--- On Fri, 1/7/11, Peter Parrish <peter.parr...@calsolareng.com> wrote:
> What ever is done to reduce the reative power, it has to be done> in real time (with a fraction of 0.016 seconds, the 60 Hz cycle).> You can’t wait until later in the evening to solve a problem that> is occuring during the day. Peter is absolutely correct. Power factor correction MUST occur on a half-cycle by half-cycle basis, and at the exact moment of power consumption by the reactive load. Anything else won't be effective, and may in fact worsen the power factor at a given point in the grid. > Real time compensation can be often done with capacitors alone> or in conjuction with some smart electronics. Remember that for> short periods of time capacitors can store considerable amounts> of energy and can smooth out these reactive currents. Capacitors placed across a power line will store energy for exactly one-half cycle. At that point, the polarity reverses, the capacitor is discharged to to zero, then recharged to the opposite polarity. This process repeats every cycle. What DOES take place is a phase shift (displacement) in the current flow relative to the voltage waveform. Power factor correction is done with capacitor banks (we see them in substations and on power poles) to offset the power factor of the grid itself, which by its design is inherently inductive due to long runs of wire. Very large motors will have individual "tuning" capacitors installed to offset inductive reactive current flow. These capacitors are disconnected whenever the respective motor to which they're connected is not in use. On occasion, excessive capacitance exists in a circuit that must be offset by inductance, but this is rare. Like Tom Cruise said in Top Gun .. "It's complicated." Dan --- On Fri, 1/7/11, Peter Parrish <peter.parr...@calsolareng.com> wrote: From: Peter Parrish <peter.parr...@calsolareng.com> Subject: Re: [RE-wrenches] Xslent? To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org> Date: Friday, January 7, 2011, 5:39 PM I know only a little about Power Factor “charges”, but we can figure out some other “engineering” issues. Power Factor is a measure of the amount of reactive (out-of-phase) power compared to real (in-phase) power. It is somewhat complicated but the PF is unity for 100% in phase and 0 for 100% out-of-phase power. The important thing to remember is that (while holding the real power constant) for PFs less than unity there is in addition to the real power, and “in-flow” of power and an “outflow” of power four times a cycle. One might say, “Why do I care about reactive power? It flows in and out with no net contribution over the long run!). True, but the in-flow and out-flow represents higher currents on the lines and more losses. Or it means that there have to be oversized service conductors to avoid the extra losses. Even if the losses are avoided, the higher currents can trip overcurrent protection devices, and of course the utility company needs to supply (and take back) the extra currents in real time. What ever is done to reduce the reative power, it has to be done in real time (with a fraction of 0.016 seconds, the 60 Hz cycle). You can’t wait until later in the evening to solve a problem that is occuring during the day. Real time compensation can be often done with capacitors alone or in conjuction with some smart electronics. Remember that for short periods of time capacitors can store considerable amounts of energy and can smooth out these reactive currents. I can well imagine how an inverter can be designed to generate both real and reactive power, and therfore an inverter can reduce the amount of reactive power that needs to be supplied by the utility company – but not when the sun isn’t shining. I suspect that these types of inverters will have oversized output circuit wiring to handle the reactive currents without adversely impacting their efficiency rating. If I have time this weekend, I will take a look at Apparent’s website. - Peter Peter T. Parrish, Ph.D., President California Solar Engineering, Inc. 820 Cynthia Ave. , Los Angeles , CA 90065 CA Lic. 854779, NABCEP Cert. 031806-26 peter.parr...@calsolareng.com Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Jamie Johnson Sent: Friday, January 07, 2011 2:03 PM To: RE-wrenches Subject: Re: [RE-wrenches] Xslent? It's an interesting product for a niche market if it actually works as they say (Disclaimer:I am not claiming that it does), after speaking with an individual who I believe is the VP of Production for Apparent (use to work for EnPhase according to their website), he claims that the product is currently installed at the Google campus on a solar canopy for some of their EV chargers (can anyone verify this?) They have several other beta installs as well, however the individual I spoke to said they were only installing small systems at beta test sites (where the Util co charges for VAR's using separate meters like for EV charging) for now. No pricing has been set for the inverters, and they are not available for sale to installers yet. Apparently they claim the inverter can create/produce VAR's by taking 1 watt of power from the grid at night or from the solar output during the day and turning it into approximately 9 VAR's to offset the customers charges for VAR usage from the Grid. This is where the KVAh production on the graph before sunrise and after sunset comes from. I still would need to see a third party head to head comparison test before I believed it. Again niche market inverter for when the utility co charges for VAR's. Jamie -------- Original Message -------- Subject: Re: [RE-wrenches] Xslent? From: August Goers <aug...@luminalt.com> Date: Fri, January 07, 2011 10:24 am To: RE-wrenches <re-wrenches@lists.re-wrenches.org> Hi All - Thanks for the helpful info! We did a little more research on our end and I guess Apparent is the new brand name for the Xslent product. What baffles me is the chart where they show that they're producing power before and after sunrise and sunset: http://www.apparent.com/products/mgi.html The system must include batteries? Someone on their marketing team is really going to town... Best, August -----Original Message----- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of jay peltz Sent: Thursday, January 06, 2011 4:43 PM To: RE-wrenches Subject: Re: [RE-wrenches] Xslent? HI Peter, I agree with you that for now on residential it makes no sense. However for commercial that might have to pay extra for PF issues, to have the inverter adjust for this makes sense. Its the reason they( inverter companies ) are doing it. I"ve heard a better more complete reason of course from Bill Brooks, who maybe can chime in. sorry got away from me, jay peltz power On Jan 6, 2011, at 2:34 PM, Peter Parrish wrote: > I can't understand how any inverter WOULDN'T deliver its power with the > voltage and current 100% IN PHASE. > > When the voltage and current are not 100% in-phase that represents reactive > power. Reactive power flows positive for a quarter of the AC cycle, then > negative for a quarter of a cycle, then positive and then negative. The net > result over one AC cycle is ZERO power delivered to the load. > > So reactive power is worthless. > > Worse, it results in higher currents (and voltages) for the same amount of > in-phase power, putting additional stress on circuits. > > - Peter > > > Peter T. Parrish, Ph.D., President > California Solar Engineering, Inc. > 820 Cynthia Ave. , Los Angeles , CA 90065 > CA Lic. 854779, NABCEP Cert. 031806-26 > peter.parr...@calsolareng.com > Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 > _______________________________________________ _______________________________________________ -----Inline Attachment Follows----- _______________________________________________ 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
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