1. Introduction
Access to affordable, clean, and reliable energy has attracted much attention from the research as well as the humanitarian community in recent years. Driven by the United Nation’s Sustainable Development Goals (SDGs) [
1], researchers and practitioners are exploring innovative approaches to provide access to electricity, particularly for remote and isolated areas removed from a viable utility grid. Remote isolated areas usually rely on standalone diesel generators (DGs) to supply the electricity demand in these communities. However, fuel security is a great concern for community members, as fuel prices and transportation costs can vary dramatically and unexpectedly. This is more evident in the current global pandemic, where the effects of COVID-19, such as reduction of gasoline and fuel consumption, as well as reduction in electricity demand and CO
2 emissions, are still being analyzed [
2,
3]. Renewable energy sources, particularly solar and wind energy, have been implemented in isolated communities to reduce greenhouse gas (GHG) emissions. Nonetheless, the intermittent nature of renewable resources can limit the efficiency and reliability of such systems. Hybrid systems combine various power sources such as diesel generators, solar power systems, and battery energy storage systems (BESSs) to provide a reliable, more efficient electricity production, with fewer emissions and maintenance requirements when compared to a standalone DG. Nevertheless, the techno-economic performance of these systems is also dependent on the conditions of the site to be installed, such as the dominant energy mix and the energy costs. In the Ecuadorian context, the government subsidized the price of diesel fuel until 2020. Nowadays, this subsidy is being gradually reduced until the fuel price reaches international market values. Then, the main contribution of this paper is to know the impact of the rise of diesel fuel price on the costs, electricity productions, renewable energy penetrations, and CO
2 emissions in each analyzed scenario.
2. Literature Review
Hybrid systems have been extensively analyzed in the literature to determine techno-economic feasibility, sensitivity, and size and production optimization analysis of different combinations of power systems [
4,
5,
6]. In [
7], Lau et al. describe the performance analysis of a hybrid solar power system (SPS)/DG configuration in Malaysia. NREL’s Homer Pro was used to analyze the impact of SPS penetration and costs under various hybrid configurations. The emphasis of the analysis was on fuel savings and the reduction of carbon emissions. The optimization analysis results showed that the standalone DG design would produce the lowest cost of energy (COE) as well as the lowest total net present cost (NPC) given the price of diesel, however, the hybrid SPS/DG configuration provided significant carbon emission reductions and is still a viable option in remote locations in Malaysia. In [
8], Hossain Lipu et al. describe the design optimization and sensitivity analysis for a Hybrid SPS/wind/DG configuration for Saint Martin Island in Bangladesh. Homer Pro is used to perform the simulation and optimization based on NPC and COE for different scenarios. The results show that a hybrid SPS/wind/DG configuration provides the lowest NPC and COE parameters than wind/DG, wind/SPS, SPS/DG, standalone SPS, and standalone wind scenarios. These results were validated and compared to other hybrid renewable energy systems in locations such as Bangladesh, India, Malaysia, Thailand, and Turkey, resulting in one of the minimum NPC and COE indicators of the projects analyzed.
In [
9], the authors considered the performance analysis of an off-grid hybrid wind/SPS/DG and battery system for a remote area. The analysis was performed on Homer Pro using solar radiation and wind data for the site in Malaysia. The results show that an optimized system including an 18 kW SPS, 2–10 kW wind turbines, and a 15 kW DG produces a COE of USD
$1.88/kWh, which is lower than conventional power plants. In addition, the hybrid system provides a reduction of CO
2 and greenhouse gas (GHG) emissions, as well as limiting the requirements for fuel transportation which is an issue for remote locations. In [
10], the authors present the feasibility study of a hybrid SPS/wind/biomass configuration including battery storage for an islanded microgrid in a rural location in Punjab, India. The optimal sizing of components was achieved through a swarm-based artificial bee colony (ABC) algorithm, to minimize the NPC to select the system with the least levelized cost of energy (LCOE). The optimization was also validated using Homer Pro. The results show that the ABC algorithm provides a better estimation for the optimal system showing a combination of 250 kW of solar PV, 19 kW of wind turbines, 1400 batteries, and a 40 kW gasifier with an annualized system cost of USD
$63,006/year and an LCOE of USD
$0.173/kWh. In [
11], the authors propose a co-optimization scheme for distributed energy resource (DER) planning in community microgrids to minimize total annualized cost at maximal fuel savings. A combination of Lagrange multipliers, Fourier transform, and particle swarm optimization methods are used to determine the optimal system. The results are compared with a simulation using Homer Pro. The optimal system is sized by identifying renewable energy resources, considering fuel savings and CO
2 emissions reductions as a first step; then, sizing dispatchable generation units such as BESSs; performing parity checks; and using technical and economical evaluation indices such as renewable energy utilization, fuel savings, and annualized cost. A case study of a village community in Ohio, USA, shows the validity of the model by sizing a hybrid wind/SPS/biomass configuration, which was validated through cost minimization using Homer Pro.
