How much renewable energy can we build and incorporate into our electric grid? Five or ten years ago, not many people were asking that question. Fast forward to today: in the U.S., investment bank Lazard has documented that the costs of producing energy from wind and solar photovoltaics have declined by 61% and 82%, respectively, since 2009. The financial community has bought in, with global clean energy investment hitting a record $329 billion in 2015 even as the per-unit costs of technology are dropping. Those trends, coupled with the imperative to reduce climate-changing CO2 emissions, mean that the clean energy industry is expected to continue its rapid growth for the foreseeable future, and it's leading many to wonder just how much renewable energy we're capable of deploying.
Previously, grid operator PJM - which covers all or parts of 13 states and D.C. - found that up to 30% wind and solar could be added to its service territory, with only minor adjustments to the existing grid and proper system planning. The National Renewable Energy Laboratory has reached similar conclusions when examining both the Eastern and Western Interconnections. But how much renewable energy could we build if we instead significantly upgraded and modernized our outdated electric grid? A rigorous new study adds an impressive new data point to this conversation.
Last week's study, published in the premier journal Nature Climate Change by researchers at the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado-Boulder, examines the potential for a major overhaul of our electric transmission system and its implications for our renewable energy and climate goals. Much of our existing electric infrastructure, similar to our roads and bridges, was built decades ago and is overdue for some much-needed upgrades. The study found that, with the grid updates described in more detail below, the U.S. electric system could integrate up to 55% wind and solar energy in 2030, resulting in carbon dioxide emissions about 79% below 1990 levels, or 84% below 2005 levels.How can the electric grid be updated?
The analysis focuses on high voltage, direct current (HVDC) transmission lines, which can improve the efficiency of delivering electricity - less of it gets wasted along the way. Both the higher voltage and the direct current (as opposed to alternating current (AC)) allow electricity to be transmitted across long distances with significantly less losses than traditional transmission lines. While not exactly a groundbreaking innovation - there have been a few HVDC lines around since the early 1900's - HVDC lines have received renewed interest lately because of other enabling technological developments that have made the process more cost-effective and efficient, along with their potential to transmit renewable energy across long distances. In fact, Navigant Research estimated that over 100 new HVDC lines would be built between 2013 and 2020. However, like wind and solar projects themselves, construction of any new transmission lines should involve a careful examination of the environmental impacts and should minimize the impacts on lands and wildlife (such an examination was beyond the scope of this study).
HVDC lines are sometimes referred to as "power superhighways" and can transform the way we think about delivering electricity. The study examines an extensive network of HVDC lines that connect the entire contiguous U.S., analogous to our interstate highway system. Such a network, as shown in the figure below from the study, could convert the grid from its current structure - two interconnects that consist of multiple self-contained balancing authority areas (BAAs), and many transmission bottlenecks in each area - into a single connected electric system.
Source: Nature Climate ChangeWhat are the implications of HVDC lines for renewable energy and our climate goals?
Overall, the study finds that HVDC lines can play an important role in enabling renewable energy deployment and decarbonizing our electric sector. The study examines three core scenarios with a range of forecasts for natural gas prices and renewable energy technology costs. In the mid-range scenario, the study finds that the power sector can reduce emissions 62% below 1990 levels. In the scenario with the most favorable economics for renewables (combining high gas prices and low RE technology costs), the modeling results show that wind and solar energy can reliably provide up to 55% of national electricity generation in 2030. Achieving this transformation of the grid would also result in electricity sector CO2 emissions nearly 80% below 1990 levels, an important step towards maintaining a sustainable climate.
HVDC lines can bring renewable energy from high-resource areas to low-resource areas, including population centers. Many locations with the strongest wind potential are located far from densely populated urban centers, which also represent pockets of high electricity demand. With a network of HVDC lines in place, clean, zero-emitting renewable power can be efficiently delivered to population centers, displacing fossil energy and resulting in low-cost emission reductions. This network can also deliver clean power to regions with historically little renewable energy development, such as the Southeast and parts of the Great Lakes. (That said, advancements in wind turbine technology, along with the rapidly falling costs of solar, have the potential to transform these areas into major players in the clean energy economy.)
A broad network of HVDC lines can help mitigate the variability of renewable energy, enabling higher levels of penetration. This study stands out from other electric sector studies because of its use of detailed, complex weather data incorporated into a model developed by the country's foremost experts on, well, weather. By utilizing such detailed weather system data, the authors are able to conclusively demonstrate that high amounts of renewable energy can be integrated into the grid despite weather fluctuations, which have typically been thought to be a barrier to high (>40%) penetration of variable renewable energy. In fact, as the authors write, "Paradoxically, the variability of the weather can provide the answer to its perceived problems...the average variability of weather decreases as size increases; if wind or solar power are not available in a small area, they are more likely to be available in a larger area."
If the transmission network envisioned by this study sounds ambitious, that's because it is. A national network of HVDC lines would involve a major overhaul of the transmission infrastructure that's been around for decades, and this overhaul would need to be done methodically and sustainably. But HVDC lines are a commercially available, proven technology that, along with energy storage, advanced inverters, and other new technologies, are now rapidly emerging as cost-effective options to modernize the grid and further enable the higher generation shares of renewable energy that we'll need in order to avoid the worst impacts of climate change.
Furthermore, this is not an all-or-nothing finding: the study finds that while a single fully-linked network would be most efficient, any increase in the interconnectedness of the grid would also play an important role in enabling higher levels of renewable generation. This has important implications for policy-makers as they consider any similar measures to improve or modernize our electric "backbone": steps such as strengthening the links between the Eastern and Western Interconnections would also have significant benefits.
The authors conclude by acknowledging the magnitude of the challenge, comparing it to the construction of "transcontinental railroads of the nineteenth century, and the interstate highway system of the twentieth century." Developing a modernized, low-carbon grid might be this country's most important challenge yet, but we're up to the task.