Many countries around the world have been diligently working towards implementing renewable energy plants for over a decade. According to the International Energy Agency (IEA), renewables in the form of hydropower, bioenergy, wind and solar will account for 18% of primary energy by 2035. Since 2013, more electrical grid capacity was added in the form of renewable energy than for coal, gas, and oil combined! Although these statistics are promising, one of the issues with renewable energy is that the power can be intermittent. For solar and wind, the amount of energy produced can vary depending upon the season, location, or weather conditions. In many instances, the regions that are best suited for the production of renewable energy are often far away from the greatest demand. In these cases, long-distance or overseas transport is required. In northern countries, the potential for solar production is the highest during the summer season -- when the energy consumption is the lowest. Wind conditions can vary daily and can change rapidly. The energy generated through hydropower also may not be utilized properly during low consumption periods.
Countries such as Germany have implemented renewable energy (wind and solar)-based power plants with great diligence and fervor but have come up against the issue of unsteady or unreliable electricity. Common electric grid quality problems include voltage dip or swell, flicker, overvoltage, undervoltage, interruptions, transients, distortion, noise, and frequency deviation. To solve these grid reliability and quality issues, energy storage is required to provide continuous and uninterrupted energy. An effective energy storage system (ESS) will (1) respond to daily electricity demand fluctuations that occur with daily, weekly, or seasonal cycles, (2) will react to intermittency issues from renewable energy grid-connected systems, (3) recover energy that may otherwise be wasted. This is especially important for large scale applications to improve energy security and aid in balancing the energy prices.
Traditional fossil fuels provide excellent energy storage -- which is why they have been used so extensively. However, the goal is to move away from fossil fuels due to (obvious) supply, emission, and political reasons. There are many types of energy storage solutions and each type has pros and cons. There are differences in size, storage duration, equipment, and energy transport capabilities. There are many types of fuels that can be utilized for energy storage (oil, gas, biofuel), but these fuels may not always be optimal for specific applications due to volumetric requirements, storage period duration, or the amount of fuel that needs to be transported. Non-fuel-based energy storage, such as batteries, has a range of power availabilities (1 kW to 1 MW); however, the gravimetric energy density is low, and electricity cannot be stored in batteries for long periods of time. Therefore, different methods of energy storage suit different purposes.
Hydrogen is a flexible energy carrier that can be produced from various types of energy sources and offers many opportunities for long-term energy storage. Hydrogen can be compressed, liquefied, or stored in a solid or liquid form for use in fuel cells, turbines, or internal combustion engines. The main challenge associated with hydrogen is its production and storage. Approximately 48% of hydrogen is produced from natural gas (NG) using steam methane reforming (SMR), 30% is a by-product from the petroleum refining, 18% is produced from coal, and 4% from water electrolysis. In the US, 59% of hydrogen is produced in oil refineries and ammonia plants, and almost 36% as a by-product from catalytic reforming at oil refineries and at chlor-alkali plants. In energy equivalents, global annual hydrogen demand (172 Mtoe, 60 Mt) is below 2% of the world energy production.
The widespread use of hydrogen in the global economy faces two important challenges: (1) the production of hydrogen from low-carbon sources is costly, and (2) the development of the hydrogen infrastructure is slow and holding back widespread adoption. Cost of building hydrogen distribution infrastructure and transport over large distances are major economic barriers to the implementation of hydrogen-based technologies. Additionally, large-scale central production will depend on market volumes to evolve in order to compensate for the capital expenditures of building up capacity. In future, carbon-neutral hydrogen could be produced by water electrolysis using electricity based on renewables. This distributed method of production using electrolyzer systems is viewed as an attractive near- to mid-term option for supplying hydrogen.
Electrolyzers use electricity to break water into hydrogen and oxygen. The electrolysis of water occurs through an electrochemical reaction that does not require external components or moving parts. It is very reliable and can produce ultra-pure hydrogen (> 99.999%) in a non-polluting manner when the electrical source is renewable energy. Electrolysis provides a decentralized and modular approach to energy utilization, delivery, and cost for the development of an on-demand hydrogen energy storage system. The electrolyzer enables the reforming of water into a hydrogen-rich gas to aid in the storage of potentially large amounts of electric power that can be used under non-continuous conditions.
The hydrogen fuel produced from an electrolyzer is perfect for use with hydrogen fuel cells. The reactions that take place in an electrolyzer are very similar to the reaction in fuel cells, except the reactions that occur in the anode and cathode are reversed. In a fuel cell, the anode is where hydrogen gas is consumed, and in an electrolyzer, the hydrogen gas is produced at the cathode. The disadvantage of electrolyzers is the requirement of electrical energy to complete the reaction.
The electrical energy needed for the electrolysis reaction would ideally come from renewable energy sources such as wind, solar or hydroelectric sources. Electrolyzers are useful and ideal when incorporated into certain stationary, portable, and transportation power systems that can convert excess energy into long-term energy storage. Applications where electrolyzers are particularly advantageous include energy storage for the grid, long-term field use, fuel cell–powered vehicles, and portable electronics. Some of the advantages of using electrolyzers are:
• The hydrogen produced is very pure
• It can be produced directly at the location
• It is cheaper than transporting hydrogen gas in high-pressure cylinders
There are more than enough solar and wind natural resources globally to produce all the hydrogen needed for stationary, transportation, and portable applications. Electrolysis has the potential to meet the cost requirements specified by many governments around the world.
The use of hydrogen for energy storage is a effective solution to solve the intermittent energy issues associated with solar and wind energy. The main challenge associated with hydrogen implementation is related to its production and storage. Many hydrogen storage options have been proposed with the feasibility of different strategies depending on the demands of their target sectors. An ideal energy storage system would consist of an electrolyzer that is powered by excess wind or solar electricity coupled with a hydrogen storage system. A fuel cell power generation system will utilize the hydrogen to harvest and supply power when required.
Image source: Powermag.com