The need to reduce carbon emissions is real. In 2018, the International Panel on Climate Change (IPCC) reported that global emissions would need to reach net-zero (or carbon-neutral) by 2050 to prevent severe climate change impacts. Electricity is a major contributor—electricity generation was responsible for approximately 33% of total CO2 emissions in the U.S. in 2018.
Electric utilities stand to play a critical role in reducing carbon emissions. Many are up to the task of decarbonizing their operations and supplying carbon-free or carbon-neutral energy to their customers.
Carbon neutral and carbon free systems must install enough capacity (with the right capabilities) to meet energy needs in worst-case scenarios. At a minimum, to assure reliability and avoid blackouts, utility system planners and policy makers need to account for seasonal trends in availability of renewable resources. Energy storage systems designed for daily shifting with less than 12 hour duration are not cost optimal for long-term storage and energy time-shifting in high renewable power systems.
We are at least a decade away from renewable energy plus storage being economically viable for grid-scale wind and solar, and we don’t have that kind of time to wait.
In the meantime, our inflexible power systems cannot keep up with wind and solar’s variability, so power plants have to stay online and burn fuel even on sunny or windy days when they are not needed. In practice, this limits power systems to using perhaps 30% renewable generation. Any more than that gets curtailed.
One form of long-term energy storage is generation of synthetic methane using curtailed renewable energy. Synthetic methane is created in a multi-step process. Electricity powers hydrolysis to extract Hydrogen from water. A separate process uses electricity for direct-air carbon capture (DACC), a process by which Carbon is pulled from the air. A third process (called methanation) combines hydrogen and carbon to form renewable methane, CH4. Synthetic methane in this context is renewable insofar as the electricity powering the process is provided by renewable (wind, solar primarily) or other carbon-free sources (such as hydro or nuclear). The ingredients (water and air) are also renewable, their consumption does not alter the mass balance of either on a global basis. The final fuel is carbon-neutral. All carbon in the fuel is sequestered from the atmosphere, therefore any release of CO2 upon combustion is net-zero. The process results in no net increase in CO2 emissions, and is therefore carbon-neutral, or in effect carbon-free.