Table 2.
Compares of some energy sources available in the ambient.
| Reference | Energy Source | Method | Merit | Power Density | Efficiency | Weakness | Applications |
|---|---|---|---|---|---|---|---|
| [10,11,12] | Light Energy |
Photovoltaic | Predictable, Mature | 5–100 mW/cm2 (Outdoor) 0.5–1000 μW/cm2 (Indoor) |
30% 15% |
Expensive, light not steadily available, Maximum Power Point Tracking (MPPT) is needed. | Biometric, agriculture, monitoring, ZNE building, indoor and portable devices |
| [13] | Radio-frequency energy | Rectenna | Continuously available, can carry and process information simultaneously | 0.01–0.3 μW/cm2 | ±50% | Efficiency decreases with distance, impedance matching is needed | Sensor, nuclear, wirelessly powering |
| [14] | Thermal radiation is emitted by objects at moderate temperatures, typically within the range of 300 to 4000 K. This also encompasses the radiation emitted by the Earth’s surface. | Rectenna | Continuous available, waste heat can be used | 60 mW/cm2 | 1% | Limited conversion efficiency, thermal losses, narrow bandwidth, challenges in design and fabrication, impedance matching needed | Energy harvesting, thermal imaging, remote sensing, communications, spectroscopy |