Thursday, 12 April 2012

What's inside a solar panel?

A crystalline solar panel consists of five layers: Tempered lass/EVA/solar cell/EVA/TPT, around which it’s aluminum frame for protection,encapsulation and convenient installation। On the panel back there are accessories of junction box with diode inside and output cable with connector।

Different types of Solar Panels

Let’s talk about the basic types of solar panels and how they’re used.
•Monocrystalline silicon (mono-silicon or single silicon)

Right now, these are the most efficient type of solar panels. In other words, when sunlight hits these puppies, more of it turns into electricity than the other types below. As a result of their high silicon content, they’re also more expensive, but you need fewer of them. That’s why they’re ideal for roofs. You can tell if you have a monocrystalline solar panel by its square-ish cells.

Polycrystalline silicon (multicrystalline, multi-silicon, ribbon)

“Poly” panels have lower silicon levels than “mono” panels. In general, that makes them less expensive to produce, but they’re also slightly less efficient. The good news is that their overall construction design can often make up for the efficiency loss, so they’re also good for roofs. You can tell poly-silicon panels by their groovy mélange of silicon woven through thin rectangular conduit wires.

Thin film (amorphous silicon, cadmium telluride, copper indium gallium (di)selenide)

Thin film solar panels are very inefficient, which means you’ll see them in big solar farm projects with a lot of land, but not on your roof.

Wednesday, 29 September 2010

how do solar panels work?

Solar panels collect solar radiation from the sun and actively convert that energy to electricity. From a solar-powered calculator to an international space station, solar panels generate electricity using the same principles of electronics as chemical batteries or standard electrical outlets. With solar panels, it's all about the free flow of electrons through a circuit.
To understand how solar panels generate electrical power, it might help to take a quick trip back to high school chemistry class. The basic element of solar panels is the same element that helped create the computer revolution -- pure silicon. When silicon is stripped of all impurities, it makes a ideal neutral platform for the transmission of electrons. Silicon also has some atomic-level properties which make it even more attractive for the creation of solar panels.
Silicon atoms have room for eight electrons in their outer bands, but only carry four in their natural state. This means there is room for four more electrons. If one silicon atom contacts another silicon atom, each receives the other atom's four electrons. This creates a strong bond, but there is no positive or negative charge because the eight electrons satisfy the atoms' needs. Silicon atoms can combine for years to result in a large piece of pure silicon. This material is used to form the plates of solar panels.
Here's where science enters the picture. Two plates of pure silicon would not generate electricity in solar panels, because they have no positive or negative charge. Solar panels are created by combining silicon with other elements that do have positive or negative charges.
Phosphorus, for example, has five electrons to offer to other atoms. If silicon and phosphorus are combined chemically, the result is a stable eight electrons with an additional free electron along for the ride. It can\'t leave, because it is bonded to the other phosphorus atoms, but it isn't needed by the silicon. Therefore, this new silicon/phosphorus plate is considered to be negatively charged.
In order for electricity to flow, a positive charge must also be created. This is achieved in solar panels by combining silicon with an element such as boron, which only has three electrons to offer. A silicon/boron plate still has one spot left for another electron. This means the plate has a positive charge. The two plates are sandwiched together in solar panels, with conductive wires running between them.
With the two plates in place, it's now time to bring in the 'solar' aspect of solar panels. Natural sunlight sends out many different particles of energy, but the one we're most interested in is called a photon. A photon essentially acts like a moving hammer. When the negative plates of solar cells are pointed at a proper angle to the sun, photons bombard the silicon/phosphorus atoms.
Eventually, the 9th electron, which wants to be free anyway, is knocked off the outer ring. This electron doesn't remain free for long, since the positive silicon/boron plate draws it into the open spot on its own outer band. As the sun's photons break off more electrons, electricity is generated. The electricity generated by one solar cell is not very impressive, but when all of the conductive wires draw the free electrons away from the plates, there is enough electricity to power low amperage motors or other electronics. Whatever electrons are not used or lost to the air are returned to the negative plate and the entire process begins again.
One of the main problems with using solar panels is the small amount of electricity they generate compared to their size. A calculator might only require a single solar cell, but a solar-powered car would require several thousand. If the angle of the solar panels is changed even slightly, the efficiency can drop 50 percent.
Some power from solar panels can be stored in chemical batteries, but there usually isn't much excess power in the first place. The same sunlight that provides photons also provides more destructive ultraviolet and infrared waves, which eventually cause the panels to degrade physically. The panels must also be exposed to destructive weather elements, which can also seriously affect efficiency.
Many sources also refer to solar panels as photovoltaic cells, which references the importance of light (photos) in the generation of electrical voltage। The challenge for future scientists will be to create more efficient solar panels are small enough for practical applications and powerful enough to create excess energy for times when sunlight is not available.

