Solar panels with the highest efficiency. Well, the verdict is ready
Record holder for efficiency among solar panels, from among those available on the market today are, developed by the Institute of Solar Energy Systems of the Fraunhofer Society in Germany, solar cells based on multilayer photocells. Since 2005, their commercial implementation has been carried out by Soitec.
The size of the photocells themselves does not exceed 4 millimeters, and focusing sunlight on them is achieved by using auxiliary concentrating lenses, thanks to which the saturated sunlight converted into electricity with an efficiency reaching 47%.
The battery contains four p-n junction, so that four different parts of the photocell can effectively receive and convert radiation of a specific wavelength, from sunlight concentrated 297.3 times, in the wavelength range from infrared to ultraviolet.
Researchers led by Frank Dimiroth initially set themselves the task of growing a multilayer crystal, and a solution was found - they spliced growth substrates, and the result was a crystal with different semiconductor layers, with four photovoltaic subcells.
Multilayer photocells have long been used on spacecraft, but now solar stations based on them have been launched in 18 countries. This is becoming possible thanks to improved and cheaper technology. As a result, the number of countries equipped with new solar stations will increase, and there is a tendency for competition in the market for industrial solar panels.
In second place are solar batteries based on Sharp three-layer photocells, the efficiency of which reached 44.4%. Indium gallium phosphide is the first layer of the solar cell, gallium arsenide is the second, and indium gallium arsenide is the third layer. The three layers are separated by a dielectric, which serves to achieve a tunnel effect.
The concentration of light on the photocell is achieved thanks to a Fresnel lens, like the German developers - the light of the sun is concentrated 302 times and converted by a three-layer semiconductor photocell.
Scientific research into the development of this technology has been continuously conducted by Sharp since 2003 with the support of NEDO, a Japanese public management organization promoting scientific research and the development and dissemination of industrial, energy and environmental technologies. By 2013, Sharp had achieved a record of 44.4%.
Two years before Sharp, in 2011, the American company Solar Junction had already released similar batteries, but with an efficiency of 43.5%, the elements of which were 5 by 5 mm in size, and focusing was also carried out by lenses, concentrating the light of the sun 400 times. The solar cells were three-junction germanium-based cells, and the team even planned to create five- and six-junction solar cells to better capture the spectrum. Research is still ongoing by the company.
Thus, solar panels made in combination with concentrators, which, as we see, are produced in Europe, Asia, and America, have the highest record efficiency. But these batteries are mainly manufactured for the construction of large-scale ground-based solar power plants and for efficient power supply to spacecraft.
Recently, a record has been set in the field of conventional consumer solar panels, which are affordable for most people who want to install them, for example, on the roof of a house.
In mid-autumn 2015, Elon Musk's company SolarCity introduced the most efficient consumer solar panels, the efficiency of which exceeds 22%.
This indicator was confirmed by measurements carried out by the Renewable Energy Test Center laboratory. The Buffalo plant already sets a daily production target of 9 to 10 thousand solar panels, the exact characteristics of which have not yet been reported. The company already plans to supply at least 200,000 homes annually with its batteries.
The point is that optimized technological process allowed the company to significantly reduce the cost of production, while increasing the efficiency by 2 times compared to widespread consumer silicon solar panels. Musk is confident that his solar panels will be the most popular among homeowners in the near future.
I'm interested in meeting people who are in constant search. Among them is my colleague Alexander, a fan of electric vehicles. You will find information about its developments and the formation of a fleet of electric vehicles in Ukraine here. But, oddly enough, in addition to the electric car, he is also interested in solar panels with high efficiency.
After asking him a question, I had to sweat a little, and this is what came out of it.
Silicon crystalline photomodules
The efficiency of silicon module cells today is about 15 - 20% (polycrystals - single crystals). This figure may soon be increased by several percent. For example, SunTech Power, one of the world's largest manufacturers of crystalline silicon modules, has announced its intention to launch photovoltaic modules with 22% efficiency within two years.
Existing laboratory samples of monocrystalline cells show a productivity of 25%, polycrystalline - 20.5%. The theoretical maximum efficiency of silicon unijunction (p-n) elements is 33.7%. While it has not been achieved, the main task of manufacturers, in addition to increasing the efficiency of cells, is to improve production technology and reduce the cost of photomodules.
