SMA now delivers large inverters that provide several options for power
factor correction provided by the output of the inverter.
So we are not talking about the viability of the technology. There may
still be a question of how well the technology is implemented in this
particular microinverter.
The main question here is the efficacy of claims of an advantage for
small residential customers such that reduced PV array sizes deliver
equivalent energy as metered by the local utility.
Having followed the the whole power factor correction device discussion,
I still have some question in my mind as to the resolution of the
question of whether or not standard residential utility meters will
measure and accure a credit for improved power factor.
Mark Frye
Berkeley Solar Electric Systems
303 Redbud Way
Nevada City, CA 95959
(530) 401-8024
_www.berkeleysolar.com_ <http://www.berkeleysolar.com/>
------------------------------------------------------------------------
*From:* re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Exeltech
*Sent:* Monday, January 10, 2011 8:59 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Xslent?
By the way, in answer to answer your original question, capacitors of
proper value, when installed in a circuit containing inductive loads,
are capable of allowing the circuit to attain a power factor of 1.0. As
part of our Underwriter's Laboratories testing for our grid-tied
inverters, a test fixture is used that's capable of both inductive and
capacitive reactance (it's part of the anti-islanding tests). I've
witnessed the power factor being adjusted from 0.7 leading and lagging
to an absolute perfect 1.0000 (yes, four decimals). It's all done by
varying the value of capacitance in the circuit. Thus, if one were to
use lab-grade test equipment, and take the time needed to make such a
precision adjustment, it's possible to achieve absolute unity in an
inductive circuit by "tuning" it with a capacitive circuit.
Dan
--- On *Mon, 1/10/11, North Texas Renewable Energy Inc
/<nt...@1scom.net>/* wrote:
From: North Texas Renewable Energy Inc <nt...@1scom.net>
Subject: Re: [RE-wrenches] Xslent?
To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org>
Date: Monday, January 10, 2011, 8:29 AM
How efficient is a capacitor in offsetting the power factor error?
99.9%...±2%...?
Jim Duncan
-----Original Message-----
*From:* re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org]*on Behalf Of
*Exeltech
*Sent:* Sunday, January 09, 2011 9:03 PM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Xslent?
--- 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
morelosses. 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
>
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