New energy photovoltaics: from grid-connected to off-grid

From the current point of view, there are two typical applications of photovoltaics, grid-connected systems and off-grid systems. The grid-connected system relies on the power grid, and adopts the working mode of "self-consumption, surplus power on-grid" or "full on-grid". The off-grid system does not depend on the power grid, and relies on the working mode of "storage and use" or "first storage and then use". For households in areas without grid or frequent power outages, off-grid systems have strong practicality.

Since off-grid is a rigid demand, the profit is relatively high. As a grid-connected installer, if you want to do an off-grid project, you need to change part of your thinking. If you continue to use the grid-connected idea to do off-grid, you may not be able to make deals or meet customer requirements.

1、Off-grid systems do not count as ROI

When we invest money in real estate, stocks, industry and other projects, we need to calculate how much money we can earn each year and how many years we can pay back our capital. There are state subsidies for grid-connected power generation. Building a power station is an investment behavior, and customers are most concerned about the return on investment. But when we buy a mobile phone, computer, clothes and other necessities of life, we will not count how many years we can earn back the capital. The same is true for off-grid systems. Except for a few places where electricity prices are particularly expensive and very rich, most of them are To meet the people's basic living electricity needs, if the same off-grid user calculates the return on investment, it may not be able to pay back in 10 or even 15 years, and customers may cancel the idea of installing off-grid as soon as they hear it. Why is an off-grid system not economically considered a grid-connected system, because the cost of an off-grid system is much higher than that of a grid-connected system.

2、High cost of off-grid systems

The off-grid system consists of photovoltaic arrays, solar controllers, inverters, battery packs, loads, etc. Compared with the grid-connected system, there are more batteries, which occupy 30-40% of the cost of the power generation system, which is almost the same as the components. Moreover, the service life of the battery is not long. The lead-acid battery is generally 3-5 years, and the lithium battery is generally 8-10 years, and needs to be replaced after that.

For inverters of the same power, the off-grid price is 1.5 to 3 times that of grid-connected inverters. Off-grid inverters are more complex than grid-connected inverters. The grid inverter generally has a four-level structure, including controller, boost, inverter, isolation, and the cost is about twice that of the grid-connected inverter.

For the same power, the overload capacity of the off-grid inverter is more than 30% higher than that of the grid-connected inverter. The front-stage of the grid-connected inverter is connected to the components, and the output is connected to the grid. Generally, the overload capacity is not required, because there are few output power of the components. If the output of the off-grid inverter is greater than the rated power, the output of the off-grid inverter is connected to the load, and many loads are inductive loads. The starting power is 3-5 times the rated power, so the overload capacity of the off-grid inverter is a hard indicator. The power of the device will increase, which means that the cost will be high.

The output of off-grid inverters is low. At present, the photovoltaic grid-connected market share is about 98%, and the off-grid market share is about 2%. The shipment volume is very low, it cannot be automated production, and the raw material and production costs are much higher.

3、Why should the off-grid system be equipped with energy storage batteries?

In the photovoltaic off-grid system, the energy storage battery accounts for a large proportion, and the cost is similar to that of the solar module, but the lifespan is much shorter than that of the solar module. Electricity. Off-grid systems must be equipped with energy storage batteries, why?

First, the photovoltaic power generation time and the load power consumption time are not necessarily synchronized. In the photovoltaic off-grid system, the input is the component, which is used for power generation, and the output is connected to the load. Photovoltaic generates electricity during the day, and it can only generate electricity when there is sunlight. Usually, the power generation is the highest at noon. However, at noon, the demand for electricity is not high. Many households use off-grid power stations to use electricity at night. What should I do with the electricity generated during the day? First, the energy storage device is the energy storage battery. Wait for the peak of electricity consumption, such as seven or eight o'clock in the evening, and then release the power.

Second, photovoltaic power generation and load power are not necessarily the same. Photovoltaic power generation is affected by radiation, which is not very stable, and the load is not stable, such as air conditioners and refrigerators. The load will cause the system to be unstable, and the voltage will fluctuate. The energy storage battery is a power balancing device. When the photovoltaic power is greater than the load power, the controller sends the excess energy to the battery pack for storage. When the photovoltaic power cannot meet the load needs, the controller sends the battery power to the load. .

In addition to the above three points, the design of the off-grid system is different from that of the grid-connected system. Components, inverters, and energy storage batteries must be customized according to the needs of users. Only by changing these thinking, can the off-grid system be done well.