The following is a contributed article by Arne Olson, senior partner, and Dan Mullen, consultant, at the consulting firm Energy and Environmental Economics.
In clean energy circles, 2019 may be remembered as the "Year of 100 Percent." Five states plus Puerto Rico passed laws in 2019 targeting 100% clean energy, while dozens of corporations and utilities made voluntary pledges.
Amid federal inaction despite increasingly visible climate impacts and overwhelming scientific consensus, clean energy's current hold on the public imagination is undeniably a bright spot.
Renewables, primarily wind and solar, are the clean resource of choice. Mitigating climate damage will require massive investments in renewables, not just to reduce fossil generation but also to power electrified vehicles, buildings and industries.
But a smart transition to 100% clean energy will also invest in the complementary resources needed to maintain grid reliability when renewables and short-duration storage aren't available.
The good news
The good news is that reducing electric sector GHG emissions by 80% or more is achievable without sacrificing a reliable electric grid, at a reasonable cost. Thanks to steep reductions in the cost of wind, solar and storage technologies, renewable options are now cost-competitive with conventional resources in a large and growing number of jurisdictions.
In the Pacific Northwest, for example, E3 recently found that renewables and storage could reduce emissions 60% or potentially even 80% below 1990 levels at close to zero net cost (Figure 1). A 90% reduction adds 4-16% to average electricity rates — a manageable increase — but requires 60 GW of renewable energy, a sevenfold increase over the region's currently installed renewable base.
It's true that costs may be somewhat higher in other regions with limited access to high-quality renewables (and without the Northwest's extensive hydropower resources).
But our recent work analyzing highly renewable electricity systems in California, Minnesota and across North America has produced remarkably consistent results: reducing power sector GHG emissions by 80% or more is both achievable and affordable.
A cautionary tale
The chart above also contains an important warning: building a 100% clean electricity system with only variable renewables and short-duration storage would be massively, unsustainably expensive.
The reason is simple: wind and solar don't produce enough energy to keep the lights on and the heaters cranking for days at a time in the dark of winter, even with generous quantities of batteries.
Figure 2 shows why. It depicts 10 simulated wintertime days on a Northwest grid with no fossil generation (the "100% Reduction" scenario from Figure 1).
On Days 5-7, a large increase in demand due to a cold snap coincides with an extended period of low wind and solar production, causing a significant energy deficit. Energy storage helps but is quickly depleted due to limited duration and lack of energy for charging.
The result is a 48-hour crisis (shown in red) in which as much as half of the region's electricity demand cannot be met. This type of event is not acceptable in a modern electricity system.
A different kind of resource is needed to get to zero emissions reliably.
Firm capacity and flexibility on a highly renewable grid
Much attention has been paid to the variable nature of wind and solar energy production and the increasing need for operating flexibility as renewable capacity grows. However, old fears about reliably operating large amounts of renewables are increasingly belied by experience, as instantaneous renewable penetrations today routinely exceed 50% of demand in many markets.
Further, recent studies show that wind and solar power plants can be controlled very precisely and provide essential grid services even without battery storage. This significantly reduces the need to run fuel-combusting conventional generation, saving both money and emissions. Wider use of this capability will give system operators an important new tool to ensure reliable operations in real time.
The biggest reliability challenge on a highly renewable grid is avoiding infrequent but large electricity shortages. This requires some form of "firm" capacity — resources that can start when needed and produce energy for extended periods of time.
Today, that capacity largely comes from conventional sources: coal, natural gas and nuclear. It cannot easily be replaced by wind, solar, storage or demand response. Even at 90% carbon reduction, we find that the Pacific Northwest needs 20 GW of gas generation — 8 GW more than today — to go along with 35 GW of existing hydro capacity.
These plants would run infrequently when renewables aren't available. Despite their low utilization (10% capacity factor in this example), they play an indispensable role in maintaining reliability and affordability in the absence of lower-carbon alternatives.
A smart transition to 100% clean energy
Studies like these — and the scientific literature is nearly as consistent on this topic as it is on the reality of climate change — indicate that achieving 100% renewables is somewhere between impractical and impossible with today's technologies. Renewables are simply not reliable enough, in the absence of new technology, to power the entire grid.
But just because we can't achieve a perfectly zero-carbon grid with renewables and short-duration storage doesn't mean we shouldn't aim to achieve a nearly zero-carbon grid. And we shouldn't stop investigating new technologies that could get us all the way there.
Here's how we can ensure a smart transition to 100% clean energy:
- Build lots of renewable energy. Renewable energy is cheap and abundant in most parts of the world, and rapidly deploying large quantities of it will provide immediate and long-lasting carbon reductions. A smart transition will also invest in means to integrate them at lower cost, such as flexible operations and a larger power grid.
- Invest in new, low-carbon technologies. There are many potential candidate technologies to supplement renewables and battery storage: very long duration storage; hydrogen; renewable or synthetic natural gas; fossil generation with carbon capture and sequestration; and advanced nuclear power (e.g., small modular reactors). Each faces significant obstacles to large-scale commercialization, but one or more must emerge as a viable alternative to enable carbon reductions greater than 90%.
- Keep electric rates reasonable. Electrification is an indispensable strategy for reducing carbon emissions across the entire economy, and inducing consumers to adopt electric cars and heat pumps requires reasonable electric rates. This may mean more moderate carbon goals in the electric sector (e.g., 80% instead of 100%) until one or more low-carbon generation technologies make deeper reductions affordable.
- Retain or build firm capacity for reliability. The grid will continue to need significant amounts of firm capacity for reliability, even under very high renewable penetrations. Affordable energy storage is a big help here, but it still can only meet a fraction of peak demand at today's short durations. Many regions with retiring coal generation (e.g., the Pacific Northwest) will need to add new gas generation, along with any fuel delivery infrastructure needed for dependable operation. These resources should be capable of switching to cleaner fuels such as hydrogen when they become available.
Affordable, reliable electricity is the lynchpin of the clean energy transition across the entire economy. Sacrificing reliability or affordability in the name of carbon reduction is not only unnecessary, it is counterproductive.
A smart transition will ensure that conventional resources are available when needed for reliability, while rapidly investing in clean alternatives to minimize their use.
The views expressed above are those of the authors and do not represent E3 or any of its clients.