Re: [RE-wrenches] P1 micro performance

[Bill Brooks]

Carl,

 

Just to be clear, the performance tests mandated by the California Energy
Commission, that all products in the U.S. follow, require that the maximum
power rating is continuous (24/7). Actually, continuous means that it can
operate for 3 hours straight at 40C (104F) (really hot). This does not mean
it will last forever. That is an engineering decision on how close the
manufacturer wants to operate their product up to maximum temperature of the
components in the device. Some products may publish a maximum power that is
higher than the maximum continuous power at 40C.

 

Bill.

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Carl Emerson
Sent: Tuesday, March 26, 2013 5:29 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] P1 micro performance

 

Friends,

 

Keeping the record straight.

 

I need to say that I have had correspondence 'off list' from a development
engineer from a prominent manufacturer who assures me that his product is
designed to run 'flat out' 24/7. 

 

The unit in fact is just coasting at it's maximum power rating. 

 

This allows for a projected life matching that of the PV.

 

In this case power clipping will not shorten the products life.

 

I am unable to confirm if all manufacturers are taking this approach, buyer
beware.

 

Regards
Carl Emerson

 

Nick,

 

Is Enphase going to be introducing to market any time in the near-term a new
micro with a higher output?  It seems very likely that the trend toward
higher output mods will continue.  The M215 will surely be left behind to a
greater degree as this trend continues if there are higher and reliable and
comparably priced, on a dollar/watt basis, micros available.

 

Thanks,

marco

 

Hi Carl, Marco, and Wrenches,

As a longtime installer, I understand your point of view.  Historically, I
designed my string and microinverter systems with the same consideration for
maintaining conservative DC to AC ratios.  That being said, the costs of
modules have decreased significantly and the dynamics have changed.  Solar
companies should be focused on selling systems that offers a great rate of
return.  Maximizing the customer's investment is most important.  Isn't that
what your customer wants?

What Enphase is encouraging is the development of cost effective PV systems
that will generate a healthy return.  Considering that the modules are only
20% of the total system costs today, it is smart to give up 0.2% or more of
the module production to lower the overall system costs by 5-10%.  The NEC
requires that the AC panel boards, conductors, and circuit breakers are
sized to the inverter continuous output current rating.  We should be
maximizing this infrastructure.

 

The data available indicates that when a system is installed with a 1.2 to
1.25 DC to AC ratio, it will rarely operate at peak output.  Installing a PV
system with a 1.25 DC to AC ratio is not driving the equipment to the
maximum.  In the case of the Enphase M215s; they are designed to operate
continuously at peak output, so reaching that level a few hours in the first
years is not problematic.  To be clear, this limiting will occur the most
during the spring months, because you have a combination of both cool
weather and high irradiance levels.

As Dan mentioned, this applies to string inverters as well as
microinverters.  One of the most common system designs of the early US
grid-tied market was installing 18- 165 watt modules on an SWR-2500.  I
designed hundreds of projects like that.  That was a ~1.2 multiplier, and
was at a time when the modules cost $5 per watt; not $1 per watt.  Why be
more conservative now?

  

 
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Re: [RE-wrenches] P1 micro performance

[Carl Emerson]

Friends,

 

Keeping the record straight.

 

I need to say that I have had correspondence 'off list' from a development
engineer from a prominent manufacturer who assures me that his product is
designed to run 'flat out' 24/7. 

 

The unit in fact is just coasting at it's maximum power rating. 

 

This allows for a projected life matching that of the PV.

 

In this case power clipping will not shorten the products life.

 

I am unable to confirm if all manufacturers are taking this approach, buyer
beware.

 

Regards
Carl Emerson

 

Nick,

 

Is Enphase going to be introducing to market any time in the near-term a new
micro with a higher output?  It seems very likely that the trend toward
higher output mods will continue.  The M215 will surely be left behind to a
greater degree as this trend continues if there are higher and reliable and
comparably priced, on a dollar/watt basis, micros available.

 

Thanks,

marco

 

Hi Carl, Marco, and Wrenches,

As a longtime installer, I understand your point of view.  Historically, I
designed my string and microinverter systems with the same consideration for
maintaining conservative DC to AC ratios.  That being said, the costs of
modules have decreased significantly and the dynamics have changed.  Solar
companies should be focused on selling systems that offers a great rate of
return.  Maximizing the customer's investment is most important.  Isn't that
what your customer wants?

What Enphase is encouraging is the development of cost effective PV systems
that will generate a healthy return.  Considering that the modules are only
20% of the total system costs today, it is smart to give up 0.2% or more of
the module production to lower the overall system costs by 5-10%.  The NEC
requires that the AC panel boards, conductors, and circuit breakers are
sized to the inverter continuous output current rating.  We should be
maximizing this infrastructure.

 

The data available indicates that when a system is installed with a 1.2 to
1.25 DC to AC ratio, it will rarely operate at peak output.  Installing a PV
system with a 1.25 DC to AC ratio is not driving the equipment to the
maximum.  In the case of the Enphase M215s; they are designed to operate
continuously at peak output, so reaching that level a few hours in the first
years is not problematic.  To be clear, this limiting will occur the most
during the spring months, because you have a combination of both cool
weather and high irradiance levels.

As Dan mentioned, this applies to string inverters as well as
microinverters.  One of the most common system designs of the early US
grid-tied market was installing 18- 165 watt modules on an SWR-2500.  I
designed hundreds of projects like that.  That was a ~1.2 multiplier, and
was at a time when the modules cost $5 per watt; not $1 per watt.  Why be
more conservative now?

