1B.NAGALAKSHMI M.Tech., (Ph.D.), 2Dr. R.KIRANMAYI M.Tech., Ph.D., 3Dr. K.NAGARAJU M.Tech., Ph.D. 1Asst. Prof & Research Scholar, Dept. of EEE, KVSRIT, Kurnool, JNTUA University, Ananthapuram
2Professor & Head, Dept. of EEE. JNTUA CEA, University, Ananthapuram.
3Professor, Dept. of EEE SRIT, JNTUA, University, Ananthapuram.
[email protected] [email protected] [email protected] [email protected]
The main aspect is to discuss the Natural Resources and its classification. In this RENEWABLE ENERGY SOURCES (RES) among many some of the RES’s like Solar, Wind Power, Hydro Electric Energy, Biomass, Hydrogen and fuel cells, Geothermal Power and Other Forms of Energy. Enumerate increase in Photovoltaic Solar power compared to other forms it has more advantages. Equivalent circuit of Solar cell, types, differences and its future developments is clearly discussed.
Keywords Resource classification, solar equivalent circuit Inverter types, differences and future developments.

The I Section it consists of Resources and their classification. The section II describes about Natural Resources (NR) and it can be classified into many forms but the main focus is made on On the basis of Availability and its classification 16.The main topic is concentrated on Renewable energy sources. The III Section is discussed with Renewable Energy and it also consists of many forms but most of these renewable energies depend in one way or another on sun light, wind and hydroelectric power, biomass, hydrogen and fuel cells, geothermal power are discussed141516. The IV Section is made on photovoltaic solar and its equivalent circuit. The V section is about the types of Inverters and their differences. The VI section deals with the Future developments and VII section is the conclusion.

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FIG (1) Classification of Resources
Anything that can be used to satisfy a need is a Resource. It can be classified into three types as shown in fig 1.

People use natural resources to make buildings, bridges, roads, machinery and vehicles which are known as Human or Man Made Resources.

(2) HUMAN RESOURCES (HR) People can make the best use of nature to create more resources when they have the knowledge, skill and the technology to do so. These resources are also known as Special Resources.

Resources that are drawn from nature and used without much modifications are called Natural Resources. Ex: Air, Water, Soil 16.
Natural Resources can be classified into four categories as shown in fig 2. In this paper only On the basis of Availability is discussed. Where it can be classified into two types. i e. Inexhaustible and Exhaustible. The differences between Inexhaustible and Exhaustible is shown in table (1).
The Renewable Energy Resources are discussed one by one as below

FIG (2) Classification of Natural Resources
1. These resources replaces itself naturally, in
a short period.

2. These are renewable or replenish able

3. They do not require conservation steps to be
taken as they can be renewed.

Ex: Sunlight, water, wind, soil etc.

4. Rate of renewal is greater than the rate of

5. Cost is low.

6. This has unlimited quantity.

7. These are sustainable in nature. 1. These resources are the one that are not
capable of replacing itself, in near future.

2. These are nonrenewable or non-replenish
able resources.

3. They require conservation steps to be taken,
So that they can be used in future also.

Ex: iron, coal, oil
4. Rate of renewal is lower than the rate of

5. Comparatively high.

6. This has limited quantity.

7. These are exhaustible in nature.

Table (1) Differences between Inexhaustible and Exhaustible

(A)WIND POWER The movement of the atmosphere is driven by differences of
Temperature at the earth’s surface when lit by sunlight wind energy can be used to pump water or generate electricity, but requires extensive a real coverage to produce significant amount of energy 14.
This form uses the Gravitational potential of elevated water that was lifted from the oceans by sunlight. It is not strictly speaking Renewable since all reservoirs eventually fill up and require very expensive excavation to become useful again. At this time, most of the available locations for hydroelectric dams are already used in the developed world.

(C)BIOMASS It is the term for energy from plants .Energy in this form is very commonly used throughout the world. Unfortunately the most popular is the burning of trees for cooking and warmth. This process releases copious amounts of carbon dioxide gases into the atmosphere and is a major contributor to unhealthy air in many areas. Some of the more modern forms of Biomass energy are methane generation and production of alcohol for automobile fuel and fueling power plants.

(D)GEOTHERMAL POWER Energy left over from the original accretion of the plant
and augmented by heat from radioactive decay seeps out slowly everywhere, every day. In certain areas the geothermal gradient (increase in temperature with depth) is high enough to exploit to generate electricity. This possibility technical problems exist that limit its utility.
Another form of geothermal energy is earth’s surface. Soil everywhere tends to stay at a relatively constant temperature, the yearly average, and can be used with heat pumps to heat a building in summer. This form of energy can lessen the need for other power to maintain comfortable temperatures in buildings, but cannot be used to produce electricity 13 14 16.

