Hi Marco Here is our experience with that knowing that we are at 6000 to 8000 foot elevations.
We have seen significant differences in module delta temperature to ambient for ground mounts vs roof mounts and that is where we become concerned about oversizing the module or array. For a ground mount on a nice breezy day (especially in open areas or ridgetops) we have seen delta Ts at or below 10 degrees C. (SMAs string sizing allowed you to select mounting type so that delta T could be accounted for in sizing the inverter). Then add to that high irradiance and a low coefficient of power module and you have the perfect conditions for serious clipping. I would say that it is particularly true for trackers maximum irradiance at 9:00AM until 3:00PM with lower ambient temperatures during the morning. We also see very low delta Ts with white roofs where albedo is high and roof temperatures are low because of the reflected light. In this case, the decision on module size would depend on the tilt angle of the array relative to the seasons high irradiance levels and ambient temperatures. Thanks Randy Randy Sadewic Positive Energy Office: 505 424-1112 Cell: 505 570-0137 From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Chris Mason Sent: Monday, January 28, 2013 5:16 PM To: RE-wrenches Subject: Re: [RE-wrenches] high insolation value and inverter undersizing The initial issue was concerned with waste power, but that presumes all power is priced evenly. Take a familiar situation, you specify and sell the system based on a number of 240W modules. Let's presume time passes and when you go to buy out the job, you find there is a deal on 260W modules which makes them as cheap as the 240W would have been. Why would you not just buy the larger output if all costs are the same. If they clip the inverter a little, oh well. On Mon, Jan 28, 2013 at 7:35 PM, Nick Soleil <nsol...@enphaseenergy.com> 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 <john.berd...@solaredge.com> 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 its 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 <tel:510.498.3200%2C%20X%20747> M: 530.277.4894 From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] 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 <ma...@pvthawaii.com> 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 theyre 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. Its 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. Ive 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. 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P Please think of the environment before printing this email _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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 <http://www.enphase.com/commercial?utm_source=email&utm_medium=sig&utm_campa ign=Comm2012> Enphase Commercial Solar. Limitless. <http://www.enphase.com/commercial?utm_source=email&utm_medium=sig&utm_campa ign=Comm2012> 1420 North McDowell Petaluma, CA 94954 www.enphase.com <http://www.enphaseenergy.com/> P: (707) 763-4784 x7267 F: (707) 763-0784 E: nsol...@enphaseenergy.com Certified Solar PV Installer #03262011-300 Dont get me wrong: I love nuclear energy! Its just that I prefer fusion to fission. And it just so happens that theres 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 its 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. 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