From Grey and Green Hydrogen to Blue Hydrogen: Zero Emission Buildings and Industrial Sites

Dear Colleagues,

“Black”, “grey” and “brown” refer to the production of hydrogen from nonrenewable hydrocarbons, such as coal, natural gas, and lignite. “Blue”, on the other hand, represents the transition toward “green” hydrogen production and uses renewable hydrocarbons, leading to CO₂ emissions being reduced via carbon capture, use and storage (CCUS). “Blue” is currently experiencing an upscale in production and supply logistics at an industrial scale.

“Green” is a term applied to the production of hydrogen from renewable electricity, solar, and wind sources, powering water electrolysis or any process giving low or no CO₂ emissions. In general, there are no established colors for hydrogen from biomass, nuclear or different varieties of grid electricity, as the environmental impact of each of these production routes can vary considerably depending on the feedstock, technology, energy source, region, and type of CCUS applied.

Most electricity production technologies reported for blue and green hydrogen, i.e., decarbonizing hydrogen, production are not economical and cannot compete with the currrently available technologies, while natural gas prices are predicted to remain low in the near future. “Green” hydrogen’s efficiency of electricity generation via a fuel cell, turbine or gas engine used to power to the grid can vary between 45 and 50 per cent. By contrast, hydrogen, or even the electrolyzer’s heat rejection, can be used for heating.

Building novel, “blue” communities should be focused on buildings. Stationary fuel cells provide electricity and occasionally heat but are also employed in combined heat and power (CHP) to provide both electricity and heat in the facilities needed, and uninterruptible power systems (UPS) to cover up energy deficiencies and interruptions. The heat produced as a CHP byproduct is utilized to partially cover a building’s heat demand. The mostly electricity-led mode of operation results in a low thermal output from fuel cell heating systems. The remaining heat requirements of the building are covered by an auxiliary heating system, such as a condensing boiler, therefore making fuel cells suitable for buildings with a low space heating requirement, such as low-energy or nearly zero-energy buildings. Higher space heating buildings require hybrid fuel cell heating systems, comprising a fuel cell and a condensing boiler to cover peak heating requirements.

Stationary fuel cells with an output range up to 10 kWe are usually proton exchange membrane (PEM) or solid oxide (SO ) fuel cells. The typical CHP output range in houses and apartment buildings is from 0.7 to 5 kWe. Probably the most significant advantages of fuel cells over thermal power processes are direct electrochemical conversion, during which electricity and heat generation are accumulated, as well as the associated higher electrical efficiency. In combined mode, i.e., electrical and thermal, fuel cells can reach efficiencies of up to 95%, with electrical efficiency at around 45%.

CHP plants in the industry need retrofitting to cover the steam and electricity demands of various processes which have already been underperfroming based on design. Additional electricity and energy generation from industrial CHP plants could be sold to the grid.

Prof. Sofoklis Makridis
Dr. Panagiota Pimenidou
Guest Editors

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• Hydrogen production
• CO₂ capture
• Carbon capture use storage
• Hydrogen storage
• Hydrogen compression
• Combined heat and power
• Steam reforming
• Natural gas and hydrogen
• Hydrogen transportation
• Renewable hydrogen
• Electrification