Chapter 8: The Hydrogen Economy
Hydrogen is an environmentally attractive fuel for the future. When it is used to produce energy, the only byproduct is pure water.
Hydrogen fuel is considered a key component of an “all-of-the-above” energy portfolio and one of the fastest-growing clean energy technologies. From zero-emission fuel-cell cars to clean, distributed energy production, hydrogen has a significant part to play in our secure and affordable energy future. 
This is the Hydrogen Economy
The Hydrogen Economy refers the continuous shift away from fossil fuels as the principle energy used to power how an economy functions and toward the use of Hydrogen (H2) for many of those functions including:
Transportation fuel, especially heavy industrial transportation
Heat for industrial processes and living spaces
Electric storage systems to supplement intermittent renewable power generation such as solar and wind from consumer scale to grid scale
Hydrogen will not completely replace fossil fuels; however, it is possible to reduce fossil fuel consumption to a degree that it will have a positive mitigating effect on Climate Change and the economic impact of dwindling petroleum supplies.
Hydrogen: The Energy Carrier of the Future
It is important to understand that H2 is an energy carrier or a secondary energy source. It is literally a storage and transportation medium for electricity or heat.
An energy carrier is a substance or sometimes a phenomenon that contains energy that can be later converted to other forms such as mechanical work or heat or to operate chemical or physical processes. 
They are called energy carriers, because they move energy in a useable form from one place to another. The well-known energy carriers are:
Energy carriers are used because it is easier to transport than a primary energy source.
On the other hand, any conversion of primary energy to an energy carrier is associated with some inefficiency. Therefore, when dealing with secondary energy source, we have to always consider the way the carrier was made. 
This means there will be some energy loss involved during the conversion. Is it derived from a renewable, decarbonized source or from a non-renewable source? Which choice will minimize the negative impact on the environment over time? What is the net, positive energy yield (ERoEI). 
There are 3 ways to produce Hydrogen
Hydrogen: Grey, Blue or Green 
Hydrogen does not exist alone on Earth. It always is found in combination with other elements such as Carbon, Nitrogen and Oxygen. Therefore, to access pure H2 it must be separated from the chemical compounds that contain it. It is most commonly found in hydrocarbon fossil fuels like petroleum, natural gas or coal. It is also found in water, the most abundant renewable resource in the world.
The methods for isolating H2 from fossil fuels are considered non-renewable since the source for the H2 is a fossil fuel and finite in its quantity. Isolating H2 from water, however, can be done using renewable resources throughout the production process.
Industrial Scale Hydrogen
Steam Methane Reforming Facility (SMR)
Non-renewable hydrogen is called “Grey Hydrogen”. Its byproducts include Carbon Dioxide (CO2, a greenhouse gas).
The most common, non-renewable process for H2 production is called Steam Methane Reforming.  This process uses heat to separate the H2 from the carbon atoms making up the methane molecule (CH4). The heat needed for this process, typically comes from natural gas (methane), as well making the process fossil fuel intensive.
Blue Hydrogen is produced utilizing the same process as Grey Hydrogen with the difference being that the C02 is captured during generation. Carbon capture technologies prevent CO2 from being released into the atmosphere while enabling the captured carbon to be safely stored deep underground or utilized in industrial processes. This allows Blue H2 to meet low carbon standards.
H2 Electrolysis Process Chart
To qualify as Green Hydrogen, the H2 must be sourced from a renewable feedstock  such as water and must exclusively use renewable power  for processing.
Green Hydrogen is produced utilizing a process called electrolysis. The only outputs from this process are H2 and oxygen. That’s the same element that gives us life when we breathe.
Renewable power is defined as: “Energy from renewable, non-fossil fuel sources which include: wind; solar (solar thermal and solar photovoltaic); geothermal energy; ambient energy; tide, wave, and other ocean energy; hydropower; biomass; landfill gas; sewage treatment plant gas; and biogas.”
 The Energy Return on Energy Invested (ERoEI) of any energy gathering system is a measure of that system’s efficiency.
 A raw material supplied to a machine or processing plant.
 Power = Electricity