Series Resistance Testing

Series Resistance Testing


What is Series Resistance?

The series resistance of a PV string system is the total electrical combined series resistance from the string ends connecting the inverter /optimiser and the module(s). When in darkness the PV cells have a high series resistance and in daylight healthy cells lower to a very low value of about 0.5 Ohms per module, and the connectors, junction boxes, cable all add a low but insignificant resistive value.

System imperfections, e.g., poor connectors, DC isolators, can increase the series resistance and the heat loss in each component is derived from I2R where R is the series resistance of the component.

A poor connector with a high series resistance will heat at peak current flow and though unlikely to catch fire, can get hot enough to melt/distort the connector itself, leading to a loss of water tightness, and weakened insulation and increased risk of arcing.

(Description courtesy of James Hoare CEng FIET FEI)

How is the series resistance tested?

Quite simply, Helios test for series resistance using one of the leading pieces of test equipment, the Emazys Z200. This allows us to connect up to each string of each inverter and run the test. As more information is obtained during this testing process than we can obtain from other test equipment, the time it takes us to test a string is longer, usually around 90 seconds per string.

So, it takes us longer to test for series resistance but the amount of data that we obtain makes it easier for us to locate faults.

What’s it useful for?

Series resistance testing is a useful method by which potential faulty connectors are quickly located at inverter level without the need to pay for expensive access equipment.

If faulty components are located then it may be that access equipment is then required to fix the fault however as the location of the fault has already been found, the time taken to rectify the fault is usually quicker which results in lower costs for the customer.

When’s the best time for carrying out the series resistance testing?

Very simply, when there’s good light levels. This allows us to obtain more accurate data that we can use to provide our clients with a good service.

Contact Helios today on 01525 664665 if you would like to learn more about series resistance testing and how it can help to improve the performance of your solar PV system.

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The Emazys Z200 one of the leading pieces of test equipment used by Helios.

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