[RE-wrenches] Enphase performance
Randy
randy at positiveenergysolar.com
Mon May 10 15:49:18 PDT 2010
Hi Marv,
In our experience, there are a couple of things you didn't mention that can
make a big difference. The mounting approach can affect the delta T
ambient-module temperature resulting in much higher output for groundmounts,
polemounts, or rooftop arrays in windy ridges or open spaces. Second, we
regularly get irradiance above 1000W/m2 in our area. So your statement
"depends on the particular installation" is a very important point.
Randy
Randy Sadewic
Positive Energy
Office: 505 424-1112
Cell: 505 570-0137
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Marv Dargatz
Sent: Monday, May 10, 2010 3:59 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Enphase performance
Marco,
Sorry, I missed that question in the previous e-mail.
A couple of points about the compatibility list:
1. We include only modules that have passed our internal math check for
compatibility over the temperature range of the inverter.
2. If the module manufacturer objects to being on the compatibility list,
we will not include them.
Sunpower has objected, so they are not on the list.
Zhejiang Wanxiang Solar Co. Ltd is also shown as compatible with the M210.
The list is only a guideline. Any module that falls within the voltage spec
over the expected operating temperature range of the installation, and does
not exceed the inverter DC input short circuit current rating is certainly a
valid combination, and the inverter is fully warranted. Notice that module
power rating is not a factor here.
I hope this helps.
See ya!
Marv
707 763-4784 x7016
Marco Mangelsdorf wrote:
So why is the Enphase 210 just limited "officially" to the Sanyo line?
Thanks,
marco
Dana, Marco, Wrenches,
In most locations, if the interest is in maximum lifetime energy production,
it does make sense to use modules with STC power ratings significantly
higher than the inverter max power rating.
This is explained in the whitepaper located at:
http://www.enphaseenergy.com/downloads/Enphase_White_Paper_Module_Rightsizin
g.pdf
Remember, under most real world conditions the module will not produce STC
rated power. The inverter WILL produce maximum rated power plus some small
percent to allow for the CEC max power test methods. Also, the module will
produce less power every year (under the same conditions) and the inverter
will produce its' max rated power for its' entire lifetime.
By the way, this all applies to string, central, or microinverters. Of
course, micros still retain the advantages of dealing with mismatch, partial
shading/soiling, etc.
Bottom line is, the "perfect" match will depend on your particular
installation.
See ya!
Marv
707 763-4784 x7016
Dana Brandt wrote:
Something to remember is that my simulation was for a specific location in
Washington. The answer might be different for your location and weather
patterns.
I agree that it seems wrong to have the inverter rating 20% less than the
array nameplate. Typically, I would consider that sort of pairing a poor
design. You're right that there will certainly be some clipping - especially
with cloud-edge effects. The real question in my mind is not whether the
inverter will ever clip the output of the array, but what's the real impact
of that on energy generation on an annual basis. This is what lead me to do
the modeling simulations which indicated the effect is negligible when taken
in the context of the total annual production. Compared to the whole year's
sun, there just isn't that much energy in high production spikes like cloud
edge effects that the inverters will clip - at least not around here.
One thing to consider is that if you go with smaller modules you need more
inverters. You might compare the cost of the additional inverters to the
value of the 0.2% energy loss from clipping over the lifetime of the system.
Dana
Dana Brandt
Ecotech Energy Systems, LLC
www.ecotechenergy.com
dana at ecotechenergy.com
360.510.0433
On Mon, May 10, 2010 at 11:36 AM, Marco Mangelsdorf <marco at pvthawaii.com>
wrote:
I just don't understand why going over 20 percent of module nameplate to
nameplate inverter rating makes any sense.
I regularly see 120-130 percent of nameplate amperage coming off of the
array on our office due to edge of cloud.
So I have to disagree with Dana in this instance. I see this a bad design
especially since lower output mods are so readily available these days.
And what's up with the Enphase 210? Doesn't it say on their latest
compatibility list (March 2010) that it's only good for the Sanyo line?
What's up with that especially since I know that one other manufacturer is
signing off on using the Enphase 210 with their 210-watt module, apparently
with Enphase's approval?
Marv-why is your Enphase 210 only listed for use with the Sanyo line when
there's a growing number of 210+ watt mods out there these days?