Ecuador is a country that has greatly subsidized fuel prices. Currently, the National Government is seeking to eliminate fuel subsidies progressively over the next few years [
12], bringing the local fuel prices to match regional and international prices. Diesel fuel prices in neighboring countries such as Peru, Argentina, Colombia, Chile, and Brazil are over USD
$0.57/L, at the start date of this work [
13]. Having a current fuel price of USD
$0.26/L, the Ecuadorian Government is subsidizing at least 50% of the real price of this oil derivative [
14].
This paper presents a technical, economic, and environmental analysis and optimization of the impact of the reduction of diesel subsidy in the design of an off-grid hybrid power system (OHPS). The Bellavista community in Ecuador was selected as the case study for this work due to the ongoing relationship with stakeholders in neighboring islands built through the deployment of renewable energy projects. This impact will focus on the electricity production levels of each of the OHPS components (SPS, DG, and BESS) according to the increase of fuel price and the SPS size within the optimization model in Homer Pro [
15]. The SPSs changed in three sizes, which were 8 kW, 10 kW, and 13 kW. The diesel fuel price was USD
$0.26/L at the start time of this work [
13], whose price was also increased in USD
$0.35/L, USD
$0.44/L, USD
$0.53/L, and USD
$0.62/L.
5. Discussion
Hybrid systems based on SPS/DG/BESS configurations are viable options that have been explored to supply electricity to isolated communities such as Bellavista [
5,
26,
27]. One of the main advantages of the SPS/DG/BESS configuration is that it can ensure uninterrupted power supply to the electrical load even at times of low solar radiation and during nighttime. In addition, the use of the BESS helps to improve the penetration of energy from renewable sources as well as to cope with their variabilities due to their intermittent nature [
28].
The Bellavista community is a site with high potential for solar energy generation [
29], while other sources, such as wind energy, are not suitable due to the low wind speeds (under 2 m/s) based on weather databases such as Meteonorm [
18]. The study of hybrid systems based on renewable energy systems are relevant to ensure reliable electrification for remote locations such as the case of the Bellavista community [
6,
19,
30].
In our analysis, the OHPSs provide technical–economic solutions to the community’s electricity access problem. These solutions depend on the size of the SPS and the price of fuel. The present hybrid system (SPS/DG/BESS) is a feasible configuration for this location. Other authors have analyzed the same configuration, such as Olatomiwa et al. [
26], who compared two hybrid systems: (1) SPS/DG/BESS and (2) SPS/Wind/DG/BESS. Here, the first system had the lowest NPC with reduced CO
2 emissions compared to the SPS/wind/DG/BESS configuration and standalone DG configuration. Likewise, the low diesel prices reduced the COE of simulated configurations. The latter situation is comparable to the analysis in
Table 4, where the lowest COE values corresponded to the scenarios with the lowest fuel prices (USD
$0.26/L and USD
$0.35/L). In addition, these scenarios showed low NPC values but high pollution levels due to the fact that these configurations used higher amounts of electricity from the DGs. Although the scenarios with fuel prices USD
$0.44/L, USD
$0.53/L, and USD
$0.62/L showed higher penetration of renewable energy with a considerable reduction in CO
2 emissions, these scenarios had higher values of NPC and COE.
