U.S. utilities that are mapping out plans for achieving 100% carbon-free power are running into the same challenge: they haven’t figured out a cost-effective way to get there. The clock is ticking, as utilities typically operate with a 20-year planning horizon. Additionally, more than 130 US cities and municipalities and several states have committed to 100% renewable energy, with implementation dates ranging from 2040-2050.
“There is no one solution, no one technology. The optimal solution will be a mix of technologies,” said Joseph Ferrari, general manager for utility market development at Wärtsilä North America, a smart technologies company focused on marine and energy markets. The company has been specifically researching ways that utilities can meet clean power mandates.
For California, the fastest and cheapest path to 100% clean energy will involve expanding solar and wind generation, while adding fast starting, flexible, generation plants. The idea for these plants, according to new Wärtsilä white papers, is that they burn gas now and use synthetic renewable fuels produced using power-to-hydrogen and power-to-methane processes as those technologies advance.
Wärtsilä’s modeling work suggests that a large distributed energy storage system that is capable of providing weeks – rather than hours – of renewable energy storage can be developed using these synthetic hydrogen and/or methane fuels, which can be stored indefinitely.
In these approaches, the amount of battery storage needed in a utility’s power system would be reduced; power generation from synthetic renewable fuels would occur only as needed to maintain reliability when both short-term battery storage and renewable energy sources are unable to meet load.
“For renewable developers, using power-to-hydrogen and/or power-to-methane processes could help them optimize their renewable energy resource,” Ferrari said, adding that to thrive, renewable developers need to be able to sell all of the electricity that they produce.
“What our studies have shown is that as you reach 100% renewables, the amount of oversupply and over-generation from solar in particular, on an annual basis, is staggering. It has nowhere to go and is literally wasted,” Ferrari said.
“Either [synthetic] fuel reduces the costs of the system,” he continued, noting that in both instances the idea would be to use excess renewable power to produce these carbon-free and carbon-neutral fuels.
Perfect the enemy of the good?
A power-to-hydrogen pathway’s biggest advantage over a power-to-methane pathway is that it is carbon-free; its exhaust is water. Also, when produced using excess solar or wind, electrolysis can be produced almost anywhere.
Hydrogen’s drawback is that even though hydrogen is inexpensive to produce, it can’t be used in a power system without a complete overhaul of the entire gas-fuel infrastructure. According to Ferrari, this is because the current utility infrastructure can only handle 15-30% hydrogen by volume.
“The biggest advantage that [renewable power-to-methane] has over hydrogen is that the entire United States is crisscrossed with gas pipelines, compressors and storage systems, that can all be used today with renewable synthetic methane. None of this infrastructure can be used as-is for 100% hydrogen, and there are no thermal power plants that can burn 100% hydrogen today,” Ferrari said. The cost to build a 100MW thermal plant that uses hydrogen should be in the same price and performance range as a natural gas plant, he noted.
The cost of modifying and upgrading pipelines and other components to accommodate hydrogen is unknown, however. Also, the design of pure hydrogen engines and turbines is still some years off for commercial application, according to Ferrari. Direct air carbon capture (DACC) technology, which is central to the power-to-methane process, is further along, he added.
The power-to-methane pathway for decarbonizing the electric power sector involves using renewable energy that would otherwise be curtailed to produce carbon-neural methane. According to Ferrari, this could be done in a three-step process that involves DACC of CO2 from the atmosphere (as the source of carbon), electrolysis of water (as the source of hydrogen) and methanization to combine the carbon and the hydrogen to produce methane. Because the carbon used to create the synthetic fuel is recycled from the air, the combustion of the methane would be carbon neutral.
In this type of synthetic methane approach, the final molecule can be stored and transported using the existing natural gas infrastructure, and the methane produced using this process can be used in any thermal technology that can burn gas.
A common criticism of both power-to-methane is that it is extremely energy intensive because all three steps require energy.
“Power-to-gas is less efficient than some other forms of energy storage, but it’s using energy that would otherwise be totally wasted and unused by the power system,” he said. “Even if it costs more surplus energy to make one useable unit of electricity for the grid, it can be stored and banked for months of duration. If you tried to do that with batteries, well, it would drive systems costs through the roof,” he added.
Battery storage parallel
Ferrari believes that the power-to-methane route is today where battery storage was 10-15 years ago. “Batteries have their place, but it’s becoming clear renewables plus batteries at the scale of California is untenable… What is needed are storage mechanisms with durations of weeks, not hours,” he said. “Even though the need for this will not manifest until close to the 2045 deadline in California, for this to be viable in 2045 a lot of work needs to be started now,” he added.
“From what I’m seeing, it is already started,” Ferrari said, noting that Colorado recently mandated that certain percentages of gas in the pipelines be renewable by set dates. “This will force gas companies to get renewable methane from somewhere. Bio-sources and landfills can only go so far,” he said. Similarly, in California, a new renewable fuels bill that would require at least 20% of gas in the pipes in CA be renewable by January 1, 2030 was introduced in February. The bill, if passed, would allow renewable fuels that reduce or avoid greenhouse gas emissions to be used.
“These mandates will do to the power-to-fuels industry what RPS standards did for solar and what storage mandates did for batteries. [It would] accelerate adoption, introduce competition and reduce price over time,” Ferrari said.
DACC technology has its fair share of critics who see it as offering a lifeline to the fossil fuel industry because of the burgeoning industry’s ties to fossil fuel companies and its use of the existing polluting infrastructure.
“That could not be further from the reality. Methane or other synthetic hydrocarbons do not reduce carbon footprints, they eliminate them. Every CO2 molecule released from combustion was taken from the air to begin with, no fossil fuels involved anywhere in the process,” Ferrari said. At some point fossil fuel use will be phased out, and at that point the only option the aviation and shipping industries will have is to use renewable, synthetic carbon-neutral hydrocarbons, which requires DACC, he added.
Already, an effort to use a power-to-fuel process to make synthetic carbon-neutral jet fuel is underway at Rotterdam The Hague, he pointed out.
Even so, some environmental lawyers say that any legislation that would enable DACC technology to be used by utilities would have to be written with extraordinary care to make it clear that utilities cannot use DACC to blow through their carbon budgets. Carbon Engineering, Climeworks and Global Thermostat are among the handful of companies active in the DACC space currently.