Separately positioned are photo modules from Sanyo, produced using HIT (Heterojunction with Intrinsic Thin layer) technology using several layers of silicon, similar to tandem multilayer cells. The efficiency of such elements made of single-crystalline C-Si and several layers of nanocrystalline nc-Si is 23%. This is the highest cell efficiency of serial crystalline modules to date.
Thin Film Solar Cells
Several different technologies have been developed under this name, the performance of which can be said as follows.
Today, there are three main types of inorganic film solar cells—amorphous silicon (a-Si) films, cadmium telluride (CdTe) films, and copper indium gallium selenide (CuInGaSe2, or CIGS) films.
The efficiency of modern thin-film solar cells based on amorphous silicon is about 10%, photomodules based on cadmium telluride - 10-11% (manufacturer: First Solar), based on copper-indium-gallium selenide - 12-13% (Japanese solar modules SOLAR FRONTIER) . Efficiency indicators of serial cells: CdTe have an efficiency of 15.7% (MiaSole modules), and CIGS cells produced in Switzerland - 18.7% (EMPA).
The efficiency of individual thin-film solar cells is much higher, for example, data on the performance of laboratory samples of amorphous silicon cells is 12.2% (United Solar), CdTe cells are 17.3% (First Solar), CIGS cells are 20.5% ( ZSW). So far, solar converters based on thin films of amorphous silicon lead in production volumes among other thin-film technologies - the global market volume of thin-film Si cells is about 80%, solar cells based on cadmium telluride are about 18% of the market, and copper-indium-gallium selenide is 2% market.
This is due, first of all, to the cost and availability of raw materials, as well as higher stability of characteristics than in multilayer structures. Note that silicon is one of the most common elements in the earth's crust, while indium (CIGS elements) and tellurium (CdTe elements) are scattered and mined in small quantities. In addition, cadmium (CdTe cells) is toxic, although most manufacturers of such solar panels guarantee complete recycling of their products.
Further development of photoelectric converters based on inorganic thin films is associated with improvements in production technology and stabilization of their parameters.
And yet, based on the stability of characteristics and relatively inexpensive prices, preference is given to solar cells made on the basis of amorphous silicon. But as we see, their efficiency is no more than 12.2%.
Better results have so far been achieved in laboratory conditions. An example is the development of engineers from the Swiss National Laboratory of Materials, Science and Technology EMPA, who managed to achieve a high efficiency rate (20.4%) working with a new generation of thin-film solar panels. The new panels are based on flexible polymers made from the complex compound CIGS or copper indium gallium (di) selenid (copper-indium-gallium-(di) selenide).
Perovskite crystal lattice CH3NH3PbI3
Wikimedia Commons
American researchers have shown that in solar cells based on perovskites, charge carriers with excess energy are able to travel a significant distance before dissipating it as heat. This means that it is quite possible to implement photovoltaic cells on hot carriers, for which the theoretical efficiency limit is twice as high as that of conventional silicon ones. The study was published in the journal Science.
In today's most common solar cells, which use silicon as a semiconductor, the theoretically possible efficiency barely exceeds 30 percent. This is due to the fact that silicon cells are only able to use part of the sunlight spectrum. Photons with energy below the threshold are simply not absorbed, and those with too high energy lead to the formation of so-called hot charge carriers (for example, electrons) in the photocell. The lifetime of the latter is about a picosecond (10 -12 seconds), then they “cool down,” that is, they dissipate excess energy in the form of heat. If hot carriers could be collected, this would increase the theoretical efficiency limit to 66 percent, or twice as much. Despite the fact that in some experiments it was possible to observe small conservation of energy, elements on hot carriers still remain rather hypothetical.
Scientists from Purdue University and the National Renewable Energy Laboratory (USA) contributed to the study of a new promising class of photovoltaic cells based on perovskites and demonstrated that in such cells hot carriers not only have an increased lifetime (up to 100 picoseconds), but are also able to “run » significant distances of several hundred nanometers (which is comparable to the thickness of the semiconductor layer).
