Design and analysis of a combined floating photovoltaic system for electricity and hydrogen production

Highlights

• Floating photovoltaic and hydrogen production system integration is investigated.

• Hydrogen as an energy storage medium compensated the intermittent solar energy.

• Floating application of photovoltaic plant improved the efficiency and saved lands.

• Unit electricity cost is determined.

Abstract

The current study deals with a potential solution for the replacement of fossil fuel based energy resources with a sustainable solar energy resource. Electrical energy demand of a small community is investigated where a floating photovoltaic system and integrated hydrogen production unit are employed. Data are taken from Mumcular Dam located in Aegean Region of Turkey. PvSyst software is used for the simulation purposes. Furthermore, the obtained results are analyzed in the HOMER Pro Software. Photovoltaic (PV) electricity provides the required load and excess electricity to be used in the electrolyzer and to produce hydrogen. Saving lands by preventing their usage in conventional PV farms, saving the water due to reducing evaporation, and compensating the intermittent availability of solar energy are among the obtained results of the study for the considered scenario. Stored hydrogen is used to compensate the electric load through generating electricity by fuel cell. Floating PV (FPV) system decreases the water evaporation of water resources due to 3010 m² shading area. FPV and Hydrogen Systems provides %99.43 of the electricity demand without any grid connection or fossil fuel usage, where 60.30 MWh/year of 211.94 MWh/year produced electricity is consumed by electric load at $0.6124/kWh levelized cost of electricity (LCOE).

Introduction

Energy shortage and water resources depletion are among the main threats for the humanity. Population increase and industrialization lead to the increased energy demand. This demand is mainly met by the fossil fuels and thereby, causing serious environmental impacts. Burning of the coal, oil and gas is linked to the environmental pollution which threaten the public health and rising levels of greenhouse gases in atmosphere and is a leading contributor of climate change [1]. Therefore, a strong motivation can be recognized in order to employ sustainable energy resources such as solar energy. Solar resource is one of the most viable renewable energy resources especially due to the recent developments [2]. Photovoltaic systems are the renewable energy alternative on a global basis which are getting more competitive with conventional energy resources. However, photovoltaic systems are not able to provide the energy demand through a day because of the intermittency nature of the solar energy (e.g., undesired weather conditions or nighttime periods). In order to find an alternative solution, hydrogen is considered as an environmentally friendly and sustainable energy carrier. Dincer et al. [3] introduced the hydrogenization as a crucial smart energy solution, in order to achieve a sustainable future. Authors defined the potential benefits as (i) large scale, efficient renewable energy integration, (ii) integration with smart grid, (iii) worldwide use of renewable energy across sectors and regions, (iv) enhanced energy system resilience, (v) decarbonized energy use, (vi) feedstock for many industries. Research and development on hydrogen and power production from an intermittent energy source such as wind and solar has been investigated in the recent years. For example, Safari and Dincer (2018) [4] performed an optimization study for a hydrogen and electricity production system based on the wind power where the excessive electricity is used for hydrogen and methane production. Economic forecast of solar hydrogen production is investigated with emphasize on the essential implementations and education program is addressed by Nowotny et al. [5], in order to protect the environment through sustainable development. Two methods of solar hydrogen production including photoelectrochemical water splitting (PEC) and water electrolysis using PV derived electricity are emphasized. Synergy between these two approaches of solar hydrogen production is indicated. Extensive categorization of hydrogen production methods is made. The methods are compared and analyzed in terms of environmental and economical applications [6]. 18S concept has introduced by Dincer et al. [7] as a new concept to show the critical perspectives of innovation in hydrogen production. Moreover, innovative hydrogen production methods are ranked for comparison and evaluation. A different approach has been studied for hydrogen production. Waste of the almond shell has been used in the conversion to hydrogen-rich gas via supercritical water gasification [8]. Sorgulu et al. [9] integrated hydrogen as a clean energy storage medium on renewable based energy system for residential applications. Parabolic solar collectors with a steam turbine, and a wind turbine are integrated with fuel cell, electrolyzer and absorption cooling system to supply power, cooling, heating and hydrogen.