Thanks,
marco
I've been concerned about pairing higher wattage modules (~230W) with the
190W Enphase fearing a lot of clipping and power loss when the modules are
at full power.
I did some modeling of this setup in PVSYST and found that the expected loss
from the inverter being underpowered is 0 - 0.2% annually depending on the
assumptions. The modeling was for northwestern Washington State. A fifth of
a percent seems pretty negligible to me and is easily offset by removing
module mismatch from the equation. So, I'm convinced that matching modules
in the 230W range with the 190W Enphase inverters is a good design.
I recently installed 4kW of 230s with the Enphase 190s and have seen their
output as high as 199W.
Dana
Dana Brandt
Ecotech Energy Systems, LLC
www.ecotechenergy.com
dana at ecotechenergy.com
360.510.0433
On Fri, May 7, 2010 at 4:48 PM, Chris Worcester <chris at solarwindworks.com>
wrote:
Do the Enphase inverters clip the output power to their rating like other
manufacturer's? So a M190 can only put out 190 watts max? I have had this
question for a bit now on system performances using Enphase in designs
during our cold spring and fall days.
Sincerely,
Chris Worcester
Solar Wind Works
NABCEP Certified PV Installer
Phone: 530-582-4503
Fax: 530-582-4603
www.solarwindworks.com <http://www.solarwindworks.com/>
chris at solarwindworks.com
"Proven Energy Solutions"
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Mark
Westbrock
Sent: Friday, May 07, 2010 10:33 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Enphase performance
The over-reporting of energy that Randy refers to below was much higher than
any discrepancy based on monitoring resolution. We have a pyranometer at
the site, and Enphase reported energy production as high as 38% higher that
predicted from irradiance data, as well as 38% higher than the string
inverter portion of the same system. Individual microinverters showed
instantaneous power output as high as 285 W from a nominal 190 W unit.
Enphase explained that there was a software glitch that was resulting in
"double counting". It took them over two months to correct this issue, time
which is lost from our experimental comparison of string vs. microinverter.
They indicated that this seemed to be an isolated situation, but I wonder
how many Enphase customers are reporting miraculous performance from their
system without verifying via another meter.
Screen shot of a day's power production of 22 M190 microinverters (nominal
4180 watts AC):
Error! Filename not specified.
Mark
Mark Westbrock
NABCEP Certified Solar PV Installer
NM ER-1J Journeyman Electrician
Positive Energy, Inc.
office: 575-524-2030
cell: 575-640-2432
westbrock at positiveenergysolar.com
www.positiveenergysolar.com
We definitely experienced an overstatement.
We have a client who installed 5kW on a string inverter and 5kW on enphase
and it is that side-by-side comparison that enabled us to positively
identify a problem. There was a significant overstatement of output. We
finally got a Enphase person who told us it was a software glitch. The
problem appears to be fixed. They explained to us that our problem was
isolated without giving us a detailed explanation of what happened. Since
that problem was fixed, we have seen no difference in output between a
string inverter and enphase.
Randy
Kirpal Khalsa wrote:
This same issue has come up over the years for us......first with PV Powered
inverters and then noticed in Fronius as well......We have noticed in most
of our grid tied systems that are connected thru a "revenue grade meter" for
Oregon Energy Trust production reporting, that the inverter always has a
higher performance than indicated on the "utility grade meter". We have
seen the discrepency as high as 10%. Over time this adds up to
significant kWh differences. In our experience the inverter always has the
higher kWh reporting, we have attributed this to the inverter wanting to
report a good production number, to boost their efficiency claims......maybe
even more than is accurate.....I have asked PV Powered and Fronius about
this and their line is that to put a "revenue grade meter" into the inverter
would be cost prohibitive......interesting as the readily available revenue
grade meters are only $30-$60. I would gladly pay that much extra if I
didn't have to wire in an additional meter.
I don't think this problem is unique to the Enphase units (i haven't
installed any of these), I think all inverters should be required to install
the revenue grade meters to give accurate reporting of actual production.
Similar to how states have a "weights and scales" accuracy certification,
energy consumption and production meters should be similarly calibratable.
--
Sunny Regards,
Kirpal Khalsa
NABCEP Certified Solar PV Installer
Renewable Energy Systems
www.oregonsolarworks.com
541-218-0201 m
541-592-3958 o
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