## Lesson 17. Performance evaluation of solar hot air generators

Solar hot air generators are used to generate hot air and subsequently that can be used for various applications viz. space heating, drying of various commodities such as grains, vegetables, fruits etc.  The performance such as quantity of hot air generation, hot air temperature, system efficiency etc. can be assessed.  The assessment can be carried out for a specific period say 8 hours in a day.  The seasonal variation can also be studied by performing the evaluation test during specified seasons.

Parameters to be measured

Solar insolation during the study period, S       :           W m-2

Mass of material to be dried, W1                    :           kg

Initial moisture content of produce, m1            :           %

Final moisture content of produce, m2             :           %

Effective hours of drying, P                            :           h

Length of the collector, l                                 :           m

Width of the collector, w                                :           m

Number of collector, n                                    :

Atmospheric temperature, Ta                          :           °C

Temperature of hot air, Th                              :           °C

Transmissivity of glass cover, t                        :

Absoptivity of black coated surface, a               :

Instrumentation required are

Pyranometer for solar radiation measurement

Thermometers

Flow meter for measuring mass flow rate of air inlet and outlet

Useful solar heat energy available

Area of the collector area, Ac, m2          =  n x length X width of each collector

=  n x l X w

Economics of solar hot air system

It is considered that the economics of solar air heating system is compared with the electrical based hot air generators.  The cost required for solar hot air generator system and electrical systems are calculated and the pay back period is calculated.

Problem

A farmer is drying 100 kg of chillies in a solar dryer having dimension of 2m length and 1 m width.  If the effective drying time taken was 16 hours with initial moisture content of 75% (wb) to 10 % (wb) final moisture content.  The average solar insolation during the study period was observed as 600 Wm-2.  Give a report on the performance evaluation of the solar dryer for chilly drying.  Assume relevant data based on the given details.

Economics of solar hot air system

It is considered that the economics of solar air heating system is compared with the electrical based hot air generators.  The cost required for solar hot air generator system and electrical systems are calculated and the pay back period is calculated.

Last modified: Wednesday, 9 April 2014, 5:20 AM