[RE-wrenches] Xslent?

Sun Jan 9 19:03:22 PST 2011

--- On Fri, 1/7/11, Peter Parrish <peter.parrish at 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.parrish at calsolareng.com> wrote:

From: Peter Parrish <peter.parrish at calsolareng.com>
Subject: Re: [RE-wrenches] Xslent?
To: "'RE-wrenches'" <re-wrenches at 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.parrish at calsolareng.com  

Ph 323-258-8883, Mobile 
323-839-6108, Fax 323-258-8885                                                                                                    

From:
re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at 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 <august at luminalt.com>

Date: Fri, January 07, 2011 10:24 am

To: RE-wrenches <re-wrenches at 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-bounces at lists.re-wrenches.org

[mailto:re-wrenches-bounces at 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.parrish at calsolareng.com

> Ph 323-258-8883, Mobile 
323-839-6108, Fax 323-258-8885

>

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