The scale and application form of photovoltaic systems vary. For example, the scale of the system is large, ranging from 0.3 to 2W solar garden lights, to MW solar photovoltaic power stations. Its application forms are also diverse and can be widely used in many fields such as household, transportation, communication, and space applications. Although the scale of photovoltaic systems varies, their composition and working principles are basically the same.

1 Introduction

The scale and application form of photovoltaic systems vary. For example, the scale of the system is large, ranging from 0.3 to 2W solar garden lights, to MW solar photovoltaic power stations. Its application forms are also diverse and can be widely used in many fields such as household, transportation, communication, and space applications. Although the scale of photovoltaic systems varies, their composition and working principles are basically the same. This article will briefly introduce the structure of a photovoltaic system and focus on its power calculation methods.

2. Composition of photovoltaic system

Several main components in a photovoltaic system:

1. Photovoltaic module square array: It is formed by solar cell modules (also called photovoltaic cell modules) in series and parallel according to system requirements. It converts solar energy into electrical energy output under sunlight, which is the core component of solar photovoltaic systems.

2. Storage battery: Stores the electrical energy generated by solar cell modules. When the sunlight is insufficient or at night, or the load demand is greater than the power generated by the solar cell module, the stored electrical energy is released to meet the energy demand of the load. It is a solar photovoltaic system Energy storage components. At present, lead-acid batteries are commonly used in solar photovoltaic systems. For systems with higher requirements, deep-discharge valve-regulated sealed lead-acid batteries and deep-discharge liquid-absorbing lead-acid batteries are usually used.

3. Controller: It regulates and controls the charge and discharge conditions of the battery, and controls the power output of the solar cell module and the battery to the load according to the power demand of the load. It is the core control part of the entire system. With the development of the solar photovoltaic industry, the functions of controllers are becoming more and more powerful. There is a tendency to integrate traditional control parts, inverters and monitoring systems. For example, the controllers of SPS and SMD series of AES Company have integrated the above three Kind of function.

4. Inverter: In the solar photovoltaic power supply system, if there is an AC load, then inverter equipment is needed to convert the DC power generated by the solar cell module or the DC power released by the battery into the AC power required by the load.

The basic working principle of a solar photovoltaic power supply system is that under the sun's rays, the electric energy generated by the solar cell module is charged by the controller to charge the battery or directly supply power to the load when the load is met. Then, the battery supplies power to the DC load under the control of the controller. For a photovoltaic system containing an AC load, an inverter needs to be added to convert the DC power to AC power. The application of photovoltaic systems has many forms, but the basic principles are similar.

3.Calculation method of solar panel module power

The capacity of silicon solar power generation panel refers to the flat-panel solar panel power generation WP. The amount of solar power depends on the power H (WH) that can be consumed by the load 24h. The rated power and the power consumed by the load 24h determine the capacity P (AH) consumed by the load 24h. Considering the average daily sunshine time And the influence caused by rainy and rainy days, the working current IP (A) of the solar cell array is calculated.

From the rated power of the load, the nominal voltage of the battery is selected, and the number of batteries connected in series and the floating voltage VF (V) of the battery are determined by the nominal voltage of the battery. The influence caused by the voltage drop VD (V) of the PN junction of the anti-charge diode can be used to calculate the operating voltage VP (V) of the solar cell array. The panel-type solar panel power generation WPW can be determined, thereby designing the capacity of the solar panel. The designed capacity WP and the operating voltage VP of the solar cell array determine the number of series blocks and parallel groups of the silicon battery panel.

The specific design steps of the solar panel array are as follows:

1. Calculate the consumption capacity P for 24h of load.

P = H / VH——Power consumed by the load for 24 hours (WH, Watt-hour)

V——Load rated power

2. Select the daily sunshine hours T (H).

3. Calculate the working current of the solar array.

IP = P (1 + Q) / TQ——According to surplus coefficient in rainy season, Q = 0.21 ～ 1.00

4. Determine the battery float charge voltage VF.

The single floating charge voltages of nickel-cadmium (GN) and lead-acid (CS) batteries are 1.4 to 1.6V and 2.2V, respectively.

5. Solar cell temperature compensation voltage

VT. VT = 2.1 / 430 (T-25) VF

6. Calculate the operating voltage VP of the solar cell array.

VP = VF + VD + VT

Where VD = 0.5 ～ 0.7

Approximately equal to VF

7. Solar cell array output power WP, flat solar panel.

WP = IP × VP

8. According to the VP and WP in the silicon battery flat panel combination series table, determine the number of series blocks and parallel groups of standard specifications.

In addition, AC systems or grid-connected systems must also consider inverter conversion efficiency, other power losses, etc.

4. Examples

The following uses the output power of 100W for 5 hours per day as an example to introduce the calculation method:

1. First calculate the number of watt hours consumed per day (including the loss of the inverter):

If the inverter conversion efficiency is 90%, when the output power is 100W, the actual output power should be 100W / 90% = 111W; if it is used for 5 hours per day, the power consumption is 111W * 5 hours = 555Wh.

2. Calculate the solar panel:

Calculated based on the effective daily sunshine time of 6 hours, and taking into account the charging efficiency and losses during charging, the output power of the solar panel should be 555Wh / 6h / 70% = 130W. 70% of this is the actual power used by the solar panel during the charging process.