DIYers can perform many of these tests using a standard digital multimeter and a clamp-on current meter (like the industry standard, a Fluke 376, about $385, although less expensive meters are available). An infrared thermometer and a simple irradiance meter, like Daystar’s DS-05A ($157), will allow more accurate adjustments for standard test conditions. Proper protective equipment such as high-voltage gloves and safety glasses should be worn when making electrical connections for live operational testing.
Assuming that you have proper ratings and fusing on your meters, the following tests are possible and safe to perform.
- Polarity check of individual and series string of modules
- Open-circuit voltage of individual or series strings of modules
- Short-circuit current of one module. Testing the Isc of one or more series strings of modules is not advised due to high arcing potential when touching and removing meter terminals. Even when testing an individual module, it is recommended that you do not touch meter probes in the MC4 connectors, as arcing can carbonize the terminals, causing excessive high resistance and overheating at the connectors after testing. To avoid damaging the connectors, use a sacrificial MC4 connector with a bare lead for testing.
- Performance measurements can be taken while the system is operating, using a meter to measure voltage and a clamp-on meter to measure AC and DC current. DC current can be safely measured using a clamp-on meter without disconnecting wires. This is a standard test that must be performed before turning the system on to ensure that there is no current in the wires, or after turning the system off, before disconnecting or removing them. Some power meters, like the Seaward Power Meter, can measure voltage and current at the same time. These devices will automatically calculate the power.
The following tests are not recommended without the proper equipment and training because they can be dangerous and/or provide inaccurate results.
- Ground continuity—this resistance measurement requires that a voltage and current be applied between the frame and the system ground. However, the resistance measurement on most meters is designed for measuring electrical components, such as resistors and fuses, and will not give an accurate repeatable resistance measurement of a frame or wire.
- Insulation resistance tests are performed at high voltages with either the Seaward or other available meggers. Standard digital multimeters are not appropriate devices to use for this measurement—besides being a significant hazard to the tester, damage to the modules or other sensitive electronics can occur.
- Because strings can have a high voltage (up to 600 VDC), a significant arc can occur when the leads are shorted. The Seaward meter is designed to make this connection internally to minimize and extinguish any arc.
In the field, there is simply no way to make an IV curve without an IV curve tracer. Fortunately, this is not necessary in most DIY systems—unless a major discrepancy is discovered during the simple tests above or to confirm an underperforming or failing module for warranty reasons. Many installers are now using this equipment, so if you think there’s a problem you should be able to find someone with the tools to do it for you.
An inexpensive hand-held infrared thermometer can measure module cell temperature where the laser points, but a thermal camera can take numerous measurements at one time, providing greater precision. In both cases, proper training is needed to get accurate measurements, as the results are very much related to how you use the tool.