(E)HYDROGEN AND FUEL CELLS These are also not strictly renewable energy resources but are very abundant in availability and are very low in pollution when utilized. Hydrogen can be burned as a fuel, typically in a vehicles, with only water as the combustion product. This clean burning fuel can mean a significant reduction of pollution in cities, or the hydrogen can be used in fuel cells, which are similar to the batteries, to power an electric motor.

In either case significant production of hydrogen requires abundant power. Due to the need for energy to produce the initial hydrogen gas, the result is the relocation of pollution from the cities to the power plants. There are several promising methods to produce hydrogen, such as solar power, that may alter this picture drastically.

(F)OTHER FORMS OF ENERGY: Energy from tides, the oceans and hot hydrogen fusion are other forms that can be used to generate electricity.
(G)SOLAR: This form of energy relies on the nuclear fusion power from the core of the sun. This energy can be collected and converted in a different ways. There are two types of solar energies i.e. Photovoltaic solar energy and Thermal solar energy.

(i)Photovoltaic solar power (PVSP) The Photovoltaic effect (or photoelectric effect) converts light into electricity. It was discovered by French Physicist Edmond Becquerel in 1839 and was first used in industrial applications in 1954.

(ii) Solar Thermal Power (STP) This technology captures sun’s heat. This is used directly or converted into mechanical energy and in turn electricity known as Concentrated Solar Power (CSP) 12. But the main topic is concerned with PVSP and it is discussed.

A Solar energy system consists of many devices integrated together to absorb the radiation and convert it into other form of energy for use. The absorption system absorbs the solar energy incident on the earth’s surface. The photovoltaic cells converts solar energy directly into electrical energy i.e. direct current (DC) electricity 1 14.

A collection of solar cells forms a solar panel or Modules and an integration of several modules constitutes a solar array this is shown in fig(3).


FIG (3) Cell, Module, Array
In a solar panel the photovoltaic cells are arranged in series and parallel. The solar panel is built with silicon as raw material which is a semiconductor. The cells placed in a series will yield higher voltage and the cells in parallel will produce a higher current 4 15. The equivalent circuit is shown in fig (4) and it consists of diode, series resistance, shunt resistance and diode current and the equation can be written as
130126292808 I=IL – ID – ISH (1)
the current is diverted in the diode, by shockley diode equation.
206057581231 ID = IO {exp qv / nkT – 1} (2)
By ohms law, the current diverted through the RSH is
12303379017000 ISH = V / RSH(3)
Substituting equations 2 and 3 in equation 1 we get the equation for the VI characteristics of a solar cell as and Power
1054784105410 P=VOC ISC (4)
A solar cell demonstrates a nonlinear VI and PV characteristics is shown in fig (5) and it varies with solar irradiance and cell temperature.

FIG (4) Equivalent Circuit of PV cell
FIG (5) ISCVOC and PV characteristics
SOLAR INVERTERS The simplest PV system consists of multiple solar cells connected to form a PV module. This modules are connected to the inverter which convert’s DC to AC. Inverter it acts as a gateway between the PV system and the OFF-taker or LOADS/APPLIANCES. Inverter is the brain of the solar energy system is used whether it’s a 2kw residential system or a 5MW commercial power plant 2 6. The working of an Inverter is discussed as below
•Solar panels convert the sun’s energy into DC electricity.

•The DC electricity is channeled into a solar inverter that converts it to 240v, 20HZ AC electricity.

•The 240v Ac electricity can be used to power home appliances.

•Surplus electricity is fed back into the main grid, and its working is shown in fig (6).

FIG (6) Basic System Overview
V.TYPES OF SOLAR INVERTERS It can be classified into three types based on the uses
1. OFF grid inverters
1. OFF-GRID INVERTERS This inverters also known as “STAND ALONE INVERTER’S” They do not need to be hooked up to a solar panel. Instead they draw the DC power from the batteries which are charged using PV arrays or other resources like engine generators, hydro turbines, and wind turbines. Because these inverters are isolated from utility grids, they do not require anti islanding protection. Further, they cannot export excess solar electricity into the grid. This inverters find use in remote areas or when people want to live completely independent of the grid.
Most residential households will use a grid connected PV system connected to a utility grid and functions by matching their frequencies with utility grid sine wave. They are designed to automatically shut down in the event of a power cut for safety reasons. Hence they cannot supply power during an outage. This inverter consists of four types and is shown in fig (7).


