As the incentive policies and drops in total installed system prices, solar generating has achieved remarkable growth over the past years, becoming a popular choice for business and residential consumers in every market where it has been readily available. However, in face of a variety of alternative systems in the market, how to opt to the right one may be confusion to most buyers and investors. Then this paper will give you some advice on this matter.

According to the component and output mode, the solar system is classified to off-grid system and on-grid system. The on-grid system isclassified into three classes on the basis of inverter : central inverter system, central-distributed inverter system and string inverter system.

When  the buyers analyze the factor to choose the solar system, theyfocus on the power grid, the geographical factors, the investment cost, the performance and reliablilityof system and service.

The.First of all, in this paper we analyze the factors from grid aspects.Some projects are implemented in relatively remote areas such as islands or mountains when power grid is unavailable, Theseprojects are generally considered to be an off-grid system. The system contains a battery pack, which can store the solar energy when it’s plentiful, and use the power from the battery during the rainy days. At present, the on-grid system is also adopted by some companies. The power generation system is usually composed by the on-grid inverter、energy storage inverter and generator. However, because of the multiple power source, the uncertainty caused by the load and the solar power will be a problem in the applicationIn some places that access to a power grid but unstable, the off-grid system is also recommended. The on-grid system can be adopted in places with  stable grid, becausewithout the batteries, the system will be simpler, abundant solar energies can directly be sent to the grid or used by local load, and the grid will provide electricity when the solar energy is not enough.

Secondly, the geographical factors:

Thirdly, in terms of investment cost, the total cost of off grid system is much higher than that in on grid one due to addition of battery pack especially in long backup time system. In addition, battery type also imposes considerable impact on the system cost. Currently, batteries commonly used in the solar system include lead-acid battery, gel battery, lead-carbon battery and lithium battery. In on-grid system, the general string system below 1MW has certain cost advantages, mainly because the string inverter output can be directly connected to the low-voltage grid without adding extra step-up transformer, , and it contains multi-channel PV input, eliminating the need to configure the combiner box, all of which make it enjoy certain cost advantages in the system below MW scale. However, in the MW-scale solar power generation system, the central inverter generally features price factor in the same power capacity. For systems above MW-scale, string inverter also needs a step-up transformer. Due to multiple outputs, although no DC combiner box is required at output end, it also needs AC combiner box. The distributed system is positioned between the string and the central inverter, with cost superior to the string inverter, but slightly higher than the central inverter.

 As for the performance and reliability of the systems, off grid system has a stable output and is not subject to grid abnormality due to independence from grids and battery backup. But otherwise, the additional battery pack will increase the complexity of system.As the reliability of the off-grid system is mainly affected by the battery pack, it is commonly suggested that lead-carbon batteries and lithium batteries be used, which have a longer cycle life and are suitable for a wide range of temperatures. In the grid-connected system, the string system is made up by numerous inverters, and the malfunctioning of a few inverters won’t have a large impact on the whole system, but its reliability is affected by the environment, as the system functions mainly in an outdoor condition. Central and distributed systems, compared to high-power density string inverters, has a better reliability per machine, as the inverters are usually placed in the engine room or the power supply room, and the inverter components are also designed to have a enough spare capacity , but the disadvantage to this system is the high power of single machines will have large impacts on the system once it malfunctions.

The installment and maintenance of solar systems mainly is focused on the location of the installment and the reliability of the product. For the off-grid system, in some inconvenient and remote areas, a modularized design is preferred to easy delivery and installation. Furthermore, the maintenance greatly simplified by fast changing result from the modular desgn. For the on-grid system, the main difference is that the string system is made up of multiple low-power inverters, which has smaller volume and lighter weight, easy to install and maintain, but the failure rate is relatively high, demanding for frequent maintenance. While central and distributed systems are more reliable and require less maintenance, but they are bigger in size and weight, more complicated to install and need professional engineers to maintain.