Green Hydrogen: A Reality Check
This blog is taken from the post Green Hydrogen: A Reality Check.
The previous four posts in this series have provided background information to do with the use of hydrogen as source of “green” energy.
The posts were:
Hydrogen HSE (Health, Safety and Environmental);
Colors of Hydrogen; and
Hydrogen is touted as a “green” source of energy. When burned it creates just water vapor (along with some nitrogen oxide compounds, which are greenhouse gases). However, the claim that hydrogen is “green” can be misleading, and needs to be checked against the following realities. In this post we provide a few thoughts as to the reality of its use as a replacement for fossil fuels.
The concerns expressed here do not mean that hydrogen is unsuitable as an alternative fuel. But it is not possible to simply switch from fossil fuels to hydrogen — doing so will be very expensive and will require a massive investment of fossil fuel energy.
Not Primary Source of Energy
Hydrogen is not a primary source of energy; it is not available naturally. Because its density is so low any hydrogen in the atmosphere escapes to space. However, hydrogen is widely available in water — after all oceans cover two thirds of the Earth’s surface. But this means that, if hydrogen is to be used as a fuel or a chemical feedstock, it has to be manufactured, i.e., it has to be extracted from water. This takes energy — lots of energy. The primary source of energy that is used to electrolyze water must not emit greenhouse gases. The energy used to create the hydrogen must come from sources such as wind and solar, not from the burning of fossil fuels.
The manufacture of hydrogen from water has built-in thermodynamic inefficiencies. The electrolysis process is around 35% efficient. So the amount of solar and wind required is much larger than were that energy to be used directly.
Lack of Infrastructure
There is virtually no existing electrolysis infrastructure for manufacturing hydrogen. The creation of such an infrastructure would require not only massive financial investment, it would also call for an enormous expenditure of fossil fuels.