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Generating Electricity at Night with Solar Panels - How?


A quick overview of how solar panels work:
Solar panels currently consist of an array of photovoltaic cells, which produce electricity. They are made of materials which can easily release electrons when they absorb enough energy from light. These electrons, when released, flow around a circuit, generating a direct current (because it’s constant and in one direction). Household appliances require alternating current, meaning electrons that continuously reverse the direction in which they flow around the circuit, so solar panel systems will typically include an inverter, which converts current from direct current to alternating current.

A summary of visible light:
Visible light is part of the electromagnetic spectrum. The term “electromagnetic spectrum” refers to electromagnetic radiation, which is a range of waves (varying in wavelength) that travel through the atmosphere and can transfer energy. Higher frequency waves have a higher energy than lower frequency waves. Visible light is a section of this spectrum, at around 1 micrometer in wavelength, with 1.24eV of energy. Infrared light

What is infrared light?
Infrared light is electromagnetic radiation with a slightly longer wavelength than visible light, and so it contains slightly less energy – closer to 124meV at the top end of its wavelength range. It is emitted by the Sun, and anything that is warm. Even other humans give off infrared light.


Image source: treehugger.com


How could infrared be used to generate solar power?
Whilst there is little energy being received at night in the visible light range ( in other words, it’s dark at night!), there is still a significant amount of infrared light that could be used to generate electricity, because of the fact that anything warm will emit infrared radiation, and so if solar cells could generate a current using both the visible and the infrared ranges of light, then more solar energy could be captured during the day, as well as potential electricity generation at night.

Has anything like this been built so far?
Plenty of research has been done in this area. In 2008, at the Idaho National Laboratory, researchers have developed a nano-antenna array capable of collecting solar power from both visible light and from infrared energy too, and, excitingly, using a production process that is very cheap (source: ecogeek.com). However, the reason why we aren’t yet seeing these systems appearing either on a residential or commercial scale is that the grid they constructed receives the infrared energy at 10,000,000,000,000,000 times per second, so this is an alternating current which changes direction 10 thousand billion times every second. The typical alternating current used in household appliances is 50 to 60Hz, meaning 50 to 60 changes per second. These new materials used in solar cell manufacture could increase the percentage efficiency up to about 30%, according to Peter Peumans, a Stanford University electrical engineering professor. This compares to the most efficient systems currently available of about 20%. More recently, at the Idaho National Laboratory, researcher Steven Novack has been mentioning the possibility that this figure may be even higher, around the 50% mark. Their progress so far is such that they’ve produced working panel systems, but they are not yet financially viable as a way to generate power.

When will we see it widely adopted?
The main thing that needs to be overcome is producing an efficient diode, to convert the current to a usable frequency. At the moment, diodes in production for this use are far too inefficient, under 2%, whilst the system for capturing the infrared energy can be as high as 90%. Novack’s group, and several others, are trying to produce a diode of closer to 50% efficiency, at which point a whole new breed of solar panels would take off, presuming the cost of this can be kept down to a reasonable order of magnitude – the end result would be a 45% efficient system, compared to the 20% of a standard solar panel set up.
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