Powered by the Sun: Boosting Solar Efficiency

solar1Improving the efficiency of solar power – which is currently the most promising alternative energy source – is central to ensuring that it an becomes economically viable replacement to fossil fuels, coal, and other “dirty” sources. And while many solutions have emerged in recent years that have led to improvements in solar panel efficiency, many developments are also aimed at the other end of things – i.e. improving the storage capacity of solar batteries.

In the former case, a group of scientists working with the University of Utah believe they’ve discovered a method of substantially boosting solar cell efficiencies. By adding a polychromat layer that separates and sorts incoming light, redirecting it to strike particular layers in a multijunction cell, they hope to create a commercial cell that can absorb more wavelengths of light, and therefor generate more energy for volume than conventional cells.

EMSpectrumTraditionally, solar cell technology has struggled to overcome a significant efficiency problem. The type of substrate used dictates how much energy can be absorbed from sunlight — but each type of substrate (silicon, gallium arsenide, indium gallium arsenide, and many others) corresponds to capturing a particular wavelength of energy. Cheap solar cells built on inexpensive silicon have a maximum theoretical efficiency of 34% and a practical (real-world) efficiency of around 22%.

At the other end of things, there are multijunction cells. These use multiple layers of substrates to capture a larger section of the sun’s spectrum and can reach up to 87% efficiency in theory – but are currently limited to 43% in practice. What’s more, these types of multijunction cells are extremely expensive and have intricate wiring and precise structures, all of which leads to increased production and installation costs.

SolarCellResearchIn contrast, the cell created by the University of Utah used two layers — indium gallium phosphide (for visible light) and gallium arsenide for infrared light. According to the research team, when their polychromat was added, the power efficiency increased by 16 percent. The team also ran simulations of a polychromat layer with up to eight different absorbtion layers and claim that it could potentially yield an efficiency increase of up to 50%.

However, there were some footnotes to their report which temper the good news. For one, the potential gain has not been tested yet, so any major increases in solar efficiency remain theoretical at this time. Second, the report states that the reported gain was a percentage of a percentage, meaning that if the original cell efficiency was 30%, then a gain of 16% percent means that the new efficiency is 34.8%. That’s still a huge gain for a polychromat layer that is easily produced, but not as impressive as it originally sounded.

PolyChromat-640x353However, given that the biggest barrier to multi-junction solar cell technology is manufacturing complexity and associated cost, anything that boosts cell efficiency on the front end without requiring any major changes to the manufacturing process is going to help with the long-term commercialization of the technology. Advances like this could help make technologies cost effective for personal deployment and allow them to scale in a similar fashion to cheaper devices.

In the latter case, where energy storage is concerned, a California-based startup called Enervault recently unveiled battery technology that could increase the amount of renewable energy utilities can use. The technology is based on inexpensive materials that researchers had largely given up on because batteries made from them didn’t last long enough to be practical. But the company says it has figured out how to make the batteries last for decades.

SONY DSCThe technology is being demonstrated in a large battery at a facility in the California desert near Modeso, 0ne that stores one megawatt-hour of electricity, enough to run 10,000 100-watt light bulbs for an hour. The company has been testing a similar, though much smaller, version of the technology for about two years with good results. It has also raised $30 million in funding, including a $5 million grant from the U.S. Department of Energy.

The technology is a type of flow battery, so called because the energy storage materials are in liquid form. They are stored in big tanks until they’re needed and then pumped through a relatively small device (called a stack) where they interact to generate electricity. Building bigger tanks is relatively cheap, so the more energy storage is needed, the better the economics become. That means the batteries are best suited for storing hours’ or days’ worth of electricity, and not delivering quick bursts.

solarpanelsThis is especially good news for solar and wind companies, which have remained plagued by problems of energy storage despite improvements in both yield and efficiency. Enervault says that when the batteries are produced commercially at even larger sizes, they will cost just a fifth as much as vanadium redox flow batteries, which have been demonstrated at large scales and are probably the type of flow battery closest to market right now.

And the idea is not reserved to just startups. Researchers at Harvard recently made a flow battery that could prove cheaper than Enervault’s, but the prototype is small and could take many years to turn into a marketable version. An MIT spinoff, Sun Catalytix, is also developing an advanced flow battery, but its prototype is also small. And other types of inexpensive, long-duration batteries are being developed, using materials such as molten metals.

