Showing posts with label Solar. Show all posts
Showing posts with label Solar. Show all posts

Saturday, 29 November 2014

Jackie Chan Blu-ray disc boosts solar panel efficiency by a massive 22%

Blu-ray discThis one’s a bit crazy, but stick with me. Blu-ray discs, like CDs and DVDs before them, consist of a thin layer — or layers — of recording medium sandwiched between two bits of plastic. Data is stored on this medium in a series of pits — small indentations — that are about 75nm long. To read the data, a laser is bounced off the recording medium — where the medium is smooth and untouched (usually referred to as islands), the laser light bounces straight back into a sensor; where the pits are, the laser is reflected differently. Thus, binary data can be stored and read.
The differences between CD, DVD, and Blu-ray recording medium/lasers
The differences between CD, DVD, and Blu-ray recording medium/lasers 
In the case of Blu-ray, the binary data isn’t just burnt directly to the disc — compression is applied, and error control codes are added so that data can be recovered in the case of light scratches. Because the error control codes are applied every few bytes, the end result is a disc covered in quasi-random pits and islands that have a recurring pattern every 150 to 525 nanometers. (The iridescence — rainbow effect — of optical discs is caused by this repeating pattern, in case you wondered.)

As it turns out, these two characteristics — a quasi-random pattern, repeating every 150 to 525nm — are almost perfectly tuned for trapping photons in the visible light and near-infrared spectrum. One of the main reasons that current solar cells aren’t that efficient is because many photons simply reflect off the panel, rather than being converted into electrons. You can probably see where this is going.
Nanopatterning a photovoltaic cell, using a Blu-ray's recording medium as a template
Nanopatterning a photovoltaic cell, using a Blu-ray’s recording medium as a template
Part of the solar cell has been treated with the Blu-ray nanopattern mold, the other part hasn't
Part of the solar cell has been treated with the Blu-ray nanopattern mold, the other part hasn’t
To increase the efficiency of a solar panel by 22%, the researchers at Northwestern bought a copy of Police Story 3: Supercop on Blu-ray; removed the top plastic layer, exposing the recording medium beneath; cast a mold of the quasi-random pattern; and then used the mold to create a photovoltaic cell with the same pattern. As you can see in the image above, this process actually makes the nanopatterned solar cell have the same iridescence as a Blu-ray disc

Friday, 20 June 2014

Different solar cells

Different generations of solar cells

Solar cells are usually divided into three main categories called generations. The first generation contains solar cells that are relatively expensive to produce, and have a low efficiency. The second generation contains types of solar cells that have an even lower efficiency, but are much cheaper to produce, such that the cost per watt is lower than in first generation cells. The term third generation is used about cells that are very efficient. Most technologies in this generation is not yet commercial, but there is a lot of research going on in this area. The goal is to make third generation solar cells cheap to produce.

First Generation Solar Cells:

The first generation includes cells consisting of Silicon or Germanium that are doped with Phosphorus and Boron in a pn-junction. This generation is dominating the commercial market. Silicon cells have a quite high efficiency, but very pure silicon is needed, and due to the energy-requiring process, the price is high compared to the power output.
This is the generation that we focus on in the advanced section of this site.
Multicrystalline silicon solar cell.

Second Generation Solar Cells:

Amorphous Silicon Cells

In Amorphous Silicon Cells, hydrogen is introduced to the silicon to make it possible to dope the silicon with boron and phosphorus. The cells are built up in this sequence from bottom to top: metal base contact, n-layer, intrinsic layer, p-layer, transparent contact, glass substrate. These cells experience a drop in efficiency when they are exposed to sunlight, and this effect is created in the intrinsic layer. The effect can be reduced by, instead of one layer, using several thinner layers.
Calculator with amorphous silicon solar cell.

Polycrystalline silicon on low cost substrate

These cells use antireflection layers to capture lightwaves with wavelengths several times greater than the thickness of the cell itself. This can be done by using a material with a textured surface both in front and back of the cell, rather then a flat surface. This causes the light to change directions and be reflected, and thus travels a greater distance within the cell then the cell thickness.
Polycrystalline silicon solar cell

Copper Indium diSelenide (CIS) Cells

Copper Indium Diselenide consist of CuInSe2. This material is one of the best light absorber known, and about 99% of the light is absorbed before reaching 1 µm into the material. There have been made homojunctions of CIS, but a heterojunction with cadmium sulfide(CdS) has been found to be more stable and efficient.
Flexible Copper Indium Gallium diSelenide solar cells

Cadmium Telluride Cells

These cells are made from a heterojunction with cadmium sulfide, just like the copper indium diselenide. Cadmium telluride cells also have an ideal bandgap(1.44eV).

