How it works
A SCADA system has three layers. In the field, inverters, trackers, turbines, protection relays, meters and weather stations each have a controller that measures and switches. Remote terminal units or programmable logic controllers gather those signals over the plant network. A central server polls them every second or few seconds, stores the values as time series, and shows them to operators on screens with alarms.
Commands flow the other way. An operator or an automatic controller sends a setpoint, such as an active power limit in MW or a reactive power target in MVAr, and SCADA passes it to the devices. The plant's SCADA also links to the grid operator's own system, sending live output and receiving curtailment and dispatch instructions. Each measurement is a tag with a name, unit, timestamp and quality flag. A large solar plant can have tens of thousands of tags.
Why it matters
SCADA is the plant's record of what happened and the route for every command. Performance analysis, availability calculations, fault diagnosis and contract settlement all start from its data. Poor tag naming, gaps or wrong timestamps make that work slow or unreliable. An asset manager with plants built by different contractors finds each SCADA set up differently, so bringing their data together is often the first piece of work.
A worked example
A 150 MW solar plant has 50 inverters, each reporting 40 values every second. That is 50 × 40 = 2,000 values a second, or 2,000 × 86,400 = 172.8 million a day. Most operators keep one-minute averages for analysis, which gives 2,000 × 1,440 = 2.88 million records a day. Adding 24 string combiner boxes per inverter, each reporting current every 10 seconds, brings another 50 × 24 × 8,640 = 10.4 million readings a day.
Illustrative figures.
Across markets
Cybersecurity rules for SCADA differ. In the US, plants connected to the bulk power system above a size threshold fall under NERC's critical infrastructure protection standards. In the EU, the NIS2 directive brings larger energy operators under national cybersecurity rules. In India, the Central Electricity Authority has issued cybersecurity guidelines for the power sector, and plants send live data to the load despatch centre.