Experimental Prototype of a Solar Fish Dryer
Thameem A. Razzaq1, Yoosuf Qasim1, Abdulla Naeem1, Zeeniya Hassan1, Yoosuf Nizam2*
1 Department of Environment and Natural Science, Faculty of Engineering, Science and Technology, the Maldives National University, 20371, Male’, Maldives
2 Department of Engineering, Faculty of Engineering, Science and Technology, the Maldives National University, 20371, Male’, Maldives
*Corresponding Author: [email protected]
Accepted: 1 June 2020 | Published: 15 June 2020
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Abstract: Fishing has been a major economic activity in the Maldives. Small families used to be engaged in fisheries, but the number has been in decline due to many factors. This paper is about an experimental prototype design of a “solar fish dryer” that will use the solar energy of the sun and overcomes the challenges faced to small fisheries businesses. The prototype managed to achieve the temperature range used in other similar fish drying projects (58°C), but did not achieve the targeted temperature range of 60-90°C. This is possible to achieve with some upgrades to the solar fish dryer.
Keywords: Fish dryer, solar, dried fish, renewable energy
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1. Introduction
Fishing in Maldives
Maldives is an archipelago which extends about 900 km from 7 degrees north to 0.5 degrees south in the Indian Ocean. There are 1192 coral islands and 187 are inhabited islands excluding the resort islands. The total area of Maldives is 115’300 square kilo meters including the sea. The exclusive economic zone (EEZ) is approximately 859’000 square kilometers. The large ocean area around the islands naturally tends to mainstay fishing as the main occupation of Maldives and the main source of food.
However, with the increase in population and rapid economic growth, the number of locals engaged in the fishing industry has decreased in the last few decades. With tourism being introduced in the early 1970s, more people, especially the youth has preferred to work in the tourism rather than the fishing industry. This could be mainly due to the income difference between the two industries, largely due to the extensive growth of tourism in the Maldives. In 2019, there are total of 44’860 beds operating in the tourism industry and the president of Maldives has proposed to increase this amount to 47’000 at the end of 2019 (Maldives Insider, 2019).
The total population of Maldives is 491’581 people in 2017, and only about 17’500 were engaged in the fishing industry (Statistical Pocket Book, 2018). The main types of fisheries engaged by this sector is skipjack, yellow fin tuna and different types of reef fisheries. The vessels used by the fishing sector are modernized boats which have the capability of staying on the sea for a few days compared to the old sail boats that has to return upon nightfall.
There are many local products produced from the fish at individual and large business levels.
The processed tuna can production is done at a large scale by government associated and private companies of the country. Other local products like smoked fish, dried fish or fish paste “rihaakuru” is produced by local families and this was in fact the major occupation of some of the fishing families of the islands. Due to some of the challenges faced, the number of families engaged in this line of work has reduced. These products are now mainly produced by the large scale fishing companies of the country.
Maldives export fish in fresh, frozen and also in different processed forms. Canned tuna accounts for almost half of the exports whereas dried fish export accounts for about 34% of the exports (Corporate Maldives, 2018). The main export nations are Sri Lanka, Thailand, countries of Europe and Middle east. Dry fish was the main export before the industrialization started, and they were mainly imported by Sri Lanka and southern states of India.
In order to increase the involvement of local fishing community and help them in generating a better income, the president of Maldives has ratified the Maldives fisheries bill on the 5th of September 2019 (President Office, 2019). The main theme of the bill is to build a local fish factory or referred to as “Geydhoshu Mas Factory”, where they will establish ice plants in the local islands along with fish processing plants.
This review will mainly discuss on the challenges faced to local fishing community in the fish drying process and will propose a solution to overcome this problem. The proposed solution will maximize the usage of a renewable source of energy in order to reduce the cost of production and will also help in the designing of an environmentally friendly solution.
Fish drying is one of the oldest and traditional method of preserving fish used in the Asian countries. Due to the microorganisms that lives in the digestive tracts gills of fish, they are susceptible to the food poisoning bacteria development. Drying them not only preserve the fish for a longer period, but also improves the nutritional quality of them compared to the raw flesh as per weight (Faruque, et al., 2012).
The most common type of fish caught by the Maldivian fishermen are skipjack, yellowfin, bigeye, frigate and kawakawa tuna (Ahusan, et al., 2018). Frigate and kawakawa are mainly used to produce the dry fish due to the smaller size compared with the others. Fresh skipjack and yellowfin tuna are usually sold to commercial fisheries sector as this is the main source of income for the fishermen.
