Can “second life” EV batteries work as grid-scale energy storage?

Original Article ↗ Hacker News Discussion ↗

EV BATTERY LONGEVITY & SUPPLY TIMING

  • Many commenters note EV packs are lasting far longer than early projections, with modest degradation (~5–20% over ~10 years) in well-engineered packs.
  • As a result, the anticipated “wave” of retired EV batteries hasn’t arrived yet; most packs are still within warranty and in cars.
  • Companies built around recycling/second-life (e.g., from 2017 onward) are only now seeing EV batteries become a majority of their intake, mainly from crashes and early failures, not end-of-life degradation.
  • Expectation: meaningful volumes for large-scale reuse/recycling likely appear in the 2030s–2040s, tracking the 8–15 year lag from mass EV adoption.

SECOND-LIFE VS NEW BATTERIES: ECONOMICS

  • Several argue second-life packs work technically, but may not be cost-competitive with cheap new LFP or sodium-ion grid batteries once you add testing, repackaging, and certification.
  • The expensive part of grid-scale storage is often integration (power electronics, switchgear, siting, controls), not cells—so saving on cell cost via second-life may only shave a small fraction of total project cost.
  • Competition for salvage packs is already strong (DIY, small storage firms), keeping used pack prices fairly high.

WHY “USED UP” EV PACKS CAN STILL WORK FOR THE GRID

  • Key difference: cars need high energy and power density (weight/space critical, high current bursts for acceleration and fast charging).
  • Grid and behind‑the‑meter storage mostly need lower C‑rates over hours; space and weight are cheap.
  • At ~80% capacity, EV packs may be range‑ and performance‑limited in cars but still perfectly usable for slow, daily cycling at modest power levels.
  • Degraded packs often have only a few weak modules; removing or down‑rating them and operating the rest gently can yield many additional years.

SAFETY, REGULATION & PRACTICAL OBSTACLES

  • Second-life systems must pass stationary safety standards; regulators often treat reused packs as if they were new designs, duplicating tests already done for the vehicle.
  • This adds cost and delays, and founders report difficulty competing with purpose-built Chinese grid batteries even when EV packs are “free.”
  • Large‑scale battery fires (e.g., Moss Landing) loom over the sector; operators claim improved layouts and fire management, but real‑world validation is still pending.

ALTERNATIVE STORAGE PATHS

  • Multiple commenters think the main grid‑scale future is cheap purpose‑built storage:
    • LFP and emerging sodium‑ion for batteries.
    • Thermal storage (e.g., sand/dirt heated to hundreds of °C) for low‑cost, long‑duration or heat applications.
    • Pumped hydro between reservoirs for multi‑day/seasonal storage.
  • Detailed subthreads dive into thermal‑storage physics (heat capacity of dirt/sand, steam cycle temperatures, heat‑exchanger design) and conclude it is technically feasible and potentially extremely cheap for heat, harder for electricity.

VEHICLE‑TO‑HOME/GRID & DISTRIBUTED STORAGE

  • Several see more near‑term impact from first‑life EVs used as mobile storage (V2L, V2H, V2G):
    • Even 1.5–2 kW continuous V2L, combined with a modest home battery, can significantly buffer household loads and outages.
    • Some users already feed EV V2L into “generator” ports of solar inverters as an ad‑hoc home backup and arbitrage tool.
  • Obstacles: limited V2L power, lack of standardized two‑way charging, high cost/complexity of certified V2G chargers, and lifestyle friction (managing SOC nightly to save small sums).

RECYCLING, USED MARKETS & OTHER USES

  • True recycling is still early because few packs have reached end‑of‑life; current streams are mostly production scrap and accident write‑offs.
  • Some argue the most profitable reuse may be in high‑margin consumer segments (tool packs, e‑bikes, small residential systems) rather than utility‑scale.
  • Home‑storage costs are dropping fast; DIY‑oriented commenters cite turnkey LFP systems in the ~€75–150/kWh range, arguing residential solar “wants” batteries and that second-life EV cells are competing against rapidly falling new‑cell prices.

BROADER ENERGY-SYSTEM DEBATE

  • Several threads contrast solar+storage with nuclear and prospective fusion:
    • One side: solar + batteries + other storage is already cheaper and scaling orders of magnitude faster than nuclear; fusion is viewed as perpetually “20 years away” and likely uneconomic versus mass‑manufactured PV plus storage.
    • The other: long‑duration/seasonal storage for cold, cloudy periods remains unsolved at low cost; firm generation (nuclear, possibly future fusion) still seen as necessary in some geographies.
  • Overall, most participants treat second‑life EV batteries as a useful niche contribution, not the core solution to grid decarbonization.