GreenMountain Engineering

IV-Stat 3.1: Our free solar cell testing software

This summer GreenMountain quietly released a beta version of some solar cell characterization software we’ve been developing for the past few years.  Motivated by positive feedback and a recent update extending functionality to the newest Keithley Sourcemeter series, we’ve decided to leave beta.  So without further ado, I’m pleased to introduce IV-Stat 3.1. It’s free of charge: no fees, limited-time trials or ads.

The software allows measurement of solar device IV curves by interfacing with Keithley 24XX or 26XX(A) Series Sourcemeters. The program then performs a curve fit on the measured IV data to extract standard parameters (such as Isc, Voc, efficiency, Rse, Rsh, as well as more detailed parameters such as diode currents and ideality factors for various different one-diode or two-diode solar cell models).

Originally developed in 2006 for internal use, it has also been customized for our clients a number of times.  Currently there are versions being used in the R&D labs of a few well known solar companies and research labs.  The following is a testimonial by Keith Richtman of the Massachusetts Institute of Technology Laboratory for Photovoltaic Research:

“As a rapidly growing research lab, we needed software to support solar cell I-V testing without weeks of development time. GreenMountain engineers customized IV-Stat to provide exactly the features and flexibility we required and delivered quickly.”

GreenMountain’s core business is engineering design and consulting services, not selling software. Because of this, we’ve decided to give IVstat away for free (though as part of this, we can only offer minimal support). If it helps you, we hope you’ll keep us in mind as a team who can help you solve engineering problems and be successful as you scale up your technologies.

In IV-Stat we tried to include all of the functionally we felt the typical photovoltaic researcher would need:

• Control of  the Keithley sweep settings
• Control of  analysis variables
• Raw data outputted in a spreadsheet-compatible format
• Ability to save and load all of the test settings with configuration files
• Simple tools for graphing the IV curves and saving images
• The ability to use Pulse Mode (with 2430 or 26XXA Keithleys) for high current tests

If you need additional features or customization, this is something we can do for a one-time fee; feel free to give us a call, however I also wanted to point out one additional feature we’ve included: hooks.

IV-Stat includes two “hooks” which help users customize the software or integrate it with their own hardware. Twice during each sweep IV-Stat executes an external program (“hook”) and passes it the test data. A typical use of these hooks would be to trigger some external user program which could open and close the light source shutter, transfer the generated data to an SPC database (note that we’ve designed custom web-accessible manufacturing databases for a number of clients), measure a reference cell, or perform some other function.

One example of customization we’ve done in the past is integrating IV-Stat with a custom probe station we designed (see slick marketing picture below) and the client’s solar simulator and reference “champion” cell.  This probe station featured a custom thermal vacuum chuck, adjustable probe bars, and horizontal shuttle for easy access.  The result was a robust, semi-automated, research cell testing station.

If you’re looking for more detailed technical information on IV-Stat, please review the product web page, the User Manual, or send me an email at iv_support@greenmountainengineering.com; I’ll be happy to answer any questions.

Cheers!

Rooftop testing station site goes live

John Lawler mentioned our rooftop testing station back in April. We've undertaken a fun project over the last couple of weeks, and I'm pleased to announce our web site that shows data from the instruments in our rooftop solar testing station. You can check it out at http://roof.greenmountainengineering.com/.

Data is recorded whenever the sun is up in San Francisco and is displayed "live" (well, actually updated every 60 seconds) for the current day. If you select a day in the past from the calendar, you'll see data from that day. You'll also get a fancy time-lapse video showing the weather conditions for that day.

Although the setup is explained in much more detail on the actual site, the very short version of how this all works is that we have a computer in a weather-proof case on the roof. The computer collects data from all of the various instruments and sensors (including a Trac-Stat SL1) and sends it off to our web server. Our web server stores that data, processes it, and sends it to you in the form of a web site.

This whole arrangement is a simple analogue for a number of projects we've done for our clients. Although our rooftop testing station site shows off a publicly-accessible, read-only interface to a single set of equipment, we've built secure systems to control and monitor hundreds of discrete pieces of equipment simultaneously, log hundreds of gigabytes of data per year, and provide convenient access to equipment in remote locations.

Please let us know if you have any questions about the site or if you'd like to learn more about the kinds of things we can do to develop monitoring and control systems for you.