Ada Audits the Energy-Neutral Sizing

Ada checks hourly load, storage reserve, and winter harvest against the same rounded inputs

ADA · CALCULATION AUDIT

Ada Audits the Energy-Neutral Sizing

The chapter sizes an outdoor harvesting node: a daily load of about 2.02 mAh (6.7 mWh), a storage reserve of about 26 mAh for seven low-harvest days, and a panel that must deliver at least 4.2 mW in a winter window. The radio event alone is 72.7% of the daily charge. This audit works the energy-neutral sizing to show the load, reserve, and panel must all be checked in the same units.

Companion to the chapter Energy Harvesting Design — every number here comes from that chapter.

The outdoor sensor closes only if the hourly load, storage reserve, and winter harvest window are all checked with the same units. The chapter rounds the daily load energy to 6.7 mWh before the storage and panel sizing steps, so the audit names that rounding point.

Load, reserve, panel power, and rounded inputs

Quantity	Arithmetic shown	Audit result
Sleep charge	0.018 mA x 24 h	0.432 mAh/day.
Sensing charge	6 mA x 3 s x 24 / 3600	0.120 mAh/day.
Radio charge	110 mA x 2 s x 24 / 3600	1.4667 mAh/day.
Daily load	0.432 + 0.120 + 1.4667	2.0187 mAh/day, reported as about 2.02 mAh/day.
Daily energy	2.0187 mAh x 3.3 V	6.6616 mWh/day, rounded in the chapter to 6.7 mWh/day.
Seven-day load	6.7 mWh/day x 7	46.9 mWh after the stated daily-energy rounding.
Storage reserve	46.9 / 0.8 / 0.7	83.75 mWh, rounded to 83.8 mWh.
Storage capacity	83.75 mWh / 3.2 V	26.17 mAh, so about 26 mAh before temperature and aging margin.
Panel power	6.7 mWh / (2 h x 0.8)	4.1875 mW, rounded to 4.2 mW during useful winter harvest hours.

Engineering consequence: the radio event contributes 1.4667 / 2.0187 = 72.7% of the daily charge. If the field panel misses the 4.2 mW winter target, lowering radio time or transmit retries helps the ledger more than shaving a small sensing interval.

Every number above is taken from this chapter's own worked example and re-derived step by step.