The procedure for calculating the photovoltaic system. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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The calculation of a photovoltaic system can be divided into the following steps:

• Determination of load and consumed energy.
• Determination of the required inverter power and battery capacity.
• Determination of the required number of photovoltaic modules based on data on the arrival of solar radiation at the installation site of the system.
• Calculation of the cost of the system.

After completing step 4, if the cost of the system is unacceptably high, you can consider the following options for reducing the cost of an autonomous power supply system: reducing energy consumption by replacing the existing load with energy-efficient appliances, as well as eliminating thermal, “phantom” and unnecessary load (for example, you can use refrigerators , air conditioners, etc., running on gas):

• replacing an AC load with a DC load. In this case, you can benefit from the absence of losses in the inverter (from 10 to 40%). However, it is necessary to take into account the design features of low-voltage DC systems;
• introduction of an additional electricity generator or wind turbine, diesel-gasoline generator into the power supply system;
• come to terms with the fact that you won’t always have electricity. And the more the system power differs from the power consumption, the more likely you will experience periods of no power.

1. Determination of energy consumption

Make a list of electricity consumer devices that you are going to power from the solar power plant. Determine the power consumption during their operation. Most devices are labeled with their rated power consumption in Watts or kiloWatts. If the current consumption is indicated, then you need to multiply this current by the rated voltage (usually 220 V).

Calculate the AC load. If you do not have such a load, you can skip this step and move on to calculating the DC load.

1.1. List all AC loads, their wattage ratings, and the number of hours of operation per week. Multiply the power by the number of operating hours for each appliance. Add the resulting values ​​to determine your total AC energy consumption per week.

Here is a simple step-by-step method for calculating a photovoltaic system (PVS). This method will help determine system requirements and select the required electrical system components.

1.2. Next you need to calculate how much DC power is required. To do this, you need to multiply the resulting value by a factor of 1,2, which takes into account losses in the inverter.

1.3. Determine the inverter input voltage value based on the characteristics of the selected inverter. Usually it is 12 or 24 V.

1.4. Divide the value of clause 1.2 by the value of clause 1.3. You will receive the number of Amp hours per week required to cover your AC load.

Calculate the DC load.

1.5. Record the DC load data.

1.6. Determine the voltage in the DC system. Usually it is 12 or 24 V. (As in paragraph 1.3)

1.7. Determine the required number of Ah per week for a DC load (divide the value in clause 1.5 by the value in clause 1.6).

1.8. Add the value of clause 1.4 and clause 1.7 to determine the total required battery capacity. This will be the number of Ah consumed per week.

1.9. Divide the value of clause 1.8 by 7 days; you will receive the daily value of consumed Ah.

2. Optimize the load

At this stage, it is important to analyze the load and try to reduce power consumption. This is important for any system, but is especially important for a residential electrical system, as the savings can be very significant. First, identify large and variable loads (e.g. water pumps, outdoor lighting, AC refrigerators, washing machine, electric heaters, etc.) and try to eliminate them from your system or replace them with other similar gas or powered models. direct current.

The initial cost of DC appliances is usually higher (because they are not produced in such mass quantities) than the same AC appliances, but you will avoid losses in the inverter. Moreover, DC appliances are often more efficient than AC appliances (many household appliances, especially electronic ones, convert AC to DC, which leads to energy losses in the appliance's power supplies).

Replace incandescent bulbs with fluorescent bulbs wherever possible. Fluorescent lamps provide the same level of illumination while consuming 4-5 times less electricity. Their service life is also approximately 8 times longer.

If you have a load that you can't eliminate, consider running it only during sunny periods or only in the summer. Review your workload list and recalculate the data.

3. Determine the parameters of the battery (AB)

Select the type of battery you will use. We recommend using thermetic maintenance-free lead-acid batteries, which have the best operational and economic parameters.

Next, you need to determine how much power you need to get from the battery. This is often determined by the number of days during which the battery will power the load on its own without recharging. In addition to this parameter, you need to take into account the nature of the power supply system. For example, if you are installing a system for your country house that you visit only on weekends, you are better off installing a larger battery because it can charge throughout the week and only release energy on weekends. On the other hand, if you add PV modules to an existing power supply system based on a diesel or gas generator, your battery may have a lower capacity than designed because the generator may be turned on to recharge the battery at any time.