Likewise, Oulis Rousis et al. [
27] studied an SPS/DG/BESS configuration, which presented better performance when it was compared to SPS/DG, SPS/BESS, DG, and DG/BESS configurations. Even the renewable fraction of this system was over 70% with a fuel consumption of 1905 L/year. Similarly, the SPS/DG systems presented high investment costs with high diesel fuel consumption, which produced high levels of pollution. In the present paper, scenarios 13, 14, and 15 from
Table 5 had renewable fractions above 50%, whose scenarios had a mean annual fuel consumption of around 3600 L/year (
Table 5). The SPS/BESS configuration was not considered in the present work due to certain inconveniences that may occur in its operation, such as the high excess power at times of peak SPS generation, low load consumption, and fully-loaded BESS. In grid-connected renewable power systems, these excesses can be injected into the public power grid [
31]. In the case of the off-grid systems, if these surpluses are sizeable, they should be harnessed with initiatives such as additional water pumping systems [
20]. Regarding the three scenarios studied in
Section 4.4, the optimal system (scenario 8) achieved an electricity surplus of 6.61%. Given this relatively low surplus of electricity, it is not required to design complex configurations for harnessing this excess energy.
6. Conclusions
This paper presents a technical–economic–environmental analysis and optimization of the impact of the reduction of diesel subsidy in the design of an OHPS for the Bellavista community, Ecuador. This impact was focused on the electricity production levels of each of the OHPS components (SPS, DG, and BESS) according to the increase of fuel price and SPS size within the optimization model of Homer Pro. This configuration was simulated in 15 scenarios by varying both the size of the SPS and the fuel price. At the beginning of this study, USD$0.26/L was the price of fuel throughout Ecuador. Currently, the country is in a process of gradually eliminating fuel subsidies (gasoline and diesel) until these reach regional and international prices.
The scenarios with diesel prices of USD
$0.26/L and USD
$0.35/L showed the lowest levels of renewable energy penetration, which was reflected in the mean renewable fraction from
Table 5. In addition, reduced power delivery from the BESS can be observed, which increases the electricity production of the generator as well as the emission of pollutant gases. However, these mean renewable fractions considerably increased for scenarios with prices of USD
$0.44/L, USD
$0.53/L, and USD
$0.62/L, even though these scenarios reached percentages between 38% and 52%. These increases in the energy penetration from SPSs and BESSs allowed the reduction of costs associated with the hours of operation of the diesel generator, amount of fuel, and CO
2 emissions. This can also be seen from the USD
$0.44/L price in the scenarios for each SPS size (
Table 5), the electricity production levels of the generator reduced and started to vary minimally compared to the obtained results in the scenarios of USD
$0.53/L and USD
$0.62/L. This trend was similar for the electricity output from the power converter and BESS.
Scenarios 3, 8, and 13 with the diesel price of USD
$0.44/L were chosen to perform the analysis of these configurations in their 15th years (
Section 4.4). This is because the generator electricity production of these scenarios was similar for the scenarios with the same SPS and fuel prices of USD
$0.53/L and USD
$0.62/L. Here, the performance of these three scenarios in their last year of operation was shown. Each scenario described the details of operation such as electricity production (DG, BESS, and SPS), renewable fraction, energy output/input from the converter, CO
2 emissions, and losses. The SPSs supplied less electricity this year because the PV modules have a degradation of 0.32%/year, which was set as input in the model. In addition, scenario 8 was the optimal system, although scenario 13 showed lower CO
2 emissions.
Finally, it can be concluded that with fuel prices of USD$0.26/L and USD$0.35/L, the NPCs and COEs of these scenarios are relatively low compared to those scenarios of higher prices. However, Homer Pro is a software that optimizes renewable projects, from a techno-economic perspective, which will favor generator electricity production due to low fuel prices. It would also reduce the use of energy from the BESS with an increase in CO2 emissions. It was observed that the BESSs in these scenarios had lifetimes that exceeded the 15-year horizon of the project. Even these lifetimes were of several decades due to the low discharge rates of these storage systems in each of these scenarios. In contrast, the scenarios with fuel prices of USD$0.44/L, USD$0.53/L, and USD$0.62/L showed higher penetration of renewable energy with a considerable reduction of CO2 emissions. Likewise, the BESSs of these scenarios had the respective replacement within the project horizon. These scenarios presented slightly higher investment costs compared to the two scenarios with lower fuel prices. The results obtained show that if the diesel price will increase over USD$0.62/L, the production of electricity to power the community will have similar values to the scenarios for each SPS with prices from USD$0.44/L. This price of USD$0.62/L is more likely to happen as subsidies for diesel get reduced to regional standards.