Rahul Rawat | Indian Institute of Technology Delhi (original) (raw)

Papers by Rahul Rawat

Renewable and Sustainable Energy Reviews, 2016

Solar Photovoltaic system comprises of photovoltaic (PV) array, converter, inverter and battery s... more Solar Photovoltaic system comprises of photovoltaic (PV) array, converter, inverter and battery storage unit of appropriate capacity to serve the load demand in reliable, efficient and economically feasible manner. The proper selection of technology and size of these components is essential for stable and efficient operation of PV system. Therefore, a number of modeling equations and methodologies for designing a PV system based on application have been developed in order to ensure the optimum performance of the PV system. In this paper, a comprehensive designing process of solar photovoltaic water pumping system, standalone PV system and grid connected PV system is presented. The modeling of PV modules, cell temperature, water pumping system and battery state of charge is tabularized so as to facilitate their utilization for proposing a PV system based on the techno-economic variables and environmental parameters. The financial and reliability parameters for techno-economic size optimization of PV system are also identified and different optimization techniques have been discussed. A state of art literature survey has been presented which is useful in designing and installation of solar PV systems for standalone as well as grid connected power supply.

The thin film photovoltaic (TFPV) technologies are emerging out as an alternative to the establis... more The thin film photovoltaic (TFPV) technologies are emerging out as an alternative to the established silicon wafer based PV technology due to competitive efficiency, and low energy payback period. However, the performance and degradation study of these technologies are important in order to ensure their stability and reliability in terms of operating lifetime. The current-voltage (I-V) characteristic of PV module are most widely used for assessing the electrical performance and degradation. In this paper, the degradation analysis of I-V characteristic of 40 CdTe and 69 micromorph TFPV modules has been carried out after long term outdoor exposure. The degradation rate of electrical parameters i.e. short circuit current; open circuit voltage; current, voltage and power at maximum power point of individual field aged module has been evaluated with respect to the name plate values. The defects of the modules have been identified using visual inspection and electro-luminescence imaging (EL) which are then correlated with the electrical degradation. The degradation of CdTe and micromorph TFPV technologies are found to be 0.55%year and 6.52% in the first year respectively with respect to the nameplate value. The power output of micromorph modules have degraded by 17% after 1 year of outdoor exposure with respect to the power output of unexposed modules due to light induced degradation.

Solar photovoltaic (PV) technology has gained ample attention with the continuously increasing el... more Solar photovoltaic (PV) technology has gained ample attention with the continuously increasing electricity demand and climate concerns. It can be broadly classified into wafer based and thin film PV technologies. The Cadmium Telluride (CdTe) based PV technology is the leading and foremost technology among rapidly growing thin film PV industry because of its lower energy and economic payback period and energy efficiency competitive to the wafer based technology. Although, these modules undergo a series of indoor qualification tests specified by IEC61646, the long-term performance analysis in real operation conditions is essential in order to ensure long term stability, robustness and reliability. In this paper, performance analysis of 80WP CdTe PV module has been carried out on the basis of long term time series data of short circuit current (ISC) and open circuit voltage (VOC) measured in outdoor conditions. The measured electrical parameters has been translated to alternate reporting conditions i.e. 800W/m 2 irradiance over the module surface and 40°C module temperature. The monthly averaged and normalized VOC and ISC of the module is found to be degraded by 2.86% and 2.29% after 23 months of outdoor exposure. The parameters are translated to standard test conditions for diurnal analysis which shows the degradation of 2.91% for VOC while no deviation in ISC.

The solar photovoltaic (PV) technology market has increased rapidly with the continuously increas... more The solar photovoltaic (PV) technology market has increased rapidly with the continuously increasing electricity demand and climate concerns. With the increased PV installed capacity, the performance analysis of these systems has become critically important in order to ensure its reliable operation for a long lifetime, monetary payback and to identify the scope of improvement. The well-established conventional energetic performance analysis techniques are quantitative approaches based on energy conservation while the exergetic performance analysis is the qualitative method which is based on second law of thermodynamics. In this paper, an approach for energetic and exergetic performance analysis has been developed so as to determine the long term performance of PV systems in real operating conditions. A methodology has been proposed for utilizing the long term time series outdoor data in order to assess the performance of PV system statistically and to determine the system degradation rate. The degradation rate of 3.2 kWP CdTe PV system is found to be 0.18% per year after 23 months of operation in composite climate which is lower than the reported degradation rate of earlier CdTe technology. The average performance ratio (PR), energetic and exergetic efficiency of the system is found to be 0.89%, 9.84% and 10.62% respectively. The average exergetic efficiency is found to be increased by 12% by utilizing the recoverable thermal exergy loss in photovoltaic-thermal system. The instantaneous PR of 93.5% of the per minute data is found to be in the range of 0.84–0.95. Additionally, the electrical parameters have been translated to standard test conditions so as to evaluate the system with respect to the rated capacity.

