How solar panels are designed and work
Solar energy is becoming increasingly popular around the world. We looked at how a solar panel is built, what it consists of, and where the energy is sent?
Types of solar panels. The basis of any solar panel is solar cells based on silicon or rare earth metals, and recently polymers. They allow you to efficiently accumulate solar energy and convert it into electricity.
Solar cells are already being used to power a wide variety of equipment, from mobile gadgets to electric cars. You will find out how they are designed, what they are and what modern solar panels are capable of doing in this article.
Light into energy: How solar cells work
A solar panel is a device that converts sunlight into electrical energy using a number of photovoltaic cells connected in a common circuit. The principle of the photoelectric effect underlying the photovoltaic cells was discovered in the 19th century and is still in use today.
Expensive equipment is compensated over time by the ability to get free electricity. Importantly, solar panels are an environmentally friendly source of energy. In recent years, the prices of photovoltaic panels have fallen dozens of times and they continue to fall, which shows great promise in their use.
In its classic form, such a source of electricity would consist of the following parts: directly, the solar panel (DC generator), a battery with a charge control device and an inverter, which converts DC current into AC current.
Solar cells consist of a set of solar cells (photovoltaic converters) that directly convert solar energy into electrical energy.
Most solar cells are made from silicon, which is quite expensive. This fact determines the high cost of electrical energy produced by solar panels.
Two types of photovoltaic converters are common: made of monocrystalline and polycrystalline silicon. They differ in production technology. The first have an efficiency of up to 17.5%, and the second – 15%.
The most important technical parameter of a solar panel, which has a major impact on the efficiency of the entire installation, is its useful power. It is determined by the voltage and output current. These parameters depend on the intensity of sunlight hitting the battery.
The electromotive power of individual solar cells is independent of their area and decreases when the battery is heated by the sun, about 0.4% per 1g. С. The output current depends on the intensity of solar radiation and the size of the solar cells. The brighter the sunlight, the more current is generated by the solar cells. Charging current and power output decreases dramatically in cloudy weather. This is due to a decrease in the current output of the battery.
If a battery illuminated by the sun is short-circuited to a load of resistance Rn, then an electric current I appears in the circuit, the amount of which is determined by the quality of the photoelectric transducer, the intensity of illumination, and the resistance of the load. The power Pn which is released into the load is determined by the product Pn = InUn, where Un is the voltage at the battery terminals.
The maximum power is given out in the load at some optimal load resistance Ront, which corresponds to the maximum efficiency of conversion of light energy into electric energy. Each converter has its own value of Ropt, which depends on the quality, size of the working surface and degree of illumination.
A solar panel consists of individual solar cells which are connected in series and in parallel in order to increase the output parameters (current, voltage and power). Connecting the cells in series increases the output voltage, while connecting them in parallel increases the output current.
In order to increase both current and voltage, these two connection methods are combined. In addition, with this method of connection, the failure of one of the solar cells does not lead to the failure of the entire chain, i.e. increases the reliability of the entire battery.
Thus, the solar battery consists of solar cells connected in parallel and in series. The value of the maximum possible current output of the battery is directly proportional to the number of parallel connected solar cells, and the electromotive force is proportional to the number of solar cells connected in series. Thus, by combining the types of connection, a battery with the required parameters is assembled.
The solar cells of the battery are shunted by diodes. Usually there are 4 diodes, one for each ¼ of the battery. The diodes prevent the failure of parts of the battery that for some reason happen to be darkened, i.e. if no light reaches them at any time.
The battery temporarily generates 25% less power output than when the sun normally shines on the entire surface of the battery.
In the absence of diodes, these solar cells will overheat and fail because they become current consumers for the duration of the blackout (the batteries are discharged through the solar cells), while with diodes they are bypassed and no current flows through them.
The resulting electrical energy is stored in batteries and then released to the load. Batteries are chemical current sources. A battery is charged when a potential is applied to it that is greater than the battery voltage.
The number of solar cells connected in series and in parallel must be such that the operating voltage applied to the batteries, taking into account the voltage drop in the charging circuit, is slightly higher than that of the batteries, and the load current of the battery provides the required amount of charging current.
For example, to charge a 12 V lead-acid battery, it is necessary to have a solar battery consisting of 36 cells.
In weak sunlight the charge of the battery decreases and the battery gives electrical energy to the electric receiver, i.e. the batteries constantly work in the mode of discharging and recharging.
This process is controlled by a special controller. When charging cyclically a constant voltage or constant charging current is required.In weak sunlight the charge of the battery decreases and the battery gives electrical energy to the electric receiver, i.e. the batteries constantly work in the discharging and recharging mode.
This process is controlled by a special controller. Cyclic charging requires a constant voltage or constant charging current.
In good light, the battery pack charges quickly to 90% of its nominal capacity and then at a slower rate of charge to full capacity. Switching to a lower rate of charge is done by the charger controller.
The most effective use of special batteries – gel batteries (in the battery as an electrolyte is used sulfuric acid) and lead batteries, which are made by AGM-technology. These batteries do not need special conditions for installation and do not require maintenance. The rated service life of such batteries is 10 – 12 years with a depth of discharge not exceeding 20%. Batteries should never be discharged below this value or their service life will be drastically reduced!