  

 
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Re: [RE-wrenches] P1 micro performance

[Nick Soleil]

Hi Carl, Marco, and Wrenches,

As a longtime installer, I understand your point of view.  Historically, I
designed my string and microinverter systems with the same consideration
for maintaining conservative DC to AC ratios.  That being said, the costs
of modules have decreased significantly and the dynamics have changed.
Solar companies should be focused on selling systems that offers a great
rate of return.  Maximizing the customer's investment is most important.
Isn't that what your customer wants?

What Enphase is encouraging is the development of cost effective PV systems
that will generate a healthy return.  Considering that the modules are only
20% of the total system costs today, it is smart to give up 0.2% or more of
the module production to lower the overall system costs by 5-10%.  The NEC
requires that the AC panel boards, conductors, and circuit breakers are
sized to the inverter continuous output current rating.  We should be
maximizing this infrastructure.

The data available indicates that when a system is installed with a 1.2 to
1.25 DC to AC ratio, it will rarely operate at peak output.  Installing a
PV system with a 1.25 DC to AC ratio is not driving the equipment to the
maximum.  In the case of the Enphase M215s; they are designed to operate
continuously at peak output, so reaching that level a few hours in the
first years is not problematic.  To be clear, this limiting will occur the
most during the spring months, because you have a combination of both cool
weather and high irradiance levels.

As Dan mentioned, this applies to string inverters as well as
microinverters.  One of the most common system designs of the early US
grid-tied market was installing 18- 165 watt modules on an SWR-2500.  I
designed hundreds of projects like that.  That was a ~1.2 multiplier, and
was at a time when the modules cost $5 per watt; not $1 per watt.  Why be
more conservative now?





On Sat, Mar 23, 2013 at 6:19 PM, Carl Emerson  wrote:

>  Friends,
>
> ** **
>
> I am a little puzzled by this topic.
>
> ** **
>
> What has happened to the good engineering practice of sizing electronic
> equipment so that it is not driven to the maximum.
>
> ** **
>
> My understanding is that the MTBF increases significantly the harder you
> drive the unit.
>
> ** **
>
> This seems to be a case of overdriving the units for short term gain.  ***
> *
>
> ** **
>
> *Carl Emerson*
>
> *Free Power Co. *
>
> *Auckland N.Z.***
>
> ** **
>
> *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto:
> re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Exeltech
> *Sent:* 24 March 2013 5:50 a.m.
>
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] P1 micro performance
> 
>
>  ** **
>
> Marco .. and Wrenches ..
>
> I'm going to take a run at this -- just once.
>
> First ...
>
> Without proper and *accurate* data acquisition equipment, there's no way
> to know what the actual available PV wattage is compared to the inverter's
> output wattage when its output is being *LIMITED*.  This limiting action
> occurs in an inverter when there's more available power at the input than
> the inverter can produce at its output.  Subsequently, you don't know how
> much potential energy wasn't harvested.
>
> Now then ...
>
> Let's say the inverter is producing 216 watts, and the PV  *could* produce
> 227.3 watts at max power point under those specific conditions if every
> PV-generated milliwatt were used.
>
> Next, and presuming the inverter is 95% efficient, that's a "limited loss"
> of
> ONE WATT.  227.3 x 95% = 215.94 watts (OK, so I fudged 0.06 watt).
> Under what conditions (and since you're in Hawaii, I'll use 70F) would this
> occur, and with what size PV?
>
> I went to my magic spreadsheet and grabbed the first 270-watt-rated PV I
> could find.  NESL DJ-270P,.
>
> YOU think it's producing 270 watts.  It's not.  At 77F (25C), and under the
> conditions of 100% irradiance, perfectly orthogonal to the sun at mid-day,
> light wind, that particular PV will produce 227 watts +/- its tolerance.
> (Let's say the tolerance is dead on.)
>
> Now, consider the benefit of increased energy output due to more rapid
> output wattage rise experienced during early morning, and the higher
> output later in the afternoon, AS WELL AS the increased power output
> realized during periods of less than 100% irradiance one derives from
> using larger PV compared to PV you might consider "perfectly matched"
> to the inverter.
>
> ALL of this adds up to more kilowatt-hours produced annually than had the
> inverter been connected to your "perfect" PV that doesn't produce enough
> wa

Re: [RE-wrenches] P1 micro performance

[Dave Click]

Marco,


I still challenge those who believe that “some clipping is good” to make their 
case.


Well, the way you've phrased it, you've made my job pretty easy-- though 
it seems to me that several folks have already done this for you.


Some power limiting at some point over the 25-year life of a system is 
definitely a good thing. A 25-year life corresponds to about 110,000 
hours of daylight. Let's say that you can expect one total hour of those 
110,000 in which a Montana system sees 1600 W/m2 (high slope, snow 
reflection, edge-of-cloud) while simultaneously experiencing a record 
low temperature and 50 mph winds. Would you put a 9kW inverter on your 
5kW array to avoid any power limiting ever? Of course not-- you're 
substantially increasing system cost for a $0.15 gain.


It comes down to figuring out probabilities and doing some complicated 
and annoying math to figure out the best size for an inverter. Or more 
realistically, attempting to get high-sample-rate weather data to 
simulate array performance at your target location. When you oversize an 
inverter, your system will be operating at a lower efficiency, on 
average. It increases the cost to the customer not just from the base 
cost of the larger unit, but also the larger output conductor and 
raceway sizes, the output disconnect, the interconnection 
breakers/fuses... and maybe even upsized panelboards that didn't 
actually need to be upgraded had you correctly sized the inverters. So 
you have to figure out whether the additional production is worth the 
increased cost of installation.


Oversizing an inverter may extend its life but I don't know that we'll 
ever have those numbers from manufacturers to better quantify that 
impact. More current causes more heat, which is bad, but increasing an 
inverter size to the next higher power rating available doesn't 
guarantee that the larger inverter will be more reliable.


