Photovoltaic scavenging systems: Modeling and optimization

doi:10.1016/j.mejo.2008.08.013

Microelectronics Journal

Volume 40, Issue 9, September 2009, Pages 1337-1344

https://doi.org/10.1016/j.mejo.2008.08.013 Get rights and content

Abstract

The interest in embedded portable systems and wireless sensor networks (WSNs) that scavenge energy from the environment has been increasing over the last years. Thanks to the progress in the design of low-power circuits, such devices consume less and less power and are promising candidates to perform continued operation by the use of renewable energy sources. The adoption of maximum power point tracking (MPPT) techniques in photovoltaic scavengers increases the energy harvesting efficiency and leads to several benefits such as the possibility to shrink the size of photovoltaic modules and energy reservoirs. Unfortunately, the optimization of this process under non-stationary light conditions is still a key design challenge and the development of a photovoltaic harvester has to be preceded by extensive simulations. We propose a detailed model of the solar cell that predicts the instantaneous power collected by the panel and improves the simulation of harvester systems. Furthermore, the paper focuses on a methodology for optimizing the design of MPPT solar harvesters for self-powered embedded systems and presents improvements in the circuit architecture with respect to our previous implementation. Experimental results show that the proposed design guidelines allow to increment global efficiency and to reduce the power consumption of the scavenger.

Section snippets

Introduction and related work

The challenges associated with the efficient power management and lifetime of pervasive embedded systems significantly constraint their functionality and potential application. In fact, the amount of the energy provided by batteries or other storage devices still limits their operating lifetime, hence the vision of developing perpetual powered devices without a necessary periodical maintenance is one of the ultimate goals of embedded systems design.

Energy scavengers using small photovoltaic

PV cell modeling

The electrical output power delivered by a PV panel depends on the incident solar radiation, cell temperature, solar incidence angle and load resistance. PV modules are manufactured using different technologies (mono-crystalline silicon, poly-crystalline and amorphous silicon) and exhibit different current–voltage characteristics. Furthermore, manufacturers typically provide only a few electrical parameters at Standard Test Conditions (STC), for which the irradiance is $1000 W / m^{2}$ and the panel

Solar energy harvester architecture

The last two decades, a lot of work and research has been done in the field of MPPT techniques [1], [2], [4], [19] and several methods and algorithms to estimate and track the MPP were proposed. The most used are perturb and observe (P&O) [19] and fractional open-circuit voltage (FOC) [20], which is the one adopted in our implementation. P&O method is widely used for large PV systems, because it is very accurate. It is usually implemented with DSPs or microcontrollers, which consume

Design guidelines for circuit optimization

In this section, we provide some guidelines to increase the circuit efficiency and to optimize the design of the harvester circuit. We focused on the DC–DC input stage increasing the conversion efficiency by adjusting the components values. Moreover we improved the DC–DC output stage with a dedicated control circuit to reduce start-up losses.

Experimental results

The aim of the experiments was to validate the improvement derived from the proposed design methodology with respect to the harvester prototype presented in [15]. In particular, the optimization guidelines proposed in the previous sections lead to the following development flow:

1.
Optimization of the DC–DC input stage is critically important to improve the performance of the solar harvester.
2.
Since the harvesting circuit has been customized to work under a wide range of light intensity, improving

Conclusion

In this paper we present a complete design flow for solar scavengers with a compact model of small-size PV cells suitable over a wide range of irradiance intensity, cell temperature variation and light incident angle. Furthermore, we provide a design methodology to increase the harvester efficiency and to optimize the harvester circuit design. We suggest design guidelines to implement optimal DC–DC input stages by an iterative procedure to select the optimal component values. In particular, the

Acknowledgments

The work presented in this paper has been founded by the European Network of Excellence ARTIST DESIGN. In addition, this research was partially supported by a grant of Telecom Italia.

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View full text

Photovoltaic scavenging systems: Modeling and optimization

Abstract

Section snippets

Introduction and related work

PV cell modeling

Solar energy harvester architecture

Design guidelines for circuit optimization

Experimental results

Conclusion

Acknowledgments

Solar Energy J.

Comparison of photovoltaic array maximum power point tracking techniques

IEEE Trans. Energy Convers.

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A comparative study of maximum-power-point trackers for photovoltaic panels using switching-frequency modulation scheme

IEEE Trans. Ind. Electron.

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IEEE Trans. Ind. Electron.

Perpetual environmentally powered sensor networks