# Innovative Strategies for Combining Solar and Wind Energy with Green Hydrogen Systems
## 3 Innovative Strategies
### Optimized Energy Conversion and Storage
#### 3.1.1 Techniques for Efficient Energy Conversion
In connecting to the grid, there is a need for fuel cells as a power generation technology. Fuel cells are devices that convert chemical energy directly into electrical energy through electrochemical reactions between fuels (typically hydrogen) and oxidizing agents (like oxygen). They consist of two electrodes--an anode and a cathode--separated by an electrolyte. Hydrogen is introduced at the anode, where it splits into protons and electrons, generating electricity as the electrons flow through an external circuit. The protons combine with oxygen at the cathode to produce water and heat. Fuel cells are used in various applications, including powering electric vehicles, providing backup power, and serving as stationary power sources. Different types, such as polymer electrolyte membrane fuel cells (PEMFCs) and molten carbonate fuel cells (MCFCs), can operate on various fuels, enhancing their flexibility and environmental benefits. A comparison between different fuel cells, which include alkaline fuel cells (AFCs), direct methanol fuel cells (DMFCs), and phosphoric acid fuel cells (PAFCs) is addressed in Table 2. They are particularly appealing for renewable energy generation and cogeneration systems, where both electricity and thermal energy are produced to improve efficiency [39]. PEMFCs are among the most promising power generation technologies for achieving carbon neutrality. They are characterized by high power density, rapid start-up times, excellent efficiency, lower operating temperatures, and safe handling [40]. Advancements in water electrolysis have further improved hydrogen production processes. Techniques such as sacrificial-agent-assisted water electrolysis utilize small molecules to replace the oxygen evolution reaction (OER), thereby degrading pollutants and enhancing efficiency. Organic upgrading-assisted electrolysis incorporates organic reactions to replace the OER, producing high-value chemicals along with hydrogen. Self-powered electrolysis systems combine water splitting with metal-based batteries or fuel cells, enabling hydrogen production without additional electricity input. Self-catalyzed electrolysis systems leverage spontaneous metal oxidation at the anode, facilitating hydrogen production at the cathode [41]. \begin{table}
\begin{tabular}{p{113.8 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Fuel Cell Type** & **PEMFC** & **AFC** & **DMFC** & **PAFC** & **MCFC** & **SOFC** \\ \hline Operating temp (\({}^{\circ}\)C) & 30–100 & 90–100 & 50–100 & 160–220 & 600–700 & 500–1000 \\ Fuels & Hydrocarbons or methanol & Pure hydrogen & Methanol & Hydrogen from natural gas & Natural gas, biogas, others & Natural gas, propane, hydrocarbons or methanol \\ Electrolyte & Solid polymeric membrane & Aqueoussolutionof potassium hydroxide soaked in a matrix & Solid organic polymer polyrefluorosulfonic acid & 100\% phosphoric perfluorosulfonic acid & 100\% phosphoric acid stabilized in an alumina-based matrix & 43–47 & Solid, stabilized zirconia \\ Energy conversion efficiency (heat and power) (\%) & 85–90 & 85 & 85 & 85–90 & 85 & Up to 90 \\ Electrical efficiency (\%) & 30–40 & 60 & 20–25 & 40–42 & 43–47 & 50–60 \\ Typical stack size & \textless{1–100 kW} & 10–100 kW & up to 1.5 kW & 50–1000 kW (250 kW module typical) & \textless{1–1000 kW (250 kW module typical)} & 5–3000 kW \\ Operational life & 40,000–50,000 h (stationary) Up to 5000 h (mobile) & Up to 5000 h & 10,000–20,000 h & Up to 40,000 h & Up to 15,000 h & Up to 40,000 h \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of different fuel cell types in Ref [39] with significant modifications. Photovoltaic (PV) technology advancements have significantly boosted solar energy utilization by improving the efficiency and adaptability of PV systems. These systems convert solar energy directly into electricity, while photothermal variants use reflectors to generate heat for steam turbines.