**2.2 Reliability**

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

designed to work complementing each other. The hybrid resources, improve upon by attaching hybrid energy storages so that the energy converters are supported by energy storage in an effort to attain zero loss of power supply probability (LPSP) [9]. In addition, the preceding hybrid capacity is extended by integrating electronic controller automation in the style of PLC/SCADA. Any consistency in power supply obviously means there should be insignificant loss of power supply probability (LPSP) at any given time in the operation of the system. The probability that a system delivers consistent qualitative output power over long time period is considered to be reliable as interpreted by this author [6]. Hence, a reliable system is characterized by dependable power supply expressed mathematically in terms of mean time before failure (MTBF), and arithmetically expressed as reliability.

$$\mathbf{R} = \mathbf{e}^{\left(\cdot \text{dMTBF}\right)} \tag{1}$$

However, the mean time before failure is the predicted elapse time between operating system inherent failures using a Monte Carlo tool of simulation for reliability optimization and Perturb and Observe for maximum power point tracking for (MPPT) optimization.

Dependence on the provision of adequate components spare in case of urgency by employing redundancy is a healthy technical strategy attracting extra intervention costs. Plainly, idleness is what redundancy means and though there are two types, the passive and active types synchronized with the system, whereas, the passive types are most times in the standby mode waiting to be called upon for activity as explained by. Thus, the design of hybrid renewable energy resources structure, hybrid energy conditioner, hybrid energy storages and hybrid control platform for automatic energy management.

#### **2.3 Macro grid**

The physical framework of which electric power is produced using diverse generators to supply the load using electric conductors and cables overhead or underground transmission and distribution networks, usually use assorted transmission and distribution equipment. The **Figure 1** represents electric power of three phase grid emanating from the generating station through step up transformer connected to three phase transmission lines and connected to step down transformer that distributes electric power to various consumer loads as explained by Diaf et al. [10]. The grid in **Figure 1** is a three phase alternating current network for alternating current (AC) loads, and conversely, a direct current (DC) model are also use for diverse loads as observed by Rao [11] **Figure 1**. Illustrates multiple grids made available and categorized as micro, and large networks connected to diverse conventional and renewable energy generators.

**99**

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

Micro grid is said to be a network designed to integrate distributed energy resources, control operation, power quality issue, and energy management infrastructure for load demand and power supply stability. It is the smallest facility common among the grid with diverse generators using extra low voltage three phase-four wire supply down to single phase three wire or two wires supply configuration to provide electricity supply to consumers load. Furthermore, micro grid is considered to be a group of distributed resources (DER) and loads forming an electrical network. It has a grid of low-voltage distribution energy resource (DER), energy storage system (ESS) and/or micro sources such as photovoltaic, fuel cell, wind turbine, etc. Micro grid may have controllable energy sources such as biomass, hydro, fossil fuel or uncontrollable energy sources like solar and wind or may be flow-of-the-river that is dependent on daily, monthly and annual rain falls. Controlling solar and wind-micro grid is challenging it involves measuring the parameters such as solar irradiance or Insolation, PV array voltage, PV array current, ambient temperature, wind speed, and AC load pattern for a year evaluation. Conversely, the renewable energy storage loss, energy converter average yield, peak period parameters are used for evaluation of micro grid power performance as reported

A single source of electric power delivery to the consumer, local load is a diverse generation strategy such as conventional fossil fuel generation like oil, coal, etc. or renewable energy method such as solar, wind, hydro, biomass, geothermal, etc. Diesel or gasoline generators that are usually and commonly use in the rural areas are all categorized as small diverse electric generators' power sources. The diverse generator located by left of the figure and representing either of conventional or renewable energy diverse source according to this author [13]. The integration of diverse energy sources for the operation, control, power management in real time power system make up a micro grid or network as positioned by Ashourian et al. [14]. Obviously, micro grid has distribution structure like the macro grid except that it is a smaller size, in a tiny network, and has a low power capacity. Diverse generation is made into a hybrid design mix whenever the hybrid energy storage is integrated into the micro grid structure to reliably evacuate power to the load.

It will be good to start with hybrid energy system (HES). Hybrid energy system is the engineering design of hybridizing power supply components or pairing them, for example, arranging diverse energy resources to work in parallel (equivalent) is very common in power. So, hybridizing is defined as forming crossbreed of pairs of agent for working together to achieve a purpose. Thus, hybridizing is to manually or automatically synchronize two or more electric power generator resources or components to supply electric power to the grid, therefore forming hybrid energy system. Hybrid energy system is an infrastructural design that integrates diverse or multiple energy converters to energy storage, energy conditioners, energy management system. By and large hybrid renewable energy system (HRES) is an extension of HES that uses mix diverse resources as hybrid or all hybrid renewable energy

The concept of the hybrid RE power system is the perception to implement reliability portfolio to avert LPSP that will affect the quality of power supply resulting in dynamic change and transient. Hence, reliability is the dependability of systems

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

**2.4 Micro grid**

by Mohammadi et al. [12].

**2.5 Diverse generations (DGs)**

**2.6 Hybrid energy system (HES)**

resources to supply the electric power system.

**Figure 1.**

*Electric power multiple grids (transmission and distribution).*

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