Recently, more and more people have become interested in solar energy. Solar panels have become widely available, from exotic “wings” of spacecraft they have turned into an ordinary product that can be purchased in an online store in a couple of clicks, and the buyer, of course, faced a difficult task – which solar panel to buy? Solar panels differ in size, design, color, as well as dozens and even hundreds of manufacturer logos. From this variety of data, it is necessary first of all to single out the most significant factor – the coefficient of performance (COP) .
The efficiency of any device is the ratio of the energy it releases to the energy it absorbs. Based on this understanding, before choosing a product, a responsible buyer will want to figure out what the efficiency of modern solar panels is, what types of solar panels exist and how their efficiency differs, does the efficiency of solar panels change in cloudy weather, are there ways to increase efficiency solar panels and so on.
To begin with, let’s deal a little with solar panels – what is it all about?
A solar cell is similar in design to a transistor. As is known from simple experiments in electronics, if you remove the protective cover from the transistor and illuminate it, it will begin to generate voltage. And if such transistors are arranged in rows on a flat surface, then you get the simplest solar cell panel. Solar panels are based on this principle, which are based on silicon crystals, similar to silicon crystals in traditional semiconductor elements.
Over time, solar panels have improved, their relative price has decreased, and the efficiency has increased. The efficiency of the best modern solar cells is about 20 percent. It seems that this is a little, a little more than the efficiency of an internal combustion engine, but do not forget that the first solar batteries, which were developed in the middle of the last century, had an efficiency of one to five percent, so modern twenty percent, it is not so little.
The efficiency of a solar cell is the ratio of the energy entering its surface to the energy at its output terminals. Let’s consider a specific example. Let’s say there is a 1.6 square meter solar panel that is irradiated with 500 watts of light per square meter, and it produces 100 watts of electricity at the output.
The efficiency of such a battery is calculated as follows: divide the output power by the total input power (1.6 sq.m x 500 watts / sq.m = 800 watts) and multiply by 100 percent, as a result we get 100 watts: 800 watts x 100% = 12.5%. This will be its efficiency of the solar panel with insolation with a power of half a kilowatt.
But the efficiency can vary both from the intensity of irradiation and from the angle with which the sun’s rays hit the surface of the solar battery, and from the scattering of light, and from the temperature of the solar battery itself.
Therefore, the question arises – what determines the efficiency of solar panels in the first place? The efficiency of solar panels depends on two main factors – on the correct orientation to the maximum solar radiation, and on the quality of the panel itself.
In addition to the quality of workmanship, classified in four steps, which will be discussed below, the technology that is embedded in the design of the solar cells themselves is also important.
For example, a solar battery on amorphous silicon will not give out even ten percent. But that doesn’t mean it’s definitely bad. The numerical value of the efficiency of solar panels does not yet tell about all the properties of the battery. In some cases, solar panels with low efficiency are indispensable, due to some of their features. But it should be noted that the optimal value of the efficiency of modern solar panels of good quality is in the range between fifteen and twenty percent.
The efficiency of solar panels also depends on the climate of a particular point on the earth and on the weather in it at the calculated time. In areas with a lot of dust in the atmosphere, solar panels quickly become dirty and this, of course, leads to a decrease in their efficiency. Snow can also reduce the efficiency of solar panels to almost zero if they are set too low.
In cloudy weather, the efficiency of solar panels, of course, decreases. However, there are nuances associated with the design. For example, polycrystalline solar panels do not reduce efficiency in cloudy conditions as much as monocrystalline ones. Also, the good efficiency of solar panels in cloudy weather is provided by the anti-reflective coating of the elements. It allows you not to lose radiation in scattered light.
A very big obstacle to the normal operation of the solar station is the shadow. A shadow can negate the technical performance of the best solar battery and reduce its efficiency by several times. When designing and installing solar panels , care must be taken that the solar panels do not shade each other and do not fall into the shade of buildings and trees.
Currently, there are various types of solar panels, differing in efficiency, service life and design features. But since in this review we are primarily interested in the efficiency of modern solar batteries, we will dwell on them in more detail.
The most common solar panels are based on silicon cells. They are divided into three types – single-crystal, polycrystalline and amorphous.
