Nighttime losses: was Xantrex versus Sunny Boy [RE-wrenches]

[Marco]

All this talk about nighttime losses has got me a thinkin'.  Chew on this
actual example in Kahului, Maui: 32.4 kW DC array on a PV45208 inverter and
iso transformer. (The inverter and transformer are oversized to allow for
array expansion.)  I've got a ProMon electronic kWh meter on the output side
of the transformer to record system performance.  (Those meters are really
neat, by the way with the option of communicating with them remotely if you
buy their way expensive software.) My understanding of the ProMon is that it
does not measure power flowing in both directions.  That is, only PV kWhs
are recorded with no nighttime current registered as the transformer is kept
energized.  The average AC kWhs/day = 160.  Assuming that the PV system in
putting out power an average of 12 hours/day here in the tropics, that makes
for 12 hours of nighttime losses from the transformer.  The question I have
is: what is the estimated daily kWh parasitic power loss from that big wad
of copper coils? Any idears?

marco

Jeff,

Again, Kent probably has better numbers on this, but speaking with a
colleague of mine who has tested some of these transformers, he reported
losses closer to 400 Watts on this. If this is true, that is closer to a 4%
loss--the same as the losses of a SW with battery at night. Now that muddies
the water.

It appears that there is a market for these contactors. Apparently a company
in south San Francisco named Steven Engineering (www.stevenengineering.com)
makes these contactors as an aftermarket add-on the PV series inverter.
Learn something new every day.

Apparently Oberlin College wrote a paper for the ASES 2003 conference on
their experiences with their system including these losses. They have a nice
web site at: http://www.oberlin.edu/envs/ajlc/Systems/Energy/Epvsystem.htm
for those who are interested. I didn't find the study on their website
however.

Bill.


-----Original Message-----
From: Bill Brooks [mailto:billb at endecon.com]
Sent: Friday, August 01, 2003 5:02 PM
To: RE-wrenches at topica.com
Subject: Nighttime losses: was Xantrex versus Sunny Boy [RE-wrenches]


Jeff,

It is best to take the load off the transformer at night, but that does add
cost (a big contactor) and some controls. Since there are many building
electrical configurations, Trace Tech decided not to go that direction. Kent
could probably give a much better history of that decision.

The question is does it cause load on the utility (not that we care). The
utility has literally hundreds of the thousands of transformers (PG&E alone)
running all the time. The real power load of transformers is fairly low even
though the volt-amps might be much higher (no load power factor can be 0.1
to 0.2) Power factor equals Watts/Volt-Amps. The Watts being consumed is the
heating in the windings. Amps are sloshing back and forth energizing the
transformer and inducing a voltage on the secondary side.

If the no load loss on a 30kVA isolation transformer is between 100 and 200
Watts of real power. Over 12 hours, that would consume 1.2 to 2.4 kWh of
energy (not insignificant). If the PV system produces 120 kWh on an average
day, that is a 1% to 2% loss (not 6%). If the system costs $250,000 and
loses and avoidable 1% of energy, the designer should allow an additional
cost of up to $2,500 (1% of system costs) for the addition of a contactor to
eliminate this loss.

I have measured 50 Watts of nightime power consumption on the Trace SW (with
batteries) and the Vanner RE4500 (without batteries). These are much larger
losses relative to the energy production.

All-in-all this is a very important issue and one that designers and
installers too often overlook.

Bill.


-----Original Message-----
From: Jeff Oldham [mailto:starpower4u at juno.com]
Sent: Friday, August 01, 2003 4:14 PM
To: RE-wrenches at topica.com
Subject: RE: Xantrex versus Sunny Boy [RE-wrenches]



Bill,
Right you are, this was a basic V/A measurement at night and you're also
correct that most of the time this gets under the utility billing radar. I
now have a Davidge Controls kWh meter on it and I don't know if it will pick
it up, but I think so. Now, if I can just get the owner to LOOK at it for me
(I'm 3 hrs. away). Billed or not it is still a grid load is it not? Not
considering these losses is a NIMBY attitude. I think the best design takes
the maximum load off of the grid with the PV watts you have to work with.

We all await your test w/eagerness!

-jeff o

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael_welch at sbcglobal.net

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

TOPICA - Start your own email discussion group. FREE!
http://www.topica.com/partner/tag02/create/index2.html
--^----------------------------------------------------------------