Calculation of a photovoltaic system. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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All photovoltaic systems (PV) can be divided into two types: autonomous and connected to the electrical network. Stations of the second type transfer excess energy to the network, which serves as a reserve in the event of an internal energy shortage.

An autonomous system generally consists of a set solar modulesplaced on the supporting structure or on the roof, storage battery (battery), discharge controller - battery charge, connecting cables. If the consumer needs to have an alternating voltage, then an inverter-converter of direct voltage to alternating voltage is added to this kit.

The calculation of FES means the determination of the nominal power of modules, their number, connection scheme; choice of type, operating conditions and battery capacity; inverter and charge-discharge controller capacities; determination of parameters of connecting cables.

First of all, it is necessary to determine the total power of all consumers connected at the same time. The power of each of them is measured in watts and is indicated in the product data sheets. At this stage, it is already possible to select the inverter power, which should be at least 1,25 times the calculated one. It should be borne in mind that such a cunning device as a compressor refrigerator at the time of launch consumes power 7 times more than the nameplate. The nominal range of inverters is 150, 300, 500, 800, 1500, 2500, 5000 W. For powerful stations (more than 1 kW), the station voltage is selected at least 48 V, because At higher powers, inverters work better with higher input voltages.

The next step is to determine the capacity of the battery. The battery capacity is selected from the standard range of capacities rounded to the side greater than the calculated one. And the calculated capacity is obtained by simply dividing the total power of consumers by the product of the battery voltage by the value of the depth of discharge of the battery in fractions.

For example, if the total power of consumers is 1000 Wh per day, and the permissible depth of discharge of a 12 V battery is 50%, then the calculated capacity will be:

1000 / (12 * 0,5) = 167 Ah

When calculating the battery capacity in a fully autonomous mode, it is necessary to take into account the presence of cloudy days in nature during which the battery must ensure the operation of consumers.

The last stage is the determination of the total power and the number of solar modules. The calculation requires the value of solar radiation, which is taken during the operation of the station, when solar radiation is minimal. In the case of year-round use, this is December.

In the "meteorology" section, solbat.narod.ru/meteo.htm, monthly and total annual values ​​of solar radiation for the main regions of Russia are given, as well as with gradation according to different orientations of the light-receiving plane.

Taking from there the value of solar radiation for the period of interest to us and dividing it by 1000, we get the so-called number of pico-hours, i.e., the conditional time during which the sun shines, as it were, with an intensity of 1000 W / m².

For example, for the latitude of Moscow and the month of July, the value of solar radiation is 167 kWh / m² when the site is oriented to the south at an angle of 40^о to the horizon. This means that the average sun shines in July for 167 hours (5,5 hours per day) with an intensity of 1000 W/m², although the maximum illumination at noon on a site oriented perpendicular to the light flux does not exceed 700-750 W / m².

P module_w during the selected period will generate the following amount of energy:

W = kP_w E / 1000, where E is the value of insolation for the selected period, k is a coefficient equal to 0,5 in summer and 0,7 in winter.

It (k) corrects for the power loss of solar cells when heated by the sun, and also takes into account the oblique incidence of rays on the surface of the modules during the day.

The difference in its value in winter and summer is due to the lower heating of the elements in winter.

Based on the total power of the consumed energy and the above formula, it is easy to calculate the total power of the modules. And knowing it, by simply dividing it by the power of one module, we get the number of modules.

When creating a FES, it is strongly recommended to reduce the power of consumers as much as possible. For example, use (if possible) only fluorescent lamps as illuminators. Such lamps, while consuming 5 times less, provide a luminous flux equivalent to that of an incandescent lamp.

For small FES, it is advisable to install its modules on a swivel bracket for optimal rotation relative to the incident rays. This will increase the station's capacity by 20-30%.

Collection of the most common misconceptions

- the solar battery itself is not charged, but itself charges the battery;
- the name "solar battery" does not mean that it gives nameplate power at the same illumination under which the solar-powered calculator is still working. nameplate power means that the solar battery could give this power under standard conditions (e = 1000 W / m 2 , m = 25 o s, am = 1,5), which do not exist in nature. The power of the battery is directly proportional to the illumination. In reality, due to heating of the modules and illumination lower than standard, and due to the oblique incidence of rays on the surface of the module, the generated power differs from the nameplate. For example, a station with a capacity of 1000 watts at the latitude of Moscow during the month of July will generate about 70-75 kWh, and not 1000 watts per hour, as many people think !!!
- the next common misconception is that it is impossible, by installing a couple of modules on the balcony, to become independent of Chubais.
- Energy consumers such as refrigerators, electric burners, irons, incandescent lamps, etc. are very voracious and cannot be fed with these two modules!
- it is of course possible to test a solar battery with the light of a chandelier in the room, only the parameters will be far from true, just like the illumination created by the chandelier from solar illumination, i.e. ten times!

Publication: alternativenergy.ru

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