Reactive power is one of those topics that appears on the energy bills of industrial and commercial enterprises – often without those in charge knowing exactly what's behind it. However, uncompensated reactive power can noticeably increase electricity costs, strain grid stability, and reduce the efficiency of technical systems. This article explains what reactive power is, how it is generated, what costs it causes, and how you can specifically reduce it.
What is reactive power? – Definition
Reactive power (formula symbol: Q, Unit: var / kvar) denotes the proportion of electrical power in an alternating current system that no useful work done. It oscillates back and forth between producer and consumer without being converted into heat, motion, or light.
For understanding, it helps to distinguish between the three types of power in an AC network:
| Active power (P) | Reactive power (Q) | Apparent power (S) | |
| Definition | Does actual work | Setup of electric/magnetic fields | Total from active and reactive power |
| Unit | Watt (W) / Kilowatt (kW) | Go Away VAR / Kilovar (kVAR) | Volt-ampere (VA) / kVA |
| Formula | P = U (Voltage) × I (Current) × cos φ | P = U (Voltage) × I (Current) × sin φ | S = U (Voltage) × I (Current) |
| Will it be paid for? | Yes, always | Part (Reactive Power Price) | No (reference only) |
| Generatable by | Generators, PV inverters | Capacitors, coils, inverters | Composition of both |
Power factor Power factor cos φ (Power Factor). A power factor of 1.0 means: no reactive power component, maximum efficiency. The