Matlab Simulation of Solar PV & Concentrating Solar Power Plant (Csp) As a Renewable Energy Sources

I. INTRODUCTION

The time has come where the earth‘s energy situation can be defined as critical, which might be one of the reasons why many countries are becoming more conscious on subjects related to energy consume, energy efficiency, climate change, investment in renewable energies, dependence on fossil fuels… Therefore the uses of renewable energy sources are increased. The different kinds of renewable sources which are generally used in modern times are given as below:- 1. Solar power plant 2. Hydro power plant 3. Geothermal energy 4. Wind energy 5. Biomass etc. These different renewable energy sources have their own Advantages and disadvantages. But in the latest time use of solar energy is increased due to its feasibility, simple operation, etc. Compare to other sources. So, use of solar energy is popular in worldwide.

Concentrating Solar Power (CSP) plants use mirrors to concentrate sunlight onto a receiver, which collects and transfers the solar energy to a heat transfer fluid that can be used to supply heat for end-use applications or to generate electricity through conventional steam turbines. Large CSP plants can be equipped with a heat storage system to allow for heat supply or electricity generation at night or when the sky is cloudy. There are four CSP plant variants, namely: 1. Parabolic Trough, 2. Fresnel Reflector, 3. Solar Tower

Solar energy is a highly renowned alternative energy type. The intensity of the sun‘s irradiation that reaches the globe yearly is equivalent to 92 billion tons of petroleum. A calculation from 2002 states that the energy received from the sun in one hour was greater than the world used in one year.

Solar PV systems employ solar cells made from semiconductor materials. Direct or scattered sunlight incident on these materials causes a certain portion of it to be absorbed within the cells. The energy of the photons absorbed knock electrons loose from their atoms which can then travel through an external circuit by means of metal contacts attached to the solar cells. Owing to electric fields inherent within the cells, the electrons flow in one direction thereby producing direct current (DC) electricity. A single solar cell produces only a small amount of power for which they are interconnected to form panels or modules that give 50 to 200 watts [1]. These PV modules are combined with a set of additional application dependent system components to form a PV system. Fig. 1illustrates those components that make up the PV system.

The electricity produced by the PV modules is stored in batteries for later use when there is no sun. Deep-cycle batteries are used that provide electricity over long periods of time and can repeatedly charge and discharge up to 80% of their capacity. Charge controllers regulate the rate of flow of electricity from the modules to the battery or the loads or to both simultaneously. It keeps the battery from overcharging or overloading thus prolonging its life [1].

In concentrating solar power (CSP) technology sun‘s Direct Normal Irradiation (DNI) is concentrated to produce heat of temperature 400ºC to 1,000ºC [1]. This heat is used to produce electricity by

Based on the process of collecting and concentrating solar radiation, the CSP can be categorized into four major technologies:- i) Parabolic Trough, ii) Solar Tower or Central Receiver, iii) Parabolic Dish and iv) Linear Fresnel Reflector (LFR). I) Parabolic Trough: - This technology uses parabolic trough shaped mirrors to concentrate the incident DNI onto a receiver tube which is placed at the focal line of the trough. The basic elements of parabolic trough power station are:- a) Solar collector field, b) Conventional electricity generating unit (steam Rankine cycle or combined Cycle) and c) Thermal storage (optional) [1].

parabolic mirrors that concentrate the sun‘s rays on heat receivers (i.e. steel tubes) placed on the focal line. Receivers have a special coating to maximise energy absorption and minimise infrared re-irradiation and work in an evacuated glass envelope to avoid convection heat losses. The solar heat is removed by a heat transfer fluid (e.g. synthetic oil, molten salt) flowing in the receiver tube and transferred to a steam generator to produce the super-heated steam that runs the turbine. The use of molten salt at 550‘C for either heat transfer or storage purposes is under demonstration. High temperature molten salt may increase both plant efficiency (e.g. 15%-17%) and thermal storage capacity [1].

 Modelling and Results of Solar-PV System

The output current can be measured by subtracting the diode currents and current through resistance from the light generated current. From this circuit, the output current of the cell is expressed as,

A 30 KW solar-PV array is realized considering 24,080 cells (344×70 dimensions) using equation-(1)-(2). A Matlab model forthe same is developed.

After the simulation, we obtained the following results,

For building this model Matlab tool called Simulink is used, being the general view of this model presented in Figure 3.5.

Initially two equal mass flows are defined and they are assumed to be constant values, namely m1 and m2. The mass flow m1 is the molten salts flow rate that goes out of the hot tank and passes steam generator. The mass flow m2 is the molten salts flow rate that goes out of the cold tank into the tower receiver for warming up and then continues towards the hot tank. In order to design the heat transfer fluid mass flow, equation (1) is developed as a function of , considering the maximum energy at the tower receiver for obtaining this values, which means that mass is flowing at its maximum flow rate (variable mass flows are not considered on this model), as shown in equation (2):- The dimensions of the storage tanks determine the autonomy of the CSP plant (to remark the importance of this fact) and the masses that control the cold and the hot tank are defined by Mc and Mh, respectively. It is admitted that each tank has the same dimensions, with 8 meters of diameter (d) and 4 meters of height (h tank) in a cylindrical shape. Therefore, the volume of each tank is calculated following equation (2):- In Figure 4.1 is presented the detailed model of the tower receiver subsystem which provides the modelling based in this equation and is working with a block called switch that works as a condition ―if‖ for defining when the mass flow m2 is different from zero or is zero, i.e. when this mass flow is zero means that the outlet temperature of the tower receiver (Ttr,o) is equal to the inlet temperature of the tower receiver (Ttr,i).

Fig 4.2 Receiver subsystem for outlet temperature modelling These equations applied to the hot tank modelling are defined with another subsystem in Simulink (Figure 4.2) which represents the math operations for obtaining Th, o and Th, o+. What is made initially is defining a Th, ini when the mass of the tank is zero and then the initial temperature is considered at the first hour, otherwise is taken the previous value of Th,o and then a next iteration will progress continuously in the next hour.

The SAM 2.0 model results of CSP plant is shown in fig below:-

In this paper detail description for designing of Solar PV plant and parabolic trough solar power plants with thermal storage was developed. The methodology is based on the individual design of different components and subsequent integration of the components into the whole system.CSP technology tells that the best of those technology is the possibility to accumulate heat for the electricity production, allowing its use even when the sun in not shinning, during cloudy periods or night times when it has a storage system. There are two kinds of solar power plant: - PV and CSP. CSP has so many advantages over PV type solar power plant.

REFERENCES

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Department of Electrical Engineering, SS College of Engineering, Rajasthan Technical University, Kota, India