So that's a general response. As for your Power-One 250 vs Enphase 224 
conundrum, if all else is equal but the power rating, then I'd probably 
join you in choosing the Power-One. But as you know, there are other 
factors to take into account-- [perceived] reliability, BOS cost (e.g. 
more Enphase units fitting on a 20A breaker may save you a circuit), DAS 
usefulness, resistance to corrosion, and the fact that Enphase operates 
at a higher conversion efficiency in the lower half of its operating 
range (where it spends most of its operating time). I am not saying that 
Enphase is better than Power-One in anything but low-range efficiency-- 
I don't know one way or the other.


Efficiency Curves:
http://gosolarcalifornia.com/equipment/inverter_tests/summaries/Enphase%20M215%20IG-240V.pdf
http://gosolarcalifornia.com/equipment/inverter_tests/summaries/Power-One%20MICRO-0.25-I-OUTD-US-240.pdf

After all this discussion, it's pretty funny that the peak conversion 
efficiency of the 250W Power-One micro occurs at... a 250W output. So 
even though the marketing guys tell you you should only plug in a 265W 
module, the engineers are clearly asking you to turn it up to 11.


"Do you, Mr./Mrs./Ms. Homeowner, want a PV system that produces as much 
solar kWhs for your investment as possible?" isn't the right question to 
ask. Try, "Do you, Mr./Mrs./Ms. Homeowner, want a PV system that 
produces the best value for your investment?" Then show your super 
impressive calculations, based on your years of experience, that your 
recommended inverter is the best fit for them. Allowing for maximum kWh 
harvesting, within reason, is the best design strategy.


Dave
5.376kWdc on a 5.000kWac, and loving it

On 2013/3/23 19:31, Marco Mangelsdorf wrote:

 From Dan at Exeltech:

Trying to explain in depth the "how and why" slightly larger PV is of
benefit
to a customer is like trying to explain photovoltaic equipment to the
general
public.

I still challenge those who believe that “some clipping is good” to make
their case.  And as far as the general buying public, I’m find that
people do in fact understand when you ask them the following questions:
Do you, Mr./Mrs./Ms. Homeowner, want a PV system that produces as much
solar kWhs for your investment as possible?  Usual response:
absolutely.  If I give you the choice of PV system using a 250-watt
module paired with a COMPARABLY priced 250-watt micro inverter OR that
same 250-watt module with a max output ~ 224-watt micro inverter that
will never under any circumstances allow that 250-watt module to put out
its max rated power output, which option do you think they’ll choose?
They get that.  It doesn’t take someone with an engineering degree or
10-40 years in the field to get that simple premise.

For what it’s worth, being here in the tropics in the Hawaiian islands
we don’t get those bright and sunny and cold late fall/winter/early
spring days that will allow for an array to put out its STC-rated
power.  But seeing regular times during the day—any time of year—where
the irradiance is more than 1

Re: [RE-wrenches] P1 micro performance

[Bill Loesch]

Fellow Wrenches,

No stones from this Missouri P.E. Perhaps if more Greybeards gave such 
candid comments it might influence others toward something other than a 
race to the bottom.


Bill Loesch
Solar 1 - Saint Louis Solar
314 631 1094

On 24-Mar-13 12:07 PM, Ray Walters wrote:

Hear, Hear, Carl.

That has also always been my experience as well.  In my off grid work, 
reliability trumps budget, and I almost always over size charge 
controllers, relays, inverters, fuse holders, etc.  Most failures seem 
to be related to pushing the design limits of the equipment.
I spent the past year working on multi MW systems, where they saved 
every penny possible.  The inverters were undersized by 20 to 25% but 
sitting in unairconditioned enclosures.  Even better that the 
projected 30 year life of the system did not even include inverter 
replacements.
I'm sure I shall be stoned to death for saying this, but basically the 
grid tie solar community just doesn't have enough experience under its 
belt yet to have seen what we learned a decade ago in the off grid world.
When they start putting call backs, down time, inverter replacements, 
and the related loss of respect and business into their spread sheets; 
they'll start oversizing the inverters more, like you, Marco, and many 
of us already know.


R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 3/23/2013 7:19 PM, Carl Emerson wrote:


Friends,

I am a little puzzled by this topic.

What has happened to the good engineering practice of sizing 
electronic equipment so that it is not driven to the maximum.


My understanding is that the MTBF increases significantly the harder 
you drive the unit.


This seems to be a case of overdriving the units for short term gain.

*Carl Emerson*

*Free Power Co. *

*Auckland N.Z.***



What I *can't* answer is the long-term effect this may have on the 
overall
life of the inverter.  THAT depends on various intricate design 
considerations

that went into creating the inverter in the first place.

Dan Lepinski, Senior Engineer
Exeltech / Exeltech Solar Products

With 41 years experience as a design engineer in solar energy.





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Re: [RE-wrenches] P1 micro performance

[Ray Walters]

Hear, Hear, Carl.

That has also always been my experience as well.  In my off grid work, 
reliability trumps budget, and I almost always over size charge 
controllers, relays, inverters, fuse holders, etc.  Most failures seem 
to be related to pushing the design limits of the equipment.
I spent the past year working on multi MW systems, where they saved 
every penny possible.  The inverters were undersized by 20 to 25% but 
sitting in unairconditioned enclosures.  Even better that the projected 
30 year life of the system did not even include inverter replacements.
I'm sure I shall be stoned to death for saying this, but basically the 
grid tie solar community just doesn't have enough experience under its 
belt yet to have seen what we learned a decade ago in the off grid world.
When they start putting call backs, down time, inverter replacements, 
and the related loss of respect and business into their spread sheets; 
they'll start oversizing the inverters more, like you, Marco, and many 
of us already know.


R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 3/23/2013 7:19 PM, Carl Emerson wrote:


Friends,

I am a little puzzled by this topic.

What has happened to the good engineering practice of sizing 
electronic equipment so that it is not driven to the maximum.