In the small fishing family businesses, fish drying process takes place in different stages and the work is carried out by both genders, but complementary based on the physicality required.
It is only men that is involved in the fishing stage and after bringing them in to the islands, both men and women engages in the cleaning and filleting stage. The women take responsibility in boiling and smoking of the fish. Furthermore, they also manage the drying stages which involves arrangement of sun drying beds (Wessels, 2017). The team work manages to function small business, prior to the decline in fishing sector among small local businesses.
2. Methods of preservation
Before the drying process begins, fish is boiled by the locals of Maldives. This will kill the spoilage bacteria that is present in the fish. However, there is a side effect of killing the spoilage bacteria as it would lead way to develop new pathogenic bacteria in the food (FDA, 2011). To avoid this, commercially preserved fish are further heat treated in a process called retorting where it eliminates food borne pathogens.
The boiled fish are usually ready to eat or are ready for the smoking and drying process. The cooked fish are smoked right above the cooking stoves where it is fueled with dry wood. This is where the drying procedure starts. Here, drying is referred to the removal of water from the fish meat, so that it does not provide an environment for microorganisms to grow.
The smoked fish are arranged on the fish beds placed in the direct sun for air drying. The heat from the sun evaporates the water inside the fish, hardening them. This is the most common practice of drying fish especially in the rural populations of Asian countries. The eastern costal nations of Africa also use this method to preserve fish and is backed by the resilient program carried out by the United Nation in these areas (Savins, 2017).
Besides sun drying, there are other methods of fish preservation practiced by local communities. Common salt is used as a preservative since it is non-toxic and it can draw water out of the cells by osmosis process. In addition, salt is readily available in most countries and are cheaper to purchase.
Fish can also be smoked to preserve and is common in the Maldives. For this method, the cleaned fish is cooked in a brine solution. The cooked fish will be transferred to the racks right above the cooking stoves. The heat and the smoke from the stoves dry them leaving the fish with a desirable taste and smell. This smoked fish can be further dried in the sun, preserving them along with the taste (hunterfact, 2012).
Large scale businesses are able to preserve their stock in freezers. This is impractical for small family businesses due to the large costs associated with this method. However, this would not be a problem for larger businesses due to the man power and their ability to produce a diversified product.
Fish drying as a business can be profitable for smaller fishing families given that there is a regular supply of raw materials. However, with the involvement of more private companies in the fisheries sector, it has the limited the access to fish supply for local artisanal producers (Hohne-Sparborth, Adam, & Ziyad, 2015). In addition, there are other challenges like maintaining the hygiene of the products that should meet up with the export conditions.
2.1 Challenges to local communities
The last decade has seen a negative trend in the number of fishermen active in the business except in the year 2017 (Statistical Pocket Book, 2018). On the other hand, the number of private companies in the fisheries sector increased during this period (Hohne-Sparborth, Adam, & Ziyad, 2015). This could be one massive challenge for the local fisheries businesses where it limits the supply of fish for drying. The modern fishing vessels are capable of staying on the water for longer periods and they have preferred to sell them to these fisheries companies for their convenience and other commercial benefits. There is less risk of wasting their catch if it is sold to the larger companies rather than the small local businesses.
This is a rather possible situation since smaller business are limited with labor force and money. Further challenge confronted is the land space available to establish these business.
The islands of Maldives are small in size, where only thirteen islands are greater than 2 square kilometers (MFA, n.d.). Some of the islands in the atolls have not been able to provide land space for even housing needs of the growing population for more than 30 years. This is a major setback in sustaining the small fisheries families that earns an income on preparing dry fish.
2.2 Interview with the local community
An interview was carried out with 2 families from HDh.Hanimaadhoo that were involved in the fish drying business to identify some of the challenges they had faced. One family (family 1) processed about a ton of fish per month whereas the other family (family 2) was involved in more than five tons depending on the supply and their labor force. The issue of lack of space was brought up by family 2.
The concern of heavy work load in the production of dried fish was raised by both families.
Besides the health concerns during the cooking and smoking of raw fish, an extensive amount of work has to be done to spread the fish on the drying racks in the sun. This was further challenged up by the sudden showers in the long southwest monsoon of Maldives and the number of days required to dry them. On average, it requires 7 sunny days for them to completely dry a product batch.
In order to meet up with the export requirements, special care has to be taken of the products especially during the drying process. The open area becomes an extra burden due to dust being accumulated on the fish. In addition, they were not safe from animals like rodents and birds. There has been theft occurrence, but not in large quantity. This is viable to happen since the racks are kept in open area and it is not possible to keep an eye on them all the time.
