Episode Summary
Executive Summary: The episode examines MIT/Jesse Jenkins research showing that long-duration energy storage (LDES) is useful for a clean grid only if it becomes extraordinarily cheap and lasts far longer than today’s battery use cases. The modeling suggests LDES may reduce system costs and displace some firm generation, but it will not eliminate the need for clean firm power; instead, it faces steep cost, efficiency, and duration thresholds that most current technologies cannot meet.
Main Topics: Why long-duration storage matters (Priority: 5/5): Wind and solar need firming because their output does not always match demand, especially as fossil plants are phased out. The four main grid-firming options (Priority: 5/5): The discussion compares transmission, clean firm generation, negative emissions, and long-duration storage as ways to balance a decarbonized grid. How the study models LDES (Priority: 4/5): Researchers modeled 1,280 combinations of five storage parameters across different grid contexts rather than evaluating individual technologies in isolation. Performance thresholds for meaningful impact (Priority: 5/5): The analysis finds that energy capacity cost and discharge efficiency matter most, and that most technologies need extreme cost declines and 100+ hour durations to matter at scale. Technology-by-technology prospects (Priority: 4/5): The episode reviews flow batteries, hydrogen, pumped hydro, compressed air, and thermal storage, highlighting where each might fit and where each falls short. Limits of LDES as a silver bullet (Priority: 5/5): Even very successful storage would only partly displace clean firm generation and would still leave a substantial role for other firm low-carbon resources.
Key Arguments: A net-zero grid will need storage durations far beyond the roughly six-hour range that lithium-ion batteries serve well today. The most important LDES parameters are energy storage capacity cost and discharge efficiency; power costs and charging efficiency matter less. Meaningful deployment begins only around $50/kWh storage capacity cost, with >10% system-cost reductions around $20/kWh, and more significant savings requiring $1–$10/kWh plus >60% discharge efficiency. The best-case modeled LDES could reduce total system costs by up to 50%, but existing leading technologies top out closer to 40%, and real-world systems with more clean firm options often only 20–30%. To displace all clean firm generation, LDES would need to reach roughly $10/kWh if nuclear is the only alternative, or as low as $1/kWh if other clean firm options are available. Hydrogen and hydrogen-derived fuels may be the strongest long-term candidate because they can benefit from scale in larger industrial, shipping, aviation, and fuel markets. Geographically constrained technologies can sometimes achieve very low costs, but there are currently no geographically unconstrained LDES options capable of fully replacing clean firm generation. The practical response is to continue LDES R&D, but also to plan seriously for abundant clean firm generation because storage alone is unlikely to cover all reliability needs.
Data Points: Number of modeled storage combinations: 1,280 - Researchers evaluated many combinations of five cost/efficiency parameters across multiple power-system contexts. Grid-relevant duration needed: 100 to 650 hours - Modeled cases with the greatest displacement of clean firm generation required very long storage durations. Lithium-ion battery pack average capacity cost: $137 per kWh - BNEF annual battery price report cited as a benchmark for comparing LDES costs. Projected lithium-ion battery pack cost: $100 per kWh by 2023 - Used as a reference point for how far current batteries are from LDES needs. Optimistic eventual lithium-ion cost estimate: $45 to $60 per kWh - A Columbia materials scientist’s estimate, still not cheap enough for substantial LDES deployment. Meaningful LDES deployment threshold: $50 per kWh - Below this capacity cost, the study suggests LDES begins to see meaningful deployment or declining costs. System cost reduction threshold: $20 per kWh - At this level, LDES could reduce system costs by about 10%. Large savings target: $1 to $10 per kWh and >60% discharge efficiency - Required for more significant than 10% electricity-cost savings. Best-case system cost reduction: 50% - Upper bound of what the full modeled LDES design space could achieve. Best existing LDES cost reduction: 40% - Upper bound for current technologies in the modeled scenarios. More limited system context reduction: 20% to 30% - In systems with more clean firm options available, the maximum benefit from LDES falls. Displacement threshold with nuclear only: $10 per kWh - Capacity cost needed for LDES to possibly displace all clean firm generation if nuclear is the only alternative. Displacement threshold with other clean firm options: $1 per kWh - Needed if clean firm generation includes lower-capital-cost options such as CCS or hydrogen turbines. Flow battery energy capacity costs: Hundreds of dollars per kWh - Common vanadium redox and zinc bromine flow batteries are too expensive for true LDES. Aqueous sulfur flow battery cost: $10 to $20 per kWh at 100+ hours - A promising example that could yield 10% to 20% system-cost reductions. Hydrogen storage capacity cost in caverns: $1 to $5 per kWh - Geologically constrained hydrogen storage can be very cheap on an energy basis. Hydrogen storage in depleted gas/oil fields: Around $0.50 per kWh - One of the cheapest storage-cost estimates mentioned, but highly site-specific. Pumped hydro share of US grid storage: About 99% - Shows pumped hydro’s dominance in current large-scale grid storage. Pumped hydro typical duration: 6 to 24 hours - Most current pumped hydro is built for diurnal, not multi-day, storage. Pumped hydro energy capacity costs: Hundreds of dollars per kWh - Typical installations are too expensive for long-duration use. Large pumped hydro reservoir cost: $20 to $30 per kWh - Special sites can approach long-duration viability. Compressed air storage cost in best locations: Around $1 per kWh - Possible in favorable saline aquifers with hundreds of hours of capacity. Thermal storage proposal cost: $5 to $10 per kWh - Ceramic fire-brick concepts may be cheap enough for some applications. Thermal storage efficiency: Over 50% - Mentioned for some ceramic-based thermal storage concepts.
Pivotal Quotes: "long-duration energy storage needs to get extremely cheap before it will play a substantial role in a clean grid" — David Roberts: Core thesis introduced at the start of the episode. "not until $20 per kilowatt hour will they reduce system costs by 10%" — David Roberts: Summarizes one of the study’s major quantitative findings about the cost threshold for meaningful impact. "we need to start thinking hard about where to find lots of clean, firm generation" — David Roberts: The closing practical implication: storage alone will not fully solve reliability needs.
Implications: LDES is promising but not a standalone solution: future grids will still need abundant clean firm power, while storage R&D should prioritize ultra-low energy-capacity costs and very long durations. Geographically advantaged technologies and hydrogen-linked markets may lead the field.