Low Cost Solar Dryers

Grekkon Limited is the largest supplier of  low cost solar dryers for agricultural products in Kenya .  These low cost solar dryers work on solar strength, and are also augmented with a biomass heat unit if so desired by the client. Our agricultural solar dryers design is according to the product, location, and drying volume per session.

These passive or active solar dryers for fruits and vegetables are fixed or portable as the user needs it. The fixed ones are large and impractical to move about, while the portable one are small domestic drying units

Solar dried mango slices

Low Cost Solar Dryers in Kenya

Grekkon limited designs and constructs both passive/ natural circulation, and active/ forced circulation low cost solar dryers for agricultural products. The passive solar dryers have no additional mechanical input, while the active dryers do. Active solar dryers are also know as hybrid solar dryers. Their additional mechanical inputs are;  a biomass heating unit, or solar powered exhaust plus extraction fans, and synchronizers. A hybrid solar dryer will have one (solar system or biomass heater) of these enhancements, or both. These enhance drying time by 30% to 100% compared to passive drying. Attached biomass heating units allow for night time drying, or on cloudy/ rainy days.

Solar Dryer Materials

• Light UV treated translucent polythene paper to allow heat and light. The paper also has anti-drip treatment to prevent dew formation which causes moulds to form on food
• Heavy UV treated geomembrane to conserve heat
• Steel bars galvanized with food-grade aluminum or zinc for food safety
• UV treated heavy gauge netting to prevent insect pests from entering

A simple portable solar dryer under construction by the Grekkon technical team at Rusinga Island, Homa Bay county. The local community will dry bananas for processing into flour

Below are 2 videos: The first one is of a farmer in Homa-bay county, western Kenya using a community passive/ natural circulation solar dryer to add value to banana produce. The second one is of a mango processor in Taita Taveta county at the county’s coast with an active/ forced circulation dryer. Both solar dryers are by Grekkon Limited.

Video 1.   Video 2.  

Our low cost solar dryers have shelves at different levels depending on the volume or weight of food crops to dry per session.

Low Cost Solar Dryer Design

What is the working principle of a solar dryer?

1. Passive/ Natural Circulation Food Solar Dryer

Grekkon Limited solar dryers work in the following steps;

i. Capture & collect the sun’s heat

ii. Create a ‘greenhouse effect’ which causes moisture loss from the produce

iii. Air coming into the dryer exits with this moisture from the vent

2 Active/ Forced Circulation Food Solar Dryer

In addition to what takes place in the passive solar drying unit, the fans force in hot air from outside, and force out hotter air combined with moisture from inside the dryer. At night or on cloudy/ rainy days, the biomass unit supplies the drying heat.

Pros and cons of a low cost solar dryer in Kenya

1. Speed of drying. Food dries four to five times faster.
2. Quality. As the sun’s UV rays do not get into direct contact with the drying food, the food’s; color, taste, scent, and nutritional value is unaffected
3. Cleanliness. The food is free from dust, sand, or other external contaminants
4. No pests. Insect, bird, or mammalian pests have no access to food in the dryer, so no attack occurs
5. It is more expensive to build and maintain than open-air drying

Solar dried chilli peppers

 Low Cost Solar Dryers

FAQs

III. What do a low cost solar dryers do?

Grekkon Limited’s solar dryers reduce the moisture content to less than 12% in these products;

• Plantation crops; coffee, rice, cassava
• Vegetables; tomato, onion, garlic, brassicas, hot peppers
• Cereals; sorghum, and millet
• Herbs; moringa, mint, rosemary
• Oil crops; groundnuts, sunflower, macadamia, cashew nuts
• Others; mushrooms, fish, beef, mutton

IV. How do you dry vegetables with solar?

• Wash the vegetables to remove all dirt
• Ensure there are no insect pests present
• Remove any diseased parts or produce
• Cut or grind them into smaller pieces to increase the drying surface area

Place them in the solar dryer holding trays

Dry cassava chips

V. What is the most popular use of low cost solar dryers?

To dry fruits, mushrooms, vegetables, herbs, spices, coffee, cassava, banana and fish. Banana and cassava are further processed into food flour. A solar dryer ensures that the food is free of any external contamination