Adding security is bound to increase the production cost or work load.
It is important to note that the total monthly income generated is quite high compared to other jobs in the region. Family 1 was able to generate between 20-30 thousand Maldivian rufiyaa, where is the family 2 with a wider scale of production generates more than 30 thousand Maldivian rufiyaa per month. This is not directly from dried fish only, but other sub products of fish accounts for the total income. The heavy work load and the other challenges faced in the work line has deviated families from being involved in the fishing industry and has chosen other opportunities like the tourism industry. However, they are willing to continue to work in the fishing industry, if they can find an alternative method that would fix the currently faced challenges.
2.3 Commercial Fish dryers
Most of the commercial fish dryers work on the electricity or gas. Depending on the size and quality of the machines, the product prices ranges from 2000 to 10000 US dollars. The industrial scale machines cost as much as 350’000 US dollars. China and India leads the manufacturing and the prices quoted refers to the prices from Alibaba website. Besides the setup cost, these machines are rated between 5-20kW, which would result in an increase in cost of production. Investing on a smaller sized machine would be profitable in the longer run for the fishing families. However, the intention of the project is to develop an environmental friendly solution.
2.4 Home-made fish dryers
Home designed fish dryer projects have been carried out different developing countries. A project carried out in Nigeria, by the West Agricultural Productivity Program in collaboration with the Islamic Development Bank, developed a smoking kiln which was able to smoke and dry fish in them. The kiln consists of a smoking/drying section and a separate section for charcoal burning. It is a common practice in Nigeria to smoke and dry the fish products simultaneously unlike in Maldives where drying takes place as the last process. These compartments are made of steel. A fan is used to distribute heat evenly in the compartments and is run with the solar power (Walla, 2018). Due to the success of this program, many west African countries are using similar machines to preserve fish.
The main objective of the project is to develop a system that depends on the heat from the sun rather than a conventional heating method. A research program carried in coastal regions of Maharashtra of India used a fish dryer fully dependable on the sun’s energy (figure 1). The system comprises of a drying compartment with retractable trays and air inlets and outlets.
The system was covered with an UV-stabilized 200µ plastic film which traps the solar energy required to dry the contents on the racks placed vertically (Sengar, Khandetod, & Mohod, 2009). This method resulted in drying the contents twice as faster and the color and texture of the dried products were better than the sun dried products. This is also a cheaper option, but the weaker film material limits security of the system.
Figure 1: Low cost solar dryer in Mahrashtra (Sengar, Khandetod, & Mohod, 2009)
Solar water heaters are very common in households, especially in temperate and tropical climates. China ranks the first in terms of total capacity and Cyprus and Israel have the highest capacity per capita (Enerdata, 2012). Solar heaters work on the principle of collecting infrared heat in the box where copper tubes are kept. Water running through the tubes collects heat and is then transferred to the hot water tank or for consumption. The top of the collector is covered with glass or plastic sheet to prevent heat loss. Both glass and plastics has a good transmittance value, but plastics are more prone to higher temperature and time (Reysa, 2008).
The same heating principle can be applied to a fish or fruit drying machine and has been practiced in many farms for dehydrating food. The solar collector is painted in black and the air collected in this box gets heated up and is pushed in to the food compartments. There is no fan installed for air movement, but largely depends on the convection properties air.
Unlike the fish drying kiln used in western Africa, this dehydrator uses a wooden box instead of metals. Some of the models uses aluminum foil in the internal walls of the chamber only leaving the air flow vents. Wood is an ideal material for the compartments as it is a very good insulator. The thermal conductivity of wood is 0.12 W/m°C whereas it is 50.2W/m°C for steel (Thermal Conductivity, n.d.). The inside of the solar collector is painted in black color to absorb the maximum heat. This would achieve a higher air temperature in this chamber.
Figure 2: A solar dryer used to dehydrate fruits (Hoyt, 2018).
3. Design and testing
3.1 Proposed prototype
In order to meet up with the objectives of this project, the different solar drying methods used in different parts of the world will be considered in to the development of the prototype. The design will omit the usage of any conventional fuels. Therefore, only solar heating will be implemented. This will be similar to the solar water heater’s heat collecting panel, where the compartment will be painted black for maximum heat absorption.
The device can be tested with installing heat conducting materials like copper tubes or the aluminum fins used in the air conditioners for heat capture. The solar collectors top will be covered with acrylic for testing only, since solar heat can damage acrylic easily. Glass of around 4-5mm will be used on the solar collector as this is most efficient thickness. However, special care has to be taken while handling glass of this thickness (Bakarai, Rawaichi, &
Karoli, 2014). Air movement inside the solar collector will be controlled by a 12V DC fan attached at the air inlet.
