# Micro energy harvesting: Techniques

Floor tiles, nuclear batteries and generators that feed on humidity

Source page: https://www.materialinsights.org/energy/e_micro_harvest/techniques/

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)**^[3](https://www.energy.ca.gov/sites/default/files/2023-06/CEC-500-2023-036.pdf)^[4](https://www.energy.ca.gov/sites/default/files/2023-03/CEC-500-2023-008.pdf)^[5](https://www.pavegen.com/faq) | 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 generators**^[1](https://www.electrochem.org/dl/interface/fal/fal08/fal08_p54-56.pdf)^[2](https://science.nasa.gov/wp-content/uploads/2024/02/mmrtg-factsheet-updated-5-18-20-1.pdf) | 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 harvesters**^[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC11079096/) | Up to 27% of Carnot over a 10 K span (thin film). | No cost data. | Not studied. | research | Laboratory only. |
| **Triboelectric nanogenerators**^[6](https://pubs.rsc.org/en/Content/ArticleLanding/2015/EE/C5EE01532D) | About 70% instantaneous, up to 85% total (laboratory). | No cost data. | Not studied. | research | Laboratory and prototype sensors. |
| **Radio-frequency (RF) harvesters**^[8](https://spiral.imperial.ac.uk/handle/10044/1/10270) | 20-40% in London field trials at ambient levels. | No published levelised cost. | Not studied. | early commercial | Tags and low-power sensors. |
| **Humidity-based generators**^[9](https://www.nature.com/articles/s41586-020-2010-9) | 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)**^[2](https://science.nasa.gov/wp-content/uploads/2024/02/mmrtg-factsheet-updated-5-18-20-1.pdf)^[11](https://www.energy.gov/node/4831221) | 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 cells**^[10](https://wnn.world-nuclear.org/articles/nuclear-battery-chinese-firm-aiming-for-mass-mark)^[15](https://m.researching.cn/articles/OJ7d84641c3d0cbec) | 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.^[3](https://www.energy.ca.gov/sites/default/files/2023-06/CEC-500-2023-036.pdf)^[4](https://www.energy.ca.gov/sites/default/files/2023-03/CEC-500-2023-008.pdf)^[5](https://www.pavegen.com/faq)
**Thermoelectric generators**

Semiconductor pairs between a hot and a cold side produce a voltage as heat flows (the Seebeck effect).^[1](https://www.electrochem.org/dl/interface/fal/fal08/fal08_p54-56.pdf)^[2](https://science.nasa.gov/wp-content/uploads/2024/02/mmrtg-factsheet-updated-5-18-20-1.pdf)
**Pyroelectric harvesters**

Temperature swings change the material's polarisation and drive current; the Olsen cycle adds varying electric fields.^[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC11079096/)
**Triboelectric nanogenerators**

Two materials that touch and separate exchange static charge, collected by electrodes as motion opens and closes the gap.^[6](https://pubs.rsc.org/en/Content/ArticleLanding/2015/EE/C5EE01532D)
**Radio-frequency (RF) harvesters**

An antenna and rectifier (rectenna) turn ambient or deliberately beamed radio waves into direct current.^[8](https://spiral.imperial.ac.uk/handle/10044/1/10270)
**Humidity-based generators**

A film of bacterial protein nanowires absorbs water vapour unevenly; the moisture gradient drives charge.^[9](https://www.nature.com/articles/s41586-020-2010-9)
**Radioisotope thermoelectric generators (RTGs)**

Plutonium-238 decay heat passes through thermoelectric couples, with no moving parts, for decades.^[2](https://science.nasa.gov/wp-content/uploads/2024/02/mmrtg-factsheet-updated-5-18-20-1.pdf)^[11](https://www.energy.gov/node/4831221)
**Betavoltaic cells**

Electrons from a beta emitter such as nickel-63 enter a semiconductor junction, giving a steady trickle of current.^[10](https://wnn.world-nuclear.org/articles/nuclear-battery-chinese-firm-aiming-for-mass-mark)^[15](https://m.researching.cn/articles/OJ7d84641c3d0cbec)

#### Sources

1. [Small Thermoelectric Generators (G. J. Snyder, The Electrochemical Society Interface)](https://www.electrochem.org/dl/interface/fal/fal08/fal08_p54-56.pdf) The Electrochemical Society, 2008
2. [Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) fact sheet](https://science.nasa.gov/wp-content/uploads/2024/02/mmrtg-factsheet-updated-5-18-20-1.pdf) NASA, 2020
3. [Ultra-High Power Density Roadway Piezoelectric Energy Harvesting System (CEC-500-2023-036)](https://www.energy.ca.gov/sites/default/files/2023-06/CEC-500-2023-036.pdf) California Energy Commission / University of California, Merced, 2023
4. [Force Multiplier Actuated Piezoelectric Energy Harvester for Roadway Energy Recovery (CEC-500-2023-008)](https://www.energy.ca.gov/sites/default/files/2023-03/CEC-500-2023-008.pdf) California Energy Commission / Pyro-E, 2023
5. [FAQ](https://www.pavegen.com/faq) Pavegen, 2025
6. [Progress in triboelectric nanogenerators as a new energy technology and self-powered sensors (Wang, Chen and Lin, Energy & Environmental Science 8)](https://pubs.rsc.org/en/Content/ArticleLanding/2015/EE/C5EE01532D) Royal Society of Chemistry, 2015
7. [Large pyroelectric energy conversion in lead scandium tantalate thin films (Aravindhan et al., Heliyon 10)](https://pmc.ncbi.nlm.nih.gov/articles/PMC11079096/) Elsevier / PMC, 2024
8. [Current State of Research at Imperial College London in RF Harvesting and Inductive Power Transfer (Pinuela et al.)](https://spiral.imperial.ac.uk/handle/10044/1/10270) Imperial College London, 2012
9. [Power generation from ambient humidity using protein nanowires (Liu et al., Nature 578)](https://www.nature.com/articles/s41586-020-2010-9) Nature, 2020
10. [Nuclear battery: Chinese firm aiming for mass market production](https://wnn.world-nuclear.org/articles/nuclear-battery-chinese-firm-aiming-for-mass-mark) World Nuclear News, 2024
11. [U.S. Department of Energy Completes Major Shipment of Plutonium-238 for NASA Missions](https://www.energy.gov/node/4831221) US Department of Energy, 2023
12. [Fabrication and performance optimization of SiC-based betavoltaic batteries (He et al., Nuclear Techniques 48)](https://m.researching.cn/articles/OJ7d84641c3d0cbec) Nuclear Techniques (Shanghai Institute of Applied Physics), 2025

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_micro_harvest/index.md)
- [Overview](https://www.materialinsights.org/energy/e_micro_harvest/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_micro_harvest/correlation/index.md)
- [Efficiency](https://www.materialinsights.org/energy/e_micro_harvest/efficiency/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_micro_harvest/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_micro_harvest/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_micro_harvest/links/index.md)