Solar Milk Cooling with Insulated Milk Cans

Description

The milk cooling solution developed by the University of Hohenheim is based on a commercially available DC Refrigerator equipped with an adaptive control unit for its conversion to a smart ice-maker that operates depending on the availability of solar energy. The ice-maker has a volume of 160l and is capable of producing approx. 8-13 kg ice per day. One system includes 25 reusable plastic blocks of 2 kg capacity and two 30l isolated milk cans with removable ice compartment. To cool down 30l of milk from 36°C to 15°C in one of the supplied milk cans, the systems needs 6kg of ice and 90 minutes.

The smart ice-maker is powered by 600 Wp solar PV modules together with two batteries with a total capacity of around 1.5kWh. Thanks to the thermal energy storage, in form of the 25 2kg-Ice-blocks, the system is able to run autonomously for up to 7 days even during periods of low solar radiation and high ambient temperatures.

Ice-Maker with Adaptive Control Unit

The implemented adaptive control unit allows the efficient use of conventional DC-Refrigerators for a intensive and reliable production of ice all over the year. The ice-maker is equipped with following features:

• Variable compressor speed in dependence of solar radiation and state of charge of the batteries.
• Operation of a fan in the inner chamber in order to increase freezing rate.
• Energy saving mode during night and rainy days.
• Use of batteries to increase daily ice production up to 30%.
  
• Storage of 50 kg ice blocks to assure a autonomy of at least 5 days under low radiation or high ambient temperatures.
  

Isolated Milk Cans

The milk-cans implemented are made of stainless-steel and have a capacity of 30 liter milk and 8 kg Ice. This allows a flexible use of them depending on the cooling requirements. The milk-can has been design to operate for two modes as described in following table.

 

	30 Liter milk + 6kg Ice	20 Liter milk + 8kg Ice
Cooling temperature	17°C after 90 min.	Under 10°C after 150 min.
Used for	Transport of morning milk	Storage of evening milk
Milk quality preservation	At least 6 hours	At least 12 hours

The cooling performance and bacterial growth were measured with real milk under lab conditions in a climate chamber. On-field milk quality assessments are currently carried out in order to confirm the potential of the system to retard bacterial growth depending on milk temperature and transport time under real working conditions.

Collaboration partners

Research and Development:

Agricultural Engineering in the Tropics and Subtropics (University of Hohenheim)

Commercialization:

Phaesun GmbH

Field Assestments:

• International Center for Agricultural Research in the Dry Areas (ICARDA)
  
• Tunisian Ministry of Agriculture (INRAT, OEP, CRRA)
  
• Powering Agriculture and Green Invotation Center (Tunisia and Kenya)
  

Supported by:

German International Cooperation Agency (GIZ)

• Innovation Transfer into Agriculture - Adaptation to Climate Change (ITAACC) 
  
• Powering Agriculture - Sustainable Energy for Food
  

German Ministry for Economic Cooperation and Development (BMZ)

On-field implementations

• Tunisia, July 2015 until December 2017:
  

Field Testing of an Innovative Solar Powered Milk Cooling Solution for the higher Efficiency of the Dairy Subsector in Tunisia

In order to evaluate the potential of solar milk cooling systems under real conditions, an on-field project is currently carried out in Sidi Bouzid (Tunisia) under the coordination of the International Center for Agricultural Research in the Dry Areas (ICARDA) and the support of the GIZ through the ITAACC program, founded by the German Ministry for Economic Cooperation and Development (BMZ). At national level, the project is managed by the Tunisian Institute of Agriculture Research (INRAT) and several partners from the Agriculture Ministry and the dairy industry. The assessed solar milk cooling solution has been developed by the University of Hohenheim and is commercialized through the company and project partner PHAESUN GmbH. Additionally, the project counts on the support of the Powering Agriculture initiative of the GIZ for the social related assessments.

The region of Sidi Bouzid, in central Tunisia, is responsible for approximately one sixth of the national milk production in Tunisia. The majority of its milk is produced by small and medium sized dairy farms with ten to twenty cows and a daily milk output below 200l. Their milk is currently being produced on farm and transported to milk collection facilities without cooling. In this situation, bacterial growth during on farm short-term storage and transportation represents a significant problem for the dairy sector.

The project implementation with duration until December 2017, supports the assessment of a solar-powered milk cooling solution, designed to meet the refrigeration needs of small and medium-sized dairy farmers of the region. The ice-based cooling solution was developed specifically to overcome the challenges during short-term on-farm storage of milk and transportation to collection centers.

Since April 2016, 10 solar systems of the presented milk cooling solution are operating in 7 farms in the region of Sidi Bouzid . Each system has a capacity of 60l per day while 3 farms were equipped with two system due to higher production volumes up to 120 liter milk per day.

The performance of the solar ice-makers is currently monitored in order to confirm the right use of the system by the farmers and the daily availability of 12kg ice. Additionally experts interviews are carried out for farmers and dairy industry to assets the acceptance of the milk-cans by daily use together with the social impact in terms of gender and labor organization.

From the economical side, the potential of the system to increase productivity and preserve milk quality will be analyzed as main pillars to support the milk value chain and generate business opportunities. Furthermore the system cost will be reduced by the development of milk-cans able to be produced locally.

Overview of solar milk cooling systems

• Solar Milk Cooling

References

 

Torres-Toledo, Victor, Klaus Meissner, Alberto Coronas, and Joachim Müller. 2015. “Performance Characterisation of a Small Milk Cooling System with Ice Storage for PV Applications.” International Journal of Refrigeration 60. 81–91. doi:10.1016/j.ijrefrig.2015.06.025.

Torres-Toledo, Victor. 2013. “MSc. Thesis: Design Methodology of Cost Optimized Solar Chillers for Milk Cooling in Rural Areas.” University Rovira i Virgilli, Tarragona, Spain.

For further information, please contact the author of this article.

https://www.uni-hohenheim.de/projekt/field-testing-of-an-innovative-solar-powered-milk-cooling-solution-for-the-higher-efficiency-of-the-dairy-subsector-in-tunisia