The frame of the dryer will be made from steel, including the door. For additional security, the door will have a locking feature. Fish will be stacked in retractable trays, made of a metal mesh. This will allow air flow throughout the drying chamber. Air will go out of the vents placed at the top of the chamber. The chamber will have a roof, which comprises of a solar panel to run the air inlet fan.
Figure 3: proposed design of the solar heater prototype
A thermometer kept inside the drying chamber will measure the temperature. It is estimated that 60-90°C will give a good quality dried fish, but also depends on other factors like the humidity (Komolafe, Oluwaleye, Adejumo, & Oladapo, 2013).
3.2 Testing
Testing was only carried out with a thermometer to see if the required range of temperature can be achieved. The time taken for a specific weight of fish was not measured as planned previously due to the limited time and resource availability.
A XinTang oven thermometer was used to measure the temperature of the drying compartment. The volume of the chamber is 2 cubic feet.The range of thermometer was 0 - 120°C with divisions of 1°C. Table 1 shows the temperature measurements on the following testing methods. The time taken for each readings was 15 minutes.
a. Air Temperature: The thermometer was left in the open air. The temperature recorded at that time by Maldives Meteorological Service, MMS was 31.8°C.
b. Drying Chamber Only: The solar heat collector was disconnected and the drying chamber’s temperature is measured.
c. With Solar Heater connected: The solar heater painted in black was connected to the drying unit and the temperature inside the dryer is measured.
d. With fan: The fan is used to drive the hot air in to the chamber. The thermometer measures the temperature inside the chamber at different fan speeds.
Table 1: Temperature recordings on different testing methods used
Method Temperature °C Calibrated Readings °C
a. Air temperature 31 31
b. Drying chamber only 39 40
c. With solar heat collector 55 58
d. With fan 45-49 45-50
The thermometer was calibrated at the MMS, by comparing with a meteorological thermometer as shown in table 1. This is important since it is unable to confirm that the XinTang thermometer used is a calibrated device as per the required standards. The
meteorological thermometers used in MMS are calibrated and certified devices. This values will be used in the discussion.
Figure 4: Prototype during the testing
4. Results and Discussions
The air temperature of testing time and day was 31°C and was similar to the recorded readings at Hulhule’ MMS observatory. The chamber was left in the sun without the heating part connected and the temperature that itself generated was found out to be 40°C. Upon connecting with the heat collector, the temperature rose to 58°C. This is a degree higher than the temperature obtained with the usage of UV stabilized solar tent (Sengar, Khandetod, &
Mohod, 2009).
The tests were continued with a fan, by varying speeds using a potentiometer. The idea was to help with the convection process, to push the hot air inside the collector into the drying chamber. However, the temperature decreased to 45°C at maximum fan power and 50°C at minimum fan speed.
Instead of helping with the convection, the fan acted as a cooler which resulted in the reduction in measured temperature. The initial plan was to stack sheets of metal fins that would absorb more heat and use the fan to push this heat in to the drying chamber. It is not recommended to use the fan with the current prototype and more testing is required to see its affect with the additional heat collecting elements.
Positive results have been obtained at Mahrashtra, India, with a maximum temperature of 57°C achieved in the drying room. The 58°C achieved with the prototype maintained its temperature for the total testing time of 30 minutes. Further improvements can improve the temperature inside the dryer.
The following information about the cooked raw fish must be taken to find the moisture content and the drying rates in a specific volume. The reason behind this is to achieve the required moisture content of 10-20% (Hussain, et al., 1992).
- Initial weigh of the fish to be dried - Final weight of the dried fish - Time take to dry the fish
The temperature generated in the drying chamber will dry cooked fish within 15 hours of sun (Sengar, Khandetod, & Mohod, 2009). This an improvement compared to the 7 days of fish drying in direct sun. The aim of the project is to decrease the time more and can be done with new modifications. The dryer can be stacked with copper tubes or aluminum fins used in the air conditioning units. These metals can be painted in black to maximize the heat absorption.
Further testing needs to be carried out to see the use of a fan to direct heat into the chamber will increase the dryer temperature or not. The current prototype showed negative performance with the use of a fan. Therefore, the fan and the use of a solar panel to power the fan is not required for this function.
The disadvantage of the current system is that it is unable to work without the sun. However, a heating element can be installed, that will be powered with grid AC. This does not fulfil the aims and objectives of the project but will be useful if the rainy period prevails.
