The Central Electricity Authority (CEA) has released detailed guidelines for the installation and operation of Automatic Weather Stations (AWS) at solar and wind power plants across India. These guidelines are designed to ensure accurate, real-time meteorological data measurement, which is crucial for optimizing renewable energy generation, improving predictability and efficiency, enhancing grid reliability, and ensuring regulatory compliance.
The guidelines stipulate that AWS units should be strategically located within renewable energy project sites. For solar plants, irradiance sensors must be mounted at the same tilt and orientation as the photovoltaic modules. In wind projects, AWS must be positioned to accurately reflect the site’s true wind regime, avoiding turbulence zones or artificial barriers. Typically, one AWS is required for renewable energy plants with a capacity of 50 MW and above, or as per respective State/Central Electricity Regulatory Commission (SERC/CERC) regulations.
Infrastructure and Site Specifications
An AWS site must be a 10m x 10m leveled area, free from obstructions that could cause shading or turbulence. Key infrastructure requirements include:
- Fencing: A 1.5-meter high fence made of 50mm x 50mm x 6mm angle iron, pre-coated with red-oxide and painted, with a 10cm x 10cm (Gauge 10/3mm diameter) GI chainlink mesh. It must include a 2m x 1m x 6mm MS angle entry gate with a locking facility.
- Mast: A 10-meter high, tiltable mast made of anodized Aluminum alloy, suitable for coastal stations, supported by three rust-proof stainless steel guy wires, and painted in a red and white scheme. It requires a concrete platform (2ft x 2ft x 4ft height).
- Earthing and Lightning Protection: Two earth pits are mandatory for 100% protection from lightning – one for signal earth and another for the lightning arrestor. A copper lightning arrestor rod (12mm thick, 1m length) is to be mounted on top of the AWS tower.
Sensor Installation and Parameters
Sensors must be installed at specified locations: a rain gauge 3 meters from the tower, ambient temperature/relative humidity sensors at 2 meters height on the mast, and ultrasonic wind sensors at 10 meters height on the mast. A pressure sensor will be housed within the datalogger enclosure.
The AWS must be capable of measuring critical parameters:
- For Wind Plants: Barometric Pressure, Ambient Air Temperature, Wind Speed, Wind Direction, and Relative Humidity.
- For Solar Plants (as per CERC/SERC): Global Horizontal Irradiance (GHI), Global Inclined Irradiance (GII), and Rainfall. Detailed technical specifications, including measurement ranges, resolution, and accuracy, are provided for each sensor type (Pyranometer, Temperature/Humidity, Ultrasonic Wind, Atmospheric Pressure, and Siphon Tipping Bucket Rain Gauge).
Data Acquisition System (DAS) and Communication
The DAS hardware must support various inputs, be compatible with all installed sensors without external signal conditioning, and include a 24-hour Real-Time Clock. It must store at least 30 days of data in an encrypted format (AES 256 bit or higher) with restricted access, adhering to AAA (Authentication, Authorization, Accounting) mechanisms.
For communication, the DAS must have a dedicated slot for a plug-in bi-directional communication module (3G/4G/5G compatible) for seamless, secured, and encrypted data exchange with the National Centre for Medium Range Weather Forecasting (NCMRWF). It must also integrate with local plant-level SCADA systems via MODBUS/IEC-104 through TCP/IP communications, with redundant ports and robust cybersecurity measures, including firewalls, deep packet inspection, and continuous monitoring. Remote access for troubleshooting is permitted under strict protocols involving risk assessment, multi-factor authentication (MFA), and geo-fencing. Data sampling intervals will be user-selectable, with dissemination typically every 15 minutes, convertible to 1 minute during extreme weather events.
Data Quality Control and Cybersecurity
The DAS is required to apply real-time Quality Control (QC) procedures, such as gross error checks, time consistency checks, and inter-sensor checks, in accordance with the World Meteorological Organization (WMO) Guide to Meteorological Instruments and Methods of Observation. Robust cybersecurity measures are mandated, including firewall protection with Intrusion Detection Systems (IDS), deep packet inspection, IP whitelisting, and encryption of all data and logs in transit and at rest for a minimum period of 180 days, as per CERT-In directives.
Power Supply and Enclosure
The complete AWS must be capable of unattended operation using Maintenance Free (MF) Batteries, rechargeable via a Solar Charge Controller (MPPT) and solar panel. The battery system must sustain operation for a minimum of 20 days on full load during total cloudy or foggy conditions. Two separate weatherproof FRP (Fibre Reinforced Plastic) enclosures (IP 66 rated) are required – one for the Datalogger, solar charge controller, and switch, and another for the MF batteries.
System Configuration and Data Sharing
The AWS equipment must incorporate state-of-the-art technology for unattended operation. Data transmission from the AWS site will occur through the cellular network modem following the IMD Mobile Telemetry protocol to NCMRWF, simultaneously to at least two static whitelisted IP addresses using SFTP (Secure File Transfer Protocol), ensuring uninterrupted reception and archival. Additionally, AWS data in .csv format will be received by IMD/NCMRWF Central Server. The Indian Meteorological Department (IMD) will specify provisions for testing, calibration, and maintenance of AWS.