太陽光発電蓄電池におけるKWとKVAの主な違い

In photovoltaic (PV) energy storage systems, KW (kilowatt) refers to active power, while KVA (kilovolt-ampere) denotes apparent power. The core difference lies in whether reactive power is included, which directly impacts equipment selection, power generation calculation, and grid connection. Based on the practical needs of sales and procurement scenarios, the following is a structured analysis:

1. Core Definitions and Essential Differences

Key Correlation Formula:

KW = KVA × Power Factor (PF)

– Power Factor (PF): Measures the ratio of active power to apparent power, ranging from 0 to 1. In PV energy storage systems, it typically ranges from 0.8 to 1.0 (PF of lithium-ion battery energy storage systems is usually ≥0.9, and PF of pure resistive loads is 1);

– Reactive Power (KVAR): Does not perform external work but only maintains the magnetic field of equipment (e.g., motors, transformers) while occupying circuit capacity. Formula: KVAR = √(KVA² – KW²).

1. Popular Analogy (Quick Understanding)

Compare the PV energy storage system to a “logistics fleet”:

– KW (Active Power): The “weight of goods actually transported” by the fleet (useful work, the ultimate value required by customers);

– KVA (Apparent Power): The “total rated load capacity” of the fleet (including goods + the weight of the vehicles themselves);

– Power Factor (PF): The “ratio of goods weight to total load capacity” (a PF of 0.8 means 80% of the fleet’s capacity is used for goods, and 20% is for internal consumption).

Example: A 100KVA inverter (PF=0.8) can actually output an active power of 100×0.8=80KW. If the energy storage battery has a rated output of 80KW, the inverter is perfectly matched; if the battery outputs 100KW, the inverter will trigger protection due to insufficient capacity.

Ⅲ. Practical Application Scenarios in PV Energy Storage Systems (Tailored to Sales/Procurement Work)

1. Energy Storage Batteries Themselves: Marked with KW, Not KVA

– The core indicators of energy storage batteries are “rated output power (KW)” and “capacity (KWh)”. 例えば, a “100KW/200KWh lithium-ion battery energy storage cabinet”:

– 100KW: The maximum active power (actually usable power) that the battery can output;

– 200KWh: The total electrical energy that the battery can store (100KW × 2 hours = 200KWh).

– Key Sales Communication Point: When customers ask “What is the power of the battery?”, directly respond with the KW value without mentioning KVA (KVA is a parameter for inverters/transformers).

2. Inverter Selection: KVA Must Match Battery KW + Power Factor

– The inverter is the core equipment for “DC to AC conversion”, and its rated capacity is marked with KVA. It must meet:

Inverter KVA ≥ Energy Storage Battery KW ÷ Power Factor (PF)

– Example: If a customer purchases a 100KW energy storage battery and the system PF=0.8, an inverter of ≥125KVA is required (100÷0.8=125); if PF=1.0 (pure resistive load), a 100KVA inverter can be selected.

– Key Procurement Note: Avoid using a “100KVA inverter to drive a 100KW battery” (it will overload when PF<1). A 10~20% capacity margin should be reserved.

3. Grid Connection and Power Generation Calculation: KW as the Core Indicator

– When a PV energy storage system is connected to the grid, power grid companies focus on “active power (KW)” (i.e., the actual amount of electricity fed to the grid) and calculate electricity fees/subsidies based on KW;

– KVA is only used for grid capacity applications (e.g., a 125KVA inverter corresponds to a maximum grid-connected power of 80KW) to avoid grid overload.

– Key Sales Communication Point: Explain to customers that “the actual maximum grid-connected power of a 100KW battery pack is 80~100KW (depending on PF)” to prevent customers from misunderstanding that “a 125KVA inverter = 125KW power generation capacity”.

4. Load Matching: Select Based on KW, with KVA as Capacity Guarantee

– If customers use energy storage batteries to drive industrial loads (e.g., motors, water pumps), select the battery based on the “rated KW of the load” and ensure the inverter KVA meets:

Inverter KVA ≥ Load KW ÷ Load PF (PF of motor loads is usually 0.7~0.9);

– Example: To drive a 50KW motor (PF=0.8), an inverter of ≥62.5KVA + a 50KW battery are required to avoid failure to start the motor due to insufficient inverter capacity.

1. Common Misconceptions and Sales/Procurement Pitfall Avoidance Guide
2. Misconception 1: KVA = KW

– Correction: They are only equal when PF=1 (pure resistive loads, such as electric heaters). In PV energy storage systems, PF is usually 0.8~0.95, so KVA is always ≥ KW;

– Pitfall Avoidance: When purchasing inverters, do not directly replace KVA with battery KW. Conversion must be performed using the formula.

2. Misconception 2: Energy Storage Batteries Are Marked with KVA

– Correction: Batteries only output active power (KW). KVA is the “total capacity of voltage × current” including reactive power, which is irrelevant to the core function of batteries;

– Pitfall Avoidance: When inquiring with suppliers, clearly ask for the “rated output power (KW) of the battery” to avoid being misled.

3. Misconception 3: The Larger the Inverter KVA, the Better

– Correction: Excessively large KVA leads to increased equipment costs (a 125KVA inverter is 15~30% more expensive than a 100KVA one), while excessively small KVA cannot match the battery output;

– Pitfall Avoidance: Select based on “battery KW ÷ PF” with a 10% margin reserved (e.g., 100KW battery + 0.8PF, select a 125KVA inverter).

1. まとめ (Key Points for Quick Reference)

One-Sentence Summary: In the PV energy storage business, KW is the “actually usable power” and KVA is the “total capacity that equipment can carry”. Focus on KW (power generation, load matching) when communicating with customers, and pay attention to the conversion between KVA and KW (combined with PF) when selecting equipment to avoid selection errors or customer misunderstandings due to parameter confusion.