# 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  
Maximizing energy conversion from solar and wind sources is essential for optimizing their output. Improvements in solar photovoltaic (PV) cells and wind turbines are critical to effectively capturing and converting energy. Key advancements include power-to-gas technology, advanced electrolytes, and high-efficiency PV technologies. Integrating these technologies with green hydrogen systems necessitates advanced control strategies to efficiently convert excess energy into hydrogen through electrolysis. A brief overview of these technologies is provided below. Figure 5: Current state-of-the-art hybrid renewable energy technologies. Highlighted are integrated solar and wind energy sources and a biogas unit. Power-to-gas (P2G) technology provides a solution for large-scale, long-term electricity storage by connecting the power grid with the gas grid. This technology involves converting surplus electricity into hydrogen through water electrolysis, which is then transformed into methane (CH\({}_{4}\)) or substitute natural gas (SNG) by reacting with carbon monoxide (CO) or carbon dioxide (CO\({}_{2}\)) in a methanation reaction. The produced methane can be injected into the existing gas distribution network or stored for future use, effectively bridging renewable energy generation with conventional gas infrastructure (see Figure 6). Electrolyte systems for water electrolysis are pivotal in the efficient production of hydrogen and oxygen from water. The main types include proton exchange membrane (PEM), alkaline water electrolysis (AWE), and solid oxide electrolysis (SOE), each with distinct efficiencies, flexibilities, and lifespans, as outlined by [PERSON] et al. [37], These systems are compared in Table 1, highlighting their operational characteristics. From the table, it is evident that PEM electrolysis has a lower system consumption but with a higher cost than alkaline water electrolysis. It is primarily due to PEM's higher efficiency and advanced design. PEM technology operates at lower temperatures, uses thinner proton-conductive membranes (20-300 \(\upmu\)m), and allows for faster response times and higher current densities (above 2 A/cm\({}^{2}\)), making the overall process more efficient. This leads to reduced power consumption compared to alkaline electrolysis. However, the higher cost of PEM electrolysis arises from the use of expensive noble metals like platinum and palladium for the hydrogen evolution reaction and iridium \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Key Parameters** & **Alkaline Electrolysis** & **PEM Electrolysis** & **Solid Oxide Electrolysis** \\ \hline State of development & Commercial & Commercial & Commercial \\ Cell temperature in \({}^{\circ}\)C & 40–90 & 20–100 & 800–1000 \\ Electrolyte & Alkaline solution & Solid polymer membrane & ZrO\({}_{2}\) ceramic doped with \\ Charge carrier & OH\({}^{-}\) & H3O\({}^{+}\)/H\({}^{+}\) & O\({}^{2-}\) \\ System power consumption (future) in kWh/m\({}^{3}\) (Hs) & 4.3–5.7 & 4.1–4.8 & Not Available \\ Cell voltage in V & 1.8–2.4 & 1.8–2.2 & 0.91–1.3 \\ H\({}_{2}\) production in m\({}^{3}\)/h (STP, per system) & \textless{}760\approx 2.7\) MW & Up to 450\(\approx\) 1.6 MW & Not Available \\ Cold start time & Minutes-hours & Seconds–minutes & Not Available \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Operational characteristics of the electrolytes in Ref [37] with significant modifications. Figure 6: Power-to-gas (P2G) technology process. oxide (IrO\({}_{2}\)) or ruthenium oxide (RuO\({}_{2}\)) for the oxygen evolution reaction at the electrodes. These materials, while effective, are much more costly than the materials used in alkaline electrolysis, which rely on less expensive catalysts. Additionally, the advanced components and compact design of PEM systems contribute to the overall cost, making PEM electrolysis more expensive than alkaline water electrolysis, despite its efficiency advantages [38].