FIG. (7) Classification of Grid Tied Inverters
(a)CENTRALIZED INVERTERS (CI) This CI’s is shown in fig this is the interface between photovoltaic power supply and the grid rely. Inverters are connected in into series are called Strings. And it generates a high voltage to avoid amplification. All strings are then connected in parallel to support high output power. These inverters are typically used in MW scale plant.

(b)STRING INVERTERS (SI) This is the most commonly used solar inverter for homes and business consumers. Due to the dis advantages present in CI this SI are used where the strings are connected in series with an AC module and avoids high voltage

This inverters are directly connected to the grid and most often don’t support a battery back-up. They are high Performing inverters often with 25 years design life and 5 years warranty and it has 97-99% conversions from DC to AC.

(c)MICRO INVERTERS (MI) This MI solution also called AC module shown in fig (7) is the integration of PV and inverter into one electrical device. With only one PV to control, there is no PV mismatch
This type of inverter has recently become emerging product and promised a remarkable market share in future 13 14 15. This inverters are shown in fig (8) and their comparisons is shown in table (2).

This MI’s are smaller in size and capacity
Th0an the standard inverters. The later ranges from1.5-5kw in size for residential applications, the former is usually around
200-350w in size. Unlike the SI s, these do not need an array of panels to convert the DC.
These are smaller in size and capacity than the standard inverters. These are installed on the back of every panel and are responsible for the conversion of the panels.

FIG (8) PV plant different connecting configurations ;( a) Multistring inverter,
(b)Central inverter, (c) Micro inverter,
(d) String inverter
(d)MULTILEVEL INVERTER (MLI) This MSI shown in fig (8) features the optimal MPP tracking for a single string of PVs.

A. Centralized Inverter
B. String Inverters
C. Micro Inverters
D. Multi-string Inverter Low capital price per watt, high efficiency, comparative ease of installation
Allows for high design flexibility, high efficiency, and low cost, remote system monitoring capabilities.

Increases system availability, panel level monitoring, allows increased design flexibility no need to calculate string lengths.

Draws input current with low distortion, operates at lower and higher switching frequencies, voltage reduces the stress, reduced harmonic distortion. High voltage, Controlling mismatch between strings, non-flexible design, and not used in new solar installation.

No panel level monitoring, high voltage level present.

Higher costs, increased complexity in installation extreme heat, increased maintenance costs.

Higher component count, some configurations need more than one isolated DC supply.

3375757356596500Table (2) Comparison of different Types of Inverters
In this structure, DC-DC converter is implemented for each string for MPP
tracking and power combination of different string to a DC bus .A big power stage works as a grid connected half bridge inverter without transformer. The MSI is useful when PV strings of different rated power, different orientation are combined. The DC-DC part can be implemented with high frequency pulse width modulation (PWM) converter to reduce implementation area 2 3.

The MLI has been introduced in 1975, it is used for industrial applications as alternative in high power and medium voltage situations. Sources like batteries, super capacitors, solar
Panels are medium voltage sources. It consists of several switches and their arrangement of angles are very important.

These MLI can be classified into three types and is shown in fig (9) and these are not going
to be discussed 5.

FIG (9) Classification of Multilevel Inverter
These are a mix of the above two inverters which allows mostly independent of the grid but also sync with it in case of low solar or high consumption days 13 14. Typically such inverters first charge the connected battery and then export any excess power to the grid. Similarly at night / cloud days use the stored power for the consumption and after a certain threshold, recharge the battery through the grid. The advantages and disadvantages of solar power is shown in table (3).

1.This is an inexhaustible source of energy.

2.It does not release CO2 and other gases which pollute the air.

3.It can be used for satellites, heating, drying, cooking or electricity, cars, planes, large power boats.

4.No need a power or gas grid to get solar energy.

5.Cost is inexpensive compared to other sources of energy.

6.It can be installed easily at anywhere ex: houses, industries, deserts etc. 1.Energy cannot be generated at night times.

2.During day time i.e. cloudy or rainy with little or no sun radiation.

3.Only some areas receives good amount of sunlight
4.It also requires inverters and storage batteries for the energy conversion which are expensive
5.Land space required is quite large.

6.Occupies the land for many years and it cannot be used for other purposes.