My understanding is that the MTBF increases significantly the harder 
you drive the unit.


This seems to be a case of overdriving the units for short term gain.

*Carl Emerson*

*Free Power Co. *

*Auckland N.Z.***



What I *can't* answer is the long-term effect this may have on the overall
life of the inverter.  THAT depends on various intricate design 
considerations

that went into creating the inverter in the first place.

Dan Lepinski, Senior Engineer
Exeltech / Exeltech Solar Products

With 41 years experience as a design engineer in solar energy.



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Re: [RE-wrenches] P1 micro performance

[Carl Emerson]

Friends,

 

I am a little puzzled by this topic.

 

What has happened to the good engineering practice of sizing electronic
equipment so that it is not driven to the maximum.

 

My understanding is that the MTBF increases significantly the harder you
drive the unit.

 

This seems to be a case of overdriving the units for short term gain.  

 

Carl Emerson

Free Power Co. 

Auckland N.Z.

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Exeltech
Sent: 24 March 2013 5:50 a.m.
To: RE-wrenches
Subject: Re: [RE-wrenches] P1 micro performance

 


Marco .. and Wrenches ..

I'm going to take a run at this -- just once.

First ...

Without proper and *accurate* data acquisition equipment, there's no way
to know what the actual available PV wattage is compared to the inverter's
output wattage when its output is being *LIMITED*.  This limiting action
occurs in an inverter when there's more available power at the input than
the inverter can produce at its output.  Subsequently, you don't know how
much potential energy wasn't harvested.

Now then ...

Let's say the inverter is producing 216 watts, and the PV  *could* produce
227.3 watts at max power point under those specific conditions if every
PV-generated milliwatt were used.

Next, and presuming the inverter is 95% efficient, that's a "limited loss"
of
ONE WATT.  227.3 x 95% = 215.94 watts (OK, so I fudged 0.06 watt).
Under what conditions (and since you're in Hawaii, I'll use 70F) would this
occur, and with what size PV?

I went to my magic spreadsheet and grabbed the first 270-watt-rated PV I
could find.  NESL DJ-270P,.

YOU think it's producing 270 watts.  It's not.  At 77F (25C), and under the
conditions of 100% irradiance, perfectly orthogonal to the sun at mid-day,
light wind, that particular PV will produce 227 watts +/- its tolerance.
(Let's say the tolerance is dead on.)

Now, consider the benefit of increased energy output due to more rapid
output wattage rise experienced during early morning, and the higher
output later in the afternoon, AS WELL AS the increased power output
realized during periods of less than 100% irradiance one derives from
using larger PV compared to PV you might consider "perfectly matched"
to the inverter.

ALL of this adds up to more kilowatt-hours produced annually than had the
inverter been connected to your "perfect" PV that doesn't produce enough
wattage to have the inverter begin limiting its output.  The "shoulders" of
the
output wattage curve are steeper than with lower-wattage PV.

Granted you *could* connect the inverter to [say] a 450 watt PV module,
and >that< would truly be a waste of the PV wattage.  There *is* a broad
"sweet spot" for AC Module inverters and microinverters alike, and it's
actually on the higher side of the PV's rated output wattage versus the
inverter's wattage rating. So, can you over-do it?  Sure.  But there IS an
overall kilowatt-hours-produced benefit for *modest* over-sizing the PV.

What I *can't* answer is the long-term effect this may have on the overall
life of the inverter.  THAT depends on various intricate design
considerations
that went into creating the inverter in the first place.

This isn't an Enphase issue, nor are they trying to mislead you on this
topic.
It's an industry-wide issue.  Wrenches face it every time you designed a
string
system, especially those being installed in regions with wide temperature
swings.

Trying to explain in depth the "how and why" slightly larger PV is of
benefit
to a customer is like trying to explain photovoltaic equipment to the
general
public.

As a competitor to Enphase .. I'm not coming to their defense.  However,
what Nick said (below) IS fact.

Whether you elect to believe this or not is up to you.


Regards to all,


Dan Lepinski, Senior Engineer
Exeltech / Exeltech Solar Products

With 41 years experience as a design engineer in solar energy.




--- On Sat, 3/23/13, Marco Mangelsdorf  wrote:


From: Marco Mangelsdorf 
Subject: [RE-wrenches] P1 micro performance
To: "'RE-wrenches'" 
Date: Saturday, March 23, 2013, 4:04 AM

Yes, I know that that screen shot was only a moment in time.  Here it's only
March and clipping is already taking place.  Imagine what kind of clipping
is going to take place at higher irradiance levels later in the year.  Yes,
the monitoring program cannot as of now quantify what kind of harvesting
losses would take place over time compared to an identical array using
Enphase micros.  But the principle remains unchallengeable: not allowing for
maximum kWh harvesting is plain and simple NOT the best design strategy.

 

"Some clipping is good"?  You've got to be joking.  Not being able to
harvest usable solar energy is good?  What kind of op

Re: [RE-wrenches] P1 micro performance

[Exeltech]

Marco .. and Wrenches ..

I'm going to take a run at this -- just once.

First ...

Without proper and *accurate* data acquisition equipment, there's no way
to know what the actual available PV wattage is compared to the inverter's
output wattage when its output is being *LIMITED*.  This limiting action
occurs in an inverter when there's more available power at the input than
the inverter can produce at its output.  Subsequently, you don't know how
much potential energy wasn't harvested.

Now then ...

Let's say the inverter is producing 216 watts, and the PV  *could* produce
227.3 watts at max power point under those specific conditions if every
PV-generated milliwatt were used.

Next, and presuming the inverter is 95% efficient, that's a "limited loss" of
ONE WATT.  227.3 x 95% = 215.94 watts (OK, so I fudged 0.06 watt).
Under what conditions (and since you're in Hawaii, I'll use 70F) would this
occur, and with what size PV?

