With an annual production of 12 to 14 million tonnes, India ranks among the major pulse producing countries. There are 1400 pulses processing units in the country and this industry takes credit for providing a large employment among rural and semi urban population. Since the last decade, dal processing units are shifting from open sun drying to fossil fuel fired dryers due to constraints in space availability. This has created an additional burden on the energy sector. Recently innovative solar air heating systems have been developed to reduce consumption of diesel. AMR Dal Mill is located in the south western part of Tamilnadu where huge farming lands cultivated Dal. This mill processes 20 tonnes of Urad dal per day where solar air heating system has been installed successfully.

Project Description:

The AMR Dal Mill located in Theni enjoys more than 300 sunny days in a year. Prior to the installation of solar collector, AMR Dal mill used to spend around INR 5000 per day to run thediesel-fired heater for hot air production.

To save on diesel, the solar flat plate collector was installed in 2012 at AMR Dal Mill covering an area of 230 m2.

Dal processing involves the following steps:

  • Sieving machines are used to clean the external impurities in the pulses.
  • The pulses are sprinkled with vegetable oil.
  • Then they are heated in a trough which can hold around 5 tonnes of pulses.
  • Hot air is generated by burning diesel and the blower drives the hot air into the trough. A temperature of 60 to 65°C is maintained for duration of 75 – 90 minutes in the trough.
  • The dal mill processes typically 4 to 5 batches per day and consumes around 60 to 90 litres of diesel every day for generating heat.
  • After the pulses are heated, water is sprinkled on them to separate the skin from the kernel.

The solar flat plate collector consists of a tempered glass at the top, and a black color coated special aluminum absorber kept in a box which is insulated at the sides and bottom to prevent heat loss. The insulation material used is rockwool and thermocol. The atmo-
spheric air is drawn into the solar collector and made to pass through the chambers in a zig zag motion, to increase the air temperature by the absorber. A 5 HP power blower is used to deliver the hot air from the Dal processed in the open trough solar flat plate collector to the open trough through the metal duct which is insulated.

Solar Dal Dryer

A damper is used for temperature control in the duct and ¡n the trough. Temperature sensors monitor the temperature inside the duct. The damper closes when a higher heat output is required and opens automatically when low heat output is enough. On a normal sunny day the collector delivers hot air at 65 °C — 75 oc. The maximum hot air temperature achieved through the solar flat plate collector is 110 oc ¡n the month of May. On a rainy day and at night times the diesel-fired boiler is used as a backup. The unit operator could switch from solar heating to conventional heating by flicking a single way switch. The life of the flat plate solar collector is 15 years and has been installed by SunBest systems.


The Dal mill was completely able to replace diesel during sunny days and save energy costs.

  • Savings in diesel about 60 to 90 litres/ day
  • Cost savings by replacing diesel is about INR 1 .0 – 1 .2 million per annum.
  • GHG reduction is about 60 tonnes per annum

Solar Dal Dryer