Amorphous solar cells are an elastic base with a silicon layer deposited on it. The efficiency of amorphous solar panels is low – about six percent, but these solar panels can generate electricity in very low light, which is not enough for the operation of monocrystalline and polycrystalline solar panels. There is another advantage of amorphous panels – due to their thinness and elasticity, they bend at different angles, which, if the surface they bend around is located at favorable angles, allows them to capture more solar radiation than rigid flat panels are capable of. They can also be placed on complex curved surfaces of structures, which will not only increase the overall efficiency of these solar panels, but also give scope for the imagination of architects and designers. Another very important advantage of amorphous cells is their ability to operate at high temperatures, where single-crystal and polycrystalline batteries go out of modes, which leads to a decrease in efficiency or they stop functioning altogether. In the manufacture of amorphous solar panels, a much smaller amount of silicon is consumed than is used for single-crystal and polycrystalline solar cells, since it is deposited in a thin layer, and this helps to reduce their cost.
Polycrystalline silicon panels are twice and even three times more efficient than amorphous ones, and their efficiency reaches 18 percent. They are easy to manufacture and inexpensive, since they do not require the growth of single crystals. They have better efficiency in cloudy weather than monocrystalline solar cells. Their crystals are randomly oriented, so they function better in cloudy weather, when the light is directed at them not from one point, but from all directions.
Monocrystalline solar cells are made on the basis of monocrystals, as their name implies, and are perfectly adapted to interact with a point light source, due to the same orientation of the crystals. The efficiency of monocrystalline solar panels can reach 23 percent.
There are also modern solar panels that are not based on traditional silicon. For example, film solar cells are made from a whole bunch of different chemicals – compounds of gallium, indium, copper, cadmium. The efficiency of film solar cells is not very high, about 12 percent, but these solar panels operate in almost the entire solar spectrum. True, they are not widely used due to the scarcity of the above chemical elements.
In order to reduce the cost of production of solar cells, attempts were made to create elements based on synthetic substances. As a result, another type of solar panels appeared – polymer ones. They are flexible, like amorphous silicon panels, and are comparable to them in terms of efficiency – also about 6 percent, and can also work in low light.
Of commercially produced solar cells, the record for efficiency is held by single-crystal solar cells, but it should be noted that this is true only in direct bright sunlight.
An increase in the efficiency of solar batteries is also possible due to switching, storage and conversion devices, which, together with solar panels, form a solar system.
Efficiency is directly related to the quality of materials, as well as the build quality itself. There are four grades of build quality, defined by the term GRID with letters A through D.
Grid A – solar batteries of the highest quality, assembled, as a rule, on robotic lines, from elements of the highest quality. Of course, they also have the maximum efficiency.
Grid B is the same Grid A, but these are solar panels rejected due to minor defects that do not affect performance.
Grid C – solar panels, usually assembled from scrap. They work, but the efficiency may differ from the declared one.
Grid D – solar panels assembled by unknown small manufacturers from elements of unpredictable quality. As a rule, they are characterized by low efficiency and fragility.
Increasing the efficiency of modern solar cells is one of the main concerns of their developers. In view of the growing popularity and demand for solar energy, specialists from scientific institutes, enterprises and laboratories are constantly looking for new technologies and improving existing products.
One of China’s leading solar power firms, Jinko Solar , has provided a mass-produced state-of-the-art solar array with an efficiency of 21 percent. It goes under the Tiger Pro brand and is available in various modifications with an average power of 400 watts. In its research labs, Jinko Solar has nearly achieved a record of 25 percent efficiency. High efficiency levels have been achieved through the use of TOPCon technology, and the improvement of standard methods for the production of solar panels.
Engineers from the German firm HZB have achieved an increase in the efficiency of solar panels by almost 30 percent. This was made possible by combining the traditional semiconductor material, silicon, with a new material, which is a combination of titanium and calcium. This effect is based on the fact that silicon cells transform the infrared zone of the solar spectrum into electricity, and the new connection is able to work with the rest of the spectrum, contributing to the total voltage at the output of solar cells. A significant advantage of this innovation is that the introduction of a new compound almost does not increase the cost of solar panels.
