Why are there two energy storage units? Which one is used to calculate the unit price?

Why is the expression of energy storage project scale so complicated, with two units and a "/", unlike photovoltaics, which only has one unit?

In fact, this expression contains at least three meanings, and is the most concise and intuitive way to express the scale of energy storage projects.

First, "MW" is the unit of battery power, which refers to the power that can be input or output for a given electrochemical energy storage system device under certain conditions. They are called "rated input power" and "rated output power" respectively, with units of W, kW, and MW, and the conversion ratio is 1:1000.

Secondly, "MWh" is the unit of battery capacity, which refers to the amount of electricity discharged by the battery under certain conditions. It is also one of the important performance indicators for measuring battery performance. The units are Wh, kWh, and MWh, and the conversion ratio is also 1:1000.

As for the "/" in the middle, it has no meaning in itself, and some documents will use "()" instead, but it can intuitively see the ratio of power to capacity, that is, the time scale of energy storage. For example, a 400MW/800MWh energy storage power station means that this is a power station that can be fully charged in 2 hours. The larger the ratio, the longer the charging time, that is, the longer the time scale, and vice versa.