Solar Energy - Thermal Energy

By TamilNadu Agricultural University on 03 Feb 2019 | read

1.Hemispherical Solar Distillation Unit Image title

1.Use:To produce distilled water

2.Capacity:3 liters / day

3.Salient features   

(i) No fuel, Utilize Solar thermal energy
(ii) Pollution free
(iii) Simple and easy to install

2.Solar Water Heating SystemImage title

������ Solar water heating system (SWHS) has three main components, namely, Solar Collector, Insulated hot water storage tank and Cold water tank with required insulated hot water pipelines and accessories. In the case of smaller systems (100 – 2000 litres per day), the hot water reaches the user end, by natural (thermo – siphon) circulation for which the storage tank is located above the collectors. In higher capacity systems, a pump may be used for forced circulation of water. A bank of collectors can be arranged in a series – parallel combination to get higher quantity of hot water. A typical 100 litres insulated tank with a 2 m2 collector area, will supply water at a temperature of 60 - 80°C.


The tanks are generally made of stainless steel to avoid corrosion and are insulated to reduce heat losses. They are also fitted with electrical heater as a backup during monsoon days. The tanks may also be made of G.I. sheets or aluminum. Cold water comes from the over head tank.  Hot water from the system is transferred to various utility points through to insulated pipelines. A heat exchanger may be provided when the water is hard.




Bathing, Coffee / Tea preparation, Dishwashing etc.



Pre-heating of boiler feed water, cooking / dishwashing in industrial canteens.  washing of milk canes in dairies, sterilisation of surgical instruments etc.

conomics (Tentative)

  • A 100 lpd domestic solar water heating system (SWHS) can cater to a family of 5 persons and costs about Rs.20000.
  • A 1000 lpd industrial system would cost about Rs.2.0 lakhs and would have a payback period of 2 years.
  • It saves about 1500 units of electricity per annum equivalent to about Rs.5000/- per year

3.Solar Distillation Plant

Image title                                            Solar Box Type Cooker

1.Function:Converting salt water into potable water
 i. Base:Area                   :  15 m2
Concrete             :  1:5:10
Wearing coat       :  1:1.5:3
7.5 cm thick black coated 

 ii. Side walls:Brick masonry 

 iii. Roof:Glass roof on steel truss
Thickness of glass : 5 mm 

 iv. Distilled water collecting   channel 
 v. Tank:Two numbers in brick masonry structure 

3.General Information:The unit is a basin type solar distillation plant of masonry construction, with a basin area of 15 m2 and slope of the glass cover is 15°.  

The distilled water sliding down the slope of the bottom of the glass cover is collected at the end along the aluminium channels.  The channels are fixed with a slope to collect the water at the end where the water drops in to the tank through the end cover and pipe at the bottom.
4Cost of operation 

5.Salient features:The still can yield 3 to 4 liters of distilled water per square meter area of the basin in a day. 

4.Step type Solar dryer

Image title                                                    Step type Solar dryer




Drying of fruits,  vegetables and agricultural commodities




i. Collector area


2.4 x 1.8 m

ii. Type and Model


Step type, TNAU

iii. Number of trays


10 in five steps

iv. Insulation (Bottom)


Glass wool, 10 cm. thick

v. Motive power      


Natural convection


General Information


Step type solar dryer has a collector area of about 4.32 m2.  This multi track step type dryer can hold 10 aluminium trays at a time.  The absorber is 20 gauge GI sheet, black painted at the top with bottom insulation.  The drier is covered at the top with 2 layers of 3 mm thick plain glass kept at an air gap of 2.5 cm.  At the rear side of the collector, two chimneys of 120 cm height are provided.  Chimneys are provided with butterfly valves to control the movement of air.  Holes provided at the bottom of the collector just below the first step allow the entry of atmospheric air into the dryer.  


Cost of the unit (approx)




Cost of operation




Salient features



Solar drier takes 40 hours for drying 50 kg of papaya leather, while conventional sun drying takes 61 hours.  Thus there is a saving of 21 hours which is 35% when compared to conventional drying.


The drier handles 10 kg of cocoon per batch and each batch takes 30-40 minutes for completion of stifling. 80 kg of cocoon per day in 8 batches can be conveniently stifled in a day.

5.Solar Tunnel Dryer for Agro Industrial ApplicationsImage title




Natural convection walk-in type dryer for bulk drying of agricultural & agro industrial products at moderate air temperature.




Semicylindrical shaped tunnel with a base area of 3.75 m x 18 m for capacity of 1 ton per batch for drying of sago and coconut Metallic frame structure of tunnel dryer is covered by UV stabilized semi transparent polythene sheet of 200 micron thickness. Length of the dryer depends upon type and quantity of the product to be dried per batch. A slope of 10-15o  is provided along the length of the tunnel. An exhaust fan at the upper end of the tunnel, and a few chimneys on the top of the tunnel are provided to remove the moist air.


Design Features


Sago is highly hygroscopic and the drying of roasted sago in open air is labour consuming and costly. Thus sago contains 37 % (w.b) moisture initially and it is to be brought down to 11% (w.b) by drying. This is critical process and it depends on monsoonic vagaries. Hence, it is proposed to integrate small poly cover in tunnel shaped structure for drying agro-industrial product.


Salient features


  • Simple in fabrication and installation
  • Maximum mean temperature obtained inside the dryer is 57° C while the ambient temperature was 33.5 °C.
  • The drying time for sago drying in solar tunnel dryer  is 5 h ours with 20% cost saving when compared to open  sun (11 hours drying time) method
  • Payback period is 5.8 years for sago product. 
  • The savings in drying time using coconut as produce is 16 hours, with 42 % cost saving when compared to open sun drying method.
  • This tunnel dryer can also be useful for drying of
  • chillies.


Cost  (approx)


Rs 1, 20,000 for standard size (3.75m x 18.0m)