I went to my magic spreadsheet and grabbed the first 270-watt-rated PV I
could find.  NESL DJ-270P,.

YOU think it's producing 270 watts.  It's not.  At 77F (25C), and under the
conditions of 100% irradiance, perfectly orthogonal to the sun at mid-day,
light wind, that particular PV will produce 227 watts +/- its tolerance.
(Let's say the tolerance is dead on.)

Now, consider the benefit of increased energy output due to more rapid
output wattage rise experienced during early morning, and the higher
output later in the afternoon, AS WELL AS the increased power output
realized during periods of less than 100% irradiance one derives from
using larger PV compared to PV you might consider "perfectly matched"
to the inverter.

ALL of this adds up to more kilowatt-hours produced annually than had the
inverter been connected to your "perfect" PV that doesn't produce enough
wattage to have the inverter begin limiting its output.  The "shoulders" of the
output wattage curve are steeper than with lower-wattage PV.

Granted you *could* connect the inverter to [say] a 450 watt PV module,
and >that< would truly be a waste of the PV wattage.  There *is* a broad
"sweet spot" for AC Module inverters and microinverters alike, and it's
actually on the higher side of the PV's rated output wattage versus the
inverter's wattage rating. So, can you over-do it?  Sure.  But there IS an
overall kilowatt-hours-produced benefit for *modest* over-sizing the PV.

What I *can't* answer is the long-term effect this may have on the overall
life of the inverter.  THAT depends on various intricate design considerations
that went into creating the inverter in the first place.

This isn't an Enphase issue, nor are they trying to mislead you on this topic.
It's an industry-wide issue.  Wrenches face it every time you designed a string
system, especially those being installed in regions with wide temperature
swings.

Trying to explain in depth the "how and why" slightly larger PV is of benefit
to a customer is like trying to explain photovoltaic equipment to the general
public.

As a competitor to Enphase .. I'm not coming to their defense.  However,
what Nick said (below) IS fact.

Whether you elect to believe this or not is up to you.


Regards to all,


Dan Lepinski, Senior Engineer
Exeltech / Exeltech Solar Products

With 41 years experience as a design engineer in solar energy.




--- On Sat, 3/23/13, Marco Mangelsdorf  wrote:

From: Marco Mangelsdorf 
Subject: [RE-wrenches] P1 micro performance
To: "'RE-wrenches'" 
Date: Saturday, March 23, 2013, 4:04 AM

Yes, I know that that screen shot was only a moment in time.  Here it’s only 
March and clipping is already taking place.  Imagine what kind of clipping is 
going to take place at higher irradiance levels later in the year.  Yes, the 
monitoring program cannot as of now quantify what kind of harvesting losses 
would take place over time compared to an identical array using Enphase micros. 
 But the principle remains unchallengeable: not allowing for maximum kWh 
harvesting is plain and simple NOT the best design strategy.  “Some clipping is 
good”?  You’ve got to be joking.  Not being able to harvest usable solar energy 
is good?  What kind of optimal design philosophy is that?  As module outputs 
have been going up, Enphase has a vested interest in continuing to move product 
with little regard for the harvestable energy being essentially lost.  Using 
larger micros that reduce or eliminate that clipping is prima facie a good 
thing if one cares
 about maximizing kWh harvest.  As more micro products come on the product with 
higher outputs than the venerable and solid M215, Enphase risks being left 
behind and losing market share.  I for one find that “white paper” overly 
self-serving.  marco  From: re-wrenches-boun...@lists.re-wrenches.org 
[mailto:re-wrenches-boun...@li

Re: [RE-wrenches] P1 micro performance

[Nick Soleil]

Good points David, we are in peak season for inverters to be limiting
power.

Marco, your diagram shows that the modules are only overproducing the
Enphase M215's output of 225 watts for a single 15 minute period during the
day.  That would only equate to about 3 watt-hours of lost power on a day
when the modules are producing more than 1000 watt-hours.  That tends to be
in agreement with our study, which can be viewed at;
http://enphase.com/wp-uploads/enphase.com/2011/12/Enphase_White_Paper_Module_Rightsizing.pdf.


Averaged across the entire year, this loss of power would total less than
0.1%, and would be less than 0.2% for a 265 watt module.  Keep in mind that
with degradation accounted for, you will see even less limiting in future
years.  I'd encourage Wrenches to look closely at the attached document.
It is based upon real system production data from Enlighten compared
against actual irradiance data.

Most analysts would agree that some "clipping" is good.  You will have a
better return on your investment when your DC to AC ratio is greater than
one.  In this case, bigger is better.




On Thu, Mar 21, 2013 at 9:37 PM, David Brearley <
david.brear...@solarprofessional.com> wrote:

> Thanks for sharing the screen capture, Marco.
>
> Interesting issues to think about here. This is actually prime clipping
> season in many places (not sure about Hawaii) due to the cool weather.
> While there are more sun-hours in the summer, the cell temperatures are
> often high enough that you won't tend to see rated power out of the
> modules.
>
> While I'm not running performance models for work, the people who do are
> routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having
> said that, most inverters aren't installed on a roof. (Not yet anyway.)
>
> I'd probably lean to a more conservative sizing ratio for micros. While I
> can imagine some scenarios where I'd be comfortable with a 215 W micro on a
> 265 W module—like a flat roof install in Vermont, which reportedly doesn't
> see 1,000 W/m^2 very often—I wouldn't try that here in Texas.
>
> On Mar 21, 2013, at 7:54 PM, Marco Mangelsdorf wrote:
>
> Check out the output of the modules below at 1PM on this Spring equinox
> for this system here in Hilo, Hawaii.
> ** **
> These mods are SunPower 245s with the Power-One micro 250s.  Notice that
> the AC outputs below are 223 watts and higher.
> ** **
> If we had installed Enphase M215s instead, the max output possible would be
>  ~ 224 watts.
> ** **
> If there’s clipping this early in the year, imagine the degree to which
> the clipping will be increasing in the months to come as the solar
> insolation increases.
> ** **
> And these mods were “only” 245s.  Enphase states that their M215s are fine
> with modules up to 265 watts!  Imagine the amount of clipping taking place
> when that kind of pairing takes place.
> ** **
> marco
> ** **
> 
> 
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>


