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Photovoltaic system monitoring
System monitoring: Common systems for monitoring the solar system
What system monitoring systems are there? How does the monitoring of a solar power system work? Why should the system be monitored at all? What data do the monitoring systems provide and how do you evaluate them? Which is Better: Manual or Automatic Monitoring? Questions that this post will answer for you.
A solar system, also known as a solar power system or photovoltaic system (PV system for short, PVA for short), generates usable electricity from the radiation energy supplied by the sun. No matter whether you use the self-generated regenerative solar power
- Consume partially / completely as your own electricity in the household or market it yourself
- or feed it in part / completely and collect the state feed-in tariff for it,
it is important that you know how much electricity the system generates in total and how much of it goes into the household and the public grid. Systems for system monitoring inform you about this.
Systems for monitoring the solar system
Systems for monitoring the system inform you about its performance: Depending on the system and monitoring mode, they provide you with various data, including yields and data on the amount of self-consumption and feed-in. Yield (also solar yield) means the amount of usable electricity that your photovoltaic system supplies you with.
But that's not all: Many automatic monitoring systems calculate further data from the systematically measured performance data, for example how much CO2 emissions you save by operating the system.
System monitoring with so-called data loggers
A so-called data logger is an electronic data memory. It monitors the system automatically. The data logger constantly records yields and other characteristic values about the system performance, which it mostly gets from the inverter. Thanks to automation, the data logger provides you with monitoring data without you having to think about it.
Data loggers are already installed as standard in the majority of modern inverters, which convert the direct current generated by the solar system into usable alternating current. Alternatively, you can also buy the parts separately.
Tip: when is it worth purchasing a data logger?
Current prices for data loggers start at around $150 and go well over $1,000. You have to assume that a good data logger with an internet connection will cost you at least 500 euros. In relation to the acquisition costs for a smaller photovoltaic system up to 5 kW, which currently costs around 1,500 dollars per kWp net, this price is no longer negligible.
With a PV system up to 5 kW, you should therefore consider whether the investment is worthwhile for you because even if your system fails for a few days, the resulting loss is manageable. The larger the PV system, the more worthwhile it is to purchase a data logger because the profitability of the investment increases with system sizes from 10 KWp. If the data logger prevents a 40 kWp system from failing for several weeks, its use has already paid off.
When it comes to how the data logger works, you should know that the amount of electricity that the inverter feeds into the grid (public grid and domestic grid) is monitored, measured, and recorded by the associated data logger. The data logger generates a daily report on the yield of your solar system from the logged data. Depending on the data logger, you can also get monthly and annual reports.
It is important to know that you often need an extra interface: the so-called piggyback. It must also be installed in the inverter. So that the electricity consumption of the household can be included in the evaluation, the data is transmitted from the meter to the data logger via standardized interfaces.
Monitoring is primarily done by analyzing the error codes of the inverter. Many systems evaluate the data further and compare the values of inverters or strings, for example. If the performance of one string differs from that of another string that is connected in the same way, you will receive an error message.
Modern data loggers for system monitoring today provide data such as:
- Electricity consumption (from the grid) of the household,
- and household self-consumption.
They also offer you functions such as:
- Energy management (e.g. remote shut down by the network operator)
- Monitoring of the 70 percent rule
- smart connection or disconnection of electricity consumers in the household via remote-controlled radio-controlled sockets
- if storage is available: intelligent storage management including the display of the filling level of the electricity storage
Depending on the data logger and the associated data interface, you will receive the monitoring data via cable or wirelessly, for example via Bluetooth, in the form of an SMS on a mobile phone, tablet, PC, or even a free internet portal (web-based data logger) provided by data logger manufacturer.
Alternative options for displaying the monitoring data are small displays that can be used as a tabletop or wall-mounted devices. For larger systems, it is worth transferring the data to a large display that is visible to everyone.
A web-based data logger regularly transmits the system monitoring data to an internet portal, where it is evaluated. You can log into the portal at any time to have the data presented to you – often in an attractively visualized form. The information pages of the portals are usually freely configurable so that you can call up the data that you currently want to see from the wealth of data from your system monitoring. It is also possible for the portal to automatically send you individual monitoring reports, notifications, and the like by e-mail, SMS or e-fax.
What is better for system monitoring: reading meter readings or using data loggers?
A modern system monitoring system should basically perform these tasks:
- record all relevant monitoring data
- signal irregularities
- Visualize monitoring data
With manual monitoring with meter readings, you do all this manually. This is where mistakes tend to creep in. In addition, regular and continuous reading is not always guaranteed (keywords: vacation, hospital). The probability that you will notice system problems and the resulting loss of yield later than with automated system monitoring via data logger is therefore higher.
However, a data logger that operates web-based system monitoring also costs up to several hundred euros. The investment is always worthwhile when you need to know quickly about problems or even failures in the solar system in order to prevent solar yield losses.
- That is why you can do without an expensive data logger for smaller solar systems (up to 5-kilowatt peak (kWp) output), whose failure for several days is financially bearable to some extent, especially if you put the loss of yield in relation to the price of the data logger.
- For more powerful systems from 10 kW, on the other hand, it is worth buying a data logger for system monitoring for this very reason.