Sumitomo-redox-flow-battery-YokohamaOne significant drawback to the technology is that it’s less than 70 percent efficient, which falls short of the 90 percent efficiency of many batteries. The company says the economics still work out, but such a wasteful battery might not be ideal for large-scale renewable energy. More solar panels would have to be installed to make up for the waste. What’s more, the market for batteries designed to store hours of electricity is still uncertain.

A combination of advanced weather forecasts, responsive fossil-fuel power plants, better transmission networks, and smart controls for wind and solar power could delay the need for them. California is requiring its utilities to invest in energy storage but hasn’t specified what kind, and it’s not clear what types of batteries will prove most valuable in the near term, slow-charging ones like Enervault’s or those that deliver quicker bursts of power to make up for short-term variations in energy supply.

Tesla Motors, one company developing the latter type, hopes to make them affordable by producing them at a huge factory. And developments and new materials are being considered all time (i.e. graphene) that are improving both the efficiency and storage capacity of batteries. And with solar panels and wind becoming increasingly cost-effective, the likelihood of storage methods catching up is all but inevitable.

Sources: extremetech.com, technologyreview.com


What Would Hyperspace Really Look Like?

hyperspaceRemember those iconic scenes in Star Wars when the Millennium Falcon made the jump to hyperspace? Remember how cool it looked when the star field stretched out and then the ships blasted off? And of course, every episode of Star Trek was punctuated by a jump to warp, where once again, the background stars seemed to stretch out and then hurl on past the Enterprise.

Yes, for generations, this is how people envisioned Faster-Than-Light travel. Whether it consisted of rainbow-colored streaks shooting past, or a quick distortion followed by a long, blue tunnel of bright light, these perceptions have become a staple of science fiction. But one has to wonder… in a universe where FTL was really possible, would it really look anything like this?

hyperspace3Using Einstein’s Theory of Relativity, four students from the University of Leicester produced a paper in January of last year where they theorized what a jump to light-speed would really look like. Based on the theory that the speed of light is the absolute threshold at which elementary particles can move in this universe, the four students – Riley Connors, Katie Dexter, Joshua Argyle, and Cameron Scoular – claimed that a ship that can exceed c would have an interesting view.

In short, they claim that the crew wouldn’t see star lines stretching out past the ship during the jump to hyperspace, but would actually see a central disc of bright light. This is due to the Doppler effect, specifically the Doppler blue shift, that results in the wavelength of electromagnetic radiation, including visible light, shortening as the source of the light moves towards the observer.

Hyperspace. Nuff said?
Hyperspace. Nuff said?

As the ship made the jump to hyperspace, the wavelength of the light from the stars would shift out of the visible spectrum into the X-ray range. Meanwhile, Cosmic Background Radiation (CBR), which is thermal radiation that is spread fairly uniformly across the universe and is thought to be left over from the Big Bang, would shift into the visible spectrum, appearing to the crew as a central disc of bright light.

What’s more, even a ship like the Millennium Falcon would require additional energy to overcome the pressure exerted from the intense X-rays from stars that would push the ship back and cause it to slow down. The students say the pressure exerted on the ship would be comparable to that felt at the bottom of the Pacific Ocean.

red-shift-03However, if the ship in question took its time getting up to speeds in excess of the speed of light, there would be some interesting visual effects. Given how light and the color spectrum works, as a ship continued to speed up, the stars in front of the ship would experience blueshift (shifting towards the blue end of the spectrum), while those behind it would experience redshift (shifting towards the red end).

But the moment the threshold of light speed was passed, background radiation would be all that was left to see. And once that happened, the crew would experience some rather intense radiation exposure. As Connors put it:

If the Millennium Falcon existed and really could travel that fast, sunglasses would certainly be advisable. On top of this, the ship would need something to protect the crew from harmful X-ray radiation.

And as Dexter suggested, referring to Disney’s purchase of Lucasfilm for a cool $4.05 billion: “Disney should take the physical implications of such high speed travel into account in their forthcoming films.” I won’t be holding my breath on that one. Somehow, star lines look so much cooler than a mottled, bright disc in the background, don’t you think?

Hyperspace_HomeOneSources: gizmag.com, le.ac.uk.com