Field of the Invention
The present invention relates to methods, systems, apparatuses, computer readable media, and other means for reliably using thermophotovoltaic cells to power electronic devices.
Description of Related Art
Electronic devices are known which are powered by rechargeable batteries such as nickel-cadmium, lithium-ion, nickel-metal hydride, and rechargeable alkaline batteries. The batteries of such devices are often recharged using standard recharging means and methods, such as by plugging a charging cable into the device and into a conventional alternating current (AC) outlet. The battery of a device can be conventionally charged by plugging the device into another electronic device using a universal serial bus (USB) connection (such as a USB cable or docking station). However, it can be inconvenient or impossible for the user to charge the batteries when, for example, the user is traveling. In addition, a typical recharge will power the battery for only a limited amount of run time. After the battery has been drained, the user must recharge or replace the battery to continue using the electronic device.
Some electronic devices (e.g., calculators) can further use solar cells to power the device. However, such methods and devices are limited by small size of many electronic devices, which constrains the effective surface area for absorbing sunlight, as well as the inherent characteristics of solar cells, which require the device to track the sun to maintain consistent exposure to sunlight for stable power output. Consequently, while the voltage generated by the solar cells can be enough to power less energy demanding devices, the voltage can be insufficient for electronic devices that demand more power. Furthermore, as electronic devices include an increasing number of advanced features, larger sources of stable and consistent power are required. Thus, there are competing interests between the portability of these devices and the amount of available power.
The effectiveness of using known photovoltaic cells to charge electronic devices is additionally limited by composition and other properties of the cells which frustrate charge separation and transport and permit significant electron-hole pair recombination to occur. Unless rapidly separated and transported from the cell, photogenerated charges recombine and contribute to thermalization and, in low band gap semiconductors, photocorrosion. Increasing the thermal energy of such cells further reduces overall photoconversion efficiency (PCE) by lowering charge mobility and promoting additional recombination.
Thermalization inevitably occurs in such applications notwithstanding the relative speed and degree of separation and transport. In response to AM 1.5 G solar radiation, crystalline silicon cells with a 1.1 eV absorption edge are able to absorb photons representing approximately 77% of the solar spectrum (with wavelengths ranging from about 350 nm to about 1.1 μm); the remainder (with wavelengths ranging from about 1.1 μm to 1 mm) heats the cell and its surrounding structures and environment. Further, almost all of the photons in the flux absorbed by the cell have energies greater than the bandgap energy of silicon, and produce both an electron-hole pair and thermalization losses upon absorption. In total, more than about two thirds of the solar flux striking a conventional solar cell is converted to thermal energy.
Problematically, the performance of electronic devices also degrades in response to elevated temperature. The integration of conventional solar cells into electronic devices is thus further complicated by the implicit expectation that such devices be exposed to solar radiation. However, electronic devices generate heat since such devices are comprised in part of components which only use a portion of the charge they receive. For example, the amount of power discharged from a device's battery that is not used for device function instead increases the thermal energy of the device at rates dependent on the relative efficiency of the device's components. Thus, device manufacturers go to significant lengths to manage heat, in many cases by designing their devices to dissipate heat as a form of waste since it is generally present at low grade temperatures insufficient for known heat recovery technologies to operate cost-effectively, particularly at the scale of a electronic device.
The thermal energy produced by or imparted to known electronic devices, be it from the absorption and inefficient conversion of sunlight or the inefficient use of electrical energy, will eventually dissipate as the system and its surroundings achieve thermal equilibrium. The rate and degree to which that dissipation occurs is in part a function of the ambient temperature in the local environment, which is itself directly and indirectly heated by the vast majority of the incoming solar flux that never comes in contact with the surface of the cell. Most of that energy is absorbed and stored by the environment (e.g., air, water, land, buildings, electronic devices, and so on) in the form of thermal energy which is then released at low grade temperatures by convection, conduction and, importantly, emission of infrared radiation in every direction, day and night, 24 hours a day, and 365 days per year. Humanity then adds to those emissions by engaging in activities that create waste heat, for example, by burning coal and other fossil fuels to provide power to electronic devices. Historical attempts to access and convert such low grade sources of thermal energy into electricity have been limited and unsuccessful.
The increased use of electronic devices in recent years corresponds to increased fossil fuel consumption. For example, the two billion smartphones expected to be in use worldwide by 2014 will consume the equivalent of more than 80 million barrels of fossil fuel per year. Smartphone use alone is growing by more than about 40% per year, with each new generation evolving and selecting for increased performance. It is desirable to provide a method or device for meeting the power needs of such devices that does not rely on the combustion of fossil fuels.
In view of the conventional attempts, needs remain for improved methods, devices and systems for powering and managing thermal energy in electronic devices.