Organometallic perovskites get their name from their crystalline structure. It essentially repeats the structure of a natural mineral - perovskite, or calcium titanate. Chemically, they are mixed halides of lead and organic cations. The authors of the work used a common perovskite based on lead iodide and methyl ammonium. Based on the fact that in perovskites the lifetime of hot carriers is significantly increased compared to other semiconductors, the authors decided to find out how far hot carriers can be transferred during their cooling. Using ultra-high-speed microscopy, the researchers were able to directly observe the transport of hot carriers in thin perovskite films with high spatial and temporal resolution.
Transport of hot carriers in a semiconductor during the first picosecond after excitation
Guo et al / Science 2017
It turned out that slow cooling in perovskites is associated with a range of up to 600 nanometers. This means that charge carriers with excess energy are theoretically able to overcome the semiconductor layer and reach the electrode, that is, they can be collected (however, the authors of the work do not discuss how to implement this technically). Thus, hot-carrier solar cells may be possible to realize using perovskites as a basis.
To date, the maximum efficiency, reaching 46%, has been recorded for multilayer multicomponent photovoltaic cells, which include gallium arsenide, indium, germanium with phosphorus inclusions. Such semiconductors use light more efficiently by absorbing different parts of the spectrum. Their production is very expensive, so such elements are used only in the space industry. Previously, we also wrote about elements based on cadmium telluride, which can be produced in the form of flexible and thin films. Although the total contribution to electricity production solar energy as long as it does not exceed 1%, the growth rate can be called explosive. Countries such as India and China are especially interested in using renewable solar energy. Google Company At the end of 2016, it announced that it was going to switch entirely to renewable energy this year.
Currently, silicon solar cells are mainly used in everyday life, the actual efficiency of which is 10–20 percent. Elements based on perovskites appeared less than 10 years ago and immediately aroused well-deserved interest (we have already written about them). The efficiency of such elements is rapidly increasing and has almost reached 25 percent, which is comparable to the best examples of silicon solar cells. In addition, they are very easy to produce. Despite the technological success, the physical principles of operation of perovskite cells are relatively little studied, so the work discussed by scientists from the USA makes an important contribution to the fundamental principles of photovoltaics and, of course, entails the prospect of further increase Solar efficiency elements.
Daria Spasskaya
Solar batteries are a unique converter of the energy of light rays into electricity with unlimited external source. The constantly growing demand for these products is due to the availability and environmental friendliness of energy supply without coolant consumption, as well as economic payback in 2 years with a minimum service life of the panels of 25 years.
The basis is semiconductors or film polymers; a plate of layers of different polarities converts light into the directional movement of electrons - this physical phenomenon unchanged for all solar panels. At the same time, this design limits the efficiency of photoconverters; part of the photon energy is inevitably lost when passing p-n boundaries transition. In practice, the efficiency of batteries is influenced by many factors: material, area, location, intensity luminous flux, which is taken into account when purchasing and operating.
Dependence of efficiency on the type of photoconverters
This indicator is defined as the percentage of generated electrical energy to the power of incident sunlight. The value is affected by the purity of the plate and its structure: film, poly- or monocrystalline. Latest species are among the most expensive and take the longest to pay for themselves; affordable solar panels with high efficiency for the home are so far produced only from layers of silicon of different polarities. Less effective are panels made of cadmium terruride and CIGS, produced on the basis of film technology. The efficiency of cadmium batteries is only 11%, but they are cheap and quite reliable in operation. The indicator is slightly higher for films coated with particles of gallium, copper, indium and selenium; CIGS photocells are 15% efficient.
For comparison: the efficiency of monocrystalline silicon converters is 25%, and for thin-film or amorphous submodules made of the same material - a maximum of 10; devices based on organic polymers have minimum value- 5 %. Much depends on the area of the panel; single solar cells are limited in generating electricity.
The efficiency of small solar panels does not allow them to be used for full power supply, but they are enough to run some types of electronics. In any case, increasing the efficiency of devices and minimizing their cost is a priority task of modern energy.
Factors affecting the efficiency of solar panels
The efficiency depends not only on the material and technology used, but also on a whole range of external conditions:
1. Luminous flux intensity. In turn, this indicator is related to geographical coordinates located battery, in particular - with latitude.
2. Angle of inclination of the structure. Ideally, solar panels should be installed that change it based on the gradient of the rays. Such a system is more expensive, but it allows you to accumulate an impressive amount of electricity (up to 40–60%) and is less dependent on the season and time of day.