-- 

Cordially,

*Nick Soleil*

*Field Applications Engineer
*

*Enphase Energy*

Mobile: (707) 321-2937


**

*Enphase Commercial Solar.*
*Limitless.*

*
*

1420 North McDowell

Petaluma, CA 94954

www.enphase.com 

P: (707) 763-4784 x7267

F: (707) 763-0784

E: nsol...@enphaseenergy.com

[image: nabcep logo] Certified Solar PV Installer #03262011-300

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If you received this mes

Re: [RE-wrenches] P1 micro performance

[David Brearley]

The power quality should not be adversely affected. 

While I'm sure different manufacturers may limit power in different ways, in 
theory all the inverter is doing is moving the array off its MPP. Here's a 
description from AE:

If the power available from the array exceeds the nameplate rating of the 
inverter, the inverter will limit 
the power and current coming from the array to the inverter’s maximum nameplate 
power and 
current rating. The inverter does this by reducing the DC input current, which 
causes the DC 
operating voltage to rise above the maximum power point of the array, thereby 
‘clipping’ the 
array output. This effectively limits the output of the array without stressing 
the inverter.

http://solarenergy.advanced-energy.com/upload/File/Application%20Notes/DCLoadingOfPVPinverters.55-600100-75-A.pdf

On Mar 22, 2013, at 9:52 AM, William Dorsett wrote:

> OK, if the upper limit if the curve is “flat topped” do we get increased 
> problems with harmonic noise at the knee as you would in modified “square” 
> wave?
>  
> Bill Dorsett
> Manhattan, KS
>  
> From: re-wrenches-boun...@lists.re-wrenches.org 
> [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of David Brearley
> Sent: Friday, March 22, 2013 8:43 AM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] P1 micro performance
>  
> Thanks for the clarification. 
>  
> FWIW: Flat topping is exactly what occurs. Inverter limiting clips the 
> inverter output power curve (not the voltage or current wave forms). The 
> chart below has one data point for every hour of the year. The 
> clipped/flat-top area is the result of the 225 kW inverter limiting the power 
> output of a 385 kW array: 
>  
>  
> 
>  
> On Mar 22, 2013, at 1:07 AM, boB wrote:
> 
> 
> On 3/21/2013 9:59 PM, Exeltech wrote:
> Wrenches,
> 
> I'm probably a lone voice on this .. and not intending to get overly picky.
> 
> 
> No, two lonely voices, Dan.
> 
> I associate clipping with audio waveforms which stops
> the negative or positive voltage peaks flat.  Also called
> flat-topping.
> 
> Limiting is like turning down the volume.  The waveform
> stays the same and does not distort as it would if it
> were being flat topped (and flat bottomed)
> 
> Thanks !
> boB
> 
> 
> 
> 
> 
> 
> Could we call power limiting what it is .. "limiting", and not "clipping"?
> 
> Clipping implies distortion, which isn't the case here.  Limiting is just 
> that.
> The inverter output is limited to some maximum value -- not "clipped".
> 
> The output power curve flattens when integrated over time, but this still 
> isn't
> distortion in the waveform.  It's simply a point in the output where the 
> derivative
> is zero.  Not increasing, not decreasing.  Just .. zero.  No additional 
> increase
> in the output for an increase in available energy at the input.  Think 
> "governor"
> on an engine
> 
> Thanks.
> 
> 
> Dan Lepinski, Sr. Engineer
> Exeltech / Exeltech Solar Products
> 
> 
> --- On Thu, 3/21/13, David Brearley  
> wrote:
> 
> 
> From: David Brearley 
> Subject: Re: [RE-wrenches] P1 micro performance
> To: "RE-wrenches" 
> Date: Thursday, March 21, 2013, 11:37 PM
> 
> Thanks for sharing the screen capture, Marco.
>  
> Interesting issues to think about here. This is actually prime clipping 
> season in many places (not sure about Hawaii) due to the cool weather. While 
> there are more sun-hours in the summer, the cell temperatures are often high 
> enough that you won't tend to see rated power out of the modules. 
>  
> While I'm not running performance models for work, the people who do are 
> routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said 
> that, most inverters aren't installed on a roof. (Not yet anyway.) 
>  
> I'd probably lean to a more conservative sizing ratio for micros. While I can 
> imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W 
> module—like a flat roof install in Vermont, which reportedly doesn't see 
> 1,000 W/m^2 very often—I wouldn't try that here in Texas.
> 
> 
>  
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&

Re: [RE-wrenches] P1 micro performance

[Drake]

It would be good to quantify the amount of peak 
energy that is lost through power limiting. We 
have a 2160 Watt array on a 40 degree pitched 
roof with a SB 2500HF US inverter. The other day 
I watched the meter hover over 2000 W and peak at 
2490 W. It was a clear, cold day. It runs in the 
STC range and higher many days in the spring.


I have one Enphase customer with a ground mount 
with Sharp 224s and Enphase 190s. The inverters 
can stay pegged for 4 hours at a time in the spring.


Emacs!


The graph above was from a day with some clouds, 
but still power limited much of the day.


It would be good to get a better understanding of 
the annual percentage effect. Enphase claims an 
overall power increase, even with this effect. 
Undersized string inverters are clearly an issue.


