Tag: solar cell

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

 

Powered by the Sun: Efficiency Records and Future Trends

solar_panelThere have been many new developments in the field of solar technology lately, thanks to new waves of innovation and the ongoing drive to make the technology cheaper and more efficient. At the current rate of growth, solar power is predicted to become cheaper than natural gas by 2025. And with that, so many opportunities for clean energy and clean living will become available.

Though there are many contributing factors to this trend, much of the progress made of late is thanks to the discovery of graphene. This miracle material – which is ultra-thin, strong and light – has the ability to act as a super capacitor, battery, and an amazing superconductor. And its use in the manufacture of solar panels is leading to record breaking efficiency.

graphene-solarBack in 2012, researchers from the University of Florida reported a record efficiency of 8.6 percent for a prototype solar cell consisting of a wafer of silicon coated with a layer of graphene doped with trifluoromethanesulfonyl-amide (TFSA). And now, another team is claiming a new record efficiency of 15.6 percent for a graphene-based solar cell by ditching the silicon all together.

And while 15.6 efficiency might still lag behind certain designs of conventional solar cells (for instance, the Boeing Spectrolabs mass-production design of 2010 achieved upwards of 40 percent), this represents a exponential increase for graphene cells. The reason why it is favored in the production of cells is the fact that compared to silicon, it is far cheaper to produce.

solar_power2Despite the improvements made in manufacturing and installation, silicon is still expensive to process into cells. This new prototype, created by researchers from the Group of Photovoltaic and Optoelectronic Devices (DFO) – located at Spain’s Universitat Jaume I Castelló and the University of Oxford – uses a combination of titanium oxide and graphene as a charge collector and perovskite to absorb sunlight.

As well as the impressive solar efficiency, the team says the device is manufactured at low temperatures, with the several layers that go into making it being processed at under 150° C (302° F) using a solution-based deposition technique. This not only means lower potential production costs, but also makes it possible for the technology to be used on flexible plastics.

twin-creeks-hyperion-wafer-ii-flexibleWhat this means is a drop in costs all around, from production to installation, and the means to adapt the panel design to more surfaces. And considering the rate at which efficiency is being increased, it would not be rash to anticipate a range of graphene-based solar panels hitting the market in the near future – ones that can give conventional cells a run for their money!

However, another major stumbling block with solar power is weather, since it requires clear skies to be effective. For some time, the idea of getting the arrays into space has been proposed as a solution, which may finally be possible thanks to recent drops in the associated costs. In most cases, this consists or orbital arrays, but as noted late last year, there are more ambitious plans as well.

lunaring-3Take the Japanese company Shimizu and it’s proposed “Luna Ring” as an example. As noted earlier this month, Shimizu has proposed creating a solar array some 400 km (250 miles) wide and 11,000 km (6,800 miles) long that would beam solar energy directly to Earth. Being located on the Moon and wrapped around its entirety, this array would be able to take advantage of perennial exposure to sunlight.

Cables underneath the ring would gather power and transfer it to stations that facing Earth, which would then beam the energy our way using microwaves and lasers. Shimizu believes the scheme, which it showed off at a recent exhibition in Japan, would virtually solve our energy crisis, so we never have to think about fossil fuels again.

lunaring-2They predict that the entire array could be built and operational by 2035. Is that too soon to hope for planetary energy independence? And given the progress being made by companies like SpaceX and NASA in bringing the costs of getting into space down, and the way the Moon is factoring into multiple space agencies plans for the coming decades, I would anticipate that such a project is truly feasible, if still speculative.

Combined with increases being made in the fields of wind turbines, tidal harnesses, and other renewable energy sources – i.e. geothermal and piezoelectric – the future of clean energy, clear skies and clean living can’t get here soon enough! And be sure to check out this video of the Luna Ring, courtesy of the Shimizu corporation:


Sources: gizmodo.com, fastcoexist.com

Powered by the Sun: New Film Increases Solar Efficiency

sun_magneticfieldWith every passing year, solar power is getting cheaper and more efficient. And with every development that brings costs down and increases electrical yields, the day that it comes to replace fossil fuels and coal as the primary means of meeting our power needs gets that much closer. And with this latest development, this changeover may be coming sooner than expected.

It comes from North Carolina State University where researchers have developed a new system for strengthening the connections between stacked solar cells which could allow cells to operate at concentrations of up to 70,000 suns while minimizing wasted energy. This is especially good news seeing as how stacked cells are already an improvement over conventional solar cells.solar_panelStacked solar cells are made up of several cells that are placed one on top of the other, an arrangement that allows up to 45 percent of the absorbed solar energy to be converted into electricity. This is a significant improvement over single-junction solar cells which have a theoretical maximum conversion rate of 33.7 percent, and is made possible by the fact a stack formation prevents heat from being lost between panels.

The team at NCSU discovered that by inserting a very thin film layer of gallium arsenide into the connecting junction of stacked cells, they can eliminate energy loss ever further. The idea was inspired by the fact that cells typically start to break down at the connection junctions once they reach concentrations of 700 suns. With the addition of gallium arsenide in these spots, the connections become stronger, and all without sacrificing absorption.

solar_cell1Dr. Salah Bedair, a professor of electrical engineering at NCSU and senior author of the paper on this research:

Now we have created a connecting junction that loses almost no voltage, even when the stacked solar cell is exposed to 70,000 suns of solar energy. And that is more than sufficient for practical purposes, since concentrating lenses are unlikely to create more than 4,000 or 5,000 suns worth of energy.

At the moment, this technology is geared towards large scale solar power operations. Stacked cells are usually used in conjunction with optical concentration devices, such as Fresnel lenses, and mounted on a dual-axis solar trackers that keep the cell facing the Sun’s rays during daylight. So basically, we’re not likely to be seeing this technology available for local use. But it would be surprising if domestic consumers weren’t likely to benefit from it all the same.

solar_cell_galliumAs Dr. Bedair explained, the adoption of the technology will mean lower costs for the energy industry, and smaller arrays which will mean less land that needs to be set aside for use:

This [system] should reduce overall costs for the energy industry because, rather than creating large, expensive solar cells, you can use much smaller cells that produce just as much electricity by absorbing intensified solar energy from concentrating lenses. And concentrating lenses are relatively inexpensive.

What’s more, gallium arsenide is not exactly cheap to produce at the time. However, with constant refinements being made in industrial production processes, we can expect the cost of these to come down as well. As with everything else with solar power and renewable energy, its only a matter of time…

Source: gizmag.com