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: [email protected] > [mailto:[email protected]] 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: > > > <image001.jpg> > > 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 <[email protected]> > wrote: > > > From: David Brearley <[email protected]> > Subject: Re: [RE-wrenches] P1 micro performance > To: "RE-wrenches" <[email protected]> > 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. > > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: [email protected] > > Change email address & 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] > > Change email address & 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] Change email address & 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