Third Generation Solar Cells:

There are several techologies in this generation. One of them is Quantum Dot(QD) Solar Cells. These are built up of a semiconductor(silicon) coated with a very thin layer of quantum dots. Quantum dots is just a fancy name of crystals in the size range typically a few nanometers in diameter. These crystals are mixed into a solution and placed on a piece of silicon which is rotated really fast. The crystals are then spread out due to the centrifugal force. The reason these quantum dots are given so much attention is that normally one photon will excite one electron creating one electron-hole pair. The energy loss is the original energy of the photon minus the energy needed to excite the electron(also called the band gap) However, when a photon hits a quantum dot made of the same material, there may be several electron-hole pairs created, typically 2-3, but 7 has been observed.
Another way to increase the efficiency is to use several layers solar cells with different band gaps in a stack. Each layer will utilise light with different wavelengths, and in this way we can get cells with a higher efficiency.

Sunday, 8 June 2014

Solar Simulator from a well known company

A solar simulator is a device that provides illumination approximating natural sunlight. The purpose of the solar simulator is to provide a controllable indoor test facility under laboratory conditions, used for the testing of solar cells, sun screen, plastics, and other materials and devices. The basic idea of a solar cell is to convert light energy into electrical energy. The energy of light is transmitted by photons, small packets or quanta of light. Electrical energy is stored in electromagnetic fields, which in turn can make a current of electrons flow. Thus a solar cell converts light, a flow of photons, to electric current, a flow of electrons.
When photons are absorbed by matter in the solar cell, their energy excites electrons higher energy states where the electrons can move more freely. The perhaps most well-known example of this is the photoelectric effect, where photons give electrons in a metal enough energy to escape the surface. In an ordinary material, if the electrons are not given enough energy to escape, they would soon relax back to their ground states. In a solar cell however, the way it is put together prevents this from happening. The electrons are instead forced to one side of the solar cell, where the build-up of negative charge makes a current flow through an external circuit. The current ends up at the other side (or terminal) of the solar cell, where the electrons once again enter the ground state, as they have lost energy in the external circuit

Friday, 11 April 2014

Solar Impulse 2 spreads its wings for the public

Solar Impulse 2 makes its public debut in Payerne, Switzerland

What has a wider wingspan than a 747, weighs the same as a car, and can fly almost forever without a drop of fuel? If you were in Payerne, Switzerland on Wednesday, you would have seen the answer as psychiatrist and explorer Bertrand Piccard and engineer and entrepreneur André Borschberg unveiled the Solar Impulse 2. The result of 12 years work, the ultra-light, solar-powered airplane will attempt to fly around the world next year relying exclusively on solar power to keep it aloft for days and a time.
Attended by luminaries such as Swiss Councilor Ueli Maurer and Prince Albert of Monaco, and representatives of the various companies that contributed sponsorship and technology to the project, the début of the Solar Impulse 2 marks the culmination of 12 years of effort by 80 technicians. It builds on the success of the previous Solar Impulse, which set eight world records, including a flight across the United States that saw the first day/night flight by a solar-powered plane.
The Solar Power 2 is a single-seater aircraft built of carbon composites with a 72-m (236-ft) wing span, which is larger than that of a Boeing 747-8 and 8 m (26 ft) wider than the previous Solar Impulse. Despite this huge expanse, it weighs only 2,300 kg (5,070 lb), of which 633 kg (1,395 lb) are lithium-ion batteries used to power the plane's four 17.5 hp electric motors that spin the propellers with an efficiency of 94 percent.
One of the Solar Impulse 2 motors
During daylight hours, the power to run the plane comes from the top of the wing, which is covered with flexible solar panels that conform to the wing’s curve. A central truss makes up the fuselage, and the wings are formed from a complex latticework of composites. According to Piccard, this new construction is much lighter than the first Solar Impulse with the composite fabric cover weighing a mere 25 g/sq m. The entire plane was also designed for a high degree of reliability to allow it to remain aloft for 12 hours without maintenance, yet keeping the weight trimmed to a minimum.
The solo pilot for the round-the-world attempt will sit in the 3.8 sq-m (40.9 sq-ft) cockpit, which was designed using computer-aided ergonomic simulations and is described as a "business class seat" for the circumnavigator, complete with lumbar massage and the ability to convert into a bunk so the pilot can catch a nap during the five-day ocean crossings. Everything from using an oxygen supply to eating, and even sleeping were tested on the ground using a flight simulator while the pilot’s vital signs were monitored.
To save weight, the cockpit isn't pressurized, nor is it heated. Instead, the pilot relies on an oxygen supply stowed in the cabin area for high altitude flight and both the pilot and batteries are protected against the subzero temperatures by a new insulating foam developed by Bayer.
Designing the cockpit
However, the cockpit is hardly a return to the days of Alcock and Brown. There’s an autopilot that the designers refer to as a "virtual co-pilot" that can alert the pilot in an emergency via a wrist-mounted alert buzzer, and the flight will be followed by a ground-based mission control that measures 50,000 parameters to modify the flight plan while under way. Communications with control is by means of a satellite communications system by Swisscom, which weighs less than 5 kg (11 lb), and is connected to what the team says is the lightest satellite antenna in the world – it's so light that a Swisscom logo serves as the counterweight.
The Solar Impulse 2 isn't fast, with a top speed of 45 mph (72 km/h), but Piccard says that its endurance is that if its pilot. It operates at 28,000 ft (8,500 m) during the day as it stores solar energy, then descends during the night, using the drop in altitude to maintain airspeed without drawing on the batteries, until it reaches a second cruising altitude between 6,000 and 9,000 ft (1,800 and 2,700 m) and goes back on battery power.
Comparison of Solar Impulse 2 and a 747
Despite all this, the plane is very heavy to control in turbulence. Taking off and landing are scheduled for early morning and after dark to avoid turbulence and heavy air traffic. This restricts takeoff and landings to very calm conditions, and landing and takeoff need to be carefully planned in advance because the plane has a minimal undercarriage. This means that to keep the wings stable on takeoff and landing, the ground crew use electric bicycles to hold the wings up on takeoff and catch them again on landing like a very low budget version of Thunderbirds. They grab on to posts suspended from the plane, which are also equipped with small wheels, so the Solar Impulse 2 can make emergency landings.
Piccard, compares this to conditions of the earliest heavier-than-air aviators and calls the Solar Impulse 2 the start of a new cycle of aviation.
Piccard and Borschberg unveiled the Solar Impulse 2 in Switzerland
As to the future, ground tests are under way, which will be followed by flight tests in Switzerland in May, a public air show debut later this year, and the round-the-world attempt in March 2015. If all goes according to schedule, the Solar Impulse 2 will fly over the Arabian Sea, India, Burma, China, the Pacific Ocean, the United States, the Atlantic Ocean and Southern Europe or North Africa before returning to its starting point in the United Arab Emirates. Along the way, the plane will land periodically to change pilots and participate in public events.
'A vision counts for nothing unless it is backed up by action. With eight world records for Solar Impulse 1, the first solar aircraft capable of flying during the night, crossing two continents and flying over the United States, we have shown that clean technologies and renewable energies can accomplish the impossible,” says Piccard.

