‘Reliable’ wind power: what cost battery storage?

My 'Reliable' renewables: What cost battery storage and structural inflation? (OLO, 11.06.24) opinion piece concentrated on solar power. Some noted I didn't cover wind power. I do so here.

On average, wind power is less intermittent than solar. But variable, uncertain, and seasonal changes in intermittency still apply. Consider changes in wind power intermittency averages as one example.

Suppose wind power is 30% full-on one day, but all-off the next due to dead calm conditions. Averaged over the two days, wind power is generated 15% of the time. For reliability, generation capacity must allow 48 hours of power to be produced in 15% of the time. That requires 6.7 times the capacity of always-on base-load power. Battery storage must be 6.2 times the generation capacity of base-load power.

Assume this one day on/one day off cycle applies on average over wind turbine lives. Over the 80-year life cycle for nuclear power plants, with 20 years' average life for wind turbines, and 10-20 years for batteries, installed wind generation capacity must be at least 27 times base-load capacity, and, for batteries, about 25 - 50 times base-load, both measured over 80 years.

Wind power intermittency is more variable and uncertain, day to day, than this example. For longer windless periods, wind generation and battery storage capacity must be larger, compared with always-on base-load power, to deliver the same reliability, measured over 80 years.

Seasonality may be somewhat more predictable each year. But it also has larger effects on reliability-required capacity, especially for battery storage, compared with base-load power.

Consider this conservative example for wind power. Assume 'full-on' wind power averages 31% per day in the warmer half of the year, and 29% per day in the cooler half. Of the 31% in the warmer half year, 1 percentage point must be stored in batteries for discharge during the cooler half of the year (assuming a 100% wind-only plus 100% battery storage scenario). The year-average 'full on' wind power is still the evidence-based 30%.

For wind power, harvesting the 'summer surplus' requires 3.3% extra generation capacity per day compared with baseload power. All of that extra must be stored in batteries during the warmer half year, to be fully discharged in the cooler half.

This extra daily generation production must all be stored, on average, for 182.5 days. This daily 'summer surplus' is an energy flow. On average it must accumulate a dispatchable energy stock in batteries for 182.5 days. That stock peaks at (0.033 x 182.5 = 6.1) times the average daily 'summer surplus' extra generation. It is then fully discharged over the cooler half year.

Over 80 years (the minimum life of a nuclear base-load power plant), the average daily extra 'summer surplus' wind generation must be over 24.4% more than otherwise, assuming a 20 year average turbine life and reinvesting four times over 80 years. The extra 'summer surplus' battery capacity must be over 24.4 – 49 times the average 'summer surplus' daily wind generation, assuming batteries last for 5 – 10 years and reinvesting in new ones 4 – 8 times over 80 years.

What would that mean for the National Electricity Market (the NEM) if reliability is to be maintained year-round, all seasons, using only wind turbines and battery storage back-up? Assume a fossil fuel-free NEM using all-wind generation, and all-battery seasonal storage.

In 2022-23, the average daily power produced by the NEM was over 520,000 MWh (more now). Suppose 'summer surplus' generation is added. That's 3.3% more. That's an extra 17,333 MWh per day. That extra, on average, must be stored every day for 182.5 days. That's a storage total of 3,163,330 MWh. If batteries last 20 years, over 80 years, battery capacity investment must deliver 12,653,320 MWh. If batteries last ten years, storage capacity doubles to 25,306,641 MWh.