Solar Dryer extends harvest and creates microenterprise opportunity

Elyse Peterson is an experienced food scientist in the dairy, seafood, meat, and soft drink industries, Elyse served two terms in the Peace Corps helping promote sustainable food security solutions. As part of her work in the Peace Corps, she helped to develop a Solar Food Dryer which became the catalyst for a community-based food security and economic development project in in Antigua.

We talked to Elyse about this technology, which is highly appropriate for many tropical areas, and may have application into other climate zones:

Photo: Mangoes drying in the sun.

 

TBG: How does Solar Food Drying work?
Solar drying is a low cost method of drying food.  It is important to understand moisture in food and the properties of the air around us.

All food contains moisture which comes in three forms: liquid, solid & gas.  This moisture is what microorganisms need to live and thrive, so in order to stop microorganism growth you may reduce this moisture to a safe level to preserve and extend the shelf-life of your harvest.

The design of the Solar Dryer harnesses the power of the sun's rays to raise temperatures within the unit to between 110 - 130 degrees Farenheit. 

This heat lowers relative humidity while increasing absolute humidity, so that the air inside the unit attempts to reach the absolute humidity of the climate outside the unit by taking moisture from the food.

Coupled with proper air circulation, this is what makes the solar dryer work.

Photo: Solar dryer built with locally available materials in Antigua, 2007.

TGB: What kind of Solar Dryer Designs have you developed?

There are three basic designs of solar dryers that you may follow when building your own solar dryer: direct absorption, indirect heating, and mixed mode. In this project a direct absorption solar dryer was designed because it was found to be the most sustainable for Hawaii’s needs.

In these designs the food is placed inside a cabinet or “hot box” which allows the rays of the sun to heat up food and air around it. A compartment with a transparent roof and insulated walls is used, but if designed properly all the walls can be transparent. These may also use reflectors at the bottom of the compartment to increase light (metal or foil).

Ventilation holes are required to promote proper air circulation. Indirect heating dryers dry the food with heated air collected by a “solar panel”. The food is placed in an insulated heating chamber with proper air circulation.

These models are effective but cost a lot of money. Mixed Mode dryers are a combination of the other two designs. Food is heated directly by the sun but additional heat is collected with the “solar panel”. These can cost about $1300EC to build, effective but expensive.

Businesses attempting to expand and produce higher quality products should look into building one of these models (for the purposes of this project and the situation in Hawaii the direct absorption model is the best fit). When constructing your dryer be sure to follow the design carefully, because the angles achieved are vital for efficient processing.

Photo: Mangoes selected for drying are peeled and cut.

TGB: How do we select produce to dry?
When selecting food to process in the solar dryer it is important to remember that drying will not improve the quality of the produce. Only produce that you would consume fresh should be dried.

Produce with cuts, bruises, or other evidence of contamination should not be used. Select fruit that is ripe yet firm. Using over-ripe fruit can cause the final product to come out brown and sticky. Ripeness is about 2/3 ripe.

Photo: Mango is prepared for dehydration in the Solar Dryer.

TGB: How do we prepare produce for drying?
Produce shall be soaked in a bleach solution to remove microbial contamination (1 tsp bleach in 1 gallon water). Peel fruits and cut into appropriate sized pieces. The smaller the size piece the faster the drying time. As the size of the piece increases the time for drying grows exponentially.

Example: A slice or piece two times larger with take four times longer to dry. Experiment with your dryer to see what size piece is the best.

TGB: Doesn't that mean we will be eating bleach? 

There are alternative methods for sanitation, but bleach is the most available and inexpensive. One must remember that bleach is highly volatile. It evaporates into the air, so there is essentially no bleach on the product by the time we eat it. This is a standard practice in the food industry that many of us don't know about but owe our safety to.

 

Photo: Uncle Clay's House of Pure Aloha utilizes the Solar Dryer.

TGB: Does it work in the rain? How long does it take?
No.  The dryer should only be used on days with consistent powerful sun as to reduce the time required for drying. Depending on the results you may find it necessary to rotate the trays throughout the day so every tray gets equal amounts of direct sun exposure.

