I am interested in meeting people who are in constant search. Among them is my colleague Alexander, a fan of electric vehicles. You can find information about its development and the formation of an electric vehicle fleet 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 that's what came of it.
Silicon crystal PV modules
The efficiency of the cells of silicon modules 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 PV modules with an efficiency of 22% within two years.
Existing laboratory samples of monocrystalline cells show a productivity of 25%, polycrystalline - 20.5%. The theoretical maximum efficiency of silicon single-junction (p-n) elements is 33.7%. It has not yet been achieved, and the main task of manufacturers, in addition to increasing the efficiency of cells, is to improve the production technology and reduce the cost of photo modules.
Sanyo's PV modules manufactured using HIT technology (Heterojunction with Intrinsic Thin layer) using several silicon layers, similar to tandem multilayer cells, are positioned separately. The efficiency of such elements made of single-crystal C-Si and several layers of nano-crystalline nc-Si is 23%. This is the highest efficiency of the cells 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 - silicon films based on amorphous silicon (a-Si), films based on cadmium telluride (CdTe), 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% (manufactured by 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 - 12.2% (United Solar), CdTe cells - 17.3% (First Solar), CIGS cells - 20.5% ( ZSW). So far, solar converters based on thin films of amorphous silicon lead in terms of production among other thin-film technologies - the volume of the world market for thin-film Si cells is about 80%, solar cells based on cadmium telluride - about 18% of the market, and copper-indium-gallium selenide - 2% market.
This is primarily due to the cost and availability of raw materials, as well as a higher stability of characteristics than in multilayer structures. Note that silicon is one of the most abundant 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 the improvement of production technology and stabilization of their parameters.
And yet, based on the stability of characteristics and relatively inexpensive price, preference is given to solar cells made on the basis of amorphous silicon. But the efficiency, as we can see, is no more than 12.2%.
Higher results have been achieved so far 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 factor (20.4%) working with a new generation of thin-film solar panels. The new panels are based on flexible polymers from the complex compound CIGS or copper indium gallium (di) selenid (copper indium gallium (di) selenide).
Everyone knows very well that the greater the efficiency, the better. This rule also applies to the efficiency of solar cells. Thanks to new technologies and production methods, the efficiency of photocells is constantly growing, albeit very slowly, but the main thing is that progress does not stand still.
Below is a graph of the performance gains by different manufacturers over time. From the middle to the very top - semiconductors were developed for new records and space tasks, the cost is appropriate. Everything below is already available and actually purchased in our time.
Everyone knows about efficiency, but few people understand where these percentages come from and how they are calculated. Let's try to figure it out.
Typically, the manufacturer indicates the efficiency of its assembled modules and the efficiency of the individual solar cells that make up the solar array. These parameters, as well as other characteristics, are indicated under the so-called standard conditions - STS, the main of which is insolation 1000W / m² and the temperature of the elements 25 ° C at which technical characteristics are taken, including efficiency.
Nowadays, bona fide manufacturers began to test every solar battery they produced after assembly and make a printout of individual parameters, which is invested in each battery. This is done to confirm the quality of their products.
Below is a printout of one of the SY-100 solar panels from Suoyang energy:
Each module has its own individual characteristics. If you take two identical panels of the same model, they will still have slightly different parameters.
Solar panels from this manufacturer have a positive tolerance, as a result we have 104.617 W and an efficiency of 15.74% (a separate cell is 18.7%). How did he get this meaning?
The formula for calculating the efficiency of solar cells is as follows:
Efficiency \u003d Psb / Ssb / 10, where:
Psb - power of SB;
Sсб - area of \u200b\u200bsb.
Let's substitute the values \u200b\u200binto the formula:
Efficiency \u003d 104.617 / (1.2 * 0.554) / 10 \u003d 15.74%
Everything converges, but another question arises: why then the efficiency of individual photocells is higher? The answer is simple - the whole point is that a solar battery consists of many photocells and there is a small distance between them that is not used to generate energy, plus the aluminum frame also "takes up space", accordingly the area increases, and the efficiency decreases.
Below are photos and videos of some attempts to achieve greater efficiency of photocells, by creating elements of complex shapes, forced cooling of solar cells and focusing light using lenses. Perhaps the new items will show themselves well, they will be put into mass production, and they will become available to you and me.
This is a Vitru hybrid solar battery, in the struggle for efficiency, the manufacturer is struggling with heating the elements. The water in the flask cools the elements, as a result of which the voltage does not decrease and the power does not drop.
The novelty is not yet for sale and is under testing, but as V3Solar says, the whole secret is in the conical shape and rotation of the structure, thanks to which the cells do not have time to heat up and the efficiency does not decrease throughout the day.
Crystal lattice of perovskite CH3NH3PbI3
Wikimedia Commons
American researchers have shown that in solar cells based on perovskites, charge carriers with excess energy can travel a considerable distance before dissipating it in the form of heat. This means that it is quite possible to realize photovoltaic cells on hot carriers, for which the theoretical efficiency limit is twice that of conventional silicon ones, in practice. Research published in the journal Science.
