MNRE Issues Draft Firmware Development Guidelines for Rooftop Solar Dataloggers

The Ministry of New and Renewable Energy has released draft 'Firmware Development Guidelines for Device Local Configuration & Remote Communication APIs' for dataloggers and remote monitoring systems deployed under PM Surya Ghar: Muft Bijli Yojana.

The draft sets out firmware API specifications for rooftop solar monitoring devices covering local HTTP-based configuration, cellular ISP configuration, secure SSL server communication, inverter communication through Serial and Modbus protocols, and UUID-based telemetry mapping for both single-phase and three-phase systems.

The ministry said the guidelines are intended to standardise firmware interfaces, device local configuration and remote communication APIs across manufacturers to ensure interoperability, cybersecurity, and data integrity. All APIs, payload fields, routes and parameters must be implemented exactly as prescribed, with no omission, renaming or modification permitted.

Under the draft, every RMS or datalogger device must carry a label or QR code displaying the default IP address, HTTP port, username, password, Wi-Fi SSID, IMEI number and serial number to simplify installation and commissioning.

The guidelines prescribe a token-based authentication mechanism under which users must first log in using a username and password. The device then generates an authentication token valid for 30 minutes, and every subsequent API request must include this token in the authorization header. Devices are required to verify the token’s presence, validity and expiry before processing any request.

The draft also mandates certificate-based secure communication. Each device must be provisioned with three certificates — rootCA.pem, client.pem and key.pem — uploaded separately through the prescribed API endpoint. These certificates are required before the datalogger can establish a secure TLS connection with the remote server or broker. The private key cannot be exposed, returned or logged at any stage.

A dedicated API will initiate the secure broker connection, while another API will track connection status through six defined stages, ranging from certificate loading to successful handshake publication.

The guidelines include four mandatory parameter mapping tables covering single-phase and three-phase inverters as well as single-phase and three-phase DLMS solar energy meters. These tables specify the exact parameters that manufacturers must support, including voltage, current, power, energy generation, frequency, meter serial number, power factor, tamper count, alarm thresholds and register addresses.

For single-phase inverters, the draft lists 23 mandatory parameters, while three-phase inverter systems require 43 parameters. Similarly, 31 parameters have been prescribed for single-phase DLMS meters and 38 for three-phase meters.

Each parameter must include details such as tag name, whether it is readable or writable, data type, Modbus register address, multiplication factor, virtual device group and alarm limits. The ministry has specified that all parameters are mandatory and must be implemented exactly as defined.

The document further introduces an offline data retrieval API that allows day-wise download of historical system records through a paginated format using record offsets and count.

In cases where internet connectivity is unavailable, the draft provides for an optional SMS-based fallback mechanism. Where GSM connectivity is active, the datalogger must send one SMS every day containing that day’s generation and cumulative lifetime energy. Only a pre-authorised master mobile number will be permitted to issue configuration commands to the device.

The ministry has invited comments and suggestions from datalogger manufacturers, inverter manufacturers, DISCOMs, system integrators, technical institutions and other domain experts. Stakeholders have been asked to submit their responses within 15 days of the memorandum’s issuance, making April 11, 2026, the deadline.