October 15th, 2012 by Nicholas Brown
A new, relatively high-voltage solar cell that can charge the li-ion batteries of portable electronics such as e-book readers and cellphones in partial shade has been created by the University of Warwick and Molecular Solar.
This type of solar cell is called an organic solar cell, plastic solar cell, or organic photovoltaic cell (OPV).
Professor Tim Jones, one of the lead researchers at University of Warwick, along with Dr Ross Hatton and Professor Mike Shipman, said: “We have taken a big step towards cheap-to-make solar chargers which can top up your devices whenever they are being used — both indoors and out.”
“A small light-weight solar charger no bigger than a credit card can be fitted to the battery of an e-book reader for example, and constantly top it up with power while you are reading it — even if you are sitting inside on the sofa,” Shipman added.
“Alternatively, this kind of solar cell could be ideal for outdoor use as it is light-weight and portable.
“The next step is to extend this technology outside the laboratory to make cheap OPV chargers available on a commercial scale through Molecular Solar.”
Solar Cell Voltage
The voltage (electromotive force) of solar cells is dependent on the amount of sunlight available, and when the weather becomes cloudy, the voltage of the cell decreases, and if it decreases below the voltage an e-book reader battery requires to charge, then it simply won’t charge at all, even if the cells are capable of generating the necessary current (by the way: wattage = voltage x current).
Normally, the performance of typical silicon solar cells is better than that of organic cells. However, these organic cells generate a higher voltage, which means they are more capable of continuing to charge batteries in cloudy weather, despite generating less electricity.
Normally, multiple small solar cells have to be connected in series to achieve the necessary voltage, but the required 4.2 volts can be achieved with only one organic cell.
How Solar Panel Voltage is Regulated
Solar power systems normally operate by using enough solar cells to generate a voltage which is much higher than necessary, so that even during cloudy weather, when the voltage decreases, the voltage will still be higher than necessary, which is good in this case.
A voltage regulator then maintains the exact voltage required by the battery, and it actually stays at that same voltage regardless of how much the weather fluctuates, as long as the voltage is above the minimum required by the regulator.
This is why voltage regulators are an essential part of solar power systems, and any other system of which the voltage fluctuates.
For more on this research above, the paper “Ultra-high voltage multijunction organic solar cells for low-power electronic applications” has been published in the journal Advanced Energy Materials.
Source: University of Warwick
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