Swiss researchers from Insolight also claim that solar panels are approaching the 30% efficiency mark. Their invention consists in the use of special glass elements that are installed above the light-absorbing cells of solar cells. These glass concentrators are assembled into a honeycomb-like structure, allowing them to efficiently collect light from different directions. In addition, the glass “cover” additionally protects the solar battery from the adverse effects of the environment, extending its life. Insolight plans to launch panels based on this development within two years.
In Germany, several leading organizations have come together to research methods for increasing the efficiency of solar panels. The association includes four manufacturing companies and three research institutes. The declared efficiency of the solar battery they have developed is 33 percent, which theoretically their development will allow to achieve, but the minimum program so far is 27 percent. The essence of their invention is a more rational use of the solar spectrum, which varies depending on the time of day and season. The new combined cells will make it possible to squeeze more kilowatts out of the sun, which, of course, will reduce the cost of electricity.
American scientists from California have developed a new way to convert solar radiation into electricity. As you know, the most widely used silicon solar cells do not perform well at high temperatures. It is known that if the solar battery under the influence of solar radiation heats up to the boiling point of water, it will lose its efficiency.
It turns out a paradox – on the one hand, a lot of solar radiation is needed to generate electric current, since logic dictates that the more light, the more current, but on the other hand, the sun produces not only light, but also heat, and heat has a bad effect on the operation of semiconductor devices, which in all devices are usually protected from overheating by radiators and coolers. But Stanford National University has solved this problem. Their new cell element, called PETE, is designed to operate at temperatures in excess of 200 degrees Celsius, which is a big advantage in hot dry California. When testing new cells, efficiency indicators of over twenty percent were immediately achieved, which is currently the best indicator for serial solar panels, and in theory, the new technology will allow reaching almost fifty percent efficiency! This became possible due to the peculiarities of the operation of the PETE cell. In them, excess heat does not extinguish the photoelectric effect, but stimulates. PETE cells are basically made of traditional silicon, but the addition of a cesium coating gives them these new unique properties.
And American researchers from the Laboratory “Energy of Nature” set the task of achieving the maximum efficiency of solar panels. They invented six-circuit solar cells with an efficiency of 47 percent. A multilayer film coating of compounds based on indium and gallium makes it possible to cover various energy levels of photons. And in total in this film there are more than a hundred various layers.
To date, the development of American scientists is a record for the efficiency of solar panels .
In the process of combating excess heat that interferes with the functioning of traditional silicon structures, a simple but original method was proposed – to remove heat from the panels and direct it to heat some coolant, such as water, and then direct the steam to a steam turbine that will generate additional electricity. This method will raise the overall efficiency of the solar station higher than that of any modern solar panels.
However, almost all innovative projects have their pitfalls. High records hide an unpleasant surprise – these are very expensive or rare materials, the complexity of technological processes, and the too high cost of electricity. In 2016, an international consortium of developers, which included an American laboratory for the study of renewable energy sources and a Swiss polytechnic school with a microtechnological electronic center, developed new cells based on indium and gallium compounds. They managed to achieve an efficiency of more than 32 percent. But the price of electricity turned out to be 4-6 times higher than that of serial solar panels. To reduce its cost to economically justified values, it is necessary to create large production capacities, but this also causes problems, since the prevalence of gallium and indium is millions of times less than silicon, since, as you know, silicon is sand.
Вывод
So what kind of solar panels to choose? And with what efficiency? – a potential energy tycoon will ask himself, who is about to convert his cooperative dacha into a powerful solar station. What modern solar panels will be able to give the best efficiency in all types of weather and in different periods of the year? Unfortunately, the ideal solar battery has not yet been invented, which has a high efficiency in bright direct light, and in cloudy weather, and in low light. Therefore, logic suggests the answer: apparently, only a combination of different types of batteries can cover the maximum variety of all types of solar radiation. If you approach the task creatively and do not forget about all the rules of rational orientation of solar panels, then you can increase the overall efficiency of your solar system, despite the fact that the efficiency of individual panels will not reach the maximum at a given time or in a given weather.