By: Adam Baker
Meaningful results of what’s actually going on in your DC collection system.
I wanted to discuss a subject not often brought up in U.S. solar markets: String monitoring.
There are some new innovations you should be aware of that monitor the DC health of a system deployed in the solar field through what I call ad hoc / freelance data monitoring.
Most often, string monitoring uses current transformers (CT) built inside an assembly, which goes inside the combiner box in the solar field. In a scaled-down example, in Affinity Energy’s building, we have a little panel-mounted group of CTs that monitor the 12 strings coming in from our building’s rooftop system. It uses serial communications to send data to the datalogger.
- The good thing about this type of string monitoring - whether deployed on a rooftop or a utility-scale solar plant, it’s engineered into the product upfront. In the solar field, it’s already engineered into the combiner box.
- The bad thing about this type of string monitoring – you must engineer it upfront. It’s not something you can easily add after the fact. In order to retrofit this solution, you have to take the site offline, isolate everything, remove a wire, run it through a CT, reterminate the wire, and get the site back online.
Several of my previous employers made a couple attempts to justify bringing string monitoring into the telemetry on their utility-scale solar sites. A few experiments got some great data, but they never found a good way to integrate it back into the SCADA system and provide meaningful results of what was actually going on in the DC collection system.
Is String Monitoring Worth It?
The value of string monitoring is pretty well understood. It helps you know whether your DC health is good or bad. But the implementation for what’s been available in the marketplace to date hasn’t been great.
Mostly, it all boils down to cost. String monitoring is expensive. As a rule of thumb, I usually estimate about $10 to implement each analog tag in a SCADA system. If you’ve got 12 tags per string and 12 strings per inverter, that’s 144 tags. You’re talking $1,400-$1,500 per inverter just to have some extra data.
So if you had 150 amps yesterday coming in from an inverter, and today you have 140 amps…how do you find out where those 10 amps went…without breaking the bank?
Freelance Data Collection: The Answer to Outdated and Costly String Monitoring
We have a solution that will help the solar industry: self-sustained and nonintrusive freelance data collection. We call it Solar String Analysis.
Here’s how it works. We go out to the solar site with a datalogger, clamp on CTs, and a solar panel. First, we clamp the CTs onto the DC strings and harnesses before they go into the combiner box. Over the course of a few days, we get a great apples-to-apples comparison of the current that comes from one string vs. the next during a consistent voltage window. We take 5-minute data samples for a day, then pack up the system and move it to new array or new combiner box. After the collection phase, we do some analytics and provide you a report that shows whether the system is working as expected or not.
We used the freelance data collection solution here on our building in Charlotte, North Carolina. We have a 30kw rooftop system with 12 strings. Our analysis showed one of our strings was actually giving us no current at all. That didn’t seem right, so we did some testing, swapped out instruments, verified that was true, went on the rooftop to investigate, and found a little melted MC4 connector.
That melted MC4 connector has caused us to lose about $60/month worth of energy since our system was installed almost 2 years ago.
Since fixing that one problem from just one data sample, we’ve got about an 8% improvement in energy. Now, I don’t expect to find that improvement percentage out on a solar field…but with 1,200 strings coming into a single inverter, we know there are problems out there in DC health.
Is Solar String Analysis For You?
We can take a bunch of samples, analyze the data, and give you a DC health report for much cheaper than it would cost you to retrofit, or even install a continuous string monitoring system before interconnection.
This is a field service we can provide, or work with your folks to implement, or bring in a third party local to the area to implement.
The analytics behind finding DC health problems has always fascinated me. I hope this innovation brings some value, gets you a little more energy, and adds a few more dollars to your bottom line.
Ping me if you’re interested in Solar String Analysis!
Adam Baker is Senior Sales Executive at Affinity Energy with responsibility for providing subject matter expertise in utility-scale solar plant controls, instrumentation, and data acquisition. With 23 years of experience in automation and control, Adam’s previous companies include Rockwell Automation (Allen-Bradley), First Solar, DEPCOM Power, and GE Fanuc Automation.
Adam was instrumental in the development and deployment of three of the largest PV solar power plants in the United States, including 550 MW Topaz Solar in California, 290 MW Agua Caliente Solar in Arizona, and 550 MW Desert Sunlight in the Mojave Desert.
After a 6-year stint in controls design and architecture for the PV solar market, Adam joined Affinity Energy in 2016 and returned to sales leadership, where he has spent most of his career. Adam has a B.S. in Electrical Engineering from the University of Massachusetts, and has been active in environmental and good food movements for several years.