In the most common solar cells today, using silicon as a semiconductor, the theoretically possible efficiency hardly exceeds 30 percent. This is due to the fact that silicon cells are able to use the spectrum of sunlight only partially. Photons with energies below the threshold are simply not absorbed, and those that are too high 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, dissipate excess energy in the form of heat. If hot media could be collected, this would raise the theoretical efficiency limit to 66 percent, that is, twice. Despite the fact that in some experiments a small conservation of energy was observed, elements on hot carriers still remain rather hypothetical.
Scientists from Purdue University and the National Renewable Energy Laboratory (USA) have contributed to the study of a promising new 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 through »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 lead halides and organic cations. The authors of the work used a widespread perovskite based on lead iodide and methylammonium. Proceeding from the fact that the lifetime of hot carriers in perovskites is significantly increased in comparison with other semiconductors, the authors decided to find out how far hot carriers can be transported during their cooling. Using ultrafast 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, solar cells on hot carriers may be able to be realized 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. These 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. Earlier, we also wrote about elements based on cadmium telluride, which can be produced in the form of flexible and thin films. Despite the fact that the total contribution to electricity generation from solar energy does not yet exceed 1%, the growth rates can be called explosive. Countries such as India and China are especially interested in using renewable solar energy. Google at the end of 2016 announced that it is going to completely switch to renewable energy this year.
At present, silicon solar cells are mainly used in everyday life, the real 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 cells is rapidly increasing and is practically brought to 25 percent, which is comparable to the best samples of silicon photocells. They are also very easy to manufacture. Despite the technological success, the physical principles of the operation of perovskite cells are relatively little studied, therefore the discussed work of scientists from the United States makes an important contribution to the fundamental foundations of photovoltaics and, of course, entails the prospect of further increasing the efficiency of solar cells.
Daria Spasskaya
Solar panels are a unique system that converts the sun's rays into electrical and thermal energy. The growing demand for solar products, today, is due to its quick payback and durability, and the availability of the coolant. But what voltage can solar panels generate? About how effective solar systems are, and what determines their efficiency - read the article.
Solar cells with high efficiency: types of converters
The efficiency of solar panels is a value that is equal to the ratio of the power of electricity to the power of the sun rays falling on the panel of the device. Modern solar cells have an efficiency in the range from 10 to 45%. This big difference is due to differences between the materials of manufacture and the design of the battery plates.
So, solar panels can be:
- Thin-film;
- Multi-junction.
Solar panels of the latter type, today, are the most expensive, but also the most productive. This is due to the fact that each transition in the plate absorbs waves with a certain length. Thus, the device covers the entire spectrum of sunlight. The maximum efficiency of batteries with multijunction panels, obtained in laboratory conditions, is 43.5%.
Power engineers confidently declare that in a few years this figure will rise to 50%. The efficiency of thin-film plates depends, to a greater extent, on the material of their manufacture.
So, thin-film solar cells are divided into the following types:
- Silicon;
- Cadmium.
The most popular solar panels that can be used for domestic purposes are installations with silicon film plates. The volume of such devices on the market is 80%. Their efficiency is rather low - only 10%, but they differ in availability and reliability. The efficiency rate is several percent higher for cadmium plates. Films with selenide, copper, indium and gallium particles have a higher efficiency, which is 15%.
What determines the efficiency of solar panels
The efficiency of photovoltaic converters is influenced by many factors. So, as noted above, the amount of generated energy depends on the structure of the converter panel, the material of their manufacture.
In addition, the efficiency of solar converters depends on:
- The forces of solar radiation. So, with a decrease in solar activity, the power of solar plants decreases. In order for the batteries to provide the consumer with energy at night, they are supplied with special batteries.
- Air temperatures. So, solar panels with cooling devices are more productive: heating panels negatively affects their ability to convert energy into current. So, in frosty clear weather, the efficiency of solar cells is higher than in sunny and hot ones.
- The angle of inclination of the device and the incidence of sunlight. For maximum efficiency, the solar panel must be pointed strictly towards sunlight. The most effective models are considered, the tilt level of which can be changed relative to the location of the Sun.
- Weather conditions. In practice, it has been noted that in areas with cloudy, rainy weather, the efficiency of solar converters is much lower than in sunny regions.
In addition, the efficiency of solar converters is influenced by the level of their purity. In order for the device to work efficiently, its plates must consume as much solar radiation as possible. This can be done only if the devices are clean.
Accumulation of snow, dust and dirt on the screen can reduce the efficiency of the device by 7%.
It is recommended to wash screens 1-4 times a year, depending on the degree of contamination. In this case, for cleaning, you can use a hose with a nozzle. The technical inspection of the converter elements should be carried out every 3-4 months.
