Solmetric or Pathfinder? [RE-wrenches]

Mark Frye markf at berkeleysolar.com
Mon Apr 9 17:13:31 PDT 2007


The subject is indeed a tricky one.

I used to make the SolarPathfinder trace sheet work for none south array
orientations by doing the following:

1 - using the correct trace paper for my latitude
2 - using the trace to develop a "shading mask" with each half hour slot in
each month either on or off
3 - applying this shading mask to the hourly PVWatts1 data for the
particular azimuth and tilt

Of couse I am lucky to be here in the SF Bay Area right next door to our own
WBAN station, so the PVWatts1 data is very good for our sites.

Currently however, I am using the SolarPathfinder w/ Assistant. I understand
it now performs a comparable algorithm and outputs the CSI percentage I need
here in California.

As the volume of work goes up and more and more measurements are required to
comply with the CSI EPBB calculator, I will migrate to the Solemetric Suneye
or whatever better product may be available by then.

MPF

-----Original Message-----
From: Peter Parrish [mailto:peter.parrish at calsolareng.com]
Sent: Monday, April 09, 2007 4:41 PM
To: RE-wrenches at topica.com
Subject: RE: Re: Solmetric or Pathfinder? [RE-wrenches]



I don't have a huge amount of time to devote to this post, so I will make it
a train of thought. Shading IMHO is the single most misunderstood and
miscalculated issue in the solar electric business. First, there are several
flavors of Solar Pathfinder graph paper and most people use the one
corresponding to their latitude. This can be a mistake if your tilt is
significantly less than the latitude. In our case, this works out to a tilt
angle 20 degrees or less at a latitude of 34 deg. Use the "ecological" graph
paper for that range of tilt (zero to 20 deg). This is not my opinion but
the opinion of the Pathfinder tech support guru. Second, the Solar
Pathfinder Assistant (SW package) while it finesses the graph paper problem
originally didn't give correct numbers for anything but a due south
orientation. They now claim that it works for most orientations -- and I
tend to believe them at least for SE to SW orientations. Finally, the
Solmetric gizmo also didn't work originally for anything but south; they
were very upfront about it and since the Solmetric developers are ex-Agilent
guys out of Santa Rosa they at least have a good pedigree. I got an email a
few weeks back claiming that the latest release of the product now supports
other than south orientations. Bottom line: use the manual path finder with
the right graph paper, and use the latest version of SP Assistant and the
Solmetric SW. Finally, can one buy an extra battery and wall charger for the
Solmetric and do field swaps if needed?

- Peter

Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com


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