Solar power plants are rarely used as the main source of energy. However, correctly selected and installed panels on a clear day can provide electricity to all household electrical appliances.

The amount of energy generated depends on how many light particles hit the photocell. There are also a number of other factors that do not depend on battery power or panel area.

Calculation of solar panel power

The performance of panels depends on the material and technology by which it is produced. Batteries can be divided into 2 classes: film and silicon-based.

Efficiency of silicon batteries:

  • Monocrystalline – 22%. It is advantageous to place in a limited space;
  • Flexible (amorphous) panels – 5%;
  • Polycrystalline – up to 18%.

Efficiency of film modules:

  • Indium gallium selenide film – 20%;
  • Cadmium telluride – up to 12%;
  • Polymer – no more than 5%.

There are also mixed types of panels, the efficiency of which is higher.

The first thing to consider – total power of energy consumers in kWh. The manufacturer indicates the power based on the fact that per 1 sq.m. batteries receive 1000 watts of energy.

One way to calculate real power: E = I x V x Kо x Kpot.

E – real power; I – the amount of energy entering the panel installation site (kW*h/m2); V – nominal power of one panel; Kpot – coefficient of total losses in the system; Co – correction factor, depending on the position (angle of inclination) of the panel relative to the south direction; U – the amount of solar radiation is always constant 1 kW*h.
It is worth noting that radiation is calculated on a daily, monthly and annual basis. For example, if the indicator is 7 kWh/m2 day means that per day per 1 sq.m. 7 kW of solar energy is supplied.

Another calculation example

If we take a module with an area of 2 m2 as a calculation. The total amount of energy per sunny day is 1000 W per m2. The formula will be as follows: 1000 W multiplied by performance (20%) and multiplied by panel area (2m) = 400 W.

What determines battery power

The panels use high-transparency glass with a low iron content and, nevertheless, it reduces efficiency by several percent.

The optimal operating time for the panels is from 9 am to 4 pm – this period accounts for 70% of the energy generated. During this time, a 1 kW battery complex produces 7 kWh of electricity, that is, 210 kWh per month. You can add another 3 kW in the morning and evening. This is ideal. But in reality this figure is less:

  • Not all days in a month are sunny. If we take into account rainy and cloudy days, let’s say there were 5 such days – This will already be about 180 kWh.
  • The duration of daylight hours in winter is shorter, requiring a larger array of batteries or the installation of a wind generator.
  • Energy is lost in the inverter and battery. Batteries cannot be discharged to 100%, and their efficiency is no higher than 80%.

The amount of energy generated depends on the number of clear days in a year. Installing a battery will be impractical if there are less than two hundred sunny days a year. In addition, the sun's rays must hit the panel at right angles – For this purpose, it is recommended to install sun tracking systems. These devices are expensive.

The quality of battery performance is also affected by the heating level of the modules. Energy production drops by 0.5 percent if the module warms up 1 degree. Constant operation with a temperature increased by 100 C will reduce the efficiency of the device by 30%. Therefore, SES requires high-quality ventilation and cooling.
Energy losses can be: in wires 1%; shunt diode 0.5%; inverter – from 3 to 7%.

Another factor influencing current generation – total number of installed modules, because everyone can take in a limited amount of energy.

Energy generation in cloudy weather

Condition% from the "full" sun

Bright sun — the panels are perpendicular to the sun's rays

100 %
Light clouds
60-80 %
Cloudy weather20-30%

Behind the window glass, one layer, glass and module are perpendicular to sunlight

91 % 

Behind the window glass, 2 layers, glass and module are perpendicular to sunlight

84 %

Behind the window glass, one layer, glass and module at an angle of 45 degrees sunlight

64 %
Artificial light in the office, on the surface of the desk0,4 %
Artificial light inside a bright room (for example, a store)1,3 %
Artificial light inside the living room0,2 %

The batteries produce energy only during daylight hours and deliver the declared power only on a clear day when the rays hit them at right angles.

In bad weather, the calculation is as follows: 1000 W is multiplied by the sine of the angle of the sun's rays and the panel is multiplied by the percentage of energy on a day without sun. For example, the angle of incidence of the rays is 40%, the following is obtained: 1000 W/m2 x sin 40% x 60% = 240 W/m2

In some countries, solar panels often operate at illumination levels below 1000 W/m2. Cheap modules are produced without anti-reflective coating. As a result – a significant portion of the sun's rays are reflected by low-quality glass. They also work poorly in diffuse light.

In different months, the light intensity is different, therefore, a different number of panels and batteries are needed to generate the same amount of energy.

Some home owners install panels behind the windows of the house. This is also a mistake. Single glass reduces the efficiency of the panel by 9%, and double glass by 16% - provided that the glass is perfectly clean. Dirt on the glass reduces transparency, causing back reflection of light – The battery is not working efficiently.

The energy generated depends on the amount of incoming light – the voltage rises to a certain limit. For silicon elements this figure is 0.6. The voltage increase is achieved by connecting the modules in series. SES needs a voltage reserve. It keeps the battery charged while working in cloudy weather. The maximum power under load is generated by the battery with a drawdown of up to 0.47 – 0.5 V. A battery of 36 cells at optimal load gives a voltage of 17 V.

Each panel has a lower limit of illumination sensitivity. Below this limit the panel will stop generating energy. In bad weather, the power of the modules drops by 10-20 times. So, for crystalline silicon panels this limit is 150-200 W/m2. For thin-film films this parameter is lower – 100-200 W/m2. Film panels perform better than silicon panels in cloudy weather. However, a threshold illumination difference of 50 W/m2 will have virtually no effect on energy production.

So that the power is sufficient – it is necessary to calculate the required number of batteries. To do this, the power consumption is divided by the panel power. Total consumption is produced by summing the operating time (hours per day) of all electrical appliances in the house – power is added to the number of hours. Consumption can also be calculated from the receipt for electricity: the maximum consumption figure (kWh) for the last months is taken and multiplied by 1.5 (reserve).

You can increase exposure to sunlight by installing panels on a biaxial tracker – a platform that rotates behind the sun in 2 planes. In addition, in winter the panels should be positioned more horizontally than in summer. In summer, the angle of inclination of the modules is less. For each geographic latitude there is an optimal angle of inclination.

In autumn and spring, choose an angle equal to the latitude of the area. In winter, 10-15 degrees are added to the desired value, and in summer, 10-15 degrees are subtracted. If the modules are installed motionlessly– choose an angle based on the latitude of your region of residence.

It is always necessary to have a reserve of power – Over time, battery performance degrades. Every year the power decreases by 0.6 – 0.7%. After 25 years of use, the power loss is 20%. However, the missing power can be made up without problems by connecting additional modules.

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