A group of ex-IITians working as consulting engineers of Clique Developments Private Limited with research support from IITBombay has achieved a landmark in the field of Solar Energy Utilization. They have successfully installed and commissioned a large solar concentrator that can generate process heat at about 200°C, store it and supply it at desired process temperature any time of the day or night. The technology holds potential to save up to 6 to 10% of India's oil imports thus saving on huge foreign exchange reserves. It also opens up the doors for solar power generation by thermal route at less than half the cost of the Solar Photo-Voltaic (SPV) systems available presently.

The experience of successful commercial development of solar flat plate water heaters in household sector has made it clear that solar energy is economic today in its thermal form. However, for widespread and technically convenient utilization of solar energy in industrial sector, higher temperatures from 100°C to 200°C are needed. Hence, solar concentrators of high efficiency and improved economy is the need of the day. Many efforts have been reported on the development of Parabolic Trough as well as Paraboloid Concentrator with Point Focus. Most of the efforts involve construction of a curved paraboloid support structure fixed with small mirrors or reflecting surfaces to form the paraboloid reflector.

However, with a combined synergy of IIT Bombay's research capacity and Clique's industrial designing and implementation capacity, an easier, cheaper and more efficient technology was developed consisting of Fresnel Paraboloid Reflector with point focus (or a focus of small area) with reflector facets fixed on to a flat tracking surface. Further, the system has tracking mechanism to continuously face the Sun which helps in operating the system near its peak capacity for 7 to 8 hours a day.

The Solar Concentrator System, named ARUN [Trademark Registered] is a Fresnel Paraboloid Concentrating Solar Collector System, with two-axes tracking flat reflector dish of 160 sq.m aperture area having 800 mm diameter cavity receiver at focal point. It is a solar device providing medium range temperatures for industrial thermal applications. The dish and support structure are made up of mild steel (MS). The reflectors made up of flat mirrors are inclined at pre-calculated angle. They reflect and concentrate the solar beam radiation at its focus having about 500 mm diameter area and generate high temperature heat energy. It is absorbed by hat-shaped downward facing cavity receiver designed for minimum thermal loss This receiver has low view factor of about 0.1 that reduces radiative losses. Its downward cavity shape helps in stagnation of hot air and reduces convective losses. An insulate pipeline delivers this heat-energy to user. The system fluid outlet temperature can be up to 200°C. The Micro-Processor based electronic control circuit automatically drives the dish on two axes such that it always faces the Sun. Process and safety controls are built into the Micro - Processor based control circuit along with emergency alarm system and userfriendly display unit. The reflectors are made up of glass, which can be easily cleaned and its reflectivity can be maintained even in the industrial environment. Accessories are provided for cleaning the reflectors daily with ease. The system, named ARUN, installed at Latur for milk pasteurisation is seen in Figures 1 and 2.

Salient features of ARUN:
1. Fresnel Paraboloid Solar Concentrating Reflector with Point Focus
2. Two-axes tracking mechanism for automatically tracking the sun giving maximum daily output
3. Specially designed receiver with minimum thermal losses developed by IIT-Bombay fixed at focus
4. Water or thermic fluid or industrial oils or air as working fluid
5. Storage vessel for heat delivery any time of the day or night
6. Built-in safety controls with emergency alarm system and user-friendly operating unit
7. Testing procedure developed by IIT-Bombay
8. Available in two sizes: ARUN 70 and ARUN 160

Applications of Solar Concentrator
The ARUN Solar Concentrator System can be used in 'ADD ON' mode and can be retrofitted to the existing boiler or heater system in the industry. In this mode it delivers energy whenever beam radiation is available and saves fuel used. This uses minimum storage capacity. The thermal energy generated can also be stored in thermal storage to supply energy requirements during evening and night. Pressurized water system is used for evacuation and storage of thermal energy. The unit is best suited for the industrial applications using thermal energy from electricity or liquid fossil fuels. The thermal medium can be high or low pressure process steam, hot water, hot air, hot thermic fluid or oil. It can be used for providing process heat for a wide range of industries and chemical processing plants using boilers or heaters, textile mills, sugar mills, vegetable oil mills, agro and food processing industries, timber industry, milk processing, drying of horticultural, food and fruits products, drying of chemicals as well as units using vapour absorption refrigeration for space cooling. It is also suitable for hotels and hospitals for providing hot water, steam and cooling.

This Arun Solar Concentrator can be fitted with 25 kW Stirling engine to generate electrical power through thermal route. Presently a one MW plant using 40 units of solar concentrators of similar size is being installed at Mojave Dessert near Las-Vegas, USA. Solar farms with 500 MW and 800 MW capacity are also planned there. With the ARUN solar concentrators already in place, India is not far behind.

The Underlying Economics
The system with 160 sq m of aperture area including tracking controls and mechanism as well as thermal circuit is designed and fabricated using indigenously available material and has system cost of Rs.15,000 to 17,000/sq m of aperture area. It can save about 18,000 to 22,000 liters of liquid fossil fuels or about 160,000 kWh of electricity if used for heat generation. This system installed at Latur for supplying thermal energy (heat) for pasteurizing 20,000 lit of milk daily, can save 50 to 70 litres of furnace oil per day or a saving of approximately 20,000 liters of furnace oil annually. A smaller system of 70 sq m of aperture area has also been designed.

Soft loans can be available through financing institutes covering 80% of the initial cost for installing this Solar Thermal Concentrator System @ 7.5% pa. The system can save more than the EMI of this loan for non-cloudy clear months if it is used to replace heating that otherwise uses FO, LDO, diesel or electrical heating. The annual operating and maintenance cost of the system can be as low as 2% of its capital investment. Economic analysis suggests that a payback period of 4 to 5 years is possible when liquid fossil fuels are saved. The system then provides free energy for 20 more years. The IRR comes to 30 to 70% depending on the fuel saved. The economics improves when electricity is saved.

Contact: sbkedare@iitb.ac.in