Renewable energy is on the rise, but how we store that energy is still up for debate.
“Renewable energy is growing, but it’s intermittent,” says Grigorii Soloveichik, program director at the United States Department of Energy’s Advanced Research Projects Agency. “That means we need to store that energy and we have two ways to do that: electricity or liquid fuels.”
According to Soloveichik, electricity and batteries are sufficient for short term energy storage, but new technologies such as liquid fuels derived from renewable energy must be considered for long term storage.
During the PRiME 2016 meeting in October, Soloveichik presented a talk titled, “Development of Transformational Technologies,” where he described the advantages that carbon neutral liquid fuels have over other convention means – such as batteries – for efficient, affordable, long term storage for renewable energy sources.
Rise of renewables
In the United States, 16.9 percent of electricity generation comes from renewables – a 9.3 percent increase since 2015. Globally, climate talks such as the Paris Agreement help bolster the rise of renewable energy around the world. Soloveichik expects that growth to continue in light of the affordability of clean energy technologies and government mandates that aim at environmental protection and a reduction of the carbon footprint. However, the continued rise in renewable dependence will impact the current grid infrastructure.
“More renewables will result in more stress on the grid,” Soloveichik says. “All of these new sources are intermittent, so we need to be able to store huge amounts of energy.”
The energy grid is the central component of energy distribution and consumption. Currently, a constant flow of energy is pumped through the grid, generated primarily by fossil fuels. As the energy landscape shifts away from fossil fuels toward clean energy, the flow into the grid changes from consistent to intermittent due to the nature of renewable sources, such as wind and solar. By pumping this intermittent energy into the grid infrastructure as it currently stands, large scale blackouts could occur when the wind isn’t blowing or the sun isn’t shining. Alternatively, extremely windy or sunny days could produce an excess of energy and fry the grid.
New modes of energy storage
Being able to make renewable energy sources intertwine with current grid technology is where Soloveichik’s work plays a huge role. While many researchers are looking at on-grid battery technology to mediate this situation, Soloveichik is focusing his attention to off-grid liquid fuels.
Instead of transferring energy harvested from renewable energy sources directly into the grid or a battery in the form of electricity, Soloveichik believes that energy could be used more effectively if transformed from electricity into carbon neutral liquid fuels. These liquid fuels can then be store infinitely and used for everything from hydrogen delivery to electricity generation. According to Soloveichik, clean liquid fuels such as synthetic gasoline or ammonia have a much higher energy density than batteries. In some cases, that energy density could be 10 to 20 times higher than their electrical competitor.
Also, liquid fuels take up far less space than batteries and do not require special air conditioning units to regulate temperature, typically leading to them being more cost effective. Because pipeline infrastructure already exists to transport the carbon neutral liquid fuels, huge amounts of capital would not need to be invested to make the utilization practical.
Carbon neutral fuels and transportation
In addition to providing highly efficient energy storage, Soloveichik believes that renewable liquid fuels could transform the transportation sector.
“We cannot burn fossil fuels at the same pace we use to anymore,” Soloveichik says, noting accelerating carbon dioxide emissions and rising sea levels.
Currently, the electric propulsion that powers electric vehicles happens either by battery or fuel cell. While battery powered cars have proven popular with companies such as Tesla, Soloveichik believes that fuel cells, which can be powered by carbon neutral fuels, will soon find a more prominent home in the transportation sector.
“The issue with batteries is range,” Soloveichik says. “The range is still limited. If you need to increase range, you will also need to increase the cost, which is probably not acceptable for most consumers.”
Today’s battery powered electric vehicles cannot exceed 300 miles on a single charge and lack of charging stations along highways causes range anxiety in many drivers taking longer distance trips. Soloveichik thinks liquid fuels could be the answer to that problem.
With a carbon neutral liquid fuel, such as ethanol, the fuel efficiency and energy density would be roughly the same as burning gasoline in a traditional combustion engine. Additionally, the fueling station infrastructure already exists, so there would be no need to build millions of charging stations. Essentially, renewable, carbon neutral liquid fuels would deliver the same driving experience without high greenhouse gas emissions.
Future of renewable fuels
However, natural gas is cheap right now, which poses an issue for the rise of renewable liquid fuels. In order to make the production of these fuels more affordable, Soloveichik and his team is working on new processes to not only make production affordable, but also scalable.
Currently, a carbon neutral liquid fuel such as ammonia is produced in huge plants by the Haber-Bosch process, which was developed at the beginning of the 20th century. The problem here is that the process to create a carbon neutral fuel is not itself carbon neutral. To combat this, Soloveichik is looking to make processes that achieve the same goals, such as electrolysis or water splitting, affordable and efficient.
While the science behind the production of carbon neutral, renewable liquid fuels is still growing at the fundamental level, researchers in the field can see the potential impact that it will have on the world once the science matures.
“If we can convert renewable energy into liquid fuels, we can use it in any means,” Soloveichik says. “There’s a lot of work to do, but we can see the possibilities.”