Drying should take about 12 hours of full sun power (possibly one day with good sun). Optimal temperature for solid drying is 110-120°F but 130°F will be the most effective temperature. Putting a thermometer in the dryer during processing is a  safe way of monitoring the efficiency of your dryer.

Keep a close eye on the produce towards the end of drying because drying happens at a faster rate just before it’s reached 10% moisture. To test for doneness you should see that vegetables at about 10% moisture will be brittle and easily can be broken apart.

Fruits should be soft and chewy, but test the moisture content to verify 5-8% moisture (refer to Principles of Solar Drying). There are a few quality issues that need to be considered when solar drying produce.

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For more information and detailed instructions on how to build your own Solar Food Dryerin Hawaii, download the Solar Dryer Manual here:

solar-dryer-manual-hawaii.pdf Download this file

Greens in April, in Mongolia...?

Photo: Raddishes have been harvested since early April in the GERES' Passive solar greenhouse R&D site in Ulaanbaatar.

From GERES' Community of Practice website, by Anne Randall:

 

The '“Food Security and Innovative Farming Approaches for Mongolia” Project (2010-2013, funded by the European Union) is led by a consortium of two French NGOs: Secours Catholique and GERES, who are working closely to support Mongolian NGO Caritas Mongolia.

 

The objective is to develop more efficient and diversified ways to grow vegetables at household level, in order to reduce the food insecurity which affects the most vulnerable families (1,000 families in Ulaanbaatar and in Gobi-Altai province).

 

Activities are intended to develop, implement and diffuse passive solar greenhouses (180 family and community greenhouses and 75 nurseries), improved techniques of soil and water management and bioclimatic cellars. GERES is bringing its technical expertise to the local partner during the first research and development phase on these 3 techniques. 

 

In Autumn 2010, a Research and Display Center was built in the middle of the peri-urban “yurt areas” [['ger districts' - TGB Editorial]] of Ulaanbaatar. The Research carried out in the center aims at testing:

1. The thermal performance of different designs of passive solar greenhouses.
2. Potential optimizations for solar greenhouses (ex: hotbeds for early seedlings, thermal storage in water tanks).
3. Improved soil and water management practices (ex: rainwater harvesting, windbreaks).

Photo: Ulaanbaatar peri-urban Research & Development site for passive solar greenhouse design.

 

At the same time, GERES has developed a new low-cost passive solar greenhouse design for peri-urban areas of Ulaanbaatar (see picture). The greenhouse size is relatively small (8,8 m*4,4m) compared to “usual rural solar greenhouses” diffused in Asia. The constraints (in terms of suitable space available) are high: the standard size of the plot is small (700m2), with a large amount of available area often already occupied by other structures.  Each plot is fenced with a 2 meters wood barrier and the orientation of the plot may not be suitable. 

 

The size has thus been adapted to fit the families’ site constraints while insuring a sufficient vegetable production meeting their needs.

 

Passive Solar Greenhouses represent a new technology in Mongolia and have aroused a big interest from Non-Governmental Organizations (NGOs) and Governmental Agencies, since the project's beginning. This shows promise for this resource’s development in the country.

 

In this early spring 2011, greenhouses began their first full growing season. Thermal and agronomic performances tested since last autumn are revealing first results that meet our expectations. 

 

Research greenhouses can be used from late February to early December (we have to keep in mind that atmospheric pollution in Ulaanbaatar reduces winter solar radiations).

Photo: April 27, 2011.  Inside the Ulaanbaatar research greenhouse.

 

Family greenhouses can be used from mid-March for direct hardy vegetables seedling (radish, lettuce, turnip, spinach) and beginning of April for sensitive vegetables/fruits transplantation (tomatoes, cucumber, sweet pepper). At this date, greenhouses generally used in Ulaanbaatar (tunnel-type greenhouse) are frozen and usually start to be used from mid-May. Spring is a critical period regarding food security; thanks to these greenhouses, Ulaanbaatar families will be able to consume fresh and nutritive vegetables starting from April. 

Thermal performance inside Ulaanbaatar greenhouse from Mar 17 - 20, 2011. 

