I assume the device just operates the module away its MPP. That would reduce its power output.
On Jan 29, 2013, at 8:48 AM, Larry Crutcher, Starlight Solar Power Systems wrote: > Nick, > > You said "the microinverter only draws enough current..." Could you explain > how this works? I primarily work with battery based systems and the charge > controllers that perform current limiting do so by shunting the excess > current as heat. How are you leaving current "in the module"? > > Thank you, > > Larry Crutcher > Starlight Solar Power Systems > > > > > > On Jan 28, 2013, at 4:35 PM, Nick Soleil wrote: > > Hi John, > > It's important to clarify that the "clipped" power does not turn into heat > within the microinverter. The microinverter only draws enough current to > achieve it's max output rating, and the remaining current is "left in the > module", so to speak. So, the heat generated at peak times is the same, > whether using a 260W module or a 280W module. > > Many string inverters actually work similarly. What's different for them, > however, is their overall thermal situation. The primary thermal driver for a > string inverter is the amount of heat generated by their electronics, and the > ability of their "fans & fins" to expel that heat. > > For example, a 5kW string inverter generates ~200W of heat at peak, and it > has fans and fins sized accordingly. But, the effectiveness of the fans and > fins depends on the ambient temperature (and on elevation/air mass), and if > your inverter was operating at max power during hot weather (which would > require significant oversizing due to the modules' temperature derates), it > could exceed the capability of the fans and fins. This would then require the > inverter to ramp-down output. (Actually, some string inverters can respond > improperly--depending on whether their fan is continuous, load-controlled or > thermally-controlled--and actually fry the electronics.) > > But, the thermal environment of a microinverter is very different. > > The main thermal driver in our situation is actually the external > environment, not the electronics. Regardless of sizing ratio, an M215 > generates less than 10 watts of heat at peak, whereas the heat radiated from > the module at peak times will be substantially greater than that. > Consequently, we've already over-engineered the microinverter for extreme > heat management, and the thermal effects of sizing ratio are simply a drop in > the bucket compared to the other factors. > > For that reason, we don't put limits in our warranty with regard to sizing > ratio (which contrasts with at least some string inverter warranties), and we > would not expect to see any microinverter ramp-down behaviors driven by > sizing ratio. > > > > > On Mon, Jan 28, 2013 at 11:06 AM, John Berdner <[email protected]> > wrote: > Jason: > > > > Be careful of drawing false comparisons. There is no free lunch. > > Beyond the energy yield issues there are some reliability issues. > > > > You should also consider that running an inverter flat out all the time will > shorten it’s life (due to the Arrhenius effect). > http://en.wikipedia.org/wiki/Arrhenius_equation > > > > Think of the inverter temperature in the same way you would the power output > curve (the two are closely related). Moving the whole power curve up “more > on the shoulders” also moves the whole temperature curve up as well. > > The average lifetime (all this stuff is only probabilities) was projected > with certain assumptions about how many hours at what temperature. As module > sizes increase a given inverter will spend more time at a higher power level, > i.e. runs hotter longer, which non-linearly reduces the life of the product. > > > > Just my $0.02… With the high labor cost of replacement it might be better to > undersize the module relative to the power electronics or vice versa. This > may or may not increase the installed system cost depending on the products > you choose. Running everything flat out all the time is probably not the > greatest idea. > > > > Best Regards, > > > > John Berdner > > General Manager, North America > > > > > > > > SolarEdge Technologies, Inc. > > 3347 Gateway Boulevard, Fremont CA 94538 USA (*Please note of our new > address.) > T: 510.498.3200, X 747 > > M: 530.277.4894 > > > > From: [email protected] > [mailto:[email protected]] On Behalf Of Jason > Szumlanski > Sent: Monday, January 28, 2013 5:30 AM > > > To: RE-wrenches > Subject: Re: [RE-wrenches] high insolation value and inverter undersizing > > > > I found the latest module "rightsizing" paper by Enphase pretty interesting. > It does stand to reason that there are a lot of hours in the day where the > inverter is producing less than rated power, so increasing the module size > makes sense. Obviously there is an optimum point in every system where > clipping exceeds gains, but that's virtually impossible to nail down due to > so many factors being involved. I think the point would be that PV mods are > coming down in price so much that "rightsizing" is basically equivalent to > "upsizing," within reason, of course. Spending an extra 25% on PV might > increase the installed system cost by 5-10%. > > Jason Szumlanski > Fafco Solar > > > > On Sun, Jan 27, 2013 at 6:00 PM, Marco Mangelsdorf <[email protected]> > wrote: > > I have had a concern for a long time that as PV modules have gone up in > output that there is inevitably going to be more and more clipping taking > place as they’re paired with comparatively lower output inverters. In > effect, matching, say. a 260-watt module with a micro inverter with a max > output of 225 watts reduces that 260-watt mod to 225 watts. It’s not a > matter of if clipping will take place, but how much and how much actual > harvestable energy will be lost. > > > > Out here in the tropics, even in January with the lower sun angle, we see > irradiance levels well above 1,000 watts/square meter range. Take a look at > what I copied today from a weather station that we installed at nearby > installation. > > > > Given the clipping issue inherent in using undersized inverters, it seems to > me that moving to larger output micros makes a whole lotta sense. I’ve got > one of the first installs using the Power-One 250-watt and 300-watt micros > and am so far quite impressed. Why use a 225-watt rated micro with a > 225-watt or higher output mod when larger micros are now readily available? > > > > What are the views out there regarding this clipping issue? Is it as minimal > as our Enphase friends suggest in their latest white paper or more of an > issue as I conclude? > > > > marco > > > > > > Environmentals from Weather Station at a Hilo, Hawaii installation > > > > Sunday, January 27th 2013, 12:40:00 pm > > > > > Ambient Temp. 25.30 °C > > Cell Temp. 41.70 °C > > > > > > > Insolation 127.81 kWh/m² > > Irradiance 1,175.00 W/m² > > > > CONFIDENTIALITY NOTICE: This e-mail and its attachments are intended only for > the use of the individual or entity who is the intended recipient and may > contain information that is privileged, confidential and exempt from > disclosure or any type of use under applicable law. If the reader of this > e-mail is not the intended recipient, or the employee, agent, or > representative responsible for delivering the e-mail to the intended > recipient, you are hereby notified that any dissemination, distribution, > copying, or other use of this e-mail is strictly prohibited. If you have > received this e-mail in error, please reply immediately to the sender. > P Please think of the environment before printing this email > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: [email protected] > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > > > > -- > 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: [email protected] > <image002.jpg> Certified Solar PV Installer #03262011-300 > > “Don’t get me wrong: I love nuclear energy! It’s just that I prefer fusion to > fission. And it just so happens that there’s an enormous fusion reactor > safely banked a few million miles from us. It delivers more than we could > ever use in just about 8 minutes. And it’s wireless! .” > > - William McDonough > > This email message is for the sole use of the intended recipient(s) and may > contain confidential and/or privileged information. If you are not an > intended recipient, you may not review, use, copy, disclose or distribute > this message. If you received this message in error, please contact the > sender by reply email and destroy all copies of the original message. > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: [email protected] > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: [email protected] > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org >
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