Drake



At 12:37 AM 3/22/2013, you wrote:

Thanks for sharing the screen capture, Marco.

Interesting issues to think about here. This is 
actually prime clipping season in many places 
(not sure about Hawaii) due to the cool weather. 
While there are more sun-hours in the summer, 
the cell temperatures are often high enough that 
you won't tend to see rated power out of the modules.


While I'm not running performance models for 
work, the people who do are routinely increasing 
dc-to-ac ratios, often as high as 1.4-to-1. 
Having said that, most inverters aren't installed on a roof. (Not yet anyway.)


I'd probably lean to a more conservative sizing 
ratio for micros. While I can imagine some 
scenarios where I'd be comfortable with a 215 W 
micro on a 265 W module—like a flat roof install 
in Vermont, which reportedly doesn't see 1,000 
W/m^2 very often—I wouldn't try that here in Texas.


On Mar 21, 2013, at 7:54 PM, Marco Mangelsdorf wrote:

Check out the output of the modules below at 
1PM on this Spring equinox for this system here in Hilo, Hawaii.


These mods are SunPower 245s with the Power-One 
micro 250s.  Notice that the AC outputs below are 223 watts and higher.


If we had installed Enphase M215s instead, the 
max output possible would be ~ 224 watts.


If there’s clipping this early in the year, 
imagine the degree to which the clipping will 
be increasing in the months to come as the solar insolation increases.


And these mods were “only” 245s.  Enphase 
states that their M215s are fine with modules 
up to 265 watts!  Imagine the amount of 
clipping taking place when that kind of pairing takes place.


marco



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Re: [RE-wrenches] P1 micro performance

[Bill Loesch]

Hi boB,

Kudos to you, too. Flat-topping (bottoming) is so very descriptive and 
hopefully universally understandable. Excellent analogies.
Technical education/expertise sharing is one of the most prized benefits 
of belonging/participating on the RE-wrenches list.

Thanks,

Bill Loesch
Solar 1 - Saint Louis Solar
314 631 1094

On 22-Mar-13 1:07 AM, boB wrote:

On 3/21/2013 9:59 PM, Exeltech wrote:

Wrenches,

I'm probably a lone voice on this .. and not intending to get overly 
picky.





No, two lonely voices, Dan.

I associate clipping with audio waveforms which stops
the negative or positive voltage peaks flat.  Also called
flat-topping.

Limiting is like turning down the volume.  The waveform
stays the same and does not distort as it would if it
were being flat topped (and flat bottomed)

Thanks !
boB






Could we call power limiting what it is .. "limiting", and not 
"clipping"?


Clipping implies distortion, which isn't the case here. Limiting is 
just that.

The inverter output is limited to some maximum value -- not "clipped".

The output power curve flattens when integrated over time, but this 
still isn't
distortion in the waveform.  It's simply a point in the output where 
the derivative
is zero.  Not increasing, not decreasing.  Just .. zero.  No 
additional increase
in the output for an increase in available energy at the input.  
Think "governor"

on an engine

Thanks.


Dan Lepinski, Sr. Engineer
Exeltech / Exeltech Solar Products


--- On *Thu, 3/21/13, David Brearley 
//* wrote:



From: David Brearley 
Subject: Re: [RE-wrenches] P1 micro performance
To: "RE-wrenches" 
Date: Thursday, March 21, 2013, 11:37 PM

Thanks for sharing the screen capture, Marco.

Interesting issues to think about here. This is actually prime
clipping season in many places (not sure about Hawaii) due to the
cool weather. While there are more sun-hours in the summer, the
cell temperatures are often high enough that you won't tend to
see rated power out of the modules.

While I'm not running performance models for work, the people who
do are routinely increasing dc-to-ac ratios, often as high as
1.4-to-1. Having said that, most inverters aren't installed on a
roof. (Not yet anyway.)

I'd probably lean to a more conservative sizing ratio for micros.
While I can imagine some scenarios where I'd be comfortable with
a 215 W micro on a 265 W module---like a flat roof install in
Vermont, which reportedly doesn't see 1,000 W/m^2 very often---I
wouldn't try that here in Texas.








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Re: [RE-wrenches] P1 micro performance

[Bill Loesch]

Hi Dan,

A very heartfelt thanks for the education.
It is exactly this kind of attention to detail that separate the 
professional from the practitioner. Moreover, at least in this case, the 
proper terminology is hopefully better and more widely understood.

Thanks again,

Bill Loesch
Solar 1 - Saint Louis Solar
314 631 1094

On 21-Mar-13 11:59 PM, Exeltech wrote:

Wrenches,

I'm probably a lone voice on this .. and not intending to get overly 
picky.


Could we call power limiting what it is .. "limiting", and not "clipping"?

Clipping implies distortion, which isn't the case here. Limiting is 
just that.

The inverter output is limited to some maximum value -- not "clipped".

The output power curve flattens when integrated over time, but this 
still isn't
distortion in the waveform.  It's simply a point in the output where 
the derivative
is zero.  Not increasing, not decreasing.  Just .. zero. No additional 
increase
in the output for an increase in available energy at the input.  Think 
"governor"

on an engine

Thanks.


Dan Lepinski, Sr. Engineer
Exeltech / Exeltech Solar Products


--- On *Thu, 3/21/13, David Brearley 
//* wrote:



From: David Brearley 
Subject: Re: [RE-wrenches] P1 micro performance
To: "RE-wrenches" 
Date: Thursday, March 21, 2013, 11:37 PM

Thanks for sharing the screen capture, Marco.

Interesting issues to think about here. This is actually prime
clipping season in many places (not sure about Hawaii) due to the
cool weather. While there are more sun-hours in the summer, the
cell temperatures are often high enough that you won't tend to see
rated power out of the modules.

