**1. Introduction**

Global warming and other environmental problems are driving the adoption of renewable energy sources at the residential, commercial, and industrial levels. Estimating the impact of climate change on the ecosystem involves the accurate knowledge of the carbon cycle and its associated uncertainty. Calculating cumulative emissions in order to prevent an extreme warming level is a key step to guide the manner in which industrial processes, including power generation, should be carried out. Actions for reducing global warming are adjusted following the threshold of 1.5 or 2 ◦C as the critical limit in a time interval between the years 2000 and 2050 or 2100. However, depending on the established assumptions and scenarios, the risk of experiencing extreme conditions at the middle of the century could be a realistic prospect [1].

Under these circumstances, many countries have been changing their energy mix from a fossil-fuel based one to a renewable-based one, incorporating wind and solar photovoltaic energies, as well as demand response programs [2]. In addition, financial tools such as mutual funds are also implemented to provide economic support for these technologies [3].

As renewable energies are intrinsically variable, the power system requires a high degree of flexibility to effectively manage the uncertainty introduced by these sources, and this could be achieved by implementing demand side managemen<sup>t</sup> or by installing any type of energy storage system (ESS).

Incorporation of ESS can improve the accommodation of renewable generation while reducing greenhouse gas (GHG) emissions. As an example, incorporation of renewable power combined with ESS in California could reduce carbon dioxide (CO2) emissions from 90% to 72%, whereas renewable power curtailment reduces from 33% to 9%. In the case of Texas, CO2 emissions could be reduced from 58% to 54% and renewable power curtailment could be reduced from 3% to 0.3% [4]. Combination of carbon capture and storage devices with conventional generation units is also an option to reduce GHG emissions. However, the combination of renewable generation with ESS can be energetically more e ffective [5].

Historically, the acquisition costs of a battery energy storage system (BESS) have been considerably high, limiting their economic performance and consequently their mass adoption. However, when very low GHG emissions are required, BESS can be a critical device to achieve such an ambitious goal.

In the case of energy provision for an isolated hybrid energy system (HES), incorporation of BESS becomes profitable due to the fact that the fuel consumption and operating hours of a conventional generator are considerably reduced. In the case of a grid-connected HES, retailing rates and feed-in tari ffs as well as favorable resources are crucial for their successful adoption [6].

Heuristic techniques are commonly used to carry out the optimal sizing of a specific HES. Consequently, some of them have been implemented in computational programs such as HOMER Pro ® [7], iHOGA ® [8], and Hybrid2 ® [9], among others. Dispatch strategies implemented in most of these tools are based on load following and cycle charging concepts. Load following consists of generating power from conventional units only to satisfy net load (NL), and this approach is frequently suggested in a HES with high share of renewable power, which is much higher than load demand over the year. Conversely, a cycle charging strategy forces conventional generator to operate at its rating power when needed to charge BESS with the remaining energy, so this strategy is frequently implemented when renewable generation is limited [10]. It is important to mention that these strategies do not require any forecast of renewable generation or load demand. However, they are very e ffective in the managemen<sup>t</sup> of HES of small scale used on rural electrification projects.

In the case of a HES of larger scale, energy forecasts are frequently employed to optimize the daily operation. This is a topic that has been widely studied and it is the focus of this work. A complete literature review is presented in the next section.
