Nanowire solar cells raise efficiency limit

Source: EurekAlert!

A joint research program of the Nano-Science Center at the Niels Bohr Institut (Denmark) and the Ecole Polytechnique Fédérale de Lausanne (Switzerland) has resulted in an innovative, new type of solar cells. Scientists have shown that a single nanowire can concentrate the sunlight up to 15 times of the normal sun light intensity. The results are surprising and the potential for developing a new type of highly efficient solar cells is great.

Due to some unique physical light absorption properties of nanowires, the limit of how much energy we can utilize from the sun's rays is higher than previous believed. These results demonstrate the great potential of development of nanowire-based solar cells. The research groups have during recent years studied how to develop and improve the quality of the nanowire crystals, which is a cylindrical structure with a diameter of about 10,000 part of a human hair. The nanowires are predicted to have great potential in the development not only of solar cells, but also of future quantum computers and other electronic products. It turns out that the nanowires naturally concentrate the sun's rays into a very small area in the crystal by up to a factor 15. Because the diameter of a nanowire crystal is smaller than the wavelength of the light coming from the sun it can cause resonances in the intensity of light in and around nanowires. Thus, the resonances can give a concentrated sunlight, where the energy is converted, which can be used to give a higher conversion effeciency of the sun's energy, says Peter Krogstrup, who with this discovery contributes to that the research in solar cell technology based on nanowires get a real boost. The typical efficiency limit - the so-called "Shockley-Queisser Limit" - is a limit, which for many years has been a landmark for solar cells efficiency among researchers, but now it seems that it may be increased. It's exciting as a researcher to move the theoretical limits, as we know. Although it does not sound like much, that the limit is moved by only a few percent, it will have a major impact on the development of solar cells, exploitation of nanowire solar rays and perhaps the extraction of energy at international level. However, it will take some years years before production of solar cells consisting of nanowires becomes a reality. The research is conducted in collaboration with the Laboratory des Matériaux Semiconducteurs, Ecole Polytechnique Fédérale de Lausanne, the Foundation and the company SunFlake A/S.

How to Use Solar Energy at Night

Source: Scientific American

Solar energy is great. But what can we do if there is no sulight and the energy is still needed? I've asked myself this question already many times and I even had an idea of how one could solve this. :-) Indeed, my girlfriend once bought this massage thing. It is a plastic filled with some pseudo-fluid material and a small piece of metal. When you click it, the salts start to crystalize and heat is released. It not only feels great, it can also be reused over and over again. To restore the massage thing, you simply have to boil it and the crystals disappear.



Anyway, if this would make sense, it would already be developed I think. Still, I was happy to read an article on the Scientific American website where they explain how salts can be used to store solar energy. Part of a so-called parabolic trough solar-thermal power plant, the salts will soon help the facility light up the night—literally. Because most salts only melt at high temperatures (table salt, for example, melts at around 1472 degrees Fahrenheit, or 800 degrees Celsius) and do not turn to vapor until they get considerably hotter—they can be used to store a lot of the sun's energy as heat. Simply use the sunlight to heat up the salts and put those molten salts in proximity to water via a heat exchanger. Hot steam can then be made to turn turbines without losing too much of the original absorbed solar energy.

Cylindral Solar Panels

Source: Solyndra, CREAX

The Solyndra system is designed to optimize photo voltaic (PV) performance on commercial rooftops by converting more of the sunlight that strikes the total rooftop area into electricity.

Solyndra's panels employ cylindrical modules which capture sunlight across a 360-degree photovoltaic surface capable of converting direct, diffuse and reflected sunlight into electricity. Solyndra's panels perform optimally when mounted horizontally and packed closely together, thereby covering significantly more of the typically available roof area and producing more electricity per rooftop on an annual basis than a conventional panel installation. The result is significantly more solar electricity per rooftop per year.

The Solyndra system is lightweight and the panels allow wind to blow through them. These factors enable the installation of PV on a broader range of rooftops without anchoring or ballast, which are inherently problematic. The horizontal mounting and unique "air-flow" properties of Solyndra's solar panel design substantially simplify the installation process for Solyndra's PV systems. The ease of installation and simpler mounting hardware of the Solyndra system enables its customers to realize significant savings on installation costs.



