Calculator Inputs
Formula Used
Solar source power: P = irradiance × area × panel efficiency.
Thermal source power: P = TEG coefficient × ΔT².
Harvested energy: Eharvest = source power × harvest hours × harvester efficiency × charger efficiency.
Load energy: Eload = Σ(current × voltage × time) × cycles.
Adjusted load: Eadjusted = Eload ÷ converter efficiency + leakage, then apply safety margin.
Net balance: Enet = usable harvested energy − adjusted load energy.
Usable storage: Estorage = capacity × storage voltage × usable depth of discharge.
Autonomy: days = usable storage ÷ adjusted daily load.
How to Use This Calculator
Select the harvesting source. Enter source data or measured power. Add harvest hours and efficiency values. Then enter active, transmit, and sleep load details. Add storage capacity, voltage, leakage, reserve days, and margin. Press Submit. Review net energy, autonomy, reserve gap, and sustainable cycles.
Example Data Table
| Scenario | Source | Harvest Hours | Cycles Per Day | Storage | Expected Result |
|---|---|---|---|---|---|
| Outdoor sensor | Solar, 120 cm² | 5 | 288 | 500 mAh | Often surplus |
| Pipe monitor | Thermal, 12 °C | 24 | 96 | 1000 mAh | Depends on ΔT |
| Machine sensor | Vibration, 8 mW | 8 | 144 | 300 mAh | Check downtime |
| Beacon node | RF, 0.5 mW | 24 | 48 | 200 mAh | Use deep sleep |
Energy Harvesting Power Budget Guide
Energy harvesting systems need strict power planning. Small sources can run sensors for years. They can also fail quickly. The difference is often the budget. This calculator turns scattered device values into one daily balance.
What The Budget Means
A power budget compares energy collected with energy used. Harvested energy comes from solar, thermal, vibration, RF, or a measured source. Load energy comes from active work, radio bursts, sleep current, leakage, and conversion loss. A positive balance means the design can recharge. A negative balance means storage will drain.
Why Duty Cycle Matters
Most low power devices do not run continuously. They wake, measure, transmit, and sleep. Each state has a current and time. The tool converts every state into energy per cycle. It then multiplies by cycles per day. This reveals the real daily load, not only the peak load.
Storage Reserve
Storage must cover weak harvest periods. A supercapacitor or battery should support the load during darkness, shade, motion gaps, or temperature loss. The calculator estimates required reserve from no-harvest days and depth of discharge. It also reports expected autonomy. This helps compare a small cell, a larger cell, or a hybrid buffer.
Efficiency And Margin
Energy rarely moves without loss. Chargers, regulators, rectifiers, and converters reduce usable energy. The tool includes harvester efficiency and converter efficiency. It also applies a safety margin. This margin covers aging, dirt on panels, temperature drift, capacity fade, and forecast error.
Design Decisions
Use the result to change the design before hardware testing. Reduce radio time. Lower sample rate. Increase panel area. Improve sleep current. Add storage only after the load is optimized. Storage hides problems, but it does not create energy.
Practical Use
Start with measured currents when possible. Use data sheet values only for early estimates. Enter realistic harvest hours. Test worst case days. A reliable system should show surplus energy during normal use. It should also survive the chosen no-harvest reserve period.
Advanced Checks
Check the peak current too. Some storage devices pass average energy tests, yet sag during radio bursts. Compare peak current with buffer limits. Add brownout margin for cold cells. Review every assumption after field measurements. Then update the calculator inputs.
FAQs
What is an energy harvesting power budget?
It is a daily comparison between collected energy and consumed energy. It includes source power, runtime, duty cycle, storage, leakage, and conversion loss.
Why does duty cycle affect the result so much?
Duty cycle controls how often the device wakes. Short active time and long sleep time can reduce daily energy demand greatly.
Should I use measured source power or source estimates?
Use measured power for final design work. Use solar, thermal, vibration, or RF estimates during early planning and component comparison.
What does a negative net balance mean?
It means the load uses more energy than the harvester stores. The battery or capacitor will drain unless the design changes.
Why include a safety margin?
Real systems face aging, heat, cold, shade, dirt, and radio retries. A margin keeps the design safer under imperfect conditions.
How is no-harvest reserve used?
It estimates how much storage is needed during darkness, downtime, shade, calm vibration, or missing thermal difference.
Can this calculator size a supercapacitor?
Yes, it can estimate required stored energy. For capacitor sizing, also check voltage limits, ESR, leakage, and peak current sag.
Why is converter efficiency important?
Converters waste part of stored energy. Lower efficiency means the storage must deliver more energy for the same useful load.