Solar power per square meter
As noted above, on average, one square meter of photovoltaic converters provides 13-18% of the power of the sun's rays falling on it. That is, under the most favorable conditions, 130-180 watts can be obtained from a square meter of solar panels.
The power of solar systems can be increased by expanding panels and increasing the area of \u200b\u200bphotovoltaic converters.
You can also get more power by installing panels with higher efficiency. Nevertheless, the rather low (in comparison, for example, with induction converters) efficiency of the available solar panels is the main obstacle to their widespread use. Increasing the capacity and efficiency of solar systems is the primary task of modern power engineering.
The most efficient solar panels: rating
The most efficient solar converters today are manufactured by Sharp. Three-layer, high-power, concentrating solar panels have an efficiency of 44.4%. Their cost is incredibly high, so they have found application only in the aerospace industry.
The most affordable and efficient are modern solar panels from companies:
- Panasonic Eco Solutions;
- First Solar;
- MiaSole;
- JinkoSolar;
- Trina Solar;
- Yingli Green;
- ReneSola;
- Canadian Solar.
Sun Power manufactures the most reliable solar converters with 21.5% efficiency. The products of this company are absolutely popular in commercial and industrial facilities, yielding, perhaps, to devices from Q-Cells.
Solar cell efficiency (video)
Modern solar panels, as environmentally friendly energy conversion devices with an inexhaustible coolant, are gaining increasing popularity. Already today devices with photovoltaic converters are used for household purposes (charging phones, tablets). The efficiency of solar installations is still inferior to alternative methods of generating energy. But, increasing the efficiency of converters is the primary task of modern power engineering.
Science and technology do not stand still in the use of alternative energy, and the use of solar energy in everyday life and industry will continue to develop and improve, trying to replace traditional energy sources. Unfortunately, the global domination of solar energy is still a long way off, and this is due to the low efficiency of solar panels.
Factors affecting the efficiency of solar panels
The efficiency of solar panels is influenced by objective and subjective factors, such as:
- materials used in the manufacture,
- technology,
- place of use (latitude),
- angle of incidence of sun rays,
- dustiness and damage.
Moreover, all these factors are related and dependent on each other in terms of their influence on the efficiency of solar panels. But the initial factor that determines the efficiency is the cost of manufacturing a solar cell.
Solar energy efficiency leaders
Consider the leaders in the manufacture of the most efficient solar panel components and sort them according to their efficiency:
- 44.7% efficiency from the first non-university research institute in Germany. The result was obtained for concentrators of a triple transition of layers of a complex semiconductor composition (Ga 0.35 V 0.65 P / Ga 0.83 V 0.17 As / Ge). Such solar cells are complex, not used for residential or commercial purposes because they are very expensive. They are used in space technology by manufacturers like NASA, where space is limited.
- 37.9% efficiency is obtained from a single layer semiconductor junction module (InGaP / GaAs / InGaAs). In this case, the result was obtained exclusively for the 90 ° normal to the Sun. These solar cells are also difficult and time consuming to manufacture, but their industrial production seems more promising.
- 32.6% were achieved by Spanish researchers from the Institute (IES) and the University (UPM). They used multi-modules from two-junction semiconductor hubs. Again, these items are far from widespread use for commercial or residential applications.
Solar cell efficiency balance
There are about a dozen of the largest manufacturers producing solar panels with relatively good efficiency and moderate cost. Leading companies producing solar cells with the most modern technologies can industrially produce solar cells with an efficiency close to 25%. At the same time, mass production of modules with the efficiency of solar cells, as a rule, does not exceed 14-17% is well established. The main reason for this difference in efficiency is that research methods used in laboratories are not suitable for commercial production of photovoltaic products and, therefore, more affordable technologies have relatively low production costs, which leads to a decrease in efficiency in use.
To do this, we will show on the graph the dependence of the cost of the finished module on the cost of generated electricity for technological series of solar cells with their characteristic efficiency indicators.
The comparative graph clearly shows the economic efficiency of solar panels with initial laboratory efficiency indicators, manufactured using different technologies, in relation to the optimal cost of generated electricity at 6 cents per kWh (3.4 rubles / kWh).
Thus, the most readily available and inexpensive solar cells made of amorphous silicon in the form of a thin bendable film pay for themselves in relatively small sizes, but are not economically efficient in the case of high power requirements. They are widely used for portable phone chargers, lamps, etc.
Polycrystalline silicon batteries are already becoming effective in residential buildings and small greenhouses. 
The elements of the experimental solar power plants are made on the basis of highly purified silicon monocrystals (99,999). They have optimal performance indicators and have an economically justified payback period.
The latest scientific developments of photovoltaic cells, which have the highest efficiency, are used exclusively in those branches of science and industry where cost is not the main selection criterion.
The use of solar cells is more and more included in various areas of our life, but unfortunately, due to the imperfection of the production technology (and as a consequence of the sufficiently low efficiency) at a significant cost, it is not widely used.
