Application

A customer from abroad enquired us about a monitoring and datalogging system for a photovoltaic energy plant. The request was not only to simply control electrical values like current and voltages but also to monitor some enviromental parameters in a Country where big temperature excursions happen during the day.

Proposal

The system measures and logs the generated voltages and current, but also other parameters like:

  • Temperature
  • Humidity
  • Solar Radiation
  • Wind Speed

NI2400 datalogger will be the heart of the system. This rugged device, derived from the Next Instruments geotechnical dataloggers series, is the ideal equipment for this application.

NI2400 has protected inputs and conformal coating on all the internal electronics; this is very important in case of outdoor installation with big temperature variations and the possibility of internal moisture formation. 2 GB of internal non-volatile data memory and an embedded web-server are other distinctive characteristics for this application, together with the possibility to work for some months with a small sealed lead-acid battery.

Requirements

Current measurements

Current transducers type NI-T201DC are installed on the electrical cables and connected to the datalogger on a 4..20mA interface to perform this fundamental measurement. Similar to a normal TA, these transducers can measure DC currents until 100A as galvanic isolated device, and is over-temperature protected. They are interfaced to the datalogger on 4-20 mA connections.

Voltage measurements

In order to measure this value in a safe and reliable way, we have suggested the NI-Z204. The Z204 module can measure alternate and/or continue voltage values with high precision. These sensors can have also current-loop interface, but we have decided for this case to configure outputs as 0..10V, with direct connection to the data logger inputs.

Temperature & Humidity measurement

This outdoor installation requires an high quality sensor, like the device we have choosen; NI-EE160 temperature and relative humidity sensor. This instrument has high long term stability and resistance against pollutants.This sensor is connected to the NI2400 datalogger by using a 4-20 mA interface.

Solar radiation

A device called “solarimeter” is usually used to measure radiation of the sun. This sensor will continuosly transmit to the datalogger the level of solar irradiance. The solarimeter on our catalog, the NI-DW6450 is perfectly suited for this application, with a moderate cost. It is based on a silicon cell sensor, which the best solar radiation measurement technology for the photovoltaic field. The instrument output is a 0-3V voltage level, that we have connected to one of the datalogger’s analog inputs. NI2400 data logger will automatically transform and log the voltage values in W/m2.

Wind speed measurement

An anemometer is required to measure the wind speed, a device normally used in weather stations. The simple, classical wind-cups type is still the more reliable anemometer for this kind of applications; like the NI-WSS01. We have connected the anemometer power supply input to the datalogger power output, and the sensor output to one of the NI2400 analog inputs (the anemometer outputs a voltage level up to 2.0V). The datalogger is able here also to make the conversion between voltage and wind speed.

FTP Transfer , Modbus TCP or Cloud Monitoring

In this kind of applications, customers usually want to monitor data and analyze them with a remote software or “PV Software Analysis”. The simplest way – and first solution – to be able to comunicate with this kind of software is through FTP.

NI2400 works properly in this way; it sends data to the server through FTP and then the “PV Software Analysis” elaborates them.The second way of working is through MODBUS TCP/IP, if this is supported by your scada software. The third possible solution is the “Cloud Monitoring Service” which is compatible with tablet and smartphone views.

NI2400 Cloud Web Portal is a web service to monitor and control remotely all your field devices. By logging at portal you are faced with a host portal of “cloud management services” that enable you to monitor and control your equipment in a fast, efficient and professional way.

Conclusion

This is an example of a solar energy generation system monitoring with NI2400 Universal Datalogger, including not only measurements related to the produced energy, but also various enviromental parameters.With the connection of a radio-modem to the datalogger, the customer can obtain a complete remote monitoring of the plant, with the possibility to send user-defined alarms by e-mail or SMS.