Most Texans already know that the state’s fortunes were and are fueled by oil and natural gas. What many don’t realize, however, is just how much the future of the Lone Star State will be powered by renewable energy. With the Green Energy in Texas series, we will explore various aspects of the green energy industry and keep you informed on how those changes and innovations might affect your Texas electricity bill.
Improving Solar Energy Efficiency
Energy efficiency is extremely important when it comes to generating power. For example, a car’s gasoline engine is 14%–30% energy efficient depending on the age and model of the car. In the case of solar cells, energy efficiency not only effects the amount of solar energy than can be converted into electricity but also the price per watt.
Solar cell efficiency has never stood still. Bell Labs developed the first useful silicon solar panel in 1954, and it was a paltry 6% efficient. By the 1970’s, improvements had raised the efficiency to 14%. Current energy efficiency for solar cells now run between 14% and 23% depending on the model and manufacturer. This is because recent advances have reduced costs and injected more competition among solar panel manufacturers. Every successful tweak to solar panel technology not only pushes the efficiency further, but also pushes its reliability and —most importantly — cuts prices. Texas now boasts the cheapest residential solar installations in the country!
Since January of this year, several advances have been made that may change the future of solar energy, making it even more affordable for the average Texas home. Here’s just a few of the most recent advancements in the future of solar energy.
A Bad Reflection
One persistent problem with solar cells is that a portion of the light that falls on them is reflected back, either at the surface of the cell or from smoothed silicon structures inside the cell. In either case, reflectance reduces the amount of light available.
Researchers at Osaka University have created an anti-reflective coating process based on surface structure chemical transfer that produces tiny, submicron-sized silicon pyramid structures (or bumps) on the surface of the cell making it look black. Surface reflectance was reduced to just 3%.
Meanwhile, deep inside the cell towards the back, researchers created rougher light-trapping microstructures to trap more infrared light. Trapping the light made its photons more likely to react with the silicon’s electrons. Through just this method, energy efficiency rose to 19.8%.
Just Like Onions
A major technical advance in both electronics components and solar cells has been the ability to lay down materials in thickness-controlled ultra thin layers known as transfer printing.
Perovskite (calcium titanium oxide) solar cells are highly efficient at converting sun light to electricity. It’s also cheap and can be sprayed onto all sort of stuff to create thin, flexible solar cells. While regular silicon panels relied entirely on perfect crystalline structures to produce electricity efficiently, perovskites are littered with numerous defects and yet still make electricity more efficiently. However, for thin film panels, the fewer the defects, the better the panel’s efficiency.
Researchers at South Korea’s Ulsan National Institute of Science and Technology found that controlled layering was the key to devising a new cost-efficient way to produce thin-film perovskite solar cells that can reach 22.1% efficiency. By adding iodide ions into the solution used to form the perovskite layers, the number of defects was reduced and yielded an efficiency of 22.1%. Plus, the method could be scalable for manufacturing high-efficiency thin-film solar panels.
The record for solar energy efficiency was set in 2014 by a solar cell in direct sunlight that measured 46%. This was no ordinary cell because it was a concentrator photovoltaic (CPV) cell. Basically, a CPV uses a lens to focus a lot of incoming light onto a single solar cell. These things get hot — think magnifying glass and a piece of paper.
Last month, George Washington University researchers tested a prototype for a solar cell that harvested energy from nearly all of the light energy in the solar spectrum. That includes the longer wavelengths of light energy that are not in the visible light spectrum. The cell reached 44.5% energy efficiency.
The key behind this cell is that it is made by layering gallium antimonide (GaSb) substrates with conventional solar silicon substrates using transfer printing to form a stack of of solar cells less than one millimeter square. Each cell is keyed to grab photons from different wavelengths of light and by placing them in CPV structures, they can harvest the maximum amount of solar energy.
As prototypes go, these stacks are very exotic and expensive. However, the importance here is that by using new methods to change the current flat design to a cube that gathers in most of the sun’s light energy, the energy efficiency and the output increased dramatically. Future high efficiency solar cells may evolve just because current technology provided a way for cells to be made in a different shape.