The Ministry of New and Renewable Energy (MNRE) has released draft guidelines on “design, specifications, performance, and testing procedure for solar cold storage with thermal energy storage (TES) backup.”

The guidelines will serve as a standard reference for all stakeholders, providing the basis for design specifications, performance, and testing standards for 2 MT, 5 MT, 10 MT, and 20 MT capacity solar cold storages with TES. They cover minimum cold storage temperatures of -5 ºC, 1 ºC, and 4 ºC.

Performance and design specifications

Cold storage involves ‘cold rooms’ that are made from polyurethane foam to maintain the desired temperature and humidity for commodity storage. These rooms use refrigeration units, which provide cooling by circulating cold air for commodity preservation.

The guidelines call for fully powering cold storages with solar energy to achieve baseline performance, which involves precooling 10% of the total storage capacity for two continuous days. The cold storage systems must have sufficient TES capacity to provide cooling without solar and grid electricity.

Thermal Energy Storage

MNRE’s guidelines propose charging and discharging TES simultaneously. The energy storage medium should be a phase change material such as water or water salt eutectic mixture.

The TES capacity must be designed for two days of autonomy, factoring in a daily precooling requirement of 10% of the cold storage capacity.

The guidelines state that this design prevents solar energy waste when cold storage is not fully utilized. Any surplus solar energy will be captured in thermal storage to improve precooling capacity or to extend autonomy during cloudy or rainy days.

Solar Systems

The guidelines call for solar systems to include the latest IEC/BIS-qualified modules. All solar modules must be certified from an NABL-accredited test laboratory.

Solar modules must have a warranty for their peak ‘watt output capacity,’ guaranteeing at least 90% capacity at the end of 10 years and 80% at the end of 25 years.

The guidelines state that the solar module mounting structures must be made of metal and designed to withstand module loads and wind velocities of up to 150 km/hr. The foundation for ground-mounted modules should be based on the site condition and soil properties.

Solar systems will include maximum power point trackers to harness the generated energy efficiently, ensuring optimal power input for the refrigeration unit and battery charging.

The project contractor must also provide five years of comprehensive solar cold storage system maintenance.

Testing Procedure

According to the guidelines, the cold storage temperature must be recorded for the test using a temperature sensor with a minimum repeatability of ±0.1⁰C.

The TES’ charging performance will be observed by providing electrical energy through a grid connection to guarantee repeatable data. An energy meter, conforming to an accuracy class of 0.5 according to IEC/AS Standard 62053-11, will be set up to monitor the system’s total energy consumption.

MNRE also released test procedures for performance evaluations, including tests for the TES’ cooling delivery capacity, minimum achieved temperature specifications, solar array stimulator-based performance and autonomy testing, power source switching tests, and the system’s autonomy tests.

Last year, MNRE invited feedback from the public and stakeholders on the preliminary design specifications for solar cold storage, ranging from 2 MT to 10 MT within the temperature range of 4°C to 15°C.

Remote villages of Rajasthan, with help from self-help groups and several non-government organizations, camel milk herders are using solar-powered milk chillers to preserve the milk. The chillers can cool up to 500 liters of milk every day. The cost of setting up the solar-powered chillers is ₹650,000 (~$7,731.77).

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