Friday, 14 March 2014

World's first solar-powered toilet set for launch in India

A revolutionary toilet fuelled by the sun is being developed to help some of the 2.5 billion people that lack safe and sustainable sanitation around the world, and will be unveiled in India this month.
"The self-contained, waterless toilet has the capability of heating human waste to a high enough temperature to sterilise human waste and create 'biochar', a highly porous charcoal," said project principal investigator Karl Linden, professor of environmental engineering at University of Colorado Boulder.
The biochar can be used to both increase crop yields and sequester carbon dioxide, a greenhouse gas.
The project is part of the Bill & Melinda Gates Foundation's 'Reinvent the Toilet Challenge', an effort to develop a next-generation toilet that can be used to disinfect liquid and solid waste while generating useful end products.
Linden's team is one of the 16 teams around the world funded by the 'Reinvent the Toilet Challenge' since 2011.
All have shipped their inventions to Delhi where they will be on display from 20 March to 22 March for scientists, engineers and dignitaries.
"The invention consists of eight parabolic mirrors that focus concentrated sunlight to a spot no larger than a postage stamp on a quartz-glass rod connected to eight bundles of fibre-optic cables, each consisting of thousands of intertwined, fused fibres," Linden explained.
The energy generated by the sun and transferred to the fibre-optic cable system can heat up the reaction chamber to over 600 degrees Fahrenheit to treat the waste material, disinfect pathogens in both faeces and urine and produce char.
Biochar is a valuable material. It has good water holding capacity and it can be used in agricultural areas to hold in nutrients and bring more stability to the soils.
A soil mixture containing 10 percent biochar can hold up to 50 percent more water and increase the availability of plant nutrients.
"Additionally, the biochar can be burned as charcoal and provides energy comparable to that of commercial charcoal," Linden added.
Tests have shown that each of the eight fibre-optic cables can produce between 80 and 90 watts of energy, meaning the whole system can deliver up to 700 watts of energy into the reaction chamber, said Linden.
While the current toilet has been created to serve four to six people a day, a larger facility that could serve several households simultaneously is under design.
Unsafe methods to capture and treat human waste result in serious health problems and death. Notably, food and water tainted with pathogens from faecal matter results in the deaths of roughly 700,000 children each year.


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