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Brainstorm: Photovoltaics

Thu, 03/11/2010 - 8:20am
Edited by Jason Lomberg, Technical Editor

How can we make solar panels more efficient?

Keith CurtisKeith Curtis, Microchip, www.microchip.com

With all the time and money solar-cell manufacturers have expended improving cell efficiencies, it is a shame OEMs have done such a poor job utilizing the energy created. While this may sound harsh, it is all too often true.

Consider a typical high-end solar-powered system. The solar panel drives a Maximum Power Point converter (MPP), which drives a battery through a battery charger, which then drives the load through a regulator. Assume each of the blocks is based on switching technology, with an inherent 90% efficiency. This gives the overall system an efficiency of only 73%. Over 27% of our hard-won energy is wasted.

However, if we combine the three switcher functions into a simpler converter circuit, we can reduce the overall losses to less than 10% during the day, and less than 20% at night. With this single-switcher topology, the converter pulls current from the panel at its maximum power point. The circuit then routes the energy to the battery or load, depending upon the load’s voltage regulation. A second converter supports the load during low solar-output times. The result is only 10% loss from panel to load, and less than 20% for solar to battery to load.

Dave FreemanDave Freeman, TI, www.ti.com

Improving the efficiency of solar PV systems uses a two prong approach. The first prong investigates new materials and cell construction for higher photo efficiency. The second prong addresses the system power efficiency. Solar PV systems are typically made by connecting multiple panels in series. This arrangement allows the lowest performing panel to limit the overall system output. The individual power output may vary for many different reasons. Even high quality panels have panel to panel power variance of +10% to -5%. So the -5% panel would limit the panel string power and you would not get the benefit from the possible +10%.

Using a rated 200W per panel and 8 panels in a string, the -5% could cost you 80W from the expected power, while a couple of +10% panels could give you 40W more than expected. Additionally, many solar PV systems cannot be placed where the irradiance is always uniform. This will result once again in the lower performing panel controlling the string output. The solution to this problem is panel power conversion, either micro-converter or micro-inverter. The challenge is to design these micro systems for maximum power efficiency to maximize the total solar PV system efficiency. 

Steve LikerSteve Liker, Trident Solar, www.tridentsolarcell.com

One way to make solar panels more efficient is through the use of more efficient production process like the use of digital ink jet printing. Ink jet printing of contacts and bus bars has several key benefits over alternative technologies. The ability to print narrow features with small drop volume and high resolution makes it possible to minimize shadowing on the active layer. Ink jet printing can also be used to dispense etchants to remove the SiNx insulating coating and for dispensing phosphor and boric dopants to reduce the resistivity between silicon and contacts increasing cell efficiency by as much as 1.5%.

Choosing the right ink jet printing system can give companies an important edge in a competitive marketplace. Not all printing systems are created equally. In order to evaluate the quality of an ink jet printing system, take a look under the hood, at the printhead. The printhead is the heart of most ink jet printing systems and its characteristics often determine the cost effectiveness and quality of the ink jet printer. Durability, print quality, and cost-effectiveness are three key elements to look for in an ink jet printhead.

 

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