# How to correctly select battery modules?

The battery module is the most important module of the photovoltaic power generation system. The cost of the entire system accounts for about 50% of the total construction cost of the photovoltaic power generation system, and the quality of the battery modules is directly related to the quality, power generation efficiency, power generation, and profitability of the entire photovoltaic power generation system. Therefore, the correct selection of battery modules is very important.

## 1. Determining the shape and size of battery modules

In the design and calculation of photovoltaic power generation system modules or square array, although the total capacity and power of battery modules or the whole square array can be calculated according to the power consumption or planned power generation, and the number of series and parallel battery modules can be determined, it is also necessary to determine the shape and external size of battery modules and the overall arrangement of the whole square array according to the specific installation position of battery modules. Some special-shaped and special-sized battery modules also need to be customized with the manufacturer.

For example, in terms of size and shape, the battery module of the same power can be made into a rectangle, or into a square, circle, trapezoid, or other shapes. This requires us to choose and determine, and only after the shape and size of the battery modules are determined, can we proceed with the design of the combination, fixation, support, and foundation of the modules.

Currently, there are two main specifications of battery modules used in photovoltaic power generation systems such as rooftop and ground power stations. One is a module composed of 60 cells of 156mm×156mm, with an overall size of about 1640mm×990mm. The current technical maximum power range of polycrystalline modules is 260~275w, and single crystal modules are 270~295W; the other is a module composed of 72 pieces of 156mm×156mm cells, with an external size of 1950mm×990mm. The current technical maximum power range for polycrystalline modules is 310~330W, and single crystal modules are 325~350W.

When selecting modules of these two specifications, it cannot be mistakenly assumed that a single crystal module must be more efficient than a polycrystalline module, or a module composed of 72 cells must be more efficient than a module composed of 60 cells. In fact, the conversion efficiency of a single crystal module and a polycrystalline module with the same output power is the same. The conversion efficiency of a 60-cell module with an output power of 260W and a 72-cell module with an output power of 310W are also the same.

The price per watt of modules with similar efficiency and different specifications is basically the same, but when choosing large-size modules, the installation cost of the modules, the number of cables connected between the modules and the line loss are lower than those of small-size modules; at the same time, the support and foundation costs of large-size modules under the same arrangement will be slightly reduced.

## 2. Selection of polycrystalline and single crystal modules

The correct selection of battery modules has an important relationship with the power generation and stability of the power station. In the past few years, everyone who invested in photovoltaic power plant projects pursued the lowest initial investment. At present, everyone is more concerned about the maximization of photovoltaic power generation and long-term income.

Generally speaking, the performance and price of polycrystalline and single-crystalline photovoltaic modules are relatively similar, and there is little difference. Since the price of polycrystalline battery modules is slightly lower than that of single crystal modules, considering the cost of control engineering, the selection of polycrystalline battery modules has certain advantages. The energy consumption of polycrystalline in the production process is lower than that of single crystal. Therefore, the use of polycrystalline modules is also relatively more environmentally friendly.

Since the conversion efficiency of monocrystalline battery modules can be slightly higher than that of polycrystalline modules, monocrystalline battery modules are usually selected in order to install more capacity in the effective area. In addition, when focusing on the long-term power generation and investment yield of photovoltaic power generation systems, monocrystalline battery modules with higher conversion efficiency should also be selected, because monocrystalline modules have the advantage of cost per kilowatt-hour.

The cost of electricity per kilowatt-hour refers to the comprehensive cost incurred by a photovoltaic power generation project unit on-grid electricity, which mainly includes the investment cost, operation and maintenance cost and financial expenses of the photovoltaic project. According to calculations, based on the 25-year service life generally promised by the industry, a power station of the same scale using single crystal modules with higher conversion efficiency will generate about 13% more revenue than using polycrystalline modules. At present, although the cost per watt of monocrystalline modules is about 5% higher than that of polycrystalline modules, the highest power generation efficiency of monocrystalline modules is higher, and the same installed capacity covers a smaller area; together with the saved peripheral costs of photovoltaic brackets, photovoltaic cables and other systems, the comprehensive investment is similar to the use of polycrystalline modules, that is, investments other than photovoltaic modules can basically offset the 5% cost gap of monocrystalline modules. Therefore, from the perspective of the cost per kilowatt-hour, it will be more advantageous to choose single crystal modules.