5. Conclusion
Fishing is an important part of the culture of the Maldives. With the right opportunities and policies, more families can engage in this business especially in the islands. The main objective of this project is to overcome the challenges faced to the small communities and developing this product will ensure a better and easier conditions for fish processors. Similar projects have been a success in the developing nations and it can also be implemented in the Maldives. The prototype was able to achieve the maximum temperatures that other similar solar fish drying machines operate on, but did not reach the targeted 60-90 degrees. Further improvements to the design can increase this temperature to the target values.
References
Ahusan, M., Shiham, A. M., Ziyad, A., Shifaz, A., Shimal, M., & Jauharee, R. (2018).
Maldives National Report to the Scientific Committee of the Indian Ocean Tuna Commission. Male': Ministry of Fisheries and Agriculture.
Bakarai, R., Rawaichi, M. J., & Karoli, N. N. (2014). Effect of Glass Thickness on Performance of Flat Plate Solar Collectors for Fruits Drying. Journal of energy.
Corporate Maldives. (2018, June 14). Retrieved from https://corporatemaldives.com/the- current-trend-in-maldives-fisheries-industry/
Enerdata. (2012, January 3). Solar water heating in the world. Retrieved from Enerdata:
https://www.enerdata.net/publications/executive-briefing/solar-water-heating- world.html
Faruque, O. M., Nazrul, S., Tonny, U. S., Islam, R., Dey, S. C., Mona, S. J., & Saha, D.
(2012). Status of an ideal dry fish market of Bangladesh: A study on Asadganj dry fish market, Chittagong. International Journal of Life Sciences Biotechnology and Pharma Research, 214-225.
FDA. (2011). Pathogenic Bacteria Survival Through Cooking or Pasteurization . In FDA, Fish and Fishery Products Hazard and Controls Guidance (p. 315). Food and Drug Administration.
Hohne-Sparborth, T., Adam, M. S., & Ziyad, A. (2015). A SOCIO-ECONOMIC ASSESSMENT OF THE TUNA FISHERIES IN THE MALDIVES. London:
Sainsbury.
Hoyt, D. (2018). Solar Dehydrator Plans. Retrieved from Permies:
https://permies.com/t/solar-dehydrator
hunterfact. (2012, September 3). Different Methods of Preserving Fish. Retrieved from Knoji: https://cooking.knoji.com/different-methods-of-preserving-fish/
Hussain, M. M., Karim, A., Alam, Z., Islam, M. M., Khan, A., & Hossain, A. (1992). Effect of pre-treatment on the drying of Ghonia fish Labeo ghonius in the open sun and in a tent. Bangladesh Journal of Zoology, 231-238.
Komolafe, C. A., Oluwaleye, I. O., Adejumo, A. O., & Oladapo, M. O. (2013). Effects of drying Temperatures on the Quality of Three Tilapia Fish Species. International Journal of scientific research and management, 371-375.
Maldives Insider. (2019, February 10). Retrieved from Maldives Insider:
http://maldives.net.mv/29628/maldives-to-open-20-new-resorts-in-2019/
MFA. (n.d.). Atolls of Maldives. Retrieved from Atolls of Maldives:
http://www.atollsofmaldives.gov.mv/
President Office. (2019, September 16). Retrieved from President's Office:
https://presidency.gov.mv/Press/Article/22168
Reysa, G. (2008, June 8). Solar Collector Glazing Materials. Retrieved from Build it solar:
https://www.builditsolar.com/Projects/SpaceHeating/Glazing.htm
Savins, M. (2017). Sun-dried fish production to build resilient coastal communities in Somalia. FAO.
Sengar, S. H., Khandetod, Y. P., & Mohod, A. G. (2009). Low cost solar dryer for fish.
African Journal of Environmental Science and Technology, 265-271.
Statistical Pocket Book. (2018). Male: National Bureau of Statistics.
Thermal Conductivity. (n.d.). Retrieved from Hyperphysics: http://hyperphysics.phy- astr.gsu.edu/hbase/Tables/thrcn.html
Walla, K. (2018, October). Kiln Changes Up the Tradition of Fish Smoking in West Africa.
Retrieved from Food Tank: https://foodtank.com/news/2018/10/smoking-fish-kiln-coraf/
Wessels, P. (2017). THE ROLES OF WOMEN IN MALDIVIAN ONE-BY-ONE TUNA FISHERIES: A SCOPING STUDY . Dalhousie University, International Pole & Line Foundation.