VI. What are the main applications of a solar dryer?

Besides vegetables and fruits, commercial solar dryers in Kenya are for fish, root crops and mushroom drying. Commonly dried foods in Kenya through our solar dryers are:

i. Banana, cassava, pumpkin, millet, and sorghum to make food flour. Dried cassava is also processed for industrial starch manufacture

ii. Moringa as a medicinal herb

iii. Tomato, capsicum, traditional vegetables, kales, and spinach  as vegetable nutrients

iv.  Mango, papaya, as dried fruits for snacking

v.  Omena which is the silver cyprinid fish for both human consumption, and as additive to animal feed

vi. Coffee so that it’s suitable for milling. Coffee solar dryers are the largest, each holding over 5 tons of berries per drying session

Hybrid Solar Dryers For Sale In Kenya

Hybrid solar dryers for sale in Kenya by Grekkon Limited are active dryers designed to dry quicker, all year round. They are augmented units of the conventional passive solar dryers. The company has three types of hybrid solar dryers for sale in Kenya

1. Solar powered. These units have a solar powering system that runs the extraction and exhaust fans. The fans provide better movement of air within the dryer, and removal of the moisture from the drying produce. This hastens the drying process
2. Biomass powered. They have a biomass burning unit connected on the exterior. Biomass in the form of brickettes or charcoal heats water which produces steam that travels in tubes within the dryer. This heats up the air in the dryer, accelerating the dring process. Biomass powered dryers can be used at night or on cloudy, rainy or cold days when there is insufficient sunshine to dry

These hybrid solar dryers cost in Kenya ranges from Kes 135,000 to Kes 1,500,000. These hybrid solar dryers for sale in Kenya are for a carrying capacity of 100kgs through 1,000kgs

Hybrid Solar Dryers For Sale In Kenya

Solar Dryer Materials

• Light UV treated translucent polythene paper to allow heat and light. The paper also has anti-drip treatment to prevent dew formation which causes moulds to form on food
• Heavy UV treated geomembrane to conserve heat
• Steel bars galvanized with food-grade aluminum or zinc for food safety
• UV treated heavy gauge netting to prevent insect pests from entering

A hybrid solar dryerwith both an external biomass heating units, and a solar power system

 Hybrid Solar Dryers For Sale In Kenya

I. What is hybrid solar dryer?

It is a conventional solar dryer that receives additional drying power from an external source. This could be biomass, solar or electricity

II. What are the three types of solar dryers?

• Natural / conventional solar dryers. These dry using only the power of the sun
• Forced  / active dryers. They are augmented versions of the conventional solar dryers
• Portable or fixed solar dryers

IV. What does a solar dryer do?

Grekkon Limited’s solar dryers reduce the moisture content to less than 12% in these products;

• Plantation crops; coffee, rice, cassava
• Vegetables; tomato, onion, garlic, brassicas, hot peppers
• Cereals; sorghum, and millet
• Herbs; moringa, mint, rosemary
• Oil crops; groundnuts, sunflower, macadamia, cashew nuts
• Others; mushrooms, fish, beef, mutton

V. How do you dry vegetables with solar?

• Wash the vegetables to remove all dirt
• Ensure there are no insect pests present
• Remove any diseased parts or produce
• Cut or grind them into smaller pieces to increase the drying surface area

Place them in the solar dryer holding trays

Dry cassava chips

VI. What is the most popular use of solar dryers?

To dry fruits, mushrooms, vegetables, herbs, spices, coffee, cassava, banana and fish. Banana and cassava are further processed into food flour. A solar dryer ensures that the food is free of any external contamination

VII. What are the main applications of a solar dryer?

Besides vegetables and fruits, commercial solar dryers in Kenya are for fish, root crops and mushroom drying. Commonly dried foods in Kenya through our solar dryers are:

i. Banana, cassava, pumpkin, millet, and sorghum to make food flour. Dried cassava is also processed for industrial starch manufacture

ii. Moringa as a medicinal herb

iii. Tomato, capsicum, traditional vegetables, kales, and spinach  as vegetable nutrients

iv.  Mango, papaya, as dried fruits for snacking

v.  Omena which is the silver cyprinid fish for both human consumption, and as additive to animal feed

vi. Coffee so that it’s suitable for milling. Coffee solar dryers are the largest, each holding over 5 tons of berries per drying session

Solar Dryers For Coffee In Kenya

Solar dryers for coffee in Kenya by Grekkon Limited improve the drying efficiency of harvested coffee cherry. In Kenya, harvested cherry is largely manually open dried which takes 10 – 14 days depending on the location and the prevailing temperatures. Open coffee drying is done on wooden raised table structures with a wire mesh bed laid out where the coffee cherry is spread thinly. The coffee cherry is dried by direct solar radiation and wind movement

Cost of solar dryers for coffee in Kenya

The overall cost of a solar dryer depends on the size. The average price of a large solar dryer for coffee in Kenya is Kes 1,200/M square

