Seawater electrolysis – a hydrogen revolution or technological dud? Here are the numbers – WEF.
The advent of the hydrogen economy in the last four or so years, have ignited numerous old ideas to be revisited.
Some of these ideas include plasma electrolysis and seawater electrolysis — in which water is broken down into its constituent parts through electrolysis — both of which have been explored in the past and decried as either not economically or technologically viable.
Media coverage, meanwhile, has described seawater electrolysis as the next big technological breakthrough and an enabler of the hydrogen economy, painting it as a near-miracle level breakthrough. But this is inaccurate: seawater electrolysis is a solution that is looking for a problem.
A large portion of the vast hydrogen investments end up supporting technological breakthroughs that promised more efficient, cheaper and more reliable hydrogen production pathways. However, many proponents of these technological breakthroughs are entirely newcomers to the hydrogen industry. They often do not have suitable backgrounds to understand these concepts in sufficient detail — not to mention that many have never done electrochemistry before.
The advent of the hydrogen economy in the last four or so years, have ignited numerous old ideas to be revisited.
Some of these ideas include plasma electrolysis and seawater electrolysis — in which water is broken down into its constituent parts through electrolysis — both of which have been explored in the past and decried as either not economically or technologically viable.
Media coverage, meanwhile, has described seawater electrolysis as the next big technological breakthrough and an enabler of the hydrogen economy, painting it as a near-miracle level breakthrough. But this is inaccurate: seawater electrolysis is a solution that is looking for a problem.
A large portion of the vast hydrogen investments end up supporting technological breakthroughs that promised more efficient, cheaper and more reliable hydrogen production pathways. However, many proponents of these technological breakthroughs are entirely newcomers to the hydrogen industry. They often do not have suitable backgrounds to understand these concepts in sufficient detail — not to mention that many have never done electrochemistry before.
Seawater electrolysis: the numbers
Neither the hydrogen economy nor water electrolysis are new concepts. Water electrolysers have been in use for over a century and their performance and materials have evolved significantly over that period, resulting in robust, efficient and sophisticated solutions. The same applies to water treatment solutions.
Let’s start with exploring the energy consumption of modern water electrolysis and water purification systems. To produce 1 kg of hydrogen, 8.92 kgs of water is needed. In reality, we need more because of losses — some water does not end up as hydrogen and oxygen and leaves the system unprocessed. For the purpose of calculations, an average water consumption of 11 l/kg of hydrogen was assumed.
In perfect conditions, production of 1 kg of hydrogen requires 39.4 kWh/kg. In reality, and due to various inefficiencies, water electrolysis consumes an average of 50 – 55 kWh/kg. Energy requirement of modern water treatment plants depends largely on quality of feedstock water, quality of permeate and type of technology used.
Most commonly used reverse osmosis plants consume roughly 0.0012 kWh/l and 0.0046 kWh/l for brackish water and seawater feedstock, respectively. In addition, depending on the quality of produced water, a demineralized water treatment plant might be deployed to further purify the permeate.
The energy consumption of a demineralized water treatment plant is in the range of 0.0016 kWh/l. As such, energy consumption to purify the seawater to meet the feedstock purity requirements for electrolyser ranges roughly from 0.055 to 0.077 kWh/kg H2 (given assumed water consumption of 11 l/kg of hydrogen) or less than 0.2% of the total energy consumption to produce hydrogen.
The energy benefits of seawater electrolysis are negligible, and so are the cost benefits.
Modern reverse and demineralization plants are very cost-effective. As reported by Hydrogen Europe, the total cost for water desalination is around 0.85 USD/m3, which then adds about 0.0075 USD/kg to the production cost of hydrogen.
Instead of seawater electrolysis, future electrolyser developments operating on ultrapure water should focus on optimizing parameters such as cost expenditure and energy efficiency. An improvement of only 0.2% in energy consumption would theoretically give the same results as operating electrolysers with seawater.
Due to osmotic pressure increase and entropy decrease, electrolysis on seawater will require more energy compared to electrolysis on ultrapure water, so any potential savings in energy will even out by the laws of thermodynamics.
Highlights:
- Seawater electrolysis has been hailed as a wonder tech for creating green hydrogen — seen by some as the fuel of the future.
- Others have argued that seawater electrolysis is simply not viable when you dig into the stats.
- To get to the bottom of it, we need to dig into the figures.
READ the latest news shaping the hydrogen market at Hydrogen Central
Seawater electrolysis: a hydrogen revolution or technological dud? Here are the numbers, September 29, 2023
