Last week, California’s quest for a clean grid revolution culminated in the introduction of a bill mandating 100 percent renewable energy by 2045. Senator Kevin de León, a longtime environmental leader in the state senate, wrote the measure, which comes on the heels of last year’s major greenhouse gas reduction bill. Massachusetts legislators introduced the same goal with a deadline of 2035. Momentum behind such efforts has grown stronger in defiance of President Donald Trump’s antediluvian approach to climate science. But it’s too early to assess the chances of these passing. It’s easier to prognosticate on the effects of passing such a goal. And there’s a lot of evidence that 100 percent renewable energy is not the optimal way to decarbonize the grid.
Set in stone
Opponents of renewable energy incentives often use the argument that government shouldn’t pick winners and losers.The legal requirement to source 100 percent renewable energy looks more like the latter. But let’s say climate change requires massive government investment in clean technologies. In that case, the question shifts to one of efficacy: Since climate change justifies extraordinary measures, what is the most effective extraordinary measure to fight it? That’s where 100 percent renewables plans fall short, for both structural and practical reasons. The stated goal is to decarbonize the electric grid. Converting all electrical generation to some combination of wind, hydro and solar is one way to achieve this goal. The proposals at hand would make that particular method the endpoint. At best, this is indirect policy: Instead of saying “figure out the best way to decarbonize the grid,” it says, “figure out how to deploy a prescribed set of energy resources which should lead to the decarbonization of the grid.”
At worst, it’s picking one path to the exclusion of other, potentially better, paths.
Here’s how Jesse Jenkins, an energy systems researcher at MIT, framed this problem: “Why would we want to constrain ourselves to a narrow set of options to confront climate change and air pollution and other energy sector challenges when those challenges are already quite difficult?” This only makes sense if it’s possible to prove that some combination of wind, hydro and solar is the most practical route to a zero-carbon grid, accounting for speed, cost and probability of success. Not only should it beat every option currently available, but any future possibilities based on technological progress in the next several decades. Arguably the most prominent planners of the 100 percent renewable approach are Mark Jacobson of Stanford University and Mark Delucchi of UC-Berkeley, and they end up arguing that the ramp-up of renewable production to power the whole country is possible given our nation’s previous success with World War II-era societal mobilization.
That’s an inspiring precedent, but not one you’d like to see guiding a feasibility study.
We don’t know that a 100 percent renewable approach is the fastest, cheapest or easiest way to decarbonize the grid. We do know that it will be expensive and hard enough that its own advocates compare it to the most gargantuan collective effort in the nation’s history.
And now for the practical stuff
Setting aside the case for keeping options open, the operational realities of a completely renewables-powered grid create challenges that could be avoided with other zero-carbon configurations. Solar and wind alone cannot be relied upon for constant service. This requires some combination of: 1) overbuilding capacity over a geographically dispersed region; 2) using a whole lot of storage; and 3) dramatically improving regional import and export of electricity. If solar and wind form the baseload, you have to prepare for the scenario when the sun is mostly blocked and wind is weak. One way to do this is building enough extra capacity that with all the fleet operating at its trough of productivity, there is still enough to power the system. That requires building capacity well beyond the reserves required of thermal plants, which produce a much higher percentage of their potential output.
This multiplies the cost of the build-out, which is compounded by the diminishing returns of additional renewable capacity. With so much extra solar on the grid, grid operators have to deal with over-generation when the weather conditions are optimal. Solar and wind plants may have to curtail their output under such conditions. The more solar that goes onto the grid without a productive use, the more curtailment any additional solar facilities will face. “Value declines due to curtailment because each unit of potential PV production no longer displaces one unit of fossil generation,” states a study from the National Renewable Energy Laboratory on how to reach 50 percent PV penetration in California. “As curtailment increases, the benefits of additional PV may drop to the point where additional installations are not worth the cost, creating an economic limit to deployment.”
Storage offers a hopeful way out of this conundrum, allowing renewables to act more like traditional power plants.
California has almost single-handedly jump-started the advanced storage industry by setting a statewide mandate, but the state is still in the early stages of this rollout. That means utilities are still testing how storage works on the grid, and how it performs after several years of service — both of which are crucial to planning a grid that is all renewables. Residential storage is even more nascent, with companies scrounging for customers and small-scale pilot programs. Residential storage could play a role in balancing the grid and shifting loads, but it needs to reach millions more customers to fulfill that role. Additionally, expanding California’s grid connections with its neighbors would smooth the renewable expansion by allowing more imports and exports at opportune times. This kind of interconnectivity of transmission lines takes a long time and requires coordination with several states — and it’s also quite controversial in the region.
Even with optimal grid improvements, California would still need an estimated 15 gigawatts of additional storage just to reach 50 percent solar by 2030, according to an NREL study. That’s more than 11 times the amount of storage mandated currently in California, and 66 times the total megawatts deployed in the U.S. last year. This represents a massively expensive undertaking. A different study from Jenkins and researchers at Argonne National Lab demonstrates how the need for storage goes down if the grid includes some sort of flexible baseload power in addition to intermittent renewables. More flexible nuclear power or natural gas with carbon capture and sequestration (CCS) could fill this role, in places where substantial hydropower isn’t available.
Small modular nuclear reactors are still in a very early stage of regulatory review, and CCS has not achieved commercial success, so these are not certain options. A lot can happen in 28 years, though, and a zero-carbon mandate for the California market would be a powerful driver for development of such technologies.
Again, that’s if California’s goal is to achieve a zero-carbon grid — rather than just solely boost renewables.
In a previous interview, Jenkins described what proposals like the one in California will accomplish: “It’s not saying this is the best pathway forward in terms of any metric, particularly in terms of cost. They say, ‘How much can we push renewables and only renewables? And what will be necessary to try to decarbonize with that pathway alone?’”
Choosing that pathway alone will mean all kinds of other decarbonization pathways get shut out.
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