In this research, Renewable Energy (RE) represents the existing power systems with different levels. However, because of the intermittent nature of these sources, it is necessary to analyze systems’ reliability with different RE penetration levels. This work presented a simulation method for reliability evaluation of renewable penetrated power systems. Some reliability indices were proposed for the case of power systems with renewable power plants. The adopted approach used the historical data of renewable energy resources, mainly wind and solar to estimate the power that can be generated and compared with the demand to find the power mismatch. Therefore, this approach can be utilized to determine the penetration level that renewable energy can be shared, and it also helps the system operators in deciding the percentage of the generation that RE power plant can provide.
Integration of renewable energy sources in power system has the advantage of reducing CO2 emission, hence assisting in resolving the global warming problem. It also helps decrease our dependency on fossil fuel in power sectors. Therefore, RE resources are considered a part of the solution to mitigate environmental problems caused by the use of conventional energy resources. In this sense, these resources offer clean energy generation, allowing the electrification of no-connected and remote areas, contribute to decrease dependence on fossil fuels. They also have improved their technologies and reduced costs. However, the capital cost of renewable power plant is very high compared to conventional power plants. But the operation and maintenance cost is cheaper than the one for conventional generation and will continue to decline with recent technical development.
Since most of renewable resources are intermittent in nature, it is advantageous to utilize more than one resource when available. Hybridizing of renewable resources improves the power system reliability, efficiency and economy, especially in places with good characteristics of sun and wind.
Integration of wind turbine generator and PV in conventional small isolated power system significantly lowers operating cost by offsetting costly fuel consumed by diesel generators. However, limitations in the energy available from PV system and their intermittent behavior degrade the system reliability. Therefore, cost benefit analysis associated with application of PV is incomplete without corresponding reliability assessment [
The reliability of PV systems has been the subject of several research studies going back to at least the 1970’s. Early work was focused on component reliability [
Methods for calculating the reliability of off-grid systems using the loss of load probability method are implemented in [
This paper presents a method to evaluate the reliability of renewable power systems. Three scenarios were used: a power system with wind energy, solar energy and hybrid system. Although the actual case includes a variable load, the load was assumed to be constant for the sake of simplicity. The historical data of wind speed and solar radiation for Riyadh were used to calculate the generation power from wind and/or solar energy at each minute for one month. Since solar PV panels’ output changes with their operating temperature, the ambient temperature was also included in the study. The aim of this study is to present or propose a method to classify the availability of renewable energy based on the historical data of the renewable resources, like wind speed and solar radiation. The availability of renewable resources can cover or feed the whole load, or it can share a percentage of the total load and the remaining is fed or supplied using conventional power plants. Therefore, this paper introduces new indices for renewable energy reliability assessment that can be used in power systems planning and operation. These indices are 25% energy index, 50% energy index, 75% energy index and 100% energy index. Each index gives the probability that the expected available renewable resources will cover 25%, 50%, 75% and 100% of the energy demand respectively during the study time.
The proposed indices in this study are calculated using the following equation:
N % index = P ( r e > N % ) (1)
where re is the available renewable energy, P ( r e > N % ) the probability that re is > than N% of the load, N represents 25, 50, 75 or 100 or any percent.
Therefore, 25% index gives the percent of time (over the period of study) at which the expected renewable energy is less than 25% of load, 50% index gives the percent of time at which the expected renewable energy is less than 50% of load so on.
This index attempts to answer the question: how many days (or hours) do we expect that renewable energy resources will supply N% of the load during a specified period? The benefit of using this index is to determine the adequacy of renewable resources to supply a specified portion of the load, and consequently; the conventional generation that is required to supply the remaining part of the total load. The accuracy of this method depends on the number of weather data that is included in the calculation and can be improved further, if data from forecasting models are inserted in the calculation of the renewable resources.
The wind power generated by wind turbines is calculated using the following equation [
P w = 0.5 N t A C p w 3 η (2)
where ρ is the air density in kg/m3, A is the rotor swept area in m2, C p is the turbine coefficient of performance, w is the wind speed at hub position m/s, N t is the number of turbines and η is the net efficiency. The theatrical value of C p is 59.3%.
The solar energy can be calculated using the following equation [
P S = I A p N p η (3)
where I is the solar radiation in w/m2, A p is the panel area, N p is the number of panels, and η is the panel efficiency.
The simulation was carried out using the following steps:
1) For each i Î n, calculate the load and available ER (based on historical data of solar radiation and wind speed), where i is the time step (minutes or hours) and n is the total time.
2) Compute
REL = RE load for each i, where REL is the level of RE w.r.t. load.
3) Classify the results of step (2) into groups based on level of RE penetration preset by the utility.
The number of PVs used in this study is 2000 panels. It is assumed that there are two solar PV plants at different locations and hence different solar radiations. Each location has 1000 panels of 250 Wp.
if the number of PV panels is increased, the percentage of the load that can be supplied by the solar will definitely increases. The 50% index value is 0.43 which is lower than 25% index. This means that the solar energy can supply 50% of the energy demand has a percentage of 0.43 during the month.
Since wind energy is of intermittent and fluctuating nature compared with the solar energy, therefore, it is hard to predict and anticipate.
of 50% index, 75% index and 100% index is 0.065, 0.031 and 0.015 respectively.
It can be concluded that hybridizing different renewable resources improves the system reliability and energy availability.
This work presented a simulation method based on a statistical method to evaluate the availability of renewable energy power that can be quantified in supplying the load in advance over a period reliably and adequately. It was shown that, hybridizing different renewable resources (i.e. wind and solar) will improve the system’s reliability and dependability. The benefit of the approach adopted and used in this work is that it can utilize historical data rather than forecasted ones.
The authors declare no conflicts of interest regarding the publication of this paper.
Haidar, Z.A. and Al-Shaalan, A.M. (2018) Reliability Evaluation of Renewable Energy Share in Power Systems. Journal of Power and Energy Engineering, 6, 40-47. https://doi.org/10.4236/jpee.2018.69006