While I'm not running performance models for work, the people who
do are routinely increasing dc-to-ac ratios, often as high as
1.4-to-1. Having said that, most inverters aren't installed on a
roof. (Not yet anyway.)

I'd probably lean to a more conservative sizing ratio for micros.
While I can imagine some scenarios where I'd be comfortable with a
215 W micro on a 265 W module—like a flat roof install in Vermont,
which reportedly doesn't see 1,000 W/m^2 very often—I wouldn't try
that here in Texas.




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Re: [RE-wrenches] P1 micro performance

[boB]

On 3/21/2013 9:59 PM, Exeltech wrote:

Wrenches,

I'm probably a lone voice on this .. and not intending to get overly 
picky.





No, two lonely voices, Dan.

I associate clipping with audio waveforms which stops
the negative or positive voltage peaks flat.  Also called
flat-topping.

Limiting is like turning down the volume.  The waveform
stays the same and does not distort as it would if it
were being flat topped (and flat bottomed)

Thanks !
boB






Could we call power limiting what it is .. "limiting", and not "clipping"?

Clipping implies distortion, which isn't the case here. Limiting is 
just that.

The inverter output is limited to some maximum value -- not "clipped".

The output power curve flattens when integrated over time, but this 
still isn't
distortion in the waveform.  It's simply a point in the output where 
the derivative
is zero.  Not increasing, not decreasing.  Just .. zero. No additional 
increase
in the output for an increase in available energy at the input.  Think 
"governor"

on an engine

Thanks.


Dan Lepinski, Sr. Engineer
Exeltech / Exeltech Solar Products


--- On *Thu, 3/21/13, David Brearley 
//* wrote:



From: David Brearley 
Subject: Re: [RE-wrenches] P1 micro performance
To: "RE-wrenches" 
Date: Thursday, March 21, 2013, 11:37 PM

Thanks for sharing the screen capture, Marco.

Interesting issues to think about here. This is actually prime
clipping season in many places (not sure about Hawaii) due to the
cool weather. While there are more sun-hours in the summer, the
cell temperatures are often high enough that you won't tend to see
rated power out of the modules.

While I'm not running performance models for work, the people who
do are routinely increasing dc-to-ac ratios, often as high as
1.4-to-1. Having said that, most inverters aren't installed on a
roof. (Not yet anyway.)

I'd probably lean to a more conservative sizing ratio for micros.
While I can imagine some scenarios where I'd be comfortable with a
215 W micro on a 265 W module---like a flat roof install in
Vermont, which reportedly doesn't see 1,000 W/m^2 very often---I
wouldn't try that here in Texas.






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Re: [RE-wrenches] P1 micro performance

[Exeltech]

Wrenches,

I'm probably a lone voice on this .. and not intending to get overly picky.

Could we call power limiting what it is .. "limiting", and not "clipping"?

Clipping implies distortion, which isn't the case here.  Limiting is just that.
The inverter output is limited to some maximum value -- not "clipped".

The output power curve flattens when integrated over time, but this still isn't
distortion in the waveform.  It's simply a point in the output where the 
derivative
is zero.  Not increasing, not decreasing.  Just .. zero.  No additional increase
in the output for an increase in available energy at the input.  Think 
"governor"
on an engine

Thanks.


Dan Lepinski, Sr. Engineer
Exeltech / Exeltech Solar Products


--- On Thu, 3/21/13, David Brearley  
wrote:

From: David Brearley 
Subject: Re: [RE-wrenches] P1 micro performance
To: "RE-wrenches" 
Date: Thursday, March 21, 2013, 11:37 PM

Thanks for sharing the screen capture, Marco.
Interesting issues to think about here. This is actually prime clipping season 
in many places (not sure about Hawaii) due to the cool weather. While there are 
more sun-hours in the summer, the cell temperatures are often high enough that 
you won't tend to see rated power out of the modules. 
While I'm not running performance models for work, the people who do are 
routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said 
that, most inverters aren't installed on a roof. (Not yet anyway.) 
I'd probably lean to a more conservative sizing ratio for micros. While I can 
imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W 
module—like a flat roof install in Vermont, which reportedly doesn't see 1,000 
W/m^2 very often—I wouldn't try that here in Texas.

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Re: [RE-wrenches] P1 micro performance

[David Brearley]

Thanks for sharing the screen capture, Marco.

Interesting issues to think about here. This is actually prime clipping season 
in many places (not sure about Hawaii) due to the cool weather. While there are 
more sun-hours in the summer, the cell temperatures are often high enough that 
you won't tend to see rated power out of the modules. 

While I'm not running performance models for work, the people who do are 
routinely increasing dc-to-ac ratios, often as high as 1.4-to-1. Having said 
that, most inverters aren't installed on a roof. (Not yet anyway.) 

I'd probably lean to a more conservative sizing ratio for micros. While I can 
imagine some scenarios where I'd be comfortable with a 215 W micro on a 265 W 
module—like a flat roof install in Vermont, which reportedly doesn't see 1,000 
W/m^2 very often—I wouldn't try that here in Texas.

On Mar 21, 2013, at 7:54 PM, Marco Mangelsdorf wrote:

> Check out the output of the modules below at 1PM on this Spring equinox for 
> this system here in Hilo, Hawaii.
>  
> These mods are SunPower 245s with the Power-One micro 250s.  Notice that the 
> AC outputs below are 223 watts and higher.
>  
> If we had installed Enphase M215s instead, the max output possible would be ~ 
> 224 watts.
>  
> If there’s clipping this early in the year, imagine the degree to which the 
> clipping will be increasing in the months to come as the solar insolation 
> increases.
>  
> And these mods were “only” 245s.  Enphase states that their M215s are fine 
> with modules up to 265 watts!  Imagine the amount of clipping taking place 
> when that kind of pairing takes place.
>  
> marco
>  
> 
> 
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