Solar Photovoltaic [SPV] systems are being considerably used worldwide to utilise energy of sun f... more Solar Photovoltaic [SPV] systems are being considerably used worldwide to utilise energy of sun for power generation during recent years. Under the Indian National Solar Mission considerable emphasis is being given for solar power generation in order to supplement the conventional power generation. A large number of solar power plants are being installed under the Solar Mission in different parts of country. However, the available solar energy at a particular site needs to be utilized by a solar photovoltaic system to maximum extent for which maximum power point tracking (MPPT) techniques are used. It is essential to increase the efficiency of SPV system as much as possible by improving the efficiencies of the electronic and electrical components of the system. Considerable research has been carried out in the MPPT techniques / algorithms for increasing the overall efficiency of solar PV system. In the present study a review of MPPT techniques , its categories has been carried out with detailed flowcharts of algorithms and references and also includes an up-to-date investigation of research papers published till date on MPPT techniques in solar PV system.

Solar-photovoltaic systems are being widely used and promoted worldwide for pollution-free power ... more Solar-photovoltaic systems are being widely used and promoted worldwide for pollution-free power generation. The power extraction from solar photovoltaic (PV) systems can be maximized by using maximum-power-point tracking (MPPT) techniques between the photovoltaic array and the load. The MPPT technique searches the maximum-power-point and command system to enable operation at that point and enrich the overall efficiency of PV system. Substantial research has been performed on MPPT techniques to improve the efficiency, simplicity, response time, and steady-state error. In this paper, a study of 21 different maximum power point tracking techniques used in photovoltaic systems has been performed to provide the latest update on conventional and advanced techniques and highlight the main features and limitations. The modified variable step incremental conductance technique is found to be the best among all in terms of steady-state error, response time, convergence time, and efficiency. Possible areas of further research are also identified.

Renewable energy sources are clean sources and can meet the energy demand without causing any pol... more Renewable energy sources are clean sources and can meet the energy demand without causing any pollution to the environment. Wind and solar energy have good potential to replace the conventional sources, however, the stochastic behavior of both these energy sources, is a major drawback Therefore, the integration of solar and wind energy systems into a hybrid system improves the reliability, reduces the energy storage, and overcomes the over sizing problem. The main objective of this study is to utilize the available wind and solar resource to meet the energy needs of residential / institutional buildings in Western Himalayan Indian state of Himachal Pradesh. In the present study, a 6 kWp solar-wind hybrid system installed on the roof top of an institutional building is analyzed and optimized using HOMER software at different reliability levels. The total electricity production by the installed system is found to be 1996 kWh/yr with cost of energy (COE) as 1.156/kWhinwhich611.156/kWh in which 61% contribution is from PV array and 39% from wind turbine with annual capacity shortage of 24%. The techno-economic characteristics of existing and optimum hybrid system configurations for 0%, 5%, 10 and 20% maximum capacity shortage are studied. The various optimized system configurations for this system based on the reliability are identified. The effect of maximum annual capacity on system parameters is evaluated by sensitivity analysis. A 2 kWp PV system with 1 string of 10 batteries is found to be more economical than the existing system, with COE as 1.156/kWhinwhich610.575/kWh with 8% capacity shortage. However, in order to utilize both solar and wind resources, the optimum combination, is found to be 5kWp wind turbine, 2kWp PV system with a string of 10 batteries having COE as $ 1.051/kWh with 3.1% capacity shortage. The results of the study indicate that the solar and wind resource can be utilized economically by utilizing solar -wind hybrid energy systems for decentralized applications in the Western Himalayan complex terrain. Further research areas are also identified along with some limitations of HOMER software.