Table (3) Advantages and Disadvantages of solar power
VI. FUTURE DEVELOPMENTS OF SOLAR ENERGY •India is a rapidly growing economy with more than 1Billion people, is facing a huge energy demand. The country stands fifth in the world in the production and consumption of electricity.

•More than 72% population living in villages and half of the villages remain without electricity. So our country concentrates more on energy efficiency. To meet this surging demand, solar energy is the best form of energy to fulfill the energy needs.

•The desert has some of India’s best solar power projects, estimated to generate 700 to 2100GW
•On March 1, 2014 the then chief minister of Gujarat, Narendra Modi inaugurated at Diken in Nee much district of Madhya Pradesh, India’s biggest solar power plant.

•The Jawaharlal Nehru National Solar Mission (JNNSM) launched by the Centre is targeting 20000MW of solar energy power by 202210.
•Solar power in India is a fast developing industry. The countries solar installed capacity reached 20GW in Feb 2018 before the targeted year 2022 and the average price of solar electricity dropping to 18% below the average price of its coal fired counterpart.

•About 66MW is installed for various applications in the rural area, amounting to be used in solar lanterns, street lighting systems and solar water pumps etc.

•The Indian Renewable Energy Development Agency (IREDA) will receive `128 crore ($20 million) for payment of interest on green bonds, it plans to issue over the course of the financial year.

•Finance Minister Arun Jaitley announced an allocation of just over ` 5,020 crore ($ 790 million) for the expansion of various renewable energy technologie3s and the other activities of the Ministry of Renewable Energy (MNRE) for the financial year 2018-2019 7 10.

•MNRE is expected to commission 15.62 GW of renewable energy capacity in the financial year 2018-19. The targeted capacity addition is 7.3% higher than the capacity addition target set for the financial year 2017-18 7 9 12.

•The capacity target in the wind energy sector remains unchanged at 4GW.

•The capacity addition target for small Hydro technology has been increased from 200MW to 250MW 11.

FIG (10) Comparison of various sources during 2017-18 and 2018-19
•The Bio Power capacity addition has been increased marginally from 340MW to 370MW.

•The Solar power capacity addition includes 10 GW of ground based large projects and 1GW of rooftop projects.
The below flow chart shows the differences between 2017-18 and 2018-19 for wind, small Hydro, Bio-power and solar 12. From this it is clear that there is a rapid increase in solar power as compared to others.
The main aim of this paper is to give brief review on Renewable Energy Sources. In this RES Solar power has tremendous demand and increase as compared to other forms of energies i.e. wind, geothermal, hydro, biomass, hydrogen and fuel cells. The photovoltaic equivalent circuit and its VI characteristics, Types of Inverters and its classification, and Future developments of solar energy are discussed.

ACKNOWLEDGMENT I am very happy to be a part of the Electrical world as a Researcher. And I wish to thank all authors who supported me to write this paper. The Paper, participating in its early stage and giving the idea to extent it up to a review paper. I would also like to thank the colleagues and friends for their fruitful cooperation, contribution, and discussions. My special thanks to my husband for complete support to do this paper.

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2. Investigation of multilevel multifunctional grid connected inverter topologies and control strategies used in photovoltaic systems, volume 42, 2017, pp .361-376.
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7. Top Trends shaping the future of solar energy-New Insights and Market Analysis Now Available from Infiniti, Nov 2017, AM Eastern Standard Time. An overview on prospects of new generation single – phase transformer less Inverters for grid-connected photovoltaic (PV) Systems.
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12. India Aims To Add 15.6 Gigawatts of Renewable Energy Capacity in 2018-2019 by Saurabh.

13. Grid-Connected solar electronics, By Mervin John’s, Hanh-Phuc Le and Michael seaman.
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Author’s Information
left12065001B.Nagalakshmi M.Tech (Ph.D.) She is currently pursuing Ph.D. in the Department of EEE in JNTUA University, Ananthapuram and also working as Asst.,Proff., in the Department of EEE in KVSRIT, Dupadu(v), Kurnool, India. Her research interesting areas include Power Electronics, Control systems & Power Systems.

left153133002Dr.R.Kiranmayi M.Tech., Ph.D. Presently working as Professor & Head Department of EEE in JNTUACEA, Ananthapuram, and AP. Her areas of interest include renewable energy resources, electrical power systems. She is a life member of ISTE and IEI.

left5715003Dr.K.NagarajuM.Tech,Ph.D. Presently working as Professor Department of EEE in SRIT, Ananthapuram, AP. His areas of interest include Power Systems, Control Systems & Electrical Machines. He is life member of Indian Society for Technical Education M.I.S.T.E.


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