The battery is connected to the solar panel via a controller that controls its charge. When the battery is fully charged, a resistor is connected to the solar panel to absorb the excess power.
In order to convert the DC voltage from the battery into alternating voltage, which can be used to power most electrical appliances in conjunction with the solar panel, you can use special devices – inverters.
Without the use of an inverter from the solar battery can be used to power DC-powered electrical appliances, including various portable equipment, energy-saving light sources, such as the same LED lamps.
How solar panels work
How do solar panels work? How do they convert the energy of sunlight into electricity?
A semiconductor is a material whose atoms either have extra electrons (n-type) or, conversely, lack them (p-type). Accordingly, a semiconductor photocell consists of two layers with different conductivities. The n-layer is used as the cathode and the p-layer as the anode.
Excess electrons from the n-layer can leave their atoms, while the p-layer captures these electrons. It is the rays of light that “knock out” electrons from the atoms of the n-layer, after which they fly into the p-layer to occupy the empty spaces. In this way the electrons run in a circle, leaving the p-layer, passing through the load (in this case the battery) and returning to the n-layer.
The first photovoltaic material was selenium. It was used to produce solar cells at the end of the XIX and beginning of the XX centuries. But taking into account the extremely low efficiency (less than 1 percent), selenium was immediately replaced.
Mass production of solar cells became possible after the telecommunications company Bell Telephone developed a silicon-based solar cell. It is still the most common material in the manufacture of solar cells. However, refining silicon is a very expensive process, so alternatives are being tried little by little: compounds of copper, indium, gallium and cadmium.
Selenium is historically the first, and silicon is the most mass-produced material in the production of photovoltaic cells
It is clear that the power of individual photovoltaic cells is not enough to power powerful electrical appliances. Therefore, they are combined in an electrical chain, thus forming a solar panel (another name – solar panel).
The solar cells are attached to the framework of the solar panel in such a way that they can be replaced one by one in case of failure. To protect against the effects of external factors, the entire structure is covered with durable plastic or tempered glass.
Let’s look at the process of electron release using silicon as an example. A silicon atom has 14 electrons in three shells. The first two shells are completely filled with two and eight electrons, respectively. The third shell, on the other hand, is half empty – it has only four electrons.
Because of this, silicon has a crystalline shape; trying to fill the voids in the third shell, the silicon atoms are trying to “share” electrons with their neighbors. However, a pure silicon crystal is a poor conductor because almost all of its electrons are firmly seated in the crystal lattice.
That is why solar cells do not use pure silicon, but crystals with small impurities, i.e. atoms of other substances are introduced into the silicon. There is only one atom per million silicon atoms, such as phosphorus.
Phosphorus has five electrons in its outer shell. Four of them form crystalline bonds with nearby silicon atoms, but the fifth electron actually remains “hanging” in space, without any bonds with neighboring atoms.
When the sun’s rays hit silicon, its electrons receive additional energy, which is enough to tear them away from their respective atoms. This leaves “holes” in their place. The freed electrons roam the crystal lattice as carriers of electric current. Meeting another “hole”, they fill it.
In pure silicon, however, there are too few free electrons because of the strong bonds of the atoms in the crystal lattice. Silicon with an admixture of phosphorus is quite another matter. Much less energy is required to release the unbound electrons in the phosphorus atoms.
Most of these electrons become free carriers, which can be efficiently directed and used to generate electricity. The process of adding impurities to improve the chemical and physical properties of a substance is called doping.
Silicon doped with phosphorus atoms becomes an n-type electronic semiconductor (from the word “negative”, due to the negative charge of the electrons).
Silicon is also doped with boron, which has only three electrons in its outer shell. The result is a p-type semiconductor (from the word “positive”) in which free positively charged “holes” arise.
The device of a solar cell
What happens when you combine an n-type semiconductor with a p-type semiconductor? The former has many free electrons and the latter has many holes. The electrons tend to fill the holes as quickly as possible, but if this happens, both semiconductors become electrically neutral.
Instead, when free electrons penetrate a p-n semiconductor, the area at the junction of both substances becomes charged, forming a barrier that is not easily crossed. At the boundary of the p-n junction, an electric field is generated.
The energy of each photon of sunlight is usually enough to release one electron, and therefore to form one extra hole. If this happens near the p-n junction, the electric field sends the free electron to the n-side and the hole to the p-side.
Thus, the equilibrium is further disturbed, and if an external electric field is applied to the system, the free electrons will flow to the p-side to fill the holes, creating an electric current.
Two decades ago, microcalculators with photovoltaic cells seemed like a gimmick, allowing them not to change the “battery-tablet” for years. Now cell phones with a solar panel built into the back cover do not surprise anyone. But this is nothing compared to cars and airplanes (albeit unmanned), which have learned to move using only solar energy.
The future of solar panels is as bright as the sun itself. We want to believe that it is solar panels that will finally cure smartphones and tablets of their “dependence on electrical outlets.