An essential component which applies to all the categories of IPVFC systems is the maximum power point tracker (MPPT). It ensures that the maximum power is extracted from PV modules based on the available solar radiations, regardless of weather conditions. Examples of MPPT algorithm and implementation methodologies are perturb and observe method, incremental conductance method, short-circuit current method, open circuit voltage method, fuzzy logic controllers, and artificial neural network controllers [50,51]. Karami et al. [52] used MPPT and compensators to extract the maximum power from the PV modules and FCs as the demand for power varied with time. Padmanaban et al. [53] demonstrated how the Jaya-based MPPT method can be used to track the MPP of PV modules for an IPVFC system. Energy management system (EMS) or Power management system (PMS) is also necessary for controlling the energy flow in an integrated IPVFC system. Equally important for optimal operating conditions of IPVFC systems are the ancillaries and health monitoring of components such as compressors, pumps, fan/blowers, charge controller for the batteries, as well as sensors to measure temperature, pressure, mass flow rates, and humidity. The compressors are used to store gases from the PEME in tanks or for feeding the reactant gases into the fuel cell component as illustrated in Figure 3. Pumps are required to feed water into the electrolyser or PV/T components. Fans/blowers are used to cool the temperature of the components such as the batteries, PEME and PEMFC. In the design phase of IPVFC systems, the power consumed by the ancillaries are discounted from the power produced by the system. The deductions are done to ensure that the power consumed by the actual loads and the ancillaries are considered during capacity sizing of an IPVFC system. Touati et al. [54] assumed that 20% of a 12 kW installed capacity is consumed by the ancillaries to cool the PEMFC and pressurize gases. To enhance the reliability of the system, power supply to the ancillaries were configured so that the ancillaries for the PEMFC are not connected to the PV modules since it is subject to intermittency; although the ancillaries of the PEME can be connected to the PV modules since electrolysis can take place during the day.

Sizing of IPVFC systems depends on the load profile of the application [19]. Accurate sizing is a major challenge with IPVFC system deployment due to the intermittency of solar radiation. The interrelationships between the dynamic load profile, power generation, hydrogen generation and solar radiation availability require reliable control strategies [55]. During operation of an IPVFC system, the amount of hydrogen consumed by an FC stack is proportional to the power drawn from the FC stacks; while the hydrogen produced from the electrolyser is proportional to the power supplied to the electrolyser [56]. The power available for hydrogen production depends on the solar availability, the power consumed by the loads, the power consumed by the ancillaries, the power used for charging batteries/SC components and the power lost due to conversion losses. Hourly load current can be multiplied by the number of hours of operation of an IPVFC system to get the daily load [55]. This means that the ampere-hour for all the load components/ancillaries can be added to estimate the expected capacity of the system.

Table 1 summarizes some studies to highlight the design intents and compositions of some IPVFC systems.

Within the categories of IPVFC systems, different types of PV cells, fuel cell and electrolyser can be used. For instance, Lead acid [24], Li-ion [18] batteries and supercapacitors [30] were considered as potential energy storage components for IPVFC systems. Hydrogen can be stored as a compressed gas in tanks [20] or in metal hydride storage [17]. Alkaline electrolyser [18] or PEME [57] can be used as a source of hydrogen. PEME is adapted to compensate for the possible fluctuations of solar energy because of its fast response to current fluctuations. The US Department of Energy found out that a PEME produces hydrogen at 99.99% of purity level for less than USD 10/kg. This high level of purity of hydrogen is suitable for the operation of PEMFC. The current density is 4–5 times that of an alkaline electrolyser and it uses no corrosive electrolyte unlike alkaline electrolyser, although alkaline electrolyser is more matured technologies [58,59]. PEMFC is widely used for IPVFC applications since it uses hydrogen [57] which can be generated from water electrolysis using excess electricity from the PV array. Polycrystalline solar cells [18] have higher conversion efficiency than monocrystalline solar cells.

