Why the gap between the off-grid and photovoltaic generation (dg) in power system is so

Photovoltaic (pv) grid systems and photovoltaic off-grid system, only there, prices have thousands of difference, why is there so big gap? Said to the photovoltaic off-grid system, mainly composed of photovoltaic off-grid system by the component, solar controller/inverter, battery,

grid photovoltaic system and off-grid pv system only one word difference, but the price a few thousand. Why is there such a big difference? In terms of pv off-grid system, it is mainly composed of modules, solar controller/inverter, battery and load, etc. It is widely used in many fields, such as transportation, military and aerospace. Almost everywhere. Some people may wonder why I didn't see it. Photovoltaic off-grid system application and charging as small treasure and street lamps, involved in aerospace, transportation, etc. In our daily life, for example, the solar street light is a small off-grid system, during the use of photovoltaic power generation, battery storage photovoltaic panels generate electricity during the day, using the storage device to store electricity lighting at night. As for the battery in the off-grid system, there are several: important, expensive, and easily damaged. Off-grid system is not connected to the grid, so need batteries to store electricity. Naturally, the battery is an important part of system. At present, including lead-acid battery and lithium battery, which account for 30% of the cost of power generation system, off-grid system 50%. Of course, 'no one is perfect, no gold is barefoot', the service life of the battery are criticized, and this is the current industry one of the main technical barriers. Off-grid system from the market use batteries, lead-acid batteries for 3 years or so commonly, lithium battery life is 6 to 7 years. With the emergence of high efficient battery technology, life will become longer. Grid photovoltaic power generation system consists of parts, grid inverter, stents and other related accessories. Due to the interconnection systems need access to the power grid, so need to equipped with a bi-directional current meter. Grid system to produce electricity is an alternating current, load can be directly used in family, the rest of the power can also be sold to the grid. Is not hard to find from the web and grid system consists of the core components and inverter. But the off-grid inverter and what is the difference between grid inverter? Basically see the following: structure, cost and efficiency. First of all, from the point of view of structure, grid inverter generally have, booster and inverter two-stage structure and off-grid inverter, generally have quaternary structure, including controller, booster and inverter and isolation. From the point of the price of off-grid inverter, the cost is about 2 times of grid inverter. Off-grid inverter high cost. Mainly depends on the overload capacity is a hard Numbers. Off-grid inverter output connected to the load, many of the load is inductive load. Start the power 5 times of the rated power, overload ability. This requires higher power and the quality of parts and natural costs more expensive. Photovoltaic (pv) grid inverter is different from the front-end module and back-end output from the power grid. Third, efficiency. Under the same power, off-grid inverter overload capacity of more than 30% higher than grid inverter.