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Energy-adaptive Buffering for Efficient, Responsive, and Persistent Batteryless Systems

Harrison Williams, Matthew Hicks

TL;DR

The paper tackles the challenge of volatile power in batteryless energy harvesting by introducing REACT, a dynamic buffering system that adjusts capacitance via reconfigurable capacitor banks in response to net input power. It combines a small last-level buffer for fast cold-start with isolated banks that can be added or reconfigured to capture more energy when available and reclaim energy when power wanes, while minimizing dissipation during transitions. The design demonstrates significant gains in usable energy and responsiveness compared with static buffers and prior dynamic approaches, enabling higher performance, longer operation, and programmer-directed longevity guarantees in batteryless platforms. The work presents concrete architectural details, a practical hardware prototype, and a comprehensive evaluation across solar and RF scenarios, illustrating the practical impact of energy-adaptive buffering for pervasive, batteryless sensing and computing.

Abstract

Batteryless energy harvesting systems enable a wide array of new sensing, computation, and communication platforms untethered by power delivery or battery maintenance demands. Energy harvesters charge a buffer capacitor from an unreliable environmental source until enough energy is stored to guarantee a burst of operation despite changes in power input. Current platforms use a fixed-size buffer chosen at design time to meet constraints on charge time or application longevity, but static energy buffers are a poor fit for the highly volatile power sources found in real-world deployments: fixed buffers waste energy both as heat when they reach capacity during a power surplus and as leakage when they fail to charge the system during a power deficit. To maximize batteryless system performance in the face of highly dynamic input power, we propose REACT: a responsive buffering circuit which varies total capacitance according to net input power. REACT uses a variable capacitor bank to expand capacitance to capture incoming energy during a power surplus and reconfigures internal capacitors to reclaim additional energy from each capacitor as power input falls. Compared to fixed-capacity systems, REACT captures more energy, maximizes usable energy, and efficiently decouples system voltage from stored charge -- enabling low-power and high-performance designs previously limited by ambient power. Our evaluation on real-world platforms shows that REACT eliminates the tradeoff between responsiveness, efficiency, and longevity, increasing the energy available for useful work by an average 25.6% over static buffers optimized for reactivity and capacity, improving event responsiveness by an average 7.7x without sacrificing capacity, and enabling programmer directed longevity guarantees.

Energy-adaptive Buffering for Efficient, Responsive, and Persistent Batteryless Systems

TL;DR

The paper tackles the challenge of volatile power in batteryless energy harvesting by introducing REACT, a dynamic buffering system that adjusts capacitance via reconfigurable capacitor banks in response to net input power. It combines a small last-level buffer for fast cold-start with isolated banks that can be added or reconfigured to capture more energy when available and reclaim energy when power wanes, while minimizing dissipation during transitions. The design demonstrates significant gains in usable energy and responsiveness compared with static buffers and prior dynamic approaches, enabling higher performance, longer operation, and programmer-directed longevity guarantees in batteryless platforms. The work presents concrete architectural details, a practical hardware prototype, and a comprehensive evaluation across solar and RF scenarios, illustrating the practical impact of energy-adaptive buffering for pervasive, batteryless sensing and computing.

Abstract

Batteryless energy harvesting systems enable a wide array of new sensing, computation, and communication platforms untethered by power delivery or battery maintenance demands. Energy harvesters charge a buffer capacitor from an unreliable environmental source until enough energy is stored to guarantee a burst of operation despite changes in power input. Current platforms use a fixed-size buffer chosen at design time to meet constraints on charge time or application longevity, but static energy buffers are a poor fit for the highly volatile power sources found in real-world deployments: fixed buffers waste energy both as heat when they reach capacity during a power surplus and as leakage when they fail to charge the system during a power deficit. To maximize batteryless system performance in the face of highly dynamic input power, we propose REACT: a responsive buffering circuit which varies total capacitance according to net input power. REACT uses a variable capacitor bank to expand capacitance to capture incoming energy during a power surplus and reconfigures internal capacitors to reclaim additional energy from each capacitor as power input falls. Compared to fixed-capacity systems, REACT captures more energy, maximizes usable energy, and efficiently decouples system voltage from stored charge -- enabling low-power and high-performance designs previously limited by ambient power. Our evaluation on real-world platforms shows that REACT eliminates the tradeoff between responsiveness, efficiency, and longevity, increasing the energy available for useful work by an average 25.6% over static buffers optimized for reactivity and capacity, improving event responsiveness by an average 7.7x without sacrificing capacity, and enabling programmer directed longevity guarantees.
Paper Structure (25 sections, 2 equations, 5 figures, 1 table)

This paper contains 25 sections, 2 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Background and Related Work
  3. Choosing Buffer Capacity
  4. Reactivity and Longevity:
  5. Power Volatility and Energy Efficiency:
  6. Power-Responsive Performance Scaling
  7. Multiplexed Energy Storage
  8. Unified Dynamic Buffering
  9. Design
  10. REACT Overview
  11. Cold-start Operation and the Last-level Buffer
  12. Monitoring Buffered Energy
  13. Dynamic Capacitor Banks
  14. Capacitor Organization
  15. Bank Isolation
  16. ...and 10 more sections

Figures (5)

  • Figure 1: Static buffer operation on a simulated solar harvester. Highlighted blocks indicate the system is running.
  • Figure 2: REACT diagram and signal flow between components.
  • Figure 3: REACT capacitor banks in different bank sizes and configurations. Arrows indicate charging current path.
  • Figure 4: Structure of the unified approach presented by Yang et al. morphy. Arrows indicate charging current path.
  • Figure 5: Dissipative current flow in a fully-unified buffer during reconfiguration. Energy is dissipated by current spikes after capacitors at different voltages are placed in parallel.