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

[Kent Sheldon]

Marco, you can call the transformer companies technical support line to get the actual loss numbers for the transformer you have. I have found that they are reluctant to give out these numbers, but will if you talk to the right people. You must ask for VAR and Watts losses at each step. Each model, configuration, material, etc will have different loss characteristics. Do not settle for an impedance or percentage number. These are meaningless. You should also ask for the losses at 0, 25%, 50%, and 100% of rated kVA. The losses will not be linear across the power range. Most designs try to optimize losses between 50 and 75%, which is where most load transformers operate continuously. In doing this, the zero load losses are negatively affected, usually resulting in much higher losses as a percentage of rated kVA, which makes things worse for this discussion. And you will find that the high efficiency transformers usually have higher zero load losses than the junk models. See my!
  previous post for an example. Regards,



___________________________________
Kent Sheldon
Projects Manager, Industrial Power Systems
SMA America, Inc.
530 273 4895 ext 107

>>> Marco<marco at pvthawaii.com> 8/1/2003 6:29:16 PM >>>
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

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