Prof. H.P. Garg has been working in the field of Renewable Energy for the last 44 years and has made several original contributions. Prof. Garg’s work on Solar Energy Collectors has led to the formulation of Standard Test Procedure for characterization and rating of Solar Thermal Collectors and the same test procedure has been adopted by the American Society for Heating, Refrigeration and Air-Conditioning (ASHRAE Standard, 93-77), which is now used all over the world.

Prof. Garg’s original work on computer modeling of Natural Circulation type solar water heater carried out in 1967 for designing and performance prediction is used and quoted in all text books and papers all over the world. This work has earned him name, fame and visit to several countries. This model has explained the working, designing and parametric analysis of the system which was not clear earlier. This work was licensed to two industries through National Research Development Corporation of India (NRDC), Govt. of India.
Prof. Garg has developed an empirical formula for predicting the overall heat loss coefficient for solar energy flat-plate collectors, which is applicable for all possible range of variables (Climatic, Design and Operational) associated with the system and is used all over the world. This has helped in designing an efficient solar liquid/air heating collector. This has superseded the earlier work of Duffie and Klien of USA in this field.

The idea of built-in-storage type solar water heater was first conceived by Prof. Garg as early as in 1968 and extensive studies are conducted by him since then. Looking into the vast potential of his work, now work on this unit is in progress in countries like USA, Israel, Australia, India, Japan, South Africa etc. This system is cost effective, durable, efficient, reliable and easy to install and useful for daytime operations. A mathematical model for parametric study and optimization of the system was also developed and validated. This cost effective novel solar water heater was also licensed to five industries for commercial production through National Research Development Corporation of India (NRDC), Govt. of India

Prof. Garg has also conceived the novel idea of combining solar collector with the storage unit, which is named by him as Integrated Rock Bed Storage Collector (IRBSC) System. This System has the capability for providing hot air for 24 hours which can be used for several applications in food processing industries and for agricultural drying. This System is becoming popular in India and large scale utilization is taking place for the drying of agricultural products.

Prof. Garg’s scientific study on dirt correction factor for flat plate solar energy collectors and photovoltaic modules has earned him appreciation at International level since earlier designers have used some ad-hoc values for designing the systems.
Prof. Garg has developed a theoretical formula for the flat plate collector tilt optimization for receiving the maximum solar radiation during the desired season of solar energy utilization device. This comprehensive formula includes the direct, diffused and reflected solar radiation; thickness of the cover plate: latitude and longitude of the place: number of cover plates, orientation of the collector, etc. This formula is now used in several countries of the world for designing and installation of flat plate collector.

So far, either the mathematical model or computer simulation models are used for designing the solar systems. Prof. Garg, first time based on Liu and Jordan’s Utilizability Method, developed several graph for performance prediction and area determination for all the 12 months, for about 25 major cities of India.

Prof. Garg has also done outstanding work in the field of solar distillation and given some new ideas like the use of dye in a solar still for enhancement of distillation output and has developed graphical method useful for engineers in designing and performance prediction of single effect type solar still. Based on Prof. Garg’s work several such solar stills for water purification upto a capacity of ten thousand liters per day were put up in rural India and some African countries.

Work on multieffect distillation unit where the output was 5 times the output of Basin type solar still was also conducted in India first time by Prof. Garg. This humidification – dehumidification system works at low temperature and atmospheric pressure using flat plate collectors. This unit is under patent process.

Prof. Garg has introduced many other new concepts in solar energy like multiple pass solar air heater, diaphragm type solar thermal pump, determination of dirt correction factor, new computer model for performance of solar water heating system. His other important work include designing, development and modeling of solar cookers, crop dryers, modeling and design optimization of some novel types of solar air heaters, etc.

His important contribution to energy research includes development of improved empirical relation which predicts the global radiation at various Indian stations within a +10% error limit. Additionally, since the already existing correlations between the ratios of monthly mean daily global to extra-terrestrial radiation, and daily diffuse to global radiation were found inadequate for some Indian stations, he established new correlations which predict radiations within about 10% error. These correlations radiation maps and radiation tables for all major cities of India (about 450) were prepared and are in use by Solar Scientists for estimating solar energy potential and performance prediction of solar devices.

Since the main hindrance for an immediate large scale introduction of solar air heaters for different practical applications is the cost, Prof. Garg has made efforts for improving efficiency and simultaneously for decreasing cost of the already existing and newly designed collectors. For the purpose, the full implications of the necessary trade-offs between the fan pumping power and the collector efficiency are fully resolved. Such studies choose a design configuration with moderate pressure drop i.e. reasonable fan running cost and higher efficiency for effective coupling to utility units. Different types of air heaters investigated so far includes flat absorber with no cover, single cover and double cover, corrugated absorber with flat cover, flat absorber with corrugated cover (in single cover air heaters) and corrugated inner cover (in double cover air heaters), finned air-duct, jet plate and packed-bed air heaters. This study has helped in designing an energy efficient solar air heater/solar dryer. A system analysis, parametric studies and detailed mathematical models have been developed by him in each case for efficient operational designing and understanding.

He contributed significantly to the solar thermal systems with transparent insulation. Through extensive investigations on systems like shallow solar pond water heater, built-in-storage type water heater, isolated non - airconditioned room and cubical collector-cum-storage system; he established that systems with transparent insulation performs better and that the cubical collector-cum-storage system has high potential for seasonal storage.