 

Some thermal data: At mid-March, during cold nights (minimum -20°C), the research greenhouse allows to gain 20°C and the family greenhouse allows to increase the temperature by 15°C. 

 

Prospects: Thermal results will allow us to compare the different designs performances and suggest relevant optimizations. The main objective for 2011 as regards to agronomic experimentations is to suggest a new schedule for farmers, which will be adapted to this longer cultivation season, in order to make a better use of the opportunity offered by the passive solar greenhouses.

 

Photo: Anne Randall inspects this season's early crops.

____________________________________________

For more information about the “Food Security and Innovative Farming Approaches for Mongolia” Project, contact:

 

 

Anne RANDALL

Agronomist/Technical Adviser Mongolia - Country Representative

 

GERES - Group for the Environment, Renewable Energy and Solidarity

Sukhbaatar District, 6th khoroo,

University street 11/1, Ulaanbaatar, Mongolia

P.O.Box-1353, Ulaanbaatar-13 Mongolia

Tel: (976)98105052

Mobile: (976)98080928

a.randall@geres.eu - www.geres.eu

 

 

Permaculture and Passive solar greenhouses in Ulaanbaatar (Day 21)

Note: All photos on this post are Copyright Pierre Thiriet 2010 and appear with permission of Pierre Thiriet.

Met with Anne Randall today, Agronomist/Technical Advisor at the French NGO Group for the Environment, Renewable Energy and Solidarity (GERES - pronounced 'jheh-rehz', not 'Gee-reez' - it's French after all!) to compare notes and share information between projects.

It's one of the simplest, most important things an NGO can do - share information with other NGOs working in the same area - so that learning curves can be accelerated (mistakes don't have to be made twice if shared), and projects can grow to flourish and complement each other.  Based upon our meeting today and the information shared from both sides, the potential for this to occur between the GERES and ADRA projects is significant.

Photo: GERES Research & Development Center in Ulaanbaatar.

GERES are the good folks that brought us the Passive Solar Greenhouse design in Ladakh which have achieved year-round vegetable production down to minus 25C at approximately 3,000 meters above sea level (and which we modeled during the Permaculture Design Training for the classes on passive solar greenhouse design).

Anne picked up on theGreenBackpack doing further research for her current project, which is to develop & implement a passive solar greenhouse design which can achieve year-round production in Mongolian conditions (illustrating, by the way, another permaculture principle: Multifunction, in which this daily log also functions as an informational resource, a networking tool, and a historical record for future volunteers and aid/development workers to build upon in Mongolia).

Since operating in Mongolian conditions from only August of last year, GERES has already achieved a 3-seasons greenhouse design, using a double-layered, concrete block / brick clad walls insulated with polystyrene (floor must be insulated too), single-sheet polyurethane plastic sheeting (imported from Korea, expected 2-year lifespan), a reflective 'solar blanket' type insulative layer for nighttime, and specially calculated steep-angled 'glass' (plastic) wall to maximize solar gain for Mongolia's latitude.

Photo: GERES 3-Season Greenhouse in Ulaanbaatar.

We shared and discussed challenges, mistakes, and lessons learned about our respective projects, and spent the next two hours brainstorming possible solutions for achieving year-round production within the greenhouse in Monoglian conditions.  Here's a quick list of some of the solutions we came up with:

