PV orientation [RE-wrenches]

[William Miller]

Now throw in this question:

Both arrays are fed into one GC1000 inverter with MPPT.  How will the MPPT
loading affect the array outputs?

Allow me to speculate:  An MPPT device is basically a variable load
resistance.  The load impedance is lowered gradually while monitoring amps
and volts for maximum power.  In the morning, the east array will have the
most current capability, so the MPPT loads it heavily.  The load is that
same for both arrays, so the array with off axis sun will be loaded too
heavily, further reducing it's output. While mid day sun is equal for both
arrays, afternoon sun will of course be the converse of the morning scenario.

This problem may well erase any gains made by MPPT tracking, but I'd like
to know for certain.  Could it be that non-MPPT controls might produce more
output in this situation.  And we all know that all MPPT circuits are not
equal.

I was hoping someone some way of monitoring a system such as this, but it
would require tracking both arrays, I imagine.

William




At 01:56 PM 8/22/02 -0700, you wrote:
>Marco:
>
>The info's right there bro.
>
>1/2 the array East at 15 Degrees = 0.5 * 0.88 = 0.44
>1/2 the array West at 15 Degrees = 0.5 * 0.88 = 0.44
>
>                          Total for the array = 0.88
>
>In our case this assumes that the entire series string is on one
>orientation.
>If you wire it so that 1/2 the series string faces East and the other
>half West you will get MUCH less power. 
> 
>If you have any questions, or if I can be of any further assistance,
>please do not hesitate to contact me.
>
>Best Regards,
>
>John Berdner
>
>SMA America, Inc.
>20830 Red Dog Road
>Grass Valley, CA  95945
>530.273.4595 (voice)
>530.274.7271 (fax) 
>
>
>-----Original Message-----
>From: Mangelsdorf, Marco [mailto:mmangelsdorf at hei.com] 
>Sent: Thursday, August 22, 2002 1:35 PM
>To: RE-wrenches at topica.com
>Subject: RE: PV orientation [RE-wrenches]
>
>Massuh Bill and others,
>
>Here's a teaser.  Let's look at two identically sized PV arrays.  One
>facing due south at latitude.  The other one is split 50-50 due east and
>due west at a slope of, say, 15-20 degrees.  Figure no shading issues
>for either system along with clear sky insolation throughout the whole
>day.  I'd think that the due south system would put out more solar kWhs
>over the course of the year.  What would you estimate the percentage
>difference to be, on a yearly basis, between these two systems?
>
>marco
>ProVision Technologies
>Hilo, Hawai'i
>
>
>These are orientation multipliers for the two states
>
>For New York:
>
>Direct./ oTilt	0o	15o	30o	45o	60o	90o
>South			0.87	0.96	1.00	0.98	0.92	0.66
>SE,SW			0.87	0.93	0.94	0.91	0.85	0.62
>E,W			0.87	0.85	0.81	0.74	0.67	0.49
>
>
>For California:
>
>Direct./ oTilt	0o	15o	30o	45o	60o	90o
>South			0.89	0.97	1.00	0.97	0.89	0.58
>SSE,SSW		0.89	0.97	0.99	0.96	0.88	0.59
>SE, SW		0.89	0.95	0.96	0.93	0.85	0.60
>ESE,WSW		0.89	0.92	0.91	0.87	0.79	0.57
>E, W			0.89	0.88	0.84	0.78	0.70	0.52
>

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William Miller
Miller Power and Communications
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