**1. Introduction**

Sun, wind, and marine energies are defined as Variable Renewable Energies (VREs) due to their inherent intermittence, irregularity, and dispatchability, although VREs might

**Citation:** Olmedo-González, J.; Ramos-Sánchez, G.; Garduño-Ruiz, E.P.; González-Huerta, R.d.G. Analysis of Stand-Alone Photovoltaic—Marine Current Hybrid System and the Influence on Daily and Seasonal Energy Storage. *Energies* **2022**, *15*, 468. https:// doi.org/10.3390/en15020468

Academic Editors: Alon Kuperman, Alessandro Lampasi and Surender Reddy Salkuti

Received: 23 October 2021 Accepted: 2 January 2022 Published: 10 January 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

have several small- to large-scale applications in stand-alone power systems where energy storage is essential. Marine Renewable Energy (MRE) is broadly available in different regions. Estimations indicate that ocean energy could contribute from 500 to 1000 MW of the installed capacity by 2030 [1,2]. Ocean currents or marine currents can produce energy from tidal movements and/or ocean circulation due to thermal and salinity gradients [3]. In Mexico, this type of energy is attractive due to its natural occurrence in certain regions such as the Gulf of California and the Cozumel Current in the Yucatan Peninsula where the potential for producing energy is as high as 100 W/m<sup>2</sup> [4]. However, even with the technology to harvest ocean energy, significant challenges for renewable energy include bringing the energy into the coast, storing it, and using it in a cost-effective manner.

Stand-alone renewable energy systems are off-grid systems that are able to provide electricity for regions lacking power grids in specific remote applications. Energy supply is usually provided by VREs where the energy-storage systems (ESSs) play a very important role in balancing and controlling the generation and consumption of electricity in deferred periods of time [5]. Nowadays, the cost of energy-storage systems is high; therefore, the selection of an appropriate ESS requires studies with multiple approaches. Determining the correct one among the many options, such as Pumped Hydro Storage (PHS), Compressed Air Energy Storage (CAES), Pb batteries, li-ion batteries, flow batteries, flywheels, supercapacitors, and hydrogen, should be carried out whilst taking into account criteria such as, storage capacity, response time, lifetime, cycle life, efficiency, cost, power, energy density, and power rating [6,7]. These criteria are also important as ESSs may play an important role in the environmental impact of the system [8]. The large variety of options and complex characteristics make it difficult to choose a specific ESS to take full advantage of their properties [9]. Therefore, the first step to deciding the most appropriate ESS technology is to consider its benefits, advantages, disadvantages, and maturity [10]. Moreover, stand-alone systems require a higher degree of energy availability to provide autonomy and comfort related to the daily electricity consumption. Hybrid renewable energy systems could be an effective way to integrate different renewable energy sources, for instance, sun and marine energy sources or any other viable combination. Hybrid systems can provide major electricity-generation availability, improving the reliability of the energy supply and the overall efficiency due to a lower dependency on ESSs [11]. Likewise, they could allow energy-storage-installed capacity to be reduced while having a profound effect on the durability of the ESS since the cycle life is affected by the daily availability of the renewable source [12]. The study of the potential of renewable energies is the first stage of the development of a hybrid system where the analyses in different periods of time, from daily to seasonal, can provide substantial information on the performance and energy storage needs in these periods [13].

Cozumel, Mexico, has been considered as a potential zone for stand-alone systems for households due to its ecotourism attractions. Although many studies of ESS implementation in the main VRE systems (solar and wind energy) can be found elsewhere, only few studies for MRE exist, especially in potential regions of Mexico or other regions with an abundance MRE resources; Figure 1 shows MRE projects where ESSs are considered.

The relevance of incorporating an ESS relies on its inherent environmental and economic benefits, especially in stand-alone systems where the surplus energy can be used for other purposes such as mobility. Stand-alone systems and microgrids are quite promising in Mexico due to approximately two million people having no access to electricity, especially in isolated regions and coastal zones [14]. As MRE and photovoltaic energy are broadly available in coastal touristic zones, this work could serve as a guide for the implementation of hybrid systems where the choice of primary source might have further implications. The different hybridization degrees not only imply continuous household energy supply but also the great benefits of seasonal energy storage, thus providing further economic advantages.

**Figure 1.** Different MRE projects with ESSs and their use [15–24].
