The technology breakthroughs that are helping solar cells approach 50 percent efficiency levels are encouraging, but everyday applications are still years away.

Solar Cell Efficiency Levels; What Does it Mean for Me?

Emily Hois | SolarReviews

Every few weeks, it seems that a university, technology company or team of researchers is making headlines for a new development in solar cell technology. From the use of new semi-conductor materials to the incorporation of nanowires, the race is on to see who can create the most efficient solar cell for an affordable price.

But it’s not all apples-to-apples. There are traditional crystalline silicon cells, thin-film cells, single-junction cells, multi-junction cells and emerging PV like quantum dot cells. Some use a lens to concentrate the sun’s rays, while others are non-concentrator. In fact, the National Renewable Energy Laboratory has tracked the efficiency progress of more than 20 different types of solar cell technologies that have emerged since the 1970s.

So what does all the technical jargon mean to folks who want to go solar?

An efficiency rating measures the percentage of sunlight hitting the solar cell that gets converted into usable electricity. The greater the efficiency, the less surface area it will take for the solar panels to meet your energy requirements—but the higher the price tag.

Some people associate greater efficiency levels with higher-quality panels, but this isn’t necessarily true. High efficiency means your solar PV system will utilize less space on your rooftop. Therefore, those who live in high-density areas and have very limited space for solar are generally more concerned with efficiency levels.

Multi-junction PV cells used in space, photo by NASA

The current efficiency leader, multi-junction solar cells work by combining rare semiconductor materials with differing band gaps—such as germanium, gallium and indium—to convert a broader range of the solar spectrum into energy. The cell’s top layers are designed to absorb higher-energy photons, while transmitting lower-energy photons that are absorbed by the cell’s lower layers—meaning less energy is lost. Impressively efficient, multi-junction solar cells are incredibly expensive, and still used primarily in the space industry to power satellites.

Last week, the Japan-based Sharp Corporation garnered global praise when it achieved a new solar cell efficiency world record of converting 44.4 percent of sunlight to energy. So that beats the 37.8 percent efficiency achieved by the California-based Spectrolab in April, right? Wrong. Apples to oranges. Although they’re both multi-junction solar cells that use compound semi-conductor materials, Sharp uses a lens to concentrate the sunlight and Spectrolab’s record-breaking solar cell does not.

Sharp doesn’t divulge the cost of these highly-efficient cells, but Gregory Glenn, a PV consultant in Los Angeles, provides some insight. Because Sharp’s cells are so small (they measure 4mm-by-4mm), Glenn said that many cells can be produced per wafer. “The cost depends on how they ramp up production, but it seems reasonable to assume that with high production equipment and 150mm wafers, they could achieve 25-to-30-cents per watt,” he said, at high solar concentration levels (at least 500 suns).  

A multi-junction solar cell that surpasses 40 percent efficiency is encouraging because scientists believed this was the efficiency barrier. And boosting efficiency levels helps reduce production costs and will eventually drive the price down. “There is a fixed cost and amount of time for making each panel,” says greentech reporter Ucilia Wang. “If the company produces each panel with a higher power rating (in watts) for the same amount of time as it did before, then that panel’s cost-per-watt is lower.”

Bottom line: The technology breakthroughs that are helping solar cells approach 50 percent efficiency levels are encouraging, but everyday applications are still years away. 

 

The original article was posted on the SolarReviews blog. 


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