Solar Photovoltaic systems are used worldwide to utilize energy of sun for power generation durin... more Solar Photovoltaic systems are used worldwide to utilize energy of sun for power generation during recent years. However, the available solar energy at a particular site needs to be utilized by a photovoltaic system to maximum extent for which maximum power point tracking (MPPT) techniques are used. The most commonly used techniques for MPPT, are the Hill Climbing Techniques. These include Perturb & Observe method and Incremental Conductance method to search and make the system to operate at maximum power point. Considerable research has been carried out in the Hill Climbing MPPT techniques for increasing the overall efficiency of solar PV system. In the present study, a review of Hill Climbing MPPT techniques, has been carried out with detailed flowcharts of algorithms and includes latest research papers published on MPPT techniques.

Thesis by Rahul Rawat

Wind and solar are clean energy sources with vast potential to reduce the dependence on conventio... more Wind and solar are clean energy sources with vast potential to reduce the dependence on conventional energy sources and are being utilized for power generation worldwide. However, solar energy is available only on clear day while wind is very intermittent. The stochastic nature of these energy sources with dependence on environmental conditions raise the reliability issues of solar or wind power systems. A stand-alone solar energy system or a wind energy system may not able to supply reliable power as such, for a reliable power supply; hybrid power generation is the best option. The need for reliable power and maximum utilization of renewable resources at the location of interest has led to the development of reliable hybrid systems in recent years. The hybrid renewable energy systems are those in which two or more energy sources are integrated to operate simultaneously to supply power with at least one renewable energy source. These hybrid energy systems can become appropriate alternative to conventional energy systems and can cater to the requirements of institutions, industries and communities in urban and remote rural regions.
The main objective of the present study is to utilize the available wind and solar resource at a location to meet the energy needs of residential/institutional buildings in Western Himalayan Indian State of Himachal Pradesh.
In the present study, optimum configuration of a solar-diesel-battery hybrid energy system is determined for the uninterrupted power supply system for the National Institute of Technology, Hamirpur [NIT-H] using Hybrid Optimization Model for Electric Renewables software developed by National Renewable Energy Laboratory [NREL]. In order to assess the feasibility of the reliable hybrid renewable energy system, a 6kWp solar-wind hybrid system installed on the roof top of Centre for Energy and Environment, NIT-H is analyzed and optimized at different reliability levels.
Based on the techno-economic analysis, the optimum configurations of a standalone and a grid interactive solar-diesel hybrid system are proposed for the reliable uninterrupted power supply for NIT-H. The optimum configurations found are, a standalone solar-diesel hybrid system consisting of 300kWp solar PV system and 128kWp diesel generator with battery bank of 1080Ah and a grid interactive solar-diesel hybrid system of 100kWp solar PV system and 128kWp diesel generator with a battery bank of 120Ah with net present cost of 3,804,559and3,804,559 and 3,804,559and1,189,963 respectively. These hybrid energy systems are analyzed on the basis of economics, excess electricity and greenhouse gas emissions. The sensitivity analysis is carried out to determine the effect of diesel costs and solar radiation on the net present cost and CO2 emissions.
The results indicate that available solar and wind resource can be utilized economically using hybrid energy systems for decentralized applications in the Western Himalayan terrain. The solar-wind hybrid systems will be reliable systems for residential/Institutional buildings both in urban and rural locations in this region. The integration of a diesel generator in a solar-wind-battery hybrid system can result in avoiding over-sizing and enhancing the reliability of the system.
The work presented in the dissociation is organized as follows: In Chapter 1, an introduction to the hybrid energy system and energy scenario of India is given; a literature survey on hybrid energy systems is carried out in Chapter 2; the statement of problem, objectives and summary of solution methodology are given in Chapter 3; The methodology followed in the study is described in Chapter 4; the results of the study are presented and discussed in chapter 5 and conclusion of the study and further research are given in Chapter 6.
Further follow up research areas identified in the study are:
• Detailed resource mapping and analysis of the hilly regions of the country
• Optimization of hybrid systems for maximum renewable resource utilization at a site to maximize the promotion of renewable technologies in urban and rural areas.
• Feasibility study of hybrid energy systems employing small hydro and solar and wind resource for remote locations in Himalayan region.

Renewable and Sustainable Energy Reviews, 2016