3. Temperatures environment. Heating has a bad effect on the photoelectric effect; ventilated batteries have a very high efficiency. Paradoxically, in cold, clear weather they produce more energy than in hot weather (although the overall cumulative effect is reduced due to the short daylight hours).
4. Seasons. In practice, the efficiency of solar panels in winter decreases by 2–8 times, but this is not due to snowfall: it melts quickly on a dark surface, in addition, photoconverters perceive scattered light well.
5. Dustiness. The cleaner the outer part of the solar cells, the more photons will be converted, so to increase efficiency it is recommended to wipe the working surfaces at least once every two years.
6. Shadows. It is no secret that the efficiency of solar panels in cloudy weather is significantly reduced; there is no point in installing them in foggy and rainy areas; the same applies to shaded areas. It is not advisable to install the panels in the shade of tall trees or neighboring houses; when choosing a location, priority is given to the south side.
I scream and cry, this is probably how the video should have started, but many people immediately start thinking in the wrong direction. Yes, there is a lot of material about the efficiency of solar panels. There are so many that everyone is looking for a solar panel with an efficiency of 30 -50% and no matter how much they cost. Wait, what? Are you really one of those people who think that today the efficiency of panels is what is in open access it is not enough. In reality, is 22 -28% not enough?
Do you want an example of what actually has low efficiency, and we’ll talk about solar panels produced in 1990 with an efficiency of about 10%, and you know, now I can definitely say with confidence that the fairy tale that everyone who doesn’t understand is spreading on the Internet, this is outright untrue. And in order to say this with confidence, I needed to buy 2 panels with my own money, install them in operation, and monitor them for about a year different options connections.
Well, the verdict is ready.
The efficiency of older solar panels of earlier production before 2010 is significantly lower than the efficiency of modern panels, and even here we're talking about not about reducing the cost of the latter, but about production technology. We will not touch on the fact that modern ones are thinner, have a new absorbent coating, which is more effective than older panels and fades less. No, we'll just talk about efficiency.
To begin with, what is efficiency - coefficient of performance.
So, in simple language, this is how efficient solar panels work now, but not in the future, since the further and longer the solar panel works, the lower the efficiency becomes. What if you pull and load solar panels? short circuit, spiral, or IR lamps, as some do. The efficiency of solar panels will simply melt several times faster.
So, there really is no such information, even if it is so rough, especially since solar panels are so worn out that it is difficult to find in our country. And what do we end up with?
It’s simple: when there is sun, the solar panels produce almost all their power, but the operating and idle voltage drops. Yes, the current dropped a little, about 0.5 - 1A. And we could end here, taking into account the words of most bloggers, but no, our efficiency has also dropped, now solar panels produce less both in voltage and current, in cloudy weather or in reflected light. This is a drop in efficiency or wear of the panel. It seems to work, but it doesn’t seem to work in bad weather.
You think everything, but that’s not the case, I’m already used to telling everything or almost everything, even if slippers are flying at me in the present time, and in the future they are collected saying, but why didn’t you know :) I’ll tell you another problem with worn-out solar panels.
Namely! The point is that due to wear and tear solar panel and a heavily damaged and burnt-out absorbent and light-absorbing coating, by the way, some people who are not in the know call this coating a scattering coating or something else. But correctly absorbing and absorbing light, its task is to protect the silicon wafer, and the structure of the element itself, and absorb sunlight more effectively! Much of the efficiency depends on this thin layer.
So, when it collapses and burns out, the solar cells begin to heat up more intensely, and their power drops. The effect is very similar to a semi-pierced or overheated semiconductor, which seems to work, but heats up and its characteristics drop. So, since a solar cell is the same conductor with p-n transition, only larger in size, all the rules for electronics also apply to solar cells.
And the most important thing is that you cannot combine old solar panels with new ones, because when the output power on the weak ones drops, but on the new ones there is still power, the old panels will draw part of the power onto themselves as a load, thereby heating the street instead of working!
That's it. And now I will talk about this more often, so that the majority of both storytellers and people who are not in the subject will have more competent information. And if there are real observations, then there is information on how to extend the life of solar cells.