2. Current and Emerging Applications of IPVFC Systems

4.1. Application of IPVFC Systems in Microgrids

Microgrids are important in the utilization of renewable energy resources because they can facilitate distributed energy infrastructures in which energy can be generated close to the end-users. Ghenai and Bettayeb [77] studied the integration of a 500 kW PV array and a 100 kW PEMFC with the grid to supply power to a University building in Sharjah, United Arab Emirate. The demand was met although 26% of the power consumed was purchased from the grid. The supply mix includes 42% of the power from the PV array and 32% from the PEMFC stack while 5% of the annual output was sold to the grid. Sharma and Mishra [78] proposed a dynamic power management scheme for stand-alone micro-grid in which all the sources, energy storage and loads were connected to a DC link. Hidaka and Kawahara [119] asserted that efficient application of the grid-connected PV arrays for domestic applications requires energy storage which can be facilitated by using solar hydrogen as energy vector to compensate for the fluctuations in power generation due to the intermittency of solar radiation and ambient temperature.

4.2. Off-Grid/Stand-Alone Applications of IPVFC Systems

The dependence of IPVFC systems on solar radiation makes them suitable for remote power sources for autonomous residential applications, telecommunication infrastructure, agro-processing, research activities, sporting facilities and leisure in remote locations. Ulleberg [63] posited that PV arrays, fuel cell and water electrolysis could play a major role in the future stand-alone power systems. Silva et al. [122] conducted a pilot study on the use of an IPVFC system in the National Park of Araguaia, Tocantins-Brazil. Based on their findings, the noiseless and clean attributes make it suitable for distributed generation applications in public spaces such as train stations, zoos, museums, libraries, motor parks/bus stations, markets, etc. This is particularly useful in many underdeveloped countries where public utilities operate without electricity, water, refrigeration of food and drinks, air-conditioning of spaces, lighting, and entertainment. Cordiner et al. [123] analyzed a full year of data collected from six remote off-grid Radio Based Stations (RBS) and found that an IPVFC system can meet 24 h/7 day high quality, autonomous and continuous power supply required by an off-grid RBS, particularly in developing countries where power grids are grossly underdeveloped. Another study by Silva et al. [71] showed that it was feasible to use an IPVFC system for power generation in an isolated community in the Amazon region of Brazil. The system was composed of a PV array of 124 W with 30.1 V, a PEMFC at 5 kW at 48 V; a PEME at 6 kW per Nm³ h⁻¹ of hydrogen produced; and a lead acid battery (220 Ah at 12 V). The study implied that the costs of the components are still high but using a battery for energy storage appeared to be favored since the cost of adding an electrolyser and a fuel cell will increase the cost of the system. Based on economic analysis, a PV-battery system is cheaper than an IPVFC system of similar capacity, but the inclusion of a fuel cell can protect the battery from stresses associated with the depth of discharge, thereby elongating the life of the battery, and reducing the overall replacement costs of the battery.

An IPVFC system can be used in the agricultural sector for all-year-round crop and animal production and agro-processing given that it can be operated under distributed and off-grid modes. This allows farmers to meet short-term needs using PV arrays, batteries/supercapacitors, and long-term needs with an electrolyser and fuel cell stacks. Since solar radiation is abundant during summer, excess electricity can be stored as hydrogen so that power can be supplied during winter when solar intensity usually dwindles. Ganguly et al. [33] studied how an IPVFC system can be used to power a greenhouse in a sustainable manner based on the climatic conditions of Kolkata, India. They used 51 solar PV modules to generate hydrogen with an electrolyser (3.3 kW) and charge a battery bank such that the battery bank and two PEM fuel cell stacks (480 W each) can meet the energy demand. IPVFC systems can be used for desalination to convert seawater, brackish water, or fresh water of unknown quality to potable water as well as generate electricity and hydrogen. A feasibility study of seawater electrolysis using an IPVFC system has been conducted to generate hydrogen and oxygen from salty water instead of using fresh water which is better used for domestic, agricultural, and industrial purposes [80]. The presence of NaCl was reported to enhance hydrogen production and the system also produced fresh water as a by-product. Touati et al. [54] studied the potential application of an IPVFC system to provide a stand-alone power source for a desalination plant.