Challenges of open coffee drying

• it is labour intensive. This is needed to turn it over every 45 minutes to 1 hour on the bed to ensure eveness of drying, covering it in the evening or on rainy days with a polythene cover to prevent moisture entry. This increases the cost of coffee erries drying
• quality degradation as a result of moisture entry, dirt, elements of nature, and other contaminants
• it requires lots of space because the beds cannot be designed in a storeyed manner
• none uniformity of drying because it is turned over by hand on the raised drying beds

Open drying of coffee cherries in a coffee factory in western Kenya

The key advantage of open sun drying of coffee is that it is cheap, and has zero CO2 emissions

The coffee is dried from 60% to 10% – 11% moisture level. There are six stages in cofee drying

1) Skin drying. Moisture 55-45%.
2) White Stage drying. Moisture 44-33%.
3) Soft Black stage. Moisture 32-22%.
4) Medium Black Stage. Moisture 21-16%
5) Hard Black Stage. Moisture 15-12%
6) Fully dry coffee and conditioning. 11-10%

Coffee drying is a post-harvest handling process where the coffee quality is preserved instead of improving it. Different temperature limits are allowed for different coffee processing methods. Moisture level are checked to prevent moulding on the drying coffee

Solar dryers for coffee in Kenya by Grekkon Limited provide a low cost, efficient, zero CO2 emissions, and a clean way to dry cofee cherry. The use of solar dryers mitigates against the challenges faced under open sun drying.

How does a solar dryer for coffee work?

1. Air in the dryer in contact with the coffee is heated through solar radiation

2. Moisture in the coffee beans rises and is expelled through a ventilation

The temperature in the coffee solar dryer is on or about double that of the ambient temperature

Benefts of a solar dryer for coffee

• the coffee beans are not tuned over manually to achieve eveness of drying. This cuts out the huge labor cost coffee factories incur during coffee drying. Eveness of drying is well achieved as hot air dries every bean uniformly
• there is no external mositure entry especially from rain. This removes any occurence of moulding or mildew
• coffee dries at half the time or less that it would take under direct sun drying. This reduced drying time saves on operational costs
• there are no external contaminants

The exterior of a solar dryer built in a coffee factory by Grekkon Limited

• the polythene paper cover used has UV block treatment which preserves the quality of the coffee bean. It also has anti-drip attributes, so that dew does not form on it, then drop on the coffee
• space is eficiently used because the drying racks are stacked up over each other, unlike in open sun drying where each coffee cherry must make contact with the sun’s rays to dry
• in areas where coffee theft in factories is rampant, the solar dryer can be locked to prevent entry. This is not possible under open sun drying
• drying goes on even in hazy, cloudy or rainy conditions. Coffee is thus dried anytime of the year, creating drying efficiencies for the coffee factory

Demerits of a dryer for coffee

• it is expensive to isntall
• the polythene cover has to be changed every 3 -4 years when the UV block treatment has worn off
• it is uncomfortable to work in during the day as the internal temperature is high
• where care is not taken, over-drying of coffee may happen, which reduces its quality and its subsequent market price. A moisturemeter should always be used in the drying process to prevent this
• it requires maintainance, such as replacing the UV block treated polythene sheet every 3 years, when the UV block treatment degrades

A coffee solar dryer working principle

A conventional coffee solar dryer can be enhanced with solar module powered extraction, and exhaust fans, which converts it to a hybrid coffee solar dryer. This will further improve on the drying time as moisture is extracted faster. However, due to the large size of the unit, it is an expensive undertaking. It is largely used in smaller fish, herbs, spices,vegetable and fruit solar dryers

How to install solar dryers for coffee

• create raised tables from timber or galvanised steel not more than 1M in width. The length is as much as can be done. These tables can be storeyed upto 3 levels with vertical gaps of 0.75M – 1M between the levels. The horizontal distance from a table to another is 0.5M
• lay a food grade wire mesh over the tables to hold the coffee. A shade net or insect net can be used. The reason a perforated membrane is laid is to allow for free drying air movement on the beans
• construct the galvanised steel framework over these tables to amaximum mid height of 5M
• lay the greenhouse polythene paper over the steel frame
• place an insect net in the air entry and exit points. An insect net prevents entry of insect pests

A 2 level table bed coffee dryer by Grekkon Limited in Kagumoini area, Nyeri county

Grekkon Limited provides training on proper coffee drying in a solar dryer, and also on the maintainance and managemnt of the solar drying unit after installation to coffee societies in Kenya
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