Dahbi et al. [10] developed a power management strategy to organize the energy flow for hydrogen production in a grid integrated PV system. Hydrogen production is optimized through controlling the flow of the water. An experimental supported study is held in Yazd City in Iran for hydrogen production from a 20 kW PV power station. Experimental findings are compared with the simulation. Capability of generating electricity for hydrogen production is reported for the region [11]. The III-V group compound semiconductor, the multi-junction Si structure and the dye-sensitized solar cells for photoelectrochemical hydrogen production are reviewed. Advantages, disadvantages and for the further development, the integration of plasmonic metal nanostructures for the improvement of photon absorption and utilization are outlined [12]. Tamalouzt et al. [13] highlighted the modelling and the simulation, and presented a power management strategy for a hybrid micro-grid system associated to an electric generation system using wind turbine, doubly fed induction generators, photovoltaic generator and a proton exchange membrane fuel cell generator. Control strategies are developed for a grid connected PV-fuel cell hybrid system, to maximize the utilization of the PV power and to optimize the use of the fuel cell power in order to maximize the production and the storage of hydrogen have been developed [14]. A case study has been conducted in Algiers, Algeria with support of experiment. Proton exchange membrane (PEM) electrolyzer and PV system are simulated as a direct-coupling system. Optimization of direct connection is applied for the improvement in system efficiency [15]. The stand-alone greenhouse system is analyzed with experimental study. A photovoltaic and ground source heat pump system coupled with a stand-alone hydrogen plant [16]. Sizing method is developed for a photovoltaic hydrogen system to produce hydrogen-enriched compressed natural gas. It provides a good computing tool to maximize energy efficiency with rational system costs through obtaining the optimal system sizes of components [17]. Hydrogen production performance of a Photovoltaic/Thermal powered Proton Exchange Membrane (PEM) electrolyzer has been studied elsewhere. Employing of extra heat for the water heating purposes improved the performance of the PV panels, hence, hydrogen and heat generations are increased in their system [18]. Flat plate solar collector is used in an integrated system for hydrogen production. Exergoeconomic analysis and multi objective optimization are studied [19]. A direct mathematical approach is used in an intuitive method to design stand-alone PV based hydrogen production and storage system. A case study held in Kuala Lumpur, to test the effectiveness. Proposed system sizing is employed for economic analysis [20].

Considering the electric demand of the remote areas, vertical oriented PV modules have been used in Esperanza Base, Antarctica. For the compensation of the remarkable absence of solar energy in four of the twelve months in this region, hydrogen production and accumulation system is proposed for effective energy storage [21]. Stand-alone floating membraneless PV-electrolyzer device is described. Novel electrode configuration comprised of mesh flow-through electrodes that are coated with catalyst on only one side. Without a membrane or actively pumped electrolyte, water electrolysis has demonstrated [22]. Performance of the concentrating solar power (CSP) based high temperature Polymer Electrolyte Membrane (PEM) electrolyzer is investigated. The effects of solar intensity, electrolyzer current density and working temperature are identified on the performance of the overall system [23]. The land shortage problem slows the growth in PV industry. Therefore, floating PV applications are the alternative design solutions for photovoltaic systems. Floating application moves the PV farms from land to water surface. It makes lands free for housing, agricultural, tourism, and other facilities. The first floating PV project had been installed for research purposes in Aichi, JAPAN. They compared the performance of floating PV cells with traditional terrestrial PV systems. After that Far Niente wineries avoided to displace land that was used to grow vines. SPG Solar was contracted and they built 175 kW floating PV plant in California, USA. By the end of 2014, there are 22 installed floating photovoltaic power plants around the world, with the installed capacity from 500 W to 1157 kW [24].