One of the different types of hybrid collectors on which he has made outstanding research and development includes photovoltaic/thermal (PV/T) collector. His investigations include the computation of the optimum area of the solar cells on the absorber surface necessary to generate sufficient electrical energy for pumping the fluid through the collector duct. He concludes that PV/T system is self sufficient for certain design parameters and flow rates.
Realising the suitability of the hybrid air-to-water solar collectors for high latitude and altitude stations, Prof. Garg pursued detailed heat transfer analysis for such systems comprising conventional empty channel and rockbed air heaters and transverse and longitudinal fin shell-and-tube air-to-water heat storage-cum-exchangers, both with and without the hot water load, with a view to obtain the most effective design and functional parameters, which would efficiently satisfy all the hot water needs throughout the year.

He showed continued interest on the hybrid water-to-air collector which comprises a water heater and a rockbed water-to-air heat exchanger-cum-storage unit (the Thomason House type) which can be used for multipurpose applications i.e. for both water and space heating in late fall, winter and early spring and for space cooling (by letting cold water to flow through the system during night) in summer and for agricultural drying (by using hot air, if provisions are made for supplying hot air to a drying chamber on the back or front yard or the terrace of the house) in late spring, summer and early fall of the year. Conducting a transient study on such a system for space heating applications both with and without the hot water load (for a four persons residential building) he established that intermittent air flow results in a more stable and uniform temperature (which lies in the comfortable range of 22-27oC) of the living space without the supply of auxiliary energy to the system.

Prof. Garg has also made significant contributions in the field of solar green house. His extensive studies on green houses already existing in the country and newly constructed at IIT Delhi has resulted in optimization of various design parameters. Systems with the optimized design parameters are suitable for various climatic zones in the country and could be propagated widely for adoption by farmers having smaller holdings and less water availability. Several industries have come up in India putting up solar green houses in the field.

His novel work on solar timber drying, besides reviewing, constitutes the formulation of a mathematical model of the solar timber kiln, which can be used by employing the empirical relations between the dying time, percentage moisture content, temperature and the relative humidity inside the timber kiln for predicting the thermal behaviour and for studying the drying characteristics of the system.

His continued interest on Integrated Solar Dryer has resulted in, in addition to cost-effective designs of Solar Air Heater and Rock-bed Thermal Storage unit, a Solar Drying Device with a capacity of drying, for example, ½ tone of coriander in two days by receiving hot air from the air heater during sun-shine hours in the month of April in Delhi.
Based on his extensive research, development and demonstration work in the field of flat-plate collectors and Box type cookers, more than 31,20,000 Sq. m. flat-plate collector area and 6,57,000 box type solar cookers have been installed in the country by December, 2009. More than 30 industries in India are now manufacturing such solar thermal devices. This work has lead to creation of National Solar Mission of India and when it gets implemented (By 2020) India will be the super power in Solar Energy in the world.

Prof. Garg has also recently studied the impact of renewable energy in the society. He has developed an empirical correlation relating the renewable energy use with the cost of conventional power, the environmental effect and the human and animal health. Finally, he concluded that the renewable energy is cost effective in the long run if cost of human health and environmental degradation is included in the cost of power produced by conventional methods.

Prof. Garg was amongst the first four founder members of the Solar Energy Society of India in the year 1968; member of the National team of National Council of Science and Technology (NCST) in 1972 who recommended a separate Commission for Additional Sources of Energy (CASE) established in 1980 and active member of expert Committee of Department of Non-Conventional Energy Sources (DNES) in 1982 which later converted into Ministry of Non-Conventional Energy Sources (MNES) in 1992 and now Ministry of New and Renewable Energy (MNRE) in 1997. He is involved practically in all activities of MNRE & Indian Renewable Energy Development Agency (IREDA) like formulation of Renewable Energy Policy for the country, identification and implementation of Solar Energy activities, Clean Development Mechanism etc. He is also involved in the energy conservation/energy efficiency programme of Ministry of Power, Govt. of India and Indian Renewable Energy Development Agency (IREDA). He was also actively involved in the Rural Electrification and Renewable Energy Policy programme of Govt. of Madhya Pradesh. He has developed four models for rural electrification programme for about 1250 villages of Madhya Pradesh in India through photovoltaic route. Based on his model more than 30 villages of MP have already been electrified through PV system.

Prof. Garg, while working as the Principal Secretary, Dept. of Science and Technology (Govt. of Madhya Pradesh) and Director General, M.P. Council of Science and Technology formulated the Science and Technology Policy – Vision 2020 for the State of Madhya Pradesh, in fact the only State in the country to have a distinct Science and Technology Policy. He also worked for the promotion of Science and Technology and development of infrastructure for research work in the State. Another major achievement made by him was bringing the State at number one level in Science & Technology popularization program from the previously held 13th position within a short-span of 30 months of his stay in M.P. He led the team of scientists in the M.P. State to work in some selected areas in a mission driven mode like water conservation/storage/recharging; Biotechnology in agriculture/industry/health sector; Remote sensing applications for National Resource Information System at the district level for S&T intervention at district level; Networking of all the scientific, educational and technical institutions of Bhopal for resource sharing; Science and Technology Clinics at all the districts of M.P.; conversion of Bhopal into a Science city for employment generation and meeting needs of science and technology of the State, policy of renewable energy application and implementation and Renewable Energy Industrial Policy and dividing the M.P. State into eight economic zones for fast development scientifically. Several training, awareness and refresher courses were organized by him for employment generation through self – help groups, health care, updating of knowledge etc. Training programs for SC/ST, weaker sections of the society, women, and tribal people were organized for income generation, elimination of drudgery, inculcating awareness about sanitation and also for better environment. Several Science and Society related program were guided by him for tackling the problems of backwardness, unemployment and poverty in the rural areas and among the under privileged sections of society such as scheduled caste, scheduled tribes, landless labours, artisans, small and marginal farmers and women. During the last three years of Prof. Garg’s tenure in Madhya Pradesh in India more than 400 such S&T programs were organized which benefited more than 2 million people at all levels in the State.