Click for: Why we need solar?

Monday, 20 April 2009

Plastic Solar Cells Improved With New Method

The University of Alberta and the National Research Council's National Institute (NINT) for Nanotechnology have engineered an approach that is leading to improved performance of plastic solar cells (hybrid organic solar cells). The development of inexpensive, mass-produced plastic solar panels is a goal of intense interest for many of the world's scientists and engineers because of the high cost and shortage of the ultra-high purity silicon and other materials normally required.
Plastic solar cells are made up of layers of different materials, each with a specific function, called a sandwich structure. Jillian Buriak, a professor of chemistry at the U of A, NINT principal investigator and member of the research team, uses a simple analogy to describe the approach: "Consider a clubhouse sandwich, with many different layers. One layer absorbs the light, another helps to generate the electricity, and others help to draw the electricity out of the device. Normally, the layers don't stick well, and so the electricity ends up stuck and never gets out, leading to inefficient devices. We are working on the mayonnaise, the mustard, the butter and other 'special sauces' that bring the sandwich together, and make each of the layers work together. That makes a better sandwich, and makes a better solar cell, in our case".
After two years of research, these U of A and NINT scientists have, by only working on one part of the sandwich, seen improvements of about 30 per cent in the efficiency of the working model. Michael Brett, professor of electrical and computer engineering, NINT principal investigator and member of the research team is optimistic: "our team is so incredibly cross-disciplinary, with people from engineering, physics and chemistry backgrounds all working towards this common goal of cheap manufacturable solar cells. This collaboration is extremely productive because of the great team with such diverse backgrounds, [although] there is still so much more for us to do, which is exciting." This multidisciplinary approach, common at the National Institute for Nanotechnology, brings together the best of the NRC and the University of Alberta.
The team estimates it will be five to seven years before plastic solar panels will be mass produced but Buriak adds that when it happens solar energy will be available to everyone. She says the next generation of solar technology belongs to plastic."Plastic solar cell material will be made cheaply and quickly and in massive quantities by ink jet-like printers."

Thursday, 2 April 2009

Solar power system working principle, how to build a solar power system?

A stand alone ( or off-grid) solar power system always combined by solar modules, solar controller(regulator), and batteries. If alternating current(AC) 220V or 110V needed, there also will be an inverter.

The function for each parts:

1.Solar modules: many pieces of solar cells assembled together to create a solar module, this solar module is the hard-core of a solar power system, also the most cost parts. The solar modules absorb sunlight and convert to electricity to store in battery or power the loads.

2.Solar controller (or solar regulator): controlling the working state of whole solar power system, also Protect the battries from over charge and over dis-charge. A good controller also have a temperature compensate function when used in the area with big temperature difference. Also there are other optional function such as timer and photoswithch.

3.Batteries: commonly used the Lead Acid batteries, in the mini systems, also used the NI-Mh, Ni-Cd or lithium battery. It’s function was store the electricity generated by solar modules when there was sunlights, and release it when needed.

4.Inverter, there are only DC 12V/24V 48V from the batteries and solar panels, to power the 220V/110V AC appliance, it is need to converte the DC power into AC power by inverter.

