Powering IoT Devices with Volfpack Energy Supercapacitors and Solar Panels

A Comprehensive Guide for Engineers

At Volfpack Energy Supercapacitors, we’re committed to empowering engineers with innovative energy storage solutions. IoT devices—think wireless sensors, smart meters, or environmental monitors—often operate in remote or shaded environments where sunlight is inconsistent. Traditional batteries falter in these conditions, hindered by charge controllers with minimum voltage thresholds that small solar panels struggle to meet in low light. Our supercapacitors offer a game-changing alternative, capable of charging with even the tiniest trickle of solar energy. This white paper-style blog explores how to integrate Volfpack Energy supercapacitors with solar panels to power IoT devices requiring 4 outputs per day (1 joule each), detailing multiple connection methods, their pros and cons, and the math behind reliable operation.

Why Supercapacitors Over Batteries?

Supercapacitors store energy electrostatically, unlike batteries, which rely on chemical reactions. This distinction is key:

• Charging Flexibility: Supercapacitors can accept any voltage below their rating and charge with minimal current—ideal for low-light solar harvesting.

• Cycle Life: Volfpack Energy supercapacitors boast millions of charge-discharge cycles, far outlasting batteries’ hundreds or thousands.

• Low-Light Advantage: Batteries often need 5V–15V to start charging via a controller, while our supercapacitors begin storing energy at millivolts.

For an IoT device needing 4 joules daily, supercapacitors ensure uptime even in dim conditions, where batteries might fail.

System Requirements and Energy Calculations

Let’s define the target:

• Daily Energy Need: 4 outputs × 1 joule = 4 joules.

• Operating Voltage: Assume a typical IoT device requires 3.3V, common for microcontrollers.

Supercapacitor Selection

Choose a Volfpack Energy 5.5V, 5F supercapacitor:

Total Energy Stored

Usable Energy (5.5V to 3.3V):

• Assuming a buck converter stabilizes output at 3.3V, calculate energy between full charge (5.5V) and minimum usable voltage (3.3V):

With Efficiency Losses:

A 90% efficient buck converter means each 1J output requires 1.11J from the supercapacitor:

The 48.4J capacity covers this with a massive margin.

Solar Panel Selection

Pair it with a 1W solar panel (6V Voc, 5V Vmp, 200mA at 5V):

Full Sun: 1W = 5V × 0.2A.

Low Light (10% Irradiance): Assume 10mW (e.g., 3.3mA at 3V):

Charging Time (Full Charge)

From 0V to 5.5V at 200mA:

In low light (3.3mA):

Self-Discharge Consideration

A 5F supercapacitor might leak 5µA/V:

Leakage Current: 5×5.5=27.5 μA 

Daily Loss

The 432J daily input easily offsets this.

Connection Methods: Options, Advantages, and Disadvantages

Here are four ways to connect your solar panel to a Volfpack Energy supercapacitor, each with detailed pros and cons for engineering consideration.

1. Direct Connection

Setup:Wire the solar panel directly to the supercapacitor via a Schottky diode (e.g., 1N5817, 0.3V drop) to block reverse current.

How It Works:The panel’s output voltage charges the supercapacitor until equilibrium (e.g., ~5V in full sun). In low light, even 0.1V trickles in.

Advantages:

• Simplicity: Just a diode and wires—minimal design effort.

• Low Cost: Components total ~$0.10–$0.50 beyond the panel and supercapacitor.

• Low-Light Champion: Charges at any voltage below 5.5V, perfect for dawn or dusk.

Disadvantages:

• Overvoltage Risk: If Voc (6V) exceeds 5.5V in cold conditions (Voc rises ~0.3%/°C below 25°C), the supercapacitor could fail.

• No Regulation: No control over charging rate or protection beyond the diode.

Math Check:Panel at 5V, 200mA minus diode drop (0.3V) = 4.7V to supercapacitor. Max charge = 4.7V, storing:

Still ample for 4.44J daily.

2. Voltage Regulator (Linear)

Setup:Insert a linear regulator (e.g., LM317) between the panel and supercapacitor, set to 5.5V output.

How It Works:The regulator drops excess voltage (e.g., 6V to 5.5V) as heat, ensuring the supercapacitor never exceeds its rating.

Advantages:

• Overvoltage Protection: Caps voltage at 5.5V, safeguarding the supercapacitor.

• Ease of Use: Adjustable with two resistors, widely available (~$0.50).

Disadvantages:

• Inefficiency: Power loss = (Vin - Vout) × I. At 6V in, 5.5V out, 200mA

  

  
  

• Low-Light Limit: Dropout voltage (e.g., 1.5V) means it stops at ~7V input, missing some dim-light charging.

Math Check:Output fixed at 5.5V, full 75.625J stored, but efficiency drops in bright sun.

3. Buck Converter (Switching Regulator)

Setup:Use a buck converter (e.g., Pololu S7V8F3, adjusted to 5.5V) to step down panel voltage efficiently.

How It Works:Converts higher voltage to 5.5V via switching, minimizing losses.

Advantages:

• High Efficiency: 90%+ efficiency; at 6V, 200mA in, ~5.5V, 190mA out:

  
  

  

  
  

• Protection: Limits output to 5.5V, safe for the supercapacitor.

Disadvantages:

• Complexity: Requires inductors, capacitors (~$5–$10 total).

• Minimum Voltage: May need 5V+ to start, reducing low-light effectiveness.

Math Check:Charges to 5.5V faster than direct (~130s at 90% efficiency), storing 75.625J.

4. Supercapacitor-Specific Charge Controller

Setup:Employ a dedicated controller (e.g., Linear Technology LTC3129) optimized for supercapacitors.

How It Works:Manages charging with precision, often including MPPT-like features for solar input.

Advantages:

• Optimized Performance: Balances charge rate and protection, maximizing lifespan.

• Full Protection: Overvoltage, undervoltage, thermal safeguards built-in.

Disadvantages:

• Cost: $10–$20+, a premium for small IoT projects.

• Complexity: Needs configuration, adding design time.

Math Check: Similar to buck converter but with tighter control, ensuring 75.625J at peak efficiency.

Practical Implementation

Recommended Setup

For most IoT applications, we recommend the Direct Connection with these components:

• Supercapacitor: Volfpack Energy 5.5V, 5F (~$10).

• Solar Panel: 1W, 6V Voc, 5V Vmp (~$15).

• Schottky Diode: 1N5817 (~$0.10).

• Buck Converter: Pololu S7V8F3, 3.3V output (~$5).

• Optional Zener: 5.6V, 1W (~$0.20).

Total Cost: ~$30–$35.

Steps

1. Wire the Panel: Positive to diode anode, diode cathode to supercapacitor positive.

2. Add Protection (Optional): Zener in parallel with supercapacitor.

3. Connect Buck Converter: Supercapacitor to input, 3.3V output to IoT device.

4. Test: Verify charging in low light (e.g., 10mW) and full sun.

Conclusion

Volfpack Energy supercapacitors unlock new possibilities for IoT power systems. The direct connection shines for its simplicity and low-light prowess, while regulators or controllers offer efficiency and protection at the cost of complexity. For your 4-output-per-day IoT device, any method ensures reliability—choose based on your priorities: cost, simplicity, or robustness. Contact us for tailored advice or to explore our supercapacitor range. Let’s power the future of IoT together!