• Build coldframes within greenhouses to create an even warmer microclimate within the coldframe.
• Use repurposed waste plastic bottles as inexpensive, readily available and durable cloches within the greenhouse to protect seedlings.
• Explore plastic bottle wall construction options for 'glass' wall to create 'double-glazing' effect with air tapped inside bottles.
• Re-using plastic bottles could help keep plastic out of waste stream (and prevent them from being burnt as winter fuel).
• Improved ger stove design will decrease pressure on fuel requirements and the family budget.
• Build root cellar under ger/house to maximize heating/cooling efficiency and security (root cellar must be dug deep enough to perform effectively).
• Household heating system could potentially be extended to heat root cellar and/or greenhouse.
• Establish windbreak/suntrap behind north wall using  fast-growing Populus laurifolia (Laurel-leafed poplar)  + Caragana (Siberian peashrub) species (keeping harsh Mongolian winds off greenhouse could help increase heat retention).
• Organic matter dropped from living windbreak can then be used to build soils within the greenhouse and hasha.
• Organic matter dropped from living windbreak can be used as cover material for pit latrines, for potential future use as 'humanure' (not currently culturally appropriate) .
• Build hot compost heaps (using dungs (such as chicken or goat) which are not used for fuel) inside the greenhouse to add heat biologically and relieve potential conflicts on precious 'fuel'-dungs.
• Chickens could be a valuable addition to a small-scale-intensive, passive solar greenhouse system, conditioning and building soil during winter season in a 3 or 4-season greenhouse, providing nutritionally and financially valuable eggs from March - October, plus meat and/or more chickens when needed.
• Drip-irrigation systems maximize water efficiency and increase thermal mass within greenhouse.
• Human urine from households can be diluted into drip-irrigation system to be used as a free and safe liquid fertilizer (provided all members of household are healthy).
• Raised beds within greenhouse make management and harvesting easier; line paths with dark rocks to increase thermal mass.
• Use planting guilds to maximize production from small-scale-intensively farmed space.
• Plant potatoes in stacks to maximize production and create more space for other crops.
• Cucumbers, squash, and other climbing/rambling crops can be trained up walls or across roofs to maximize growing space for other crops. 
• Alfalpha, oats, or a native 'green manure' species (such as vetch) can be planted around hasha perimeter to help build soils within hasha walls (and provide backup animal fodder).
• Local varieties of seabuckthorn and currants can be planted within windbreak of hasha walls to boost family nutrition. 
• Research cold-climate species native to comparable climates to maximize productivity (eg Lonicera caerulea edulis, or Blue honeysuckle is a highly nutritious, climbing berry native to Siberia that will tolerate minus 40C and produce down to minus 7C).
• Low-grade animal furs not suitable for commercial use may be a locally and readily available insulative material for floor that will break down and build soil over time.
• Coal ash may be a locally and readily available insulative material that could be substituted for polystyrene within the walls, though further research into how safe this material is must be conducted before being implemented.

Ideas were flying so fast & furious that I am sure there are a few things I've missed; the point is that when like minds collaborate towards a common goal,  

1 + 1 can = 3.

In other words:

None of us
Is as smart
As ALL of us.

Best wishes to Anne and the rest of the team at GERES-Mongolia, we hope to continue to support and collaborate with them towards achieving their project goal of building 180 passive solar greenhouse for family beneficiaries throughout Mongolia over the next two years.

A bientôt!

Photo: Inside GERES' research greenhouse.

 

List of useful web resources from Anne Randall (merci beaucoup!) to help you with your passive solar greenhouse design:

• *Sunchart: University of Oregon, Sunchart Program - http://solardat.uoregon.edu/SunChartProgram.html
• *To find easily the longitude and latitude of a point: http://itouchmap.com/latlong.html
• *To find the declination of a location: http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp
• *Good source of general info on solar greenhouses: http://attra.ncat.org/attra-pub/solar-gh.html

 

 

Passive solar greenhouse design: Bayan Ulgii v1.0

via slideshare.net

Slideshow designed to use as basis for session on passive solar greenhouse design.

Hand-drawn images are based on student designs from Mongolian Permaculture Project 2010.

Other images selected from Ladakh to show passive solar greenhouse design successfully operating year-round to minus-25C. Students will apply design principles to explore & discuss what can be improved in these designs in order to adapt to harsher Mongolian conditions.

Glass and plastic bottles are available as waste products that are thrown away in the soum; examples of greenhouse, coldframes and cloches made from repurposed waste plastic bottles are shown.

Finally, images of existing greenhouses in Bayan Ulgii are shown, to be used as a class design exercise exploring 'What is working / What isn't working / How can the design be improved?'

Final version will be translated into Russian language, as most residents of Bayan Ulgii are literate in Kazakh, Russian, and Mongolian languages.

Click here to view presentation on Slideshare.