How does monitoring of photovoltaic plants work and why do you need it? These are two key questions for everyone who wants to have a better understanding of their PV plant and its power yields. To understand the whole purpose of PV monitoring, it is useful to take a closer look at the plant.
1. Why PV monitoring is useful
The importance of electricity produced from the sun is probably now clear even to the strongest advocate of nuclear power. At least, one hopes. Here are two numbers for the skeptics: About 390 GW of PV output is installed around the world and a growth of 119 GW is expected this year (2018). In addition to many benefits for the environment, consumers and the economy, increasing growth also means greater reliance on stable power production. Those who want to sell their solar power primarily dependent on the financial aspects of stable power production. Those who consume the PV power themselves are more directly affected. It is especially annoying when, for example, one’s electric car is not charged and then one is stuck at home. PV monitoring helps avoid such situations and financial losses. It monitors the power production and immediately informs the operator when something is not right.
2. PV Plant Setup and Vulnerabilities
How does it work? Good question. The easiest way to explain this is to look closely at the setup of a PV plant. Its basic components include: PV modules, solar cables, inverters and feed-in meters. The individual modules are wired together and connected to the inverter. Initially, solar power produces direct current (DC). The inverter converts the direct current and makes it available for other uses. In this system, the modules endure the most wear and tear since they are constantly exposed to the weather. This includes continuous UV exposure, shadowing and dirt. These negative influences can lead to a noticeable loss of performance. The situation is similar when it comes to cabling since it is also exposed to the elements. This can result in a cable break or short circuit. Problems with the inverter are much less common. Other possible problems could be caused by the grid feed-in (disconnection or throttling).
Possible causes of errors and malfunctions:
• Continuous UV exposure
• Cable breaks
• Inverter malfunction
• Animals (e.g. damage from rodents, bird nests)
3. This is how PV plant monitoring works
Now we have found some vulnerabilities for the PV plant. In order to detect and report these errors, the monitoring system has to have integrated monitoring components installed. This happens via an interface on the inverter. The inverter is the most important partner here since it provides the monitoring system information such as the amount power being produced. The installer has to enter the following parameters so that the monitoring system knows what the expected power production is: the PV plant’s orientation and roof pitch and the output of the modules and inverter. Based on this data, the system calculates the expected power production and compares it with the current output. When the values deviate too greatly from one another, a malfunction is reported.
4. How data improves PV monitoring
The comparison of production values is the most basic version of plant monitoring. For most plant operators, it is not enough to just know that something is wrong without any details. For those who want to know more about their plant, the following generally applies: The more measured values that the monitoring device receives, the more precise the analysis and error detection. Sensors for the irradiation, wind speed, air and module temperature are required to have the measurements to achieve more accurate monitoring. When an irradiation sensor is installed on the roof, the system already knows whether the expected performance has been achieved. This “basic monitoring” is often used at smaller residential plants. It comes more complex when monitoring larger plants with central inverters (commercial and industrial segments). It is necessary to monitor individual module groups (strings)
5. Reporting and analysis with the PV monitoring portal
The more data that is to be collected and evaluated, the more important the recording and presentation of this data becomes. There are several options for viewing yield value reports: direct on the display of the device, accessing the device with your web browser, via the online portal, via e-mail or with the mobile app. The online portal is the easiest method and offers the most functions. The monitoring system is connected to the internet and transfers the data to the portal. In addition to the yield in kilowatt hours and the current efficiency of the inverters, the module temperature developments are displayed. These factors play a significant role in determining the efficiency the PV plant. A good online portal also offers additional functions. For example, it records the collected data and compares the historical data with that from other plants in the same region. The analysis of this data not only helps detect the failure of individual components, but also the gradual processes such as dirt and degradation.