Additionally, floating structure saves the water through reducing the evaporation by shading the water surface. This is also confirmed by a research in China through developments in PV and FPV technologies and their potential in China [25]. Craig et al. [26] studied the water lost through evaporation in the open reservoirs. Authors found that the 40% of open reservoir's water could be lost through evaporation. A research held in Australia, the climate change effects on water temperature and evaporation in a large reservoir has been analyzed. Two future 20-year periods (2030–2050 and 2070–2090) have been simulated. Their annual evaporation predictions showed that the first period annual evaporation will be approximately 8% higher than the 20-year average annual evaporation estimated for current climate, and for the second period, annual evaporation will be approximately 15% higher according to their study [27]. As a research which performed in Turkey, evaporation in Yuvacik Dam has been modelled. Findings clearly show that the solar radiation is the most effective parameter on water lost through evaporation [28]. An irrigation reservoir covered by floating photovoltaic system in East Coast of Spain. According to this study, 5000 m³ of water (25% of the water reservoir storage capacity) determined as annual saving [29].

An Australian project has been investigated the possibility of floating PV plant integration with existing basins for wastewater treatment. According to their calculations, water between 15,000 and 25,000 m³ is saved by each MWp. Besides, yearly energy yield up to 10% through cooling effect [30]. Performance assessment of floating PV module through operation temperature is investigated. Two prediction models with different variables are suggested. A correlation between the temperature of the floating PV operating environment and system efficiency is derived [31]. Floating photovoltaic power plants also lead for a better water quality due to the reduced photosynthesis and algae growth by blocking sunlight. Another advantage of floating system is their less dust effect. Typically, areas with high solar energy potential are mostly dusty and arid, so in comparison to their ground mounted counterparts, floating PV systems perform in a low dust environment. Researchers pointed the less dust effect and reviewed the concept of floating PV systems installed on water bodies such as ponds, lakes, dams and reservoirs. They also listed the installed capacities of floating PV plants across the world [32]. The performance of floating PV systems is also investigated by Cazzaniga et al. [33], where main advantages of floating PV systems along with the additional features such as tracking, cooling and concentration are presented in their study. Experimental results showed an improvement in the efficiency of the system due to the cooling effect. They also highlighted higher cost of floating structure compared to terrestrial panel support is partially compensated by the lower installation and maintenance costs. Kim et al. [34] used a finite element method to perform their floating system structure safety, and economic viability evaluation was performed based on the construction cost.

In this study, a floating PV system has been studied. Analyses have been conducted by PvSyst and Homer in order to assess the effectiveness of these systems in providing the required energy. PvSyst has been used especially for identifying the parameters of efficiency losses which have relations with floating application. Prevention of water evaporation is also deduced in the study. The FPV technologies are applied to the PV system to study the feasibility for investigating and verifying environmental and technical sustainability and economic viability. In addition, a hydrogen energy storage system has been integrated to the floating photovoltaic system to investigate its effect in compensating the intermittency drawback of the system. In this regard, feasibility analysis has been occurred in order to determine most feasible component sizes of floating photovoltaic plant, hydrogen fuel cell, electrolyzer and hydrogen tank, for supplying a specific electric load.

Main novelty of this study is the integration of hydrogen as an energy storage medium with floating photovoltaic system. The main goals of the whole system are:

• Uninterrupted electrical power supply.

• Prevention of evaporation from water reservoirs.

• Land conservation from solar power plants.

The system is mainly aimed to provide the electrical load of a small community, to produce hydrogen and also to reduce the evaporation rate of Mumcular Dam. In this case, the system includes Floating PV, Hydrogen Fuel Cell, Electrolyzer, Electric Load and Hydrogen Tank shown in Fig. 1.