Factors for designing a solar power system:
1. where to use the solar system, how about the solar irradiation condition in the area.
2. Total loading power(KW), and daily consumption(KWH).
3. what will be the system output voltate, AC or DC required?
4. Working time on each day for the solar system.
5. system Backup days in continuous raining and cloudy condition.

Thursday, 26 March 2009

Solar cells elements, how solar cells work.

Solar energy is inexhaustible renewable energy for humans. It's also clean energy, do not generate any environmental pollution. Solar photovoltaic was the most watched item in the researching of solar energy utilize.

The production of solar cells based on semiconductor materials, and its working principle is photovoltaic materials photoelectron conversion reaction after absorb light energy , according to different materials, solar cells can be divided into: 1, silicon solar cells; 2 multi-material cells using inorganic salts such as gallium arsenide III-V compounds, cadmium sulfide, copper indium selenium compounds; 3, polymer materials solar cells; 4, nano-crystalline solar cells. etc.

1.Silicon solar cells
Silicon solar cell's structure and working principle,
Solar cells' elements is the photoelectric effect of semiconductors, normally simiconductors have below structure:

As shown in the picture, positive charge(+) means silicon atom, negtive charge(-) means electron around the silicon atom.

A hole will exist in the crystalline silicon when the cyrstalline silicon mixed with boron, it's shape as below picture:

In the picture, Positive charge (+) means silicon atom, Negetive charge(-) means electron around the silicon atom. and the yellow means mixed boron atom, as only 3 electron around the boron atom, it's bring the hole as in blue, this hole is unstable as it's without electron, easily absorb electron to neutralize to be a P(positive) type semiconductor.

Sameness, when mixed with phosphor atom, it's become highly active as the phosphor atom have 5 electron, it's comes the N(negative) type semiconductor. as shown in below picture, the yellow means Phosphor atom, the red means superfluous electron.

N type semiconductor contains more hole, while the P type semiconductor contains more electron, in this way, the electric potential difference will be formed when the P and N type semiconductor combine, that comes the PN junction.

When the P and N-type semiconductor combine, the two types of semiconductors at the interface region will form a special thin-layer, the P side contains negative electron, N side contains positive electron. This is because P-type semiconductor have many hole, N-type semiconductor have many free electrons. Electron from N-zone will be spread to the P-zone, hole from the P-zone will spread to the N-zone.

When the lights reach the crystalline silicon, the hole from N-type semiconductor move to P zone, and electron from P-zone move to N-zone, that formed the electric current from N-zone to P-zone, then formed the electric potential difference, that comes the electricity source. (shown in below picture)

Because the semiconductor is not a good conductor of electricity, the electron will waste very much when passed the P-N junction and flow in semiconductor as it's large resistance. However, if painted a metal upper, sunlight can not going through, electric current will not be able to produce, so in general with a metal mesh covering the p-n junction (pectinate electrode), in order to increase the size of the incident light.

In addition, the silicon surface is very bright, will reflect many of the sun lights,could not be used by the solar cells. Therefore, scientists painted it with a very small reflectance film, to decrease the sunlights reflection loss below 5% or eve less. A single solar cell can provide only a limited current and voltage, so people join many pieces of solar cells (usually 36) in parallel or series to become the solar modules.

2.Crystalline silicon solar cell manufacturing process.
Usual crystalline silicon solar cells are made up from the high-quality silicon at thickness of 350 ~ 450μm, such silicon wafers are cutted from Czochralski or casted silicon ingot

The above method consum more silicon material. In order to save materials, the current preparation of polycrystalline silicon thin-film solar cells using chemical vapor deposition method, including low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) process. In addition, liquid phase epitaxy (LPPE) and sputtering deposition method can also be used to prepare poly-silicon thin-film battery.

