Portuguese photovoltaic systems rely on monitoring solutions Reliable and economical operation of the solar parks

Complete and seamless monitoring solutions

Since the individual PV parks have a similar structure, the concept can be explained using the example of the plant in Moura. A total of 525 space-saving string combiner boxes (SCBs) collect the currents from the 7350 PV strings and conduct them to the same number of SHP75 inverters from SMA. In the SCB, the DC cables are protected and secured against surge voltages. This is important because ground-mounted systems are particularly at risk from lightning currents and surge voltages, due to their size and exposed location. Lightning current and surge arresters from Phoenix Contact significantly improve the availability of the solar park. The devices fulfill the EN 50539-11 and UL 1449 3rd edition standards for surge protection in photovoltaic installations and are KEMA-certified. The SCBs can be disconnected if maintenance is required so that service work can be carried out safely.

Reliable system operation and easy grid connection

The AC voltages converted by the inverters are transferred to 20 transformer stations installed in the field, where they are transformed from 0.4 kV to 30 kV. Before the solar power can be fed into the local power grid, transformers convert the collected AC voltages from 30 kV to 60 kV at the grid connection point. Measuring devices here record the grid parameters and communicate them to the central feed-in controller. Decentral power generation plants need to play their part in ensuring higher grid stability. For this purpose, the responsible grid operators specify the ranges to be maintained for the grid frequency and voltage as well as the reactive power in their grid connection conditions for photovoltaic systems. Regulators for power generation systems (power control units) record the voltage and reactive power present at the grid connection points to check these values. The devices from Phoenix Contact then determine the respective control values on this basis and forward them to the inverters, which can be regulated if needed.

Fast commissioning of data loggers and environmental sensors

In addition to generating power, large solar parks like Moura produce large quantities of data that must be collected, processed, and analyzed to then assess how economically the photovoltaic system is running. Because of this, there is a data logger on each of the 20 transformer stations. The devices work using an automatic detection mode, which is why all of the systems installed in the PV park can be easily connected via Plug and Play. Since this eliminates the need for configuration, startup time is reduced considerably. The inverter manager integrated into the data logger receives the data from the inverter via Ethernet and transmits it to the AXC 1050 small-scale controller from the Axiocontrol product family, which is also installed there. In addition, the AXC 1050 collects data from the connected weather sensors.

Transmission of the weather data

A total of six weather stations are mounted in the Moura solar park, with 14 module temperature sensors, eight pyranometers, twelve reference cells, two wind direction sensors, two wind speed sensors, and two combination sensors for temperature, humidity, and air pressure. The environmental sensors from Phoenix Contact are directly connected to the control system via a Modbus protocol. Because the devices are preconfigured, they are immediately available to transmit weather data. Instead of individually wiring each sensor, the sensors are simply connected in series with the M12 connections with Y distributors. This greatly reduces the amount of wiring required on site and makes it easier to integrate the sensors into the overall system. As opposed to compact weather stations, the sensors available from Phoenix Contact are individual modules. So if a device fails, only this sensor needs to be replaced.

Simple forwarding of all data to the central park control

Using weather sensors allows an operator to draw conclusions regarding the power of the solar system – the so-called performance ratio (PR). This value is calculated using the ratio between the actual and target yield, whereas the actual yield is determined from the installed energy measuring devices. The pyranometer and reference cells, installed at the module level both horizontally and tilted by 25 degrees, provide information on the target yield. If the calculated performance ratio is too low, the operator can adjust the regulation accordingly. The data loggers also receive digital signals, which contain information on the transformer temperature and the status of the switching device.

Analysis and customer-specific visualization

All data from the inverters, weather sensors, transformers, and the switching device is transmitted via a redundant ring structure via fiber-optic cables to a central park control located in the control room. With the open and flexible control platform from Phoenix Contact, forwarding to the Asset Performance Management Portal of QOS Energy is simple. The specific analyses, warnings, and reports resulting from the data then rationalize the work processes of the OEM service provider.