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An affordable Cold Room powered by solar energy

Updated: Sep 18, 2019


Factors such as insulation, energy supply, and aeration are critical in successful cold storage technologies. But what happens if the storage technologies are too expensive or limited in supply or if they break down? This then calls for building technologies with available resources and workmanship to solve an aching problem – post-harvest loss in Uganda. The objective of the project is to provide cold storage to strengthen farmers’ and traders’ ability to adapt by using cold chain technologies to reduce post-harvest loses during low/no demand in glut periods. We believe that this is a matchstick that starts the fire, but Ecolife foods shall keep fanning the fire through University – farmer research and innovations.

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Agricultural losses and waste from poor post-harvest handling are common in Uganda (Figure 1). This is more pronounced in the rainy seasons with excessive fresh produce, yet good storage facilities are lacking. The available stores and markets have no cooling facilities resulting in many produce rotting on the shelf. Most food industries dealing with commercial products employ state-of-the-art cooling equipment such as freezers and fridges. The prices of such coolers are significantly high and only affordable to commercial companies generating substantial revenues. Therefore, because of the high initial capital costs, most of the small-scale companies and farmers cannot afford them. Thus cheaper, easy-to-use and practical cooling facilities become appealing to such companies and rural farmers. Importantly, many farming areas in Uganda have an abundance of natural building materials but literacy in science and technological use of such materials is limited. Ecolife uses her upper hand in scientific research and technology, to use the existing materials to design technologies relevant to the farmers. The Eco cold room (Figure 2) is one such technology designed to reduce losses and increase incomes both farmers and traders.

Figure 1: Horticultural farm waste

Figure 2: Design of the cold room

The standard features include

· Cold room size (LxWxH): 20 m3

· PET insulation material: 100 mm

· Product capacity: 4 to 5 MT

· Loading rate: 10%

· Backup: o 14 hours with 10% loading and fewer times door opening condition

· Temperature range: 5˚C to 10˚C

· Low voltage and over-voltage protection

· Mono-crystal or poly-crystal solar panels

· Batteries require no maintenance

· Solar Panel: 3.0 kW

Unique Feature:

· Thermal Energy Storage system to provide backup during the night and cloudy weather

· Solar powered

· DG set system

· Ecofriendly insulation material

· Low maintenance

· No running cost on solar supply

Our Approach

We focus on agricultural led development interventions and work with farming communities to create affordable technological solutions to the farmers’ local challenges and generate income. Using a step by step methodology of the design process and human-centered design; we have developed, built, and tested an energy-efficient and cost-effective solar-powered cold room. In building the first prototype, we worked with community members to identify the problem through a needs assessment study. We looked at various options and agreed to design and develop the cold room. We involved students from Universities, farmers and community members in doing all the research and design work. The PET waste bottles used as insulation were collected by community members from schools, parties and other functions where bottled water was consumed or even those littered around the community. We aligned these bottles between two walls to act as the insulation and testing of the cold room with produce was done. All the produce used in the testing was got from the farmers, who were allowed to participate in the loading of the produce in the cold room and in the inspection and assessment of the produce after the test days. The produce tested was passion fruits, mangoes, traditional leafy vegetables, tomatoes, and cabbage. We obtained feedback from the farmers and community on the performance and application of the cold room. Following that feedback, we developed the second prototype which is the focus of this report.

Figure 3 : A- Insulation used in the 1st prototype, B&C-Insulation board used in second prototype

Results and Discussion of results

The minimum temperature of the cold storage was 7.5°C. The system was maintained at a temperature range of 8-10oC necessary for storage of mangoes. At this temperature, the system automatically stops its compressor. The compressor goes on an off depending on the temperature inside the cold room. The unit was operated on a sunny day, on a partially sunny day and at night. Using the automatic data recording system temperature and humidity of both the cold room and ambient environment were recorded. The Slope from day one to day two indicates the fall of temperature inside the cold storage. And the rising slope indicates the increment in temperature inside the cold storage during off time. The shelf life of mango fruits stored in the cold room was extended compared to mangoes stored at room temperature. This is due to the reduction in field heat in shortest possible time, lower moisture loss, inhibition in water loss and reduction in ethylene production in fruits (Kader, 1992). Mangoes received from the market were too ripe. Cold storage maintained the quality of the mangoes compared to room temperature samples. There was less spoilage of produce received from farmers compared to those bought from market collection center. This was associated with poor post-harvest handling technologies/transportation from farm to market. The cooling injury was observed in samples received from the market collection center. Therefore, low-temperature storage reduced quality parameters such as peel color, for cold-stored fruits as compared to mangoes stored at room temperature. The chilling injury was observed and it was progressive with storage duration especially with mangoes received from market traders.


Our test results showed that the designed low-cost cold room powered by solar can extend the shelf life of fruits and vegetables. This will, therefore, increase the revenue period for smallholder farmers as well as their bargaining power in the market place. Despite the fact that we used local materials for construction, and the insulation of the cold room was locally designed, we saw a significant difference in the shelf life of the test and control produce. Testing with different energy systems (Solar and Diesel) allowed us to profile an affordable cold storage for rural communities in Uganda for use during wet (low solar energy /no electricity) and dry seasons (high solar energy/no agricultural produce). At ambient temperatures, the shelf life of mango fruit is shorter. The quality and shelf life of mangoes was maintained throughout the test period in the cold room. The shelf life was increased with a decrease in temperature. Further investigation might be needed for determining the critical temperature for chilling injury of the fruits.

Figure 4: Temperature inside the cold storage as a function of time. AT: Ambient temperature A1 - A5: Temperature sensors inside the cold room


Testing the Eco cold room revealed that reusing plastic waste PET bottles filled with air as insulation material for cold rooms can save energy, a good innovation for developing countries in the climate change error. The first order for a sustainable approach would be to create a completely standardized procedure for recycling waste PET bottles into PET foam as an alternative material for making sandwich panels for cold rooms in Sub-Sahara Africa. It is also important to have quality technological solar supply and equipment for sufficient energy supply in the cold rooms.

We recommend establishing cold storage facilities at village collection centers for both food self-sufficiency and considerable progress towards the goals of zero food loss and human nutrition in Africa.

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