Table 2 Advantages and disadvantages of energy transduction mechanisms for small-scale water energy harvesting

Phase-change–induced capillary flow

Gas, Liquid

• Continuous energy input from the ambient

• Low cost

• Versatile material selection

• Environmental sensitivity

• Limited durability and power density

• Limited efficiency in non-optimized channels

^{17,18,19,20,21}

Ion concentration gradient

Gas

• Continuous energy input from ambient

• Simple design and flexible

• Scalable through series or parallel connection.

• Environmental sensitivity

• Low Efficiency

• Depletion of ion concentration gradient over time

^{14,21,22,23,24}

Thermoelectric harvesting

Gas, Liquid, Solid

• High Reliability

• Low Maintenance

• Large range of working temperature

• Low Conversion Efficiency

• Cost

^25,26,27,28

Thermo-osmotic and thermoelectro-kinetic conversion

Gas, Liquid

• Range of Material

• Flexibility

• High adhesive

• Self-Healing

• Small and Lightweight

• Stability and Durability

• Limited Power Output

^29,30,31,32

Electromagnetic transduction

Gas, Liquid

• Easily retrofit and Modularization

• Long lifetime

• Wide power range

• Flow threshold behavior

• Noise/cavitation

• Environmental durability issues

^{33,34,35,36,37,38}

Piezoelectric transduction

Liquid, Solid

• Low sensitivity to environment

• Compactness and Structural Simplicity

• Material Versatility

• Low power output

• Electrical Impedance Matching problem

^{39,40,41,42,43,44}

Triboelectric transduction

Gas, Liquid,Solid(Snow/Ice)

• Material Versatility

• Long term stability

• Wide range of application scenarios

• Fast response time

• Low cost

• Electrical Impedance Matching problem

• High Internal Impedance

• Environmental Sensitivity

• Instant output power

^{45,46,47,48,49,50,51,52,53,54,55,56}

Droplet-driven mechanisms

Liquid

• Material Versatility

• Long term stability

• Fast response time

• Low cost

• Limited Frequency Response

• Difficulty of maintaining the same output every drop

• Instant output power

^{50,51,52,53,57,58,59,60,61,62,63,64,65}