[Editor’s Note: If you’re not sure what an IV Swinger does Chris has a detailed two part video explaining the background of this project, what it does and why he made it. You can watch the first video here.]
The IV Swinger is an IV curve tracer for photovoltaic (PV) solar panels. I built it for my friend Professor Gil Masters to use in the lab for his CEE176B course at Stanford (“Electric Power: Renewables and Efficiency”). It was used in the Spring 2015 and 2016 CEE176B labs. It was also used by the Stanford Solar Car project in 2015.
An IV curve plots the current and voltage generated by a PV panel for different load resistances ranging from short circuit to open circuit. The point on this curve that has the largest V * I product is the maximum power point (MPP). The shape of the IV curve and the MPP for a PV panel depend on factors such as its temperature and the intensity and uniformity of the sunlight falling on its surface. A typical IV curve of an unshaded PV panel looks like this:
But if single cell on the panel (1/60 of the panel) is shaded, the IV curve looks like this:
The maximum power has dropped by 40% even though less than 2% of the surface is shaded! Understanding IV curves for PV panels under different conditions such as shading is an important part of learning about the technology. The IV Swinger enables students to quickly and accurately generate real-world IV curves for PV panels.
The IV Swinger consists of a bank of loads and relays to select whether each load is included in the circuit or bypassed. It has an ammeter and voltmeter to measure the current and voltage at each point. Python code running on a Raspberry Pi controls the sequencing, takes the measurements, and generates the IV curve graphs. The graphs are written as PDFs to one or more USB thumb drives and the raw data is also written as CSV files.
I posted the following YouTube video demonstrating the IV Swinger in action:
It should be quite possible for others to replicate and hopefully improve on the design of the IV Swinger. My hope is that the design could be used for other college or even high school courses teaching PV technology. It’s not a “weekend” project, however, and step-by-step instructions would be too lengthy for an article like this. I posted another YouTube video giving an overview of the design and construction:
If you are interested in building an IV Swinger, the full design documentation (including Fritzing file) and software is posted on GitHub.
Could the author comment on why he chose a switched resistor bank instead of a high power FET as a variable load?
Hi Antron,
That’s a great question! I have a couple answers:
1. The students in the class that this is used in first “manually” generate an IV curve using a load bank consisting of DC light bulbs and physical switches and taking current and voltage measurements with a multimeter. This is a slow and laborious process, but easy to understand. I wanted the IV Swinger to simply automate that same process. Since you can hear the relays switch (and see their LEDs light up), it is very clear what is going on, and I thought that was better from a teaching perspective.
2. I knew I could get this to work. I’d seen some descriptions of using power FETs for the variable load, but I had some doubts about how to make it work. I was especially concerned about how to dissipate 300W+, but there were other questions I had that were probably just due to my (total) lack of experience with power FETs.
Having said that, I’ve been thinking of experimenting with different implementations. I’d definitely learn something by playing with a straight power FET implementation. I’ve also considered using a buck-boost (or maybe just buck) DC/DC converter as a PWM-controlled variable load.
– Chris
“my room mate Mary Is getting paid on the internet 98$/hr”..,……..!wc380ctwo days ago grey MacLaren P1 I bought after earning 18,512 DoIIars..it was my previous month’s payout..just a little over.17k DoIIars Last month..3-5 hours job a day…with weekly payouts..it’s realy the simplest. job I have ever Do.. I Joined This 7 months. ago. and now making over. hourly 87 DoIIars…Learn. More right Here !wc380:➽:➽:➽➽➽➽ http://GlobalSuperJobsReportsEmploymentsBookGetPayHourly$98…. .❖❖:❦❦:❖❖:❦❦:❖❖:❦❦:❖❖:❦❦:❖❖:❦❦:❖❖:❦❦:❖❖:❦❦:❖❖:❦❦:❖❖:❦❦:❖❖:❦❦:❖❖:❦❦::::::!wc380………..
There is now a much better (and MUCH easier to build) IV Swinger 2. It is Arduino-based and uses a single relay and a capacitor as the load. The measurements are captured as the capacitor charges up. The results are displayed in real time on a laptop (Mac or Windows) running an app that also lets you view, modify, and combine previous results. The Instructable has links to YouTube demo videos.
http://www.instructables.com/id/IV-Swinger-2-a-50-IV-Curve-Tracer/
– Chris