Micro energy harvesting: Techniques

Floor tiles, nuclear batteries and generators that feed on humidity

What this tab covers The methods used to capture this energy: how each works, and how they compare on efficiency, cost, life-cycle emissions, maturity and scale.

Eight methods share one purpose: powering sensors, wearables or remote equipment without wires or battery changes. Most are research or niche products; only radioisotope generators deliver around 100 W reliably.

Comparison

Method	Efficiency	Cost	Life-cycle emissions	Maturity	Scale
Piezoelectric harvesting (footsteps, vibration, traffic)³⁴⁵	About 10% in a California road test; 7 to 17 J per vehicle passage.	Demonstration unit USD 9.68/W; projected USD 133/MWh at initial production falling to 21 at 10% market penetration (2023, extrapolated from lab data).	Not studied.	pilot	Over 250 Pavegen installations; roadway units at technology readiness level 5.
Thermoelectric generators¹²	0.1% in a body-heat watch; 6% in NASA's MMRTG.	Sold per module; no levelised cost.	Not studied.	early commercial	Niche: watches, sensors, space probes.
Pyroelectric harvesters⁷	Up to 27% of Carnot over a 10 K span (thin film).	No cost data.	Not studied.	research	Laboratory only.
Triboelectric nanogenerators⁶	About 70% instantaneous, up to 85% total (laboratory).	No cost data.	Not studied.	research	Laboratory and prototype sensors.
Radio-frequency (RF) harvesters⁸	20-40% in London field trials at ambient levels.	No published levelised cost.	Not studied.	early commercial	Tags and low-power sensors.
Humidity-based generators⁹	Not defined; at most 8.5 microwatts/cm2 from a 7-micrometre film (calculated from 0.5 V and 17 microamps/cm2).	No cost data.	Not studied.	research	Laboratory only.
Radioisotope thermoelectric generators (RTGs)²¹¹	About 6%; 110 W at launch falling to about 72 W after 17 years.	No public price; US plutonium-238 output targeted at 1.5 kg a year by 2026.	Not studied.	mature (niche)	A handful of units for NASA missions.
Betavoltaic cells¹⁰¹⁵	2.2-2.8% in recent laboratory cells; not published for Betavolt's BV100.	No cost data.	Not studied.	early commercial	BV100: 100 microwatts at 3 V, claimed 50-year life; 1 W version announced for 2025.

Harvesters are judged on cost per device and avoided battery changes, not cost per MWh; the whole market was about USD 0.61 billion in 2025. Most give microwatts to milliwatts; only RTGs reach about 100 W, using a scarce isotope. Roadway piezo projections of USD 21-133/MWh rest on extrapolated lab data and ignore that the energy comes from the vehicles' fuel.

How each method works

Piezoelectric harvesting (footsteps, vibration, traffic)

Crystals or ceramics flexed by footsteps, vibration or tyres produce a voltage, which a circuit rectifies and stores. Pavegen floor tiles (mechanism not disclosed) yield about 3 J per step.³⁴⁵

Thermoelectric generators

Semiconductor pairs between a hot and a cold side produce a voltage as heat flows (the Seebeck effect).¹²

Pyroelectric harvesters

Temperature swings change the material's polarisation and drive current; the Olsen cycle adds varying electric fields.⁷

Triboelectric nanogenerators

Two materials that touch and separate exchange static charge, collected by electrodes as motion opens and closes the gap.⁶

Radio-frequency (RF) harvesters

An antenna and rectifier (rectenna) turn ambient or deliberately beamed radio waves into direct current.⁸

Humidity-based generators

A film of bacterial protein nanowires absorbs water vapour unevenly; the moisture gradient drives charge.⁹

Radioisotope thermoelectric generators (RTGs)

Plutonium-238 decay heat passes through thermoelectric couples, with no moving parts, for decades.²¹¹

Betavoltaic cells

Electrons from a beta emitter such as nickel-63 enter a semiconductor junction, giving a steady trickle of current.¹⁰¹⁵

Sources

Small Thermoelectric Generators (G. J. Snyder, The Electrochemical Society Interface) The Electrochemical Society, 2008
Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) fact sheet NASA, 2020
Ultra-High Power Density Roadway Piezoelectric Energy Harvesting System (CEC-500-2023-036) California Energy Commission / University of California, Merced, 2023
Force Multiplier Actuated Piezoelectric Energy Harvester for Roadway Energy Recovery (CEC-500-2023-008) California Energy Commission / Pyro-E, 2023
FAQ Pavegen, 2025
Progress in triboelectric nanogenerators as a new energy technology and self-powered sensors (Wang, Chen and Lin, Energy & Environmental Science 8) Royal Society of Chemistry, 2015
Large pyroelectric energy conversion in lead scandium tantalate thin films (Aravindhan et al., Heliyon 10) Elsevier / PMC, 2024
Current State of Research at Imperial College London in RF Harvesting and Inductive Power Transfer (Pinuela et al.) Imperial College London, 2012
Power generation from ambient humidity using protein nanowires (Liu et al., Nature 578) Nature, 2020
Nuclear battery: Chinese firm aiming for mass market production World Nuclear News, 2024
U.S. Department of Energy Completes Major Shipment of Plutonium-238 for NASA Missions US Department of Energy, 2023
Fabrication and performance optimization of SiC-based betavoltaic batteries (He et al., Nuclear Techniques 48) Nuclear Techniques (Shanghai Institute of Applied Physics), 2025