Building a Carbon-Free Grid
We’re on our way, but the last mile may be the most difficult
Currently, the United States generates roughly 41 percent of its energy from “green” sources, including renewables and nuclear (source: energy.gov). And with declining prices of batteries, renewable energy systems, and electric vehicles, we are well on the way to getting 90% of our power from green energy. Without the de-growth policies of some well-intentioned but misguided environmental activists.
Wind, solar, and other renewable energy sources already account for 21% of the grid, and a dramatic increase in capacity of these different sources is expected to come on-line in just the next year. According to the U.S. Department of Energy, out of the roughly 46.1 GW of new generation capacity being constructed in 2022, 46% is solar alone, with non-green sources such as natural gas only accounting for 21%. Additional research by the World Economic Forum indicates an “unprecedented acceleration” in the construction of renewable energy capacity.
Despite this progress, we have a long way to go to reach even 90% green energy globally. But, with the intersection of market forces and government policy pushing for zero-net carbon energy, this goal is within our reach. And it will mostly take care of itself.
Battery costs have plummeted over the last ten years, and so have solar panel installations. In fact, the combination of renewable energy generation and utility-scale battery arrays is already a cheaper and more reliable alternative to fossil-fuel energy generation. Soon, nearly all newly installed generation capacity will be based on renewables. Then we will have to turn to the task of converting existing capacity to renewables.
Wind energy offers built-in incentives: landowners in sparsely population regions of the American West can get paid by wind farm operators to install turbines on their land. The influx of economic activity and skilled professionals only helps the economies of far-flung communities, smoothing the way in local communities who might otherwise be resistant to these changes.
Decommissioning of old plants that have reached their useful life would be a good way to phase fossil-fuels out by attrition. A variety of funding mechanisms and tax incentives can be used to install carbon capture on existing plants that must be kept on-line. With this tech, we might be able to continue using natural gas generation without negative impacts on the environment.
The means described above will get us to 90% carbon-free energy on its own. The difficulty comes from legacy systems powered by fossil-fuels that are not so easily dislodged. There is no large constituency for shutting down existing capacity. So, once we achieve that 90%, it will get increasingly more difficult to approach net-zero energy, the goal set by the Biden Administration for 2035.
Currently, more than one-third of the country’s power plant capacity is needed to meet roughly the last 10 percent of demand. This is mainly due to variations in demand over time; no matter how low average energy usage is, generation capacity must be designed around peak loads. Because of this, there are hundreds of power plants that are mostly idle but are essential to meet demand during hot and cold days. Much of this backup power is provided by natural gas power plants, which can ramp up and down on short notice regardless of weather conditions.
Fortunately, researchers are already working on that problem. A new paper in the scientific journal Joule written by researchers at the National Renewable Energy Laboratory (NREL) discusses six approaches to get to that last 10 percent, including more reliance on wind and solar, increasing use of nuclear power, and long-term energy storage using hydrogen. We’ve covered the use of wind and solar power already. But what of the other alternatives?
Other renewable sources are always an option, including geothermal and hydropower. These have the advantage of not being intermittent, so investment in utility-scale battery arrays is not necessary. However, they are all more expensive and don’t have the same economies-of-scale to support them as wind and solar energy do. Both sources are limited in where they can be built, and hydropower can further disrupt natural ecosystems. But, for limited locations and edge cases, they can be valuable.
Nuclear energy is an integral part of today’s mix of carbon-free electricity. It offers virtually limitless energy for very low costs once in operation. And with no emissions except for steam from its water-cooling systems. But new nuclear plants are very expensive and require heavy government subsidies up front. They should be a part of a multi-decade plan to build a clean grid, but that is an investment for the long-haul, and not for helping solve the immediate climate crisis. There are also the safety concerns regarding (very rare) meltdowns, and storage of nuclear waste.
Another helpful technology could be long-term energy storage using hydrogen. The idea, being tested using a coal-fired power plant in Utah, is that energy companies can use renewable energy sources to perform electrolysis on water and produce hydrogen that can then be stored underground. This would act as a backup-energy reserve for times of high grid demand, replacing the need for fossil-fuel powered plants to act as a backup. This is currently the role that natural-gas plants fill. Unfortunately, this technology is still expensive and has not yet been utilized at scale. It might turn out that a better use of the energy is to simply store it in battery arrays rather than introducing the additional steps of producing and then burning hydrogen.
Carbon dioxide removal and carbon capture will let us turn existing fossil fuel capacity green, as well as potentially reverse the clock on carbon emissions. Then, if we change our metrics for evaluating how green the energy grid is from the percentage of generation capacity that is green to net emissions inclusive of carbon capture, we can reach net-zero carbon far ahead of schedule. The last ten percent may completely disappear as a concern in this scenario.
Even if this doesn’t end up being a major part of reducing emissions in the electricity sector, it could be an essential in other sectors, like heavy industry, that are more difficult to decarbonize and require use of carbon-based energy sources for specific processes. The difficulty with these systems is their expense, and the lack of carbon capture systems performing at scale. There is ongoing work, however, to make carbon capture viable, including generous federal funding.
And then obviously, reducing electricity demand will be key. Direct messaging by the government to be mindful of energy usage helps. But, forced constraints on energy use will be difficult to get buy-in from the public and could violate norms of a free society. Measures to promote energy efficiency are more likely to work. For example, from my previous work as a mechanical engineer on construction projects, building codes have begun to require specific types of materials, sensors, equipment, and controls systems to minimize building energy usage. There are also programs, such as LEED, to encourage environmentally friendly designs.
The “last 10 percent” challenge is nothing new. What is new is the need to serve the last 10 percent with carbon-free resources. A growing number of researchers say that the power grid can use 100 percent renewable energy most of the time, which would mean renewables and energy storage could provide for peak demand by holding excess energy in reserve in batteries. In this scenario, new nuclear facilities, renewables with low intermittency, and fossil fuel plants are not even necessary.
However, some researchers maintain that nuclear and carbon capture are essential parts of getting to carbon-free electricity. This side has doubts about the ability of renewable sources to meet all needs, citing concerns about the availability of land and the intermittent nature of wind and solar. There are also environmental concerns around the materials required to produce utility-scale batteries. And, when accounting for the costs of these batteries, the cost of wind and solar is not nearly as attractive after accounting for the amounts of storage and power line capacity needed for those sources to be reliable for meeting peak demand.
Stepping back to look at the big picture should make us optimistic in either case. Not only have we figured out how to build green-energy capacity at scale and dramatically accelerate the transition to a carbon-free grid, but we are also now digging deep to figure out how to finish the job. One day, we could have both a completely clean energy grid and an atmosphere cleaned of all the emissions of the industrial age.
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