Once the solar energy is available, FPV system produces the electricity. In this period, produced electricity is directly feeding the load and in case there is extra energy, electrolyzer consumes the excess electricity to produce hydrogen. Produced hydrogen is stored in a hydrogen tank and used by fuel cell to generate required electricity, once the solar energy is not available (e.g., during the night, cloudy weather, etc.). In both charging and discharging periods, water evaporation will be diminished due to the shaded area of the water by FPV structure and modules. The system is located on the Mumcular Dam, Bodrum Municipality, Mugla Province, Aegean Region, Turkey. It lies on 38.4 °N latitude and 27.2 °E longitude, 43 m above sea level. The water surface below the floating photovoltaic plant is an irrigation dam that built between 1986 and 1989 by Turkish State Hydraulic Works (Devlet Su Isleri). The main design difference between floating PV system and terrestrial one is basically supporting structure. The main feature of the supporting structure in floating PV system is the buoyancy effect. High density poly-ethylene, fiberglass reinforced plastics are the popular floating supporting structure materials. There are standard types or special design floating structures in the PV market. In our case, pipe rafts with tires are assumed as used structure in consideration of their cost effectiveness, flexibility and strong resistance.

For the technical analysis of the FPV system, PvSyst software is employed since the floating application requires comprehensive technical analysis because its relations with efficiency parameters. PvSyst software can use several types of Meteorological Databases. In this study, MeteNorm Database has been used. MeteoNorm provides the monthly meteorological data which are measured by ground stations and satellites. According to geographical site parameters, hourly values are set synthetically as simulation values. Electrical load profile is created synthetically in regard to electric load database by HOMER Pro software. The assumed electrical load (a small community) is near the irrigation dam and it has no grid connection, so we simulate the electrical load as all-dc system since there is no need for long electric transmission or grid connection. Electrolyzer as another electric load, also consumes DC electricity.

Table 1 shows the clearness index and average temperature values for current site. Clearness index is a dimensionless number which defined as the surface radiation divided by the extraterrestrial radiation. It is always between 0 and 1. Cloudy conditions make the clearness index low; sunny conditions make it high.

PvSyst has employed for comprehensive technical analysis of FPV system. Sizing process has been occurred at feasibility simulation in HOMER Pro Software, therefore, the PV power capacity in PvSyst stands as a symbolic size. The size of the PV power capacity in the PvSyst, represents a PvSyst unit in HOMER Pro Software. Feasibility simulation multiplies the PvSyst unit to determine the required PV power capacity for the system in HOMER Pro Software. On the other hand, PV modules should not disrupt the integrity of floating structure. In this case, 60 PV modules are placed as 15 PV modules in series and 4 PV modules in parallel (Fig. 2). Placement can be seen in the 3D construction on Fig. 3.

Sunpower-P17 350Wp commercial solar modules are selected considering the efficiency, warranty, quality, price and compatibility. The 21 kWp FPV system is represented as a PvSyst unit in HOMER Pro software.

Total collected solar energy depends on various complex functions and factors. Power temperature coefficient (−0.37%/°C for Sunpower-P17-350 PV modules) is one of the most related factor with efficiency effects of floating application. In addition, the orientation is also highly influenceable on the total amount of energy production. Fixed tilted plane orientation is used in our case. The only variable in the fixed tilted plane is the tilt angle. Tilt angle is the angle between PV module plane and horizontal plane. Tilt angle should be arranged as south faced in the Northern Hemisphere and north faced in the Southern Hemisphere.

Our FPV system is located at 38.4 °N latitude and 27.2 °E longitude, 43 m above sea level. According to geographical coordinates, PvSyst software can obtain the optimum tilt angle. Higher tilt angles may cause more shadings on PV modules. Shadings may have a huge impact on the performance of PV modules. To avoid that, shading simulation for the 3D construction must be done in PvSyst software. In order to minimize shading losses to acceptable levels, tilt angle or pitch distance should be arranged. Fig. 3 shows the 3D construction of our FPV system for shading simulation.

HOMER Pro software is employed in order to determine most feasible component sizes to supply the electrical load. Floating PV system, electrolyzer, hydrogen tank, hydrogen fuel cell is used for electric generation, hydrogen production and energy storage purposes. Fig. 1 shows the system configuration. For the feasibility simulation, acceptable shortage, project lifetime and economic values as discount rate, inflation rate should be determined. For the components, technical values are pre-defined from generic devices. FPV system is exported as the PV production hourly data in kW from PvSyst software and imported to HOMER Pro software.