After you determine the required battery capacity. You can proceed to consider the following very important parameters.

3.1. Determine the maximum number of consecutive “days without sun” (i.e. when solar energy is insufficient to charge the battery and operate the load due to bad weather or cloud cover). You can also take this parameter as the number of times you select, during which the battery will power the load on its own without recharging.

3.2. Multiply the daily consumption in A*h (see paragraph 1.9 of calculating energy consumption above) by the number of days determined in the previous paragraph

3.3. Set the depth of the permissible battery discharge. Keep in mind that the greater the discharge depth, the faster your batteries will fail. We recommend a discharge depth of 20% (no more than 30%), which means that you can use 20% of the nominal capacity of your battery. Use coefficients (or 0,3). Under no circumstances should the battery discharge exceed 80%!

3.4. Divide item 3.2 by item 3.3.

3.5. Select a coefficient from the table below, which takes into account the ambient temperature in the room where the batteries are installed. Typically, this is the average temperature in winter. This coefficient takes into account the decrease in battery capacity with decreasing temperature.

Temperature coefficient for battery:

3.6. Multiply the value of clause 3.4 by the coefficient of clause 3.5. You will get the total required battery capacity.

3.7. Divide this value by the rated capacity of the battery you choose. Round the resulting value to the nearest higher integer. This will be the number of batteries that will be connected in parallel.

3.8. Divide the system's rated DC voltage (12, 24, or 48 V) by the rated voltage of the selected battery (typically 2, 6, or 12 V). Round the resulting value to the nearest higher integer. You will get the value of the batteries connected in series.

3.9. Multiply the value of item 3.7 by the value of item 3.8. in order to calculate the required number of batteries.

4. Determine the number of peak sun hours.

Several factors influence how much solar energy your solar panel will accept:

• when will the system be used? Summer? In winter? All year round?
• typical weather conditions in your area:
• whether the system will be guided by the sun;
• location and angle of inclination of photovoltaic modules.

To determine the average monthly solar radiation, you can use the table. Electricity production from a solar photovoltaic (PV) cell depends on the angle of incidence of the sun's rays on the PV. The maximum occurs at an angle of 90 degrees. When deviating from this angle, an increasing number of rays are reflected rather than absorbed by the solar system.

In winter, the amount of radiation received is significantly less due to the fact that the days are shorter, there are more cloudy days, and the Sun is lower in the sky. If you use your system only in the summer, use the summer values; if all year round, use the winter values. For reliable power supply, choose the lowest value from the average monthly values ​​for the period during which the solar power plant will be used.

The selected monthly average for the worst month must be divided by the days in the month. You will receive the monthly average number of peak sun hours, which will be used to calculate your SB.

5. Calculation of the solar battery

You need to determine the total number of modules required for your system.

The current at the maximum power point Impp can be determined from the module specifications. You can also determine Impp by dividing the module's power rating by the voltage at the maximum power point Umpp (typically 17 - 17,5V for a 12V module).

5.1. Multiply the value of clause 1.9 by factor 1.2 to take into account the losses due to charge-discharge of the battery.

5.2. Divide this value by the average number of peak sun hours in your area. You will receive the current that the SB should generate.

5.3. To determine the number of modules connected in parallel, divide the value in clause 5.2 by the Impp of one module. Round the resulting number to the nearest higher integer.

5.4. To determine the number of modules connected in series, divide the system DC voltage (typically 12, 24, 48 V) by the module's rated voltage (typically 12 or 24 V).

5.5. The total number of required photovoltaic modules is equal to the product of the values ​​in clause 5.3 and clause 5.4.

6. System cost calculation

To calculate the cost of a photovoltaic power supply system, you need to add up the costs of solar power, battery, inverter, battery charge controller and connecting fittings (wires, switches, fuses, etc.)

The cost of SB is equal to the product of the value of clause 5.5 by the cost of one module. The cost of the battery is equal to the product of the value in clause 3.9 and the cost of one battery. The cost of an inverter depends on its power and type. The cost of connecting fittings can be taken to be approximately 0,1-1% of the cost of the system.

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