Application and Principle of Solar Off-Grid System Solution

Off-grid photovoltaic power generation systems are widely used in remote mountainous areas, non-electric areas, islands, communication base stations and street lamps. The photovoltaic array converts solar energy into electric energy under the condition of light, and supplies power to the load through the solar charge and discharge controller, and charges the battery pack at the same time; when there is no light, the battery pack supplies power to the DC load through the solar charge and discharge controller. At the same time, the battery also directly supplies power to the independent inverter, which is converted into alternating current through the independent inverter to supply power to the alternating current load.

Solar System Composition

(1) Solar Battery Modules 

The solar cell module is the main part of the solar power supply system, and it is also the most valuable component in the solar power supply system. Its function is to convert the solar radiation energy into direct current electricity.

(2) Solar Controller 

The solar charge and discharge controller is also called “photovoltaic controller”. Its function is to adjust and control the electric energy generated by the solar cell module, to charge the battery to the maximum extent, and to protect the battery from overcharge and overdischarge. effect. In places with large temperature difference, the photovoltaic controller should have the function of temperature compensation.

(3) Off-grid Inverter

The off-grid inverter is the core component of the off-grid power generation system, which is responsible for converting DC power into AC power for use by AC loads. In order to improve the overall performance of the photovoltaic power generation system and ensure the long-term stable operation of the power station, the performance indicators of the inverter are very important.

(4) Battery Pack

The battery is mainly used for energy storage to provide electrical energy to the load at night or in rainy days. The battery is an important part of the off-grid system, and its pros and cons are directly related to the reliability of the entire system. However, the battery is a device with the shortest mean time between failures (MTBF) in the entire system. If the user can use and maintain it normally, its service life can be extended. Otherwise, its service life will be significantly shortened. The types of batteries are generally lead-acid batteries, lead-acid maintenance-free batteries and nickel-cadmium batteries. Their respective characteristics are shown in the table below. 

catego	Overview	Advantages and disadvantages
Lead acid battery	1. It is common for dry-charged batteries to be maintained by adding water during the use process. 2. The service life is 1 to 3 years.	1. Hydrogen will be generated during charging and discharging, and the placement site must be equipped with an exhaust pipe to avoid harm. 2. The electrolyte is acidic and will corrode metals. 3. Frequent water maintenance is required. 4. High recycling value
Maintenance-free lead-acid batteries	1. Commonly used are sealed gel batteries or deep cycle batteries 2. No need to add water during use 3. Lifespan is 3 to 5 years	1. Sealed type, no harmful gas will be generated during charging 2. Easy to set up, no need to consider the ventilation problem of the placement site 3. Maintenance-free, maintenance-free 4. High discharge rate and stable characteristics 5. High recycling value
Lithium ion battery	High-performance battery, no need to add Water life 10 to 20 years	Strong durability, high charge and discharge times, small size, light weight, more expensive

Pros：

1. Solar energy is inexhaustible and inexhaustible. The solar radiation received by the earth’s surface can meet 10,000 times the global energy demand. As long as solar photovoltaic systems are installed on 4% of the world’s deserts, the electricity generated can meet the needs of the world. Solar power generation is safe and reliable, and will not suffer from energy crises or fuel market instability;
2. Solar energy is available everywhere, and can supply power nearby, without long-distance transmission, avoiding the loss of long-distance transmission lines;
3. Solar energy does not require fuel, and the operating cost is very low;
4. There are no moving parts for solar power generation, it is not easy to be damaged, and the maintenance is simple, especially suitable for unattended use;
5. Solar power generation will not produce any waste, no pollution, noise and other public hazards, no adverse impact on the environment, is an ideal clean energy;
6. The construction period of the solar power generation system is short, convenient and flexible, and according to the increase or decrease of the load, the amount of solar energy can be added or reduced arbitrarily to avoid waste.

Cons：

1. The ground application is intermittent and random, and the power generation is related to the climatic conditions. It cannot or rarely generates power at night or in cloudy and rainy days;
2. The energy density is low. Under standard conditions, the solar radiation intensity received on the ground is 1000W/M^2. When used in large sizes, it needs to occupy a large area;
3. The price is still relatively expensive, and the initial investment is high.