GreenMountain Engineering

PV in the 1960s

For some quick entertainment, I thought I'd share a few scientific papers about PV from "back in the day".  From well before the 1977 founding of the Solar Energy Research Institute (now NREL), and back when oil was less than $20 a barrel (in 2009 dollars).

In 1963, the year the Beatles released their first album and Iron Man debuted as a comic book character, Joseph Loferski published "Recent Research on Photovoltaic Solar Energy Converters". This paper described silicon's lead as a material for high-efficiency (15% efficient, that is) solar cells, but mentioned some of the other materials under exploration, such as GaAs (13%), CdTe (6%), and CdS (6%). Note that the record 1-sun cell efficiencies of these materials are currently 25% (Si PERL cell, 1999), 26.1% (GaAs thin-film, from 2008 I believe), and 16.7% (CdTe, 2001).

In 1964, the year the Shinkansen high-speed rail system was inaugurated in Japan and Dr. Strangelove was released (and nominated for four Academy Awards), R. J. Tallent and E. J. Zapel published "Structrual and Electrical Performance of a Concentrating Solar Cell Panel". This paper described the design of a CPV module that used reflective aluminum to reach a 1.9x concentration ratio, as shown in the module and system test images below. I'm a fan of the Boeing Solar Research Laboratory bus.

And in 1965, the year of the civil rights march from Selma to Montgomery, DEC's unveiling of the PDP-8 microcomputer, and the first wide area network connection (between Massachusetts and California, the states that house the two GreenMountain Engineering offices), E. L. Ralph published "Use Of Concentrated Sunlight With Solar Cells For Terrestrial Applications", another early CPV paper describing a simple conical optic, the need for tracking, and an increase in efficiency with low concentration (via an increase in Voc), which must be balanced against losses due to series resistance and increased cell temperature.

Cheers and Happy Holidays!

This blog will likely go on hiatus until 2010, as we focus on wrapping up various end-of-year project work.

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!