Solar System for Drying Coffee

1
Solar System for Drying Coffee

• Margie Karla
• Renewable Energy
• 4/27/00

2
Overview

• Introduction
• Benefits of Solar
• General Concept
• Model Characteristics Matlab Code

• Results
• Economic Analysis
• Conclusions
• Recommendations
• References

3
Introduction

• Coffee industry is 2nd greatest cause of
  rainforest destruction
• Coffee is dried by burning rainforest wood and
  blowing hot air over beans (16,000acres per
  year)
• Coffee is 2nd most traded item next to oil

4
Benefits of using solar

• Saves rainforest wood
• No combustion emissions
• Increases quality of coffee
• Reduces spoilage (shorter drying period)
• 30 of harvest is rejected due to spoilage
• Improves quality of life of coffee farmers
• Give them capability to dry their own
• More control over price they sell for

5
General Concept

• Collectors connected to a water-air heat
  exchanger unit
• Heated air blown over beans
• Low temperature drying (122 F)
• Does not require connection to grid
• Remote locations
• Used with PV for pumps, fans, controls

6
System Photo
Costa Rica Cylindric Collectors used with PV
system
7
Model Schematic
San Juan, PR Flat Plate Collectors (20)
8
Model Explanation

• Heat exchanger with water loop (from collectors)
  and air loop (to beans)
• TMY2 data from San Juan, PR
• Flat plate collectors
• Did not use thermal storage since
• IT does not vary too much over day
• More affordable to the small coffee farmers

9
Mathematical Model
Heat Exchanger Effectiveness
Equating Qactual and Qu
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Mathematical Model (cont.)

• These two equations used in system of equations
  to find Tc1 and Tc2
• These were used to find Qjoe (amount of heat
  transferred to beans)

11
Matlab Code

• Uses It model with added calculations Tc1, Tc2,
  and Qjoe
• As a means of comparison, the code also
  calculates Qjoe2 which assumes a constant
  Tout122F

12
Results

• Total amount of heat transferred to coffee
• Qjoe 1.1108 kJ/year
• Comparable to value from Qjoe2 3108 kJ/year
• Using the efficiency of a wood stove of 70
• Using the HHV of wood, solar saves
• 8.4 tons of rainforest wood per year!

13
Economics

• How much will modeled system cost?
• Capital Cost 15180, which is 1433/year for
  20 years with 7 interest
• Regular firewood 530/year saved
• Rainforest wood 1590/year
• (approx money saved from not burning wood)
• Thus, system saves 157/year

14
Conclusions

• Coffee drying is a great application of solar
  thermal technology
• Saves 157/year over old method
• Benefits environment, local coffee farmers, and
  coffee drinkers

15
Recommendations

• Include PV system in model
• Compare the power output and economics of this
  system to one which had thermal storage

16
References

• http//solartoday.com/2000/march-Apr/feature2.html
  
• http//sunutility.com/