Nel Hydrogen of Norway, founded in 1927, state having the world's most efficient and reliable electrolyser: https://nelhydrogen.com/product/atmospheric-alkaline-electrolyser-a-series

Electrolyser DC power consumption: 3.8 - 4.4 kWh/Nm3

Nm3 = Normal cubic meter - Temperature 0C, Pressure 1 atm

Using the ideal gas law: PV = nRT
n = (101,325pa x 1m3) / (8.314 x 273.15K) = 44.618 mol

Hydrogen has a molar mass of: 2.01588 g-mol-1
1 Nm3 of H2 is therefore 44.618 mol x 2.01588 g-mol-1 = 89.945g

Hydrogen higher heating value 286 kj/mol
converted to kWh = 39.4 kWh/kg HHV

1 Nm3 of H2 has therefore an energy content of 3.544 kWh

3.544 / 3.8 kWh/Nm3 = 93.3% efficient
3.544 / 4.4 kWh/Nm3 = 80.5% efficient

• Molar mass: https://www.webqc.org/mmcalc.php
• HHV: https://en.wikipedia.org/wiki/Heat_of_combustion

Inferring from the following cost graphic, their electrolyser cost at scale (50MW) approaches ~520 €/kW (atmospheric pressure) or ~610 €/kW (15 bar).

A specialist in PEM and alkaline electrolysers, fuel cells for vehicles & stationary applications, and power-to-gas.

All figures below from:
http://europeanpowertogas.com/wp-content/uploads/2018/06/20180619_Hydrogenics_EU-P2G-Platform_for-distribution.pdf

PEM Cell Hydrogen Output: 620 Nm3/h x 3.544 kWh/Nm3
2197 kW / 3000 kW = 73.2% efficient

Alkaline HySTAT-100-10: 100 Nm3/h x 3.544 kWh/Nm3
354.4 kW / 500 kW = 70.9% efficient

Presentation quotes efficiencies as high as 89.5% (39.4/44) for PEM electrolyser by 2020 and 82.1% (39.4/48) for alkaline electrolyser by 2025. With central efficiencies of 83.8% (39.4/47) and 78.8% (39.4/50) respectively. (Source: FCH-JU, Development of Water Electrolysis in the European Union, February 2014)

Electrolyser efficiency increases with higher current density and average cell voltage.

Stack efficiency of 3MW HyLYZER 600 is 80% HHV @ 2MW, 78% HHV at 2.5MW and 75% HHV at 3.0MW, see 3MW HyLYZER 600 Brochure

Costs (Development of Water Electrolysis in the European Union, February 2014):

• 2030 PEM Central cost estimate: 760 €/kW (250-1270)
• 2030 Alkaline Central cost estimate: 580 €/kW (370-800)

Costs (Power-to-Gas Roadmap for Flanders):

• 2030 multi-MW PEM cost estimate: 700 €/kW, opex 32 €/kW, 50,000h lifetime
• 2050 multi-MW PEM cost estimate: 385 €/kW, opex 28 €/kW, 60,000h lifetime

Cell stack replacement costs are expected to fall to less than 300 €/kW by 2030 and less than 200 €/kW by 2050.

Alkaline @ 20MW scale in 2025:
FCH-JU, Early business cases for H2 in energy storage and more broadly power to H2 applications, June 2017

• Efficiency: 80.4% efficient
• CAPEX System: 480 €/kW
• OPEX: 10 €/kW
• CAPEX Replacement 216 €/kW
• lifetime 90,000h

The hydrogen production rate (40,000kg) and system power (100MW) on the ITM Power HGAS product page suggests an efficiency of 66% for their PEM electrolyser. However their technology updates suggest higher efficiency at >77%.

16th July 2013: Technology Update: Performance and Efficiency improvements (more than 77% efficiency)

ITM Impact Report 2015 (Stack efficiency 84%, 2015)

13th June 2016: Thüga Group: Power-to-Gas technology performance update (over 70% efficiency)

Cost projection to 2024 suggests less than 500 €/kW at 100MW scale Interim Results January 2019