**1. Introduction**

According to recent scientific literacy works [1–3], about 78–80% of the world commercial energy comes from fossil fuels, such as, petroleum, coal and natural gas. Those high-carbon sources have negative effects in our environments, such as, effects on heath, land, air and rain. In view of that, the attention of most countries around the globe has been shifted to low-carbon energy. Renewable energy is naturally abundant resources, which can be harnessed without compromising future energy needs. Unlike fossil fuels, which depletes as time goes on. Renewable energy sources like wind, solar, biomass, wave and tidal are abundant sources that can produce clean energy. On recent time, series of renewable energy technology improvement has been witnessed, because the cost of generating electrical power is decreasing [4].

Although, renewable energy is considered as the new technology of generating electricity, the barrier associated with renewable is stochastic and unpredictable weather behavior. Its availability varies depending on the location. That is why, it is necessary to complement renewable with other sources like batteries. Because of this intermittent nature of renewable, single renewable energy source tends to be problematic in terms of energy yield and operational cost. Based on the aforementioned drawbacks, two or more renewable are being combined to form a hybrid renewable energy system (HRES). The main goal of doing this, or to improve electrical power production, to minimize cost, to reduce negative effects associated with burning fossil fuels and to improve the overall system efficiency.

In recent times, the integrated renewable energy system is gaining more attention, because a hybridized system can be efficiently applied to supply high efficiency and reliable electricity to the end-users, unlike a single-renewable source. A HERS can be applied in stand-alone or grid-connected modes. Stand-alone system must have a large storage to handle the load. While in a grid-connected mode, the storage can be small, and the deficient power can be acquired from the grid. It should be noted that, grid-connected mode must have a power electronic controllers for load sharing, voltage, harmonic, and frequency control. Thus HERS operating model is classified into Island mode where the generated electricity is consumed locally and grid connected mode where the renewable energy source is connected to the grid [5].

It is interesting, to note that, among the renewable energy sources, wind power is the fastest growing in terms of global annual and cumulative installed capacity. Wind energy is almost everywhere around the world. But the wind speed strength varies depending on the particular area. Wind energy can be operates during the day and night times, unlike other renewable.

Solar is the cleanest and most abundant renewable energy source available on earth (SEIA 2013). Solar energy can be defined as radiant light and heat from the sun and is harnessed by human using technologies.

The amount of energy harnessed from the sun is depending on radiation and scientists define radiation in two different ways which are energy in wave form (electromagnetic wave) or energy in particle form (photons). The electromagnetic radiation emitted from the sun has the wave length interval from 0.1 nm to 104 m. However, 95% of solar energy reach earth with the intervals of 0.3–2.4 μm only [5, 6]. The photons are traveling through space at the speed of 3.0 × 108 m/s and each photon carry different amount of energy measured in electron volts. Photovoltaic (PV) is derived from two words: photo which means light and voltaic or volt means the unit of electric potential. PV or solar cells, also called the semiconductor that converts sunlight to direct current (DC) electricity. PV cell is typically a thin wafer which consists of an ultra-thin layer of phosphorus-doped (N-type) silicon on top of a thicker layer of boron-doped (P-type silicon). The p-n junction is created through the doping and the electrical field is created near the top surface of the cell. When a sunlight which carries photons strike the PV cell, the current is produced because the photons prompt the electrons flow from n- to p-junction. A typical silicon PV cell will produce about 0.5 ~ 0.6 V under open-circuit condition regardless of size. The current produces is proportional to the intensity of sunlight striking the surface as well as the efficiency and size of the cell. The photovoltaic cell normally connected in series or parallel circuit to produce the desired amount of current. PV modules consist of PV circuits sealed in an environmentally protective laminate. PV module is the fundamental building blocks for a PV system. PV panels involve one or more PV module assembled as pre-wired, field-installable unit. Series of PV panels are called a PV array which is ready-installed unit for power generation. The performance of PV modules and array are basically rated according to their maximum power output (w) tested under Standard Test Conditions (STC). Standard Test Conditions are defined as a cell (module) operating temperature of 25°C (77°F) and incident solar irradiance level of 1000 W/m2 .

Because of the aforementioned reasons, this chapter focuses on design, modeling, optimization, control and sensitivity analysis carried out on a hybrid system based on wind energy with a PV system.

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**2.2 Reliability**

*A Review of Hybrid Renewable Energy Systems Based on Wind and Solar Energy: Modeling…*

The terms are technical in nature and there brief explanations will go a long way to concept discussion the hybrid renewable energy power system characteristics, thus, optimization, reliability, grid, micro grid, macro grid, diverse generation,

The term optimization is defined as a process, act or methodology of making system design or decision functional or effective as possible according to Hong and Lian [6]. Two practical fundamental methods of optimization exist, thus, the metaheuristics and the simulation-based, will be further discussed in the section of optimization. In another perspective, it is reported that it is finding of an alternative with the highest achievable performance and most cost effective under some constraints through maximizing desired factors and minimizing the undesired ones. However, maximization means an effort to attain desired highest system performance, reliability outcomes regardless of cost and this perception is equally testified by Hong and Lian [6]. However, any practical optimization could be restricted by lack of full data or information, whereas, if some data are available while others are not then linear programming can be employed. Conversely, the optimal sizing of renewable power system components to increase their energy, capacity or performance, thus, providing power, reliability impact is considered optimization according to Kaabeche et al. [7]. Consequently, Power system hybridization is an infrastructural design exploration using optimization tools to configure hybrid renewable energy components to enhance the power reliability enabling zero or minimal loss of power supply probability (LPSP). Probability is the likely hood of getting optimal power supply reliability, and that, notwithstanding all depends on the power supply infrastructure redundancy status. Redundancy of power components can either be fully active or partially actively working with the system structure to allow smooth electric power supply distribution without interruption. Passive means the components are on standby and are only engaged at the point when component failure occurs. Subsequently, system reliability with active redundancy has smoother power supply that does not allow loss of power supply or allows only minimal loss than the passive redundancy reliability component.

Dependable, consistent, trustworthy, and steadfast are always watch words for reliability term, and relating to energy delivery to consumer electric loads it means consistent qualitative power supply. The Power supply system is actually designed with redundancy and diagnostics in order to achieve power supply optimal reliability. Redundancy takes several concepts of the simple arithmetic, such as, N + 1, N + N, or 2N for maximum reliability such as system automation as expressed [8]. The '2N' redundancy element stands out to provide a better redundancy than the others; it means the two coefficient multiplied by existing components as 'N' size. Power supply consistency depends on availability of alternative energy sources and backups such as energy storage subunits as applicable to hybrid renewable energy power supply. The term hybrid in its self means a mixture of two different components with about similar results for a specific purpose, for example, a hybrid solar-micro hydro renewable energy source (HRES) to supply a rural community with reliable electricity. Conversely, the solar resource is understood to be stochastic by nature and it is the characteristics unlike micro hydro, so they function better when hybridized or

*DOI: http://dx.doi.org/10.5772/intechopen.85838*

hybrid energy system, and hybrid renewable energy system.

**2. Pertinent terms**

**2.1 Optimization**

*A Review of Hybrid Renewable Energy Systems Based on Wind and Solar Energy: Modeling… DOI: http://dx.doi.org/10.5772/intechopen.85838*
