In the field of energy storage, MW (megawatts) and MWh (megawatt-hours) are core indicators describing system capabilities, but many people are confused about the differences between the two and their application scenarios. This article will delve into the differences between the two from the perspectives of definition, physical meaning, application in energy storage systems, and commercial value, helping readers understand the underlying logic of energy storage technology.
01 Definition: The Fundamental Difference Between Power and Energy
- MW (Megawatts) – The “Explosive Power” of Energy Storage Systems
MW is a unit of power, representing the rate of energy conversion. 1MW = 1000kW, equivalent to converting 1 million joules of energy per second. In energy storage systems, MW represents the instantaneous charging and discharging capacity. For example, a 1MW energy storage system can charge/discharge 1000 kWh (1 MWh) per hour, which determines its ability to cope with short-term high power demands, such as grid frequency regulation or sudden load response.
- MWh (Megawatt-Hours) – The “Endurance” of Energy Storage Systems
MWh is a unit of energy, representing the cumulative power over time. 1 MWh = 1000 kWh (i.e., 1000 kilowatt-hours of electricity). The MWh value of an energy storage system represents its total capacity, i.e., how much electrical energy it can store. For example, a 2 MWh battery can store 2000 kilowatt-hours of electricity, and if discharged at 1 MW power, it can operate continuously for 2 hours.
For example, a 0.5 MW/2 MWh industrial and commercial energy storage system in a factory in Huizhou. With a power of 0.5 MW and a capacity of 2 MWh, it means that at maximum power, the battery of this power station can be fully charged to 2000 kilowatt-hours in 4 hours.
Analogy: MW is like the “top speed” of a car, determining its acceleration capability; MWh is like the “fuel tank capacity,” determining its driving range.
02 Application: Coordinated Design of Power and Capacity
- System Specifications in “MW/MWh” Combinations
Energy storage projects are often labeled in the form of “XX MW/XX MWh,” such as 100MW/200MWh or 125kW/261kWh (common parameters for integrated energy storage cabinets). The ratio here (200MWh ÷ 100MW = 2 hours) is called “energy storage duration,” reflecting the continuous power supply time of the system. Short-term energy storage (e.g., 1 hour) is suitable for frequency regulation, while long-term energy storage (e.g., 4 hours) is used for peak shaving and valley filling.
- Technical Implementation of Power and Capacity
Power (MW): Determined by the converter (PCS) and the charge/discharge rate (C-rate) of the battery. For example, 1C means the battery can discharge its full capacity in 1 hour, while 0.5C requires 2 hours.
Capacity (MWh): Determined by the total energy density and number of battery cells in the battery pack. For example, lithium iron phosphate batteries have become the mainstream choice due to their high cycle life; a single containerized energy storage unit can reach 1MWh, and the current mainstream cell capacity for a single integrated energy storage cabinet is 314Ah. 1P260S indicates 1 parallel and 260 series, which is 260 * 314Ah * 3.2V = 261kWh.
- Impact of Depth of Discharge (DOD)
Actual usable capacity must take into account the depth of discharge (DOD). If a system has a nominal capacity of 100MWh and a DOD of 90%, then the actual usable energy is 90MWh, with the remaining 10% used to protect battery life.
03 Commercial Value: Unit Price Calculation and Scenario Matching
- The Core of Cost Accounting – MWh
The unit price of energy storage projects is usually calculated in “yuan/Wh,” with the total cost divided by the MWh capacity. For example, a project with an investment of 8 million yuan and a capacity of 10MWh has a unit price of approximately 0.8 yuan/Wh. Power (MW) affects equipment costs (such as PCS), but capacity (MWh) is directly related to battery costs, accounting for more than 70% of the total investment.
- Differentiated Needs of Application Scenarios
High-power (MW) scenarios: such as data center backup power supplies, which require rapid response to power outages, demanding high power but lower capacity.
High-capacity (MWh) scenarios: such as energy storage配套的能储 (supporting energy storage for wind and solar power plants), which requires smoothing out power fluctuations over long periods, making capacity critical.
04 Analogy: Power Bank mAh, Energy Storage Station MWh?
Power banks are labeled in mAh (milliampere-hours), requiring voltage (V) to calculate energy (Wh). For example, a 20000mAh power bank with 3.7V has 74Wh of energy. Energy storage stations, on the other hand, are directly labeled in MWh because their voltage is fixed (e.g., 1000-1500V DC), making energy calculation more intuitive.
05 Future Trend: Synergistic Innovation of Power and Capacity
With technological advancements, energy storage systems are developing towards “high power + high capacity.” For example, MW-level containerized energy storage, through modular energy storage cabinet design, can flexibly expand capacity while integrating an energy management system (EMS) to achieve multi-strategy control (peak shaving and valley filling, demand management), adapting to diverse scenario needs.
Modular Energy Storage Integrated Cabinet Parallel Solution
Anhui Wuhu 1MW/2MWh Energy Storage Project
06 Conclusion
The difference between MW and MWh is essentially a distinction between “instantaneous capacity” and “total reserve.” In the design and application of energy storage systems, both speed and endurance are indispensable. Understanding their relationship can not only optimize technical solutions but also accurately unlock the commercial value of energy storage. In the future, as the proportion of new energy sources increases, the synergistic optimization of the “speed” and “endurance” of energy storage systems will become a key support for energy transition.
