Hydrogen electrolysis, efficiencies

For hydrogen electrolysis efficiency and fuel cell efficiency... 

For the operating voltage at the optimum power point Vp and the Faradaic current for water splitting of /p, the overall solar to hydrogen generation PV electrolysis efficiency is given by... 

In the case of the hydrogen path, it is assumed that surplus wind electricity is used to produce hydrogen via electrolysis (efficiency 70%). Hydrogen is then stored in pressure tanks at 50 bar and is re-electrified at peak load in gas turbines (GT, efficiency 40%) or gas-steam turbines (GST, efficiency 60%), with a hydrogen-to-natural-gas ratio of 8 2. 

Further examples of recent attempts to reduce the consumption of electrical energy are the electrolysis of aqueous solutions of methanol (but CO2 is still produced at the anode) [78, 79] and water electrolysis using ionic liquids as electrolytes [80]. In the latter case, the authors claimed the possibility of obtaining high hydrogen production efficiencies using an inexpensive material such as low-carbon steel. 

Schug CA (1998) Operational characteristics of high-pressure, high-efficiency water-hydrogen-electrolysis. Int J Hydrogen Energy 23 1113-1120... 

The target cost of nuclear hydrogen production must be cheaper than that of the conventional electrolysis subtracting the distribution cost. Hydrogen production efficiency of EED-aided SI thermochemical cycle is expected around 43% with current knowledge (Cho, 2009). 

Hydrogen production efficiency, t/h (m3/h), minimum - steam methane reforming - high-temperature water electrolysis 4 x 12.5 (138.75-103) 4x6.76 (75-103)... 

The figure shows results for both HTE and low-temperature electrolysis (LTE). In addition, an efficiency curve for the SI thermochemical process is shown (Brown, 2003). The results presented in Figure 3 indicate that, even when detailed process models are considered, with realistic component efficiencies, heat exchanger performance, and operating conditions, overall hydrogen production efficiencies in excess of 50% can be achieved for HTE with reactor outlet temperatures above 850°C. For reactor outlet temperatures in the range of 600-800°C, the supercritical C02/recompression power... 

A proper estimation of the electrolysis efficiency provides guidance to the improvement of the processes and the electrolyser design. In this study, the current efficiency, r c, of the electrolysis system was determined from the experimentally produced amount of hydrogen, H2(exp), divided by the theoretical value, H2(theor) calculated from the Faraday s law ... 

The efficiency of electrolysis takes a strong dip when the Ir02 content drops and the catalyst approaches pure Pt, in accordance with earlier experience. However, already at 10% Ir content, the electrolysis efficiency is near 95%, rising only a little with further addition of Ir. At 10% Ir, the drop in the fuel cell efficiency for electricity production has been reduced only from 55 to 53%, so the technology for acceptable operation in both modes seems finally to be established. This will prove important for some of the hydrogen introduction scenarios described in Chapter 5. 

Finally, for the hydrogen fuel cell car, the solar radiation to wind conversion-efficiency is taken as 100% (following arguments of Sorensen, 1996c), the wind turbine efficiency as 35%, the electrolysis efficiency as 80%, the fuel cell conversion efficiency as 55% and the rest as for methanol. The overall accumulated efficiencies are 1.4 x 10 for the methanol route and 0.054 for the wind-hydrogen route. 

---