. If a buck converter is operated to a fixed duty cycle a change in the output load will result in varying output voltage and current as well as an input current variation. So that makes sense.

Ultimately the input power is being controlled and the output will adapt to whatever sort of load is attached.

I think that's it...

The only thing an MPPT circuit is supposed to do is to load the PV
module down to the voltage that puts out maximum power from that
module. Whatever happens on the string side (output) has to follow
along with that PV side and you get whatever you get I guess.

If a PV module that the MPPT is connected to is shaded, then it can
only load it to its max power point voltage. That is, IF there is
enough sun for that MPPT module to even run. At some point, there
won't be enough power to run the MPPT circuit itself.

If the string that is connecting all these optimizers together does
not require maximum power, then the optimizer will have to unload the
solar panel and its terminal voltage will have to rise up towards open
circuit Voc. Typically, Vmp is somewhere around 80% of Voc.
Below Vmp, its V-I curve is mostly constant current and the voltage
drops (by definition) and so does the power. It's right around that
V-I knee that is the Vmp.

I can't see these modules working their best without being able to
communicate with the rest of the system though.

A chainsaw will still work best for partial PV shading.... Adding
optimizers can only reduce efficiency as long as the panels are fairly
close to being the same type, number of cells, etc.

 

[Winfield Hill]

boB wrote...

A chainsaw will still work best ...

You know that concept is impractical in
the extreme. In the afternoon some tall
pine trees, about three properties away,
block my roof for about 45 minutes. We
have 16 panels on our garage roof, and
the taller house roof blocks 1/2 to 1/3
of that, until the sun swings around to
face the house. These issues cannot be
solved with a chainsaw. Check it out.
Click the picture, to see the shading.

https://enlighten.enphaseenergy.com/pv/public_systems/WAJT773668/overview


--
Thanks,
- Win

 

[boB]

On 2 Sep 2019 02:57:34 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

boB wrote...

A chainsaw will still work best ...

You know that concept is impractical in
the extreme. In the afternoon some tall
pine trees, about three properties away,
block my roof for about 45 minutes. We
have 16 panels on our garage roof, and
the taller house roof blocks 1/2 to 1/3
of that, until the sun swings around to
face the house. These issues cannot be
solved with a chainsaw. Check it out.
Click the picture, to see the shading.

https://enlighten.enphaseenergy.com/pv/public_systems/WAJT773668/overview

Of course I'm being a bit facecious about cutting down trees althouth
that would fix the majority of shading issues. And chimneys are
another issue. Microinverters take care of that on a per-panel basis
just fine.

Also, you should be happy you don't have to add a per-module rapid
shutdown system for HV strings. Turn off the power to the house and
your'e all set for fire-fighting first responders.

We did a bunch of contract work for Enphase a couple of years ago that
was good for profits. Would not want to have to do that again. They
were very hard to work with.

boB