Using proprietary cylindrical CIGS modules and thin-film technology, Solyndra systems are designed to provide the lowest installation cost per system and the highest annual solar electrical energy output for typical low slope commercial rooftops.

Using hot asphalt to collect solar energy

Source: Science Daily, Ecogeek, Ooms Avenhorn Groep BV

I just surfed into a really cool idea! Why not use asphalt's heat-soaking property for an alternative energy source?! Indeed, why not turn the world's roads into cheap collectors of solar power. Everybody knows that asphalt gets extremely hot when the sun shines on it, so why not harvest this solar energy?!

Actually, the Dutch company Ooms Avenhorn, has been exploring this patch for almost a decade now, and has already proved that it is working! They have developed a so-called Road Energy System^® (RES), where the collection of solar energy from the asphalt is combined with underground storage, to create a year-round system which can cover heating requirements in the winter and cooling in the summer.


A latticework of flexible plastic pipes, held in place by a plastic grid, is covered over by asphalt, which magnifies the sun's thermal power. As cool water in the pipes is heated, it is pumped deep under the ground to natural aquifers where it maintains a fairly constant temperature of about 68 F. The heated water can be retrieved months later to keep the road surface ice-free in winter.



Recently, researchers at Worcester Polytechnic Institute have done a batch of research on this and their experiments figured out that the part of the asphalt gets hottest, turns out to be about two centimeters below the surface. Then they tried to figure out how to make it even hotter. The painted an anti-reflective coating to their test blocks, and then added highly thermally conductive quartzite to the mix.



The result is blacktop that gets even hotter and stays hotter for longer than regular asphalt. Of course, this left them with the problem of how to get the energy out of the road. By laying down a series of flexible and highly conductive copper pipes before pouring the asphalt they were able to pump water through the asphalt, picking up the heat, for use in power generation.

However, project leaders hoped to replace the copper pipes with a "highly efficient heat exchanger." Whether or not that would be water based, or exchange heat some other way, we don't know.

The system has several large advantages over traditional photo-voltaic power.

1. It's really cheap
2. They don't need to find extra land
3. It's invisible to the average person
4. Blacktop stays hot, and could produce power for hours after the sun goes down
5. There are roads and parking lots everywhere power is needed.

Modifying the chemistry of the asphalt specifically to make it a good solar collector is a new move, which could further improve this technology.

Ocean Wave Power, the next hot technology?

Source: Earth2Tech, AWS Ocean Energy

As the world is running out of oil, more and more alternatives emerge. Today, solar power generation has matured and is now big business, and wind energy is following in its footsteps. However, in the past years, scientists and engineers have explored the possibilities to harvest energy from the ocean. See, for instance, some of the previous posts on this blog dealing with the Pelamis. Ocean power is set to provide an exciting new source of clean renewable energy and one which can contribute to global energy needs on a sustainable basis.



Recently, Ocean Power Technologies, Inc. has announce d that it has deployed its first PowerBuoy® under contract with Iberdrola S.A., one of the world’s largest renewable energy companies. As noted by Iberdrola, the deployment of OPT’s PB40 PowerBuoy is the latest milestone toward the building of the world’s first commercial utility-scale wave power generation venture to supply approximately 1.39 MW of electricity into Spain’s electricity grid. The PB40, incorporating OPT’s patented wave power technology, is the first of what is expected to be a 10-PowerBuoy wave power station to be built out in a later phase of the project, and generating enough electricity to supply up to 2,500 homes annually.



Another clean-tech company that is developing technology to generate electricity from the energy from the ocean's waves, is AWS Ocean Energy. AWS stands for Archimedes Wave Swing, and their lead product is the award-winning Archimedes Waveswing™ wave energy converter. This is a cylinder shaped buoy, moored to the seabed. Passing waves move an air-filled upper casing against a lower fixed cylinder, with up and down movement converted into electricity.



As a wave crest approaches, the water pressure on the top of the cylinder increases and the upper part or 'floater' compresses the gas within the cylinder to balance the pressures. The reverse happens as the wave trough passes and the cylinder expands. The relative movement between the floater and the lower part or silo is converted to electricity by means of a hydraulic system and motor-generator set.