Original:Solar and Energy Conserving Food Technologies 11

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Solar and Energy Conserving Food Technologies[edit]

(Peace Corps, 1984, 175 p.)

The economics of solar drying[edit]


One of the determining factors concerning the appropriateness of a technology is the cost in comparison to the benefits that can result from its use. In this session, the participants examine the economics of solar dryers in relation to the application of the technology in a community setting. In this way, people are able to begin planning their construction projects in light of the economic realities that exist in their own communities.


To examine the costs and benefits of solar dryers
To identify factors that influence the economic viability of solar drying in a community
To determine the approximate cost of a food dryer in each participant's community


Improved Food Drying and Storage Training Manual, Session 14
Solar Food Dryer Plans, pp. 9-11


"Materials and Tools List", with costs for each item indicated (based on Appendix F)
A Question of Economics, Handout 9A
The Economics of Solar Drying in a Community, Handout 9B


Newsprint and markers


1. (10 minutes) Warm-up Activity and Introduction

Have the planning committee conduct a short icebreaker or other warmup activity. Review the purpose of the session.

2. (20 minutes) Discussion of Community Economics

Distribute Handout 9A and have the participants form small groups. Ask them to discuss the situation described in the handout, and make recommendations based on the following questions:

- What factors help determine if solar drying is economically feasible in a local community?
- What are some specific questions to answer before deciding on solar drying as an economically appropriate technology in a community?
- When the groups re-assemble, guide a discussion based on each group's recommendations.

3. (15 minutes) Examination of Costs and Benefits of Solar Dryers

Ask for suggestions as to specific costs involved in making and using a solar food dryer. List them on newsprint.

Ask for ideas about the benefits of solar food dryers. List those ideas on newsprint.

Distribute the materials and tools request forms and ask if the prices quoted are similar in the participants' communities. Discuss any price variations as well as possible reasons for the differences.

Distribute and review Handout 9B.

4. (20 minutes) Determining the Cost of a Solar Food Dryer

Ask the participants to utilize the Materials and Tools List and Handout 96 as they calculate an approximate price limit for a solar food dryer that would be appropriate to their community setting.


If the participants have already formed construction teams, they may wish to calculate costs in each group. However, individual communities within the same region may have different economic situations, so it may be helpful for the participants to concentrate on their own communities. This preliminary cost estimate will be useful during the Solar Food Dryer Design Session.

Compare the different cost estimates and discuss some reasons for each.

5. (10 minutes) Summary

Review the session,- focusing an the following discussion points:

- What makes a new technology economically viable?
- How can a community worker cooperate best with community members to determine the best type of solar dryer for a given situation?
- How can the information presented in this session be used during the design, construction and use of the solar food dryer?


You've just arrived back in your community after attending a workshop on solar drying technologies; you are enthusiastic and ready to get back to work. As you approach your house, a group of people greet you and ask how it all went at the course. Your neighbors know you went to study some new ways of preserving food, and they are excited at the prospect of having modern technologies in the community at last. You are the "expert" now, and they are waiting to find out how you can help.

This year, it appears the tomato harvest is going to be enormous, larger than ever. The people tell you that they are worried because they have no way to store the bumper crop, and there is such a glut on the market that the village economy is in danger of collapsing if something is not done soon. They want your help in solving the problem.

You know that the people in the community are not well-off, not even what is considered "middle class". They live from harvest to harvest, with not much of a soft cushion between them and hard reality, very seldom is there extra cash for non-essential purchases.

You think about solar drying all those tomatoes, and the possibilities fur economic improvement. But, there are so many factors to consider, so many pro's and con's to introducing the new technology. How can you and your neighbors decide if solar drying is a viable plan for dealing with the tomato harvest?


Note: To answer some of the following questions, more information will be needed both from later sessions in this course as well as from investigation within your own community. Remember to use these questions as a guide.

THE QUESTION IS: Is it economically viable to solar dry foods in my community?

THE ANSWER IS: To help you answer this question, you have to ask and answer other questions along the way ... For example:

During the year, about how many days are there with a minimum of 4 hours of strong sunlight?
Do the periods of food gluts coincide with periods of sufficient sun?
How much money do people have available initially to invest in the technology?
How much money is likely to be available for maintenance and repair of the dryers?
How long is the dryer going to last? Is it a good investment, relative to its construction and maintenance costs?
How much do the fruits and vegetable cost during the time of plenty? When they are scarce? When do they have to be imported?
How much of each food can be dried in a year?
How long does it take to dry each food?
What is the capacity of the dryer? How many kilos or pounds can it hold in a load? (Remember that a dryer can hold about 5-10 kg per square meter of tray area.)
How much does the food weigh dry, as compared to fresh? (Remember, generally fruit has about 80-85% moisture when fresh, and 15-20% when dry. Vegetables usually have 70-75% moisture, fresh and approximately 10-15% when dried.)

Use these questions to come up with a formula that resembles the following:

Add up all costs: initial investment + maintenance + labor + food to be dried + any other expenses.

Add up all benefits: weight/quantity of food dried in a given amount of time multiplied by the economic value of the food + health benefits + other factors.

Compare the costs and the benefits, and decide whether it is an economically viable method for preserving food.

Now, what is the answer to the question on the previous page?

Are there other questions to be asked?

Other factors to be considered?

What are some other ways of determining whether it is economically feasible to solar dry food in a given community?