System designers can usually be confident that if a device does well in a performance simulation, then the range will perform well in the real world. Engineering tools (choose HelioScope) are reasonably excellent at factoring in dozens of inputs to task how an selection will certainly perdevelop under real-world problems.

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However, there is one location of device design that have the right to result in unexpected—and also exceptionally large—losses: under-voltage. We’ll define why.

Why under-voltage losses are especially bad

The distinct trouble of under-voltage losses have the right to be interpreted by looking at a module’s power-voltage curve. In the example listed below, we all choose to photo that the modules will job-related at their maximum power suggest, and that the power suggest is well within the inverter’s voltage and also power window:


Figure 1: Power-voltage curve

Note, though, just how the curve is lopsided – when the modules track to the ideal side of the curve, power manufacturing falls much much faster than once the operating point moves to the left side. This difference in power loss coincides to the difference between under-voltage and overvoltage problems. In under-voltage problems, the module’s MPP voltage (the peak of the curve) is below the inverter’s operating voltage window—so the power manufacturing drops incredibly conveniently. In the example below, a 20% under-voltage gap leads to a 75% drop in manufacturing, while a 20% overvoltage gap leads to simply a 10% drop in manufacturing.


Figure 2: Power-voltage curve, including under- and also over-voltage situations

The genuine difficulty isn’t simply that these losses deserve to be large—however that they can increase significantly over the life of a device.

Time reduces voltage even further

Everyone knows that modules degrade over time, and also the majority of civilization think of deterioration in terms of power. However, power is the product of current and voltage, and destruction losses come from voltage, not current.

So as module voltperiods drop over time, under-voltage losses will get worse. And as we observed shown in the picture above, under-voltage losses acceleprice conveniently as the selection is pulled off of its max power suggest.

Take, for example, an selection via a small under-voltage loss in the initial year of design. These initial under-voltage losses of 0.3% might seem acceptable to a mechanism engineer. However, as the modules degrade over time (assuming simply 0.5% yearly degradation), the under-voltage losses grow much faster than the degradation losses. At year 10, the under-voltage losses will certainly more than 5%, while at year 25 the under-voltage losses will more than 20%.

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Figure 3: Degradation losses over time

In truth, this raising stream of loss has actually a net existing loss worth of 2%. In various other words, while the year-1 losses seem to be simply 0.3%, the better losses in the future are the equivalent of a constant 2% system loss founding in the first year of operation—definitely somepoint that deserves an engineer’s attention.

How to proccasion these losses

So what have the right to a device designer do to proccasion these losses? First, encertain that the string voltperiods are at the high end of the inverter’s voltage variety, and/or manually raise the minimum string size to account for this future destruction.


Figure 2: String size calculator

Keep in mind that significantly, inverters are being offered through narrowhead voltage home windows, as that helps the inverters raise the maximum rated power for the hardware, reducing prices per watt. This raises the threat of future under-voltage losses, even for units designed at the maximum string size.

Additionally, HelioScope individuals can double-inspect a design by running a simulation through an inverter through a minimum MPP voltage that is 10-15% better than the planned inverter’s minimum MPP voltage. This will certainly display the indistinguishable under-voltage clipping loss for the array’s future once the string voltage falls by 10-15%.

Finally, O&M providers must consider this voltage destruction when perdeveloping inverter replacements. Due to the fact that the array’s operating voltage falls over time, the replacement inverter installed at year 15 should be designed to a lower voltage variety than the one mounted on day one.

Paul Grana

Paul Grana is the co-founder of Folsom Labs, where he leads sales and marketing, where he has assisted to prosper the company to countless installers in over 70 countries. He additionally established the S3 Solar Software Summit, which brings together the industry’s leading software vendors and buyers each year. He formerly operated at Abound Solar, and also led product monitoring and also technical marketing via Tigo Energy. Paul holds a BS in Mathematics and Economics from the University of Chicearlier, and also an MBA from Harvard Business School.

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