Chemical vapor deposition mainly the SiH2Cl2, SiHCl3, SiCl4 or SiH4, as the reaction gas,It's react at a certain protection atmosphere and deposite silicon atoms at the heated substrate, the general substrate materials are Si, SiO2, Si3N4, etc.. But the researching found that it's difficult to form the large crystal on the amorphous silicon (a-si) substrates and easy to cause interspace between crystal. Solutions for this problem is to deposite a thin layer of amorphous silicon on the substrate by LPCVD, then annealing this layer of amorphous silicon, to get larger crystal, and then deposite a more thick poly-crystalline silicon film at this layer, therefore, re-crystallization technology is no doubt a very important aspect, the current technology used is solid-phase crystallization and recrystallization in the FZ method. Polysilicon thin-film solar cells not onlyi use the re-crystallization process, also used almost all of the mono-crystalline silicon solar cells preparation technology, the solar cells made by this way have a remarkablly increased it's conversion efficiency.

3.Nanocrystalline chemistry solar cell
Silicon solar cells are undoubtedly the most sophisticated amone all solar cells, but because of it's high cost, can not meet the requirements of large-scale application. Therefore, Peoples always explore in process, new material and thin film solar cells etc, among this, the newly developed nano TiO2 crystalline chemistry solar cells get a great importance from home and abroad scientists.
For example, the dye-sensitized nanocrystalline solar cells (DSSCs), such solar cells mainly includes a glass substrate deposited with trasparent conductive film, dye-sensitized semiconductor materials, electrode and electrolyte etc.
As shown in below picture, the white ball means TiO2, red ball means dye molecules. Dye molecules transite to excited state after absorb solar energy, excited state unstable, the electron rapidly injected into the nearby TiO2 conduction band, Dye lost the electron is quickly be compensated from the electrolyte, electron enter the conduction band of TiO2 and eventually enter the electric conductive film, and then through the outer loop photocurrent generated.
Nanocrystalline TiO2 solar cells have it's advantages of cheap cost, simple production process and a stable performance. Photoelectric efficiency stability at 10%, and the production costs is only 1 / 5 ~ 1 / 10 of silicon solar cells. Life expectancy can achieve more than 20 years. However, because of such a solar cell researching and development still in its infancy, it is estimated to be in the market gradually.

Anode: dye-sensitized semi-conductive thin film ( TiO2 film)
Cathode: TCO glass deposted with platinic
Electrolyte: I3-/I-

Nanocrystalline chemistry solar cell application model

4 Hand made dye-sensitized nanocrystalline solar cells

1. TiO2 film Preparation

1)Grinding titanium dioxide powder with adhesive mortars

2)Spread the mixture on TCO (transparent conductive) glass

3)Sinter it on alcohol burner,them cool it down.

2.Color up the TiO2 with natural dyestuff

as shown in the picture, extrude the fresh or freezing black berry, Punica granatum seeds or black tea added with a spoon of water, then put the TiO2 film into it for color up, it's need around 5 minutes till the film become modena, if the color is nonuniform for both side, could dip in for another 5 minutes. afterwards, wash it with ethanol, then dry it with soft paper lightly.

3.Make positive electrode,

The electron outflow from dyed TiO2, means negative electrode. The positive electrode could be the conductive side of the TCO glass(the side depsited with SnO2), it's could be distinguish which side of the glass are conductive by a multi meter, also could distinguish by finger as the conductive side more coarseness. as below picture, mark the non-conductive side with "+", and use a pencil wipe the conductive side with a layer of black lead equably,

4.Join the electrolyte

Use the solution with iodin-hydronium to be the electrolyte for solar cells, mainly for revert and rebirth dyestuff. drop 1 or 2 dripping electrolyte on the TiO2 .

5.Assemble the solar cells

Put the color up TiO2 film on the tale facing up, drop on 1 or 2 dripping of iodin-hydronium electrolyte, then put the positive electrode facing down on the TiO2 film. put the 2 glass slightly staggered, use 2 clamps to nip the solar cell, the 2 glass exposed parts are for connect wires. In this way, you maked the solar cells.

6.Solar cell testing:

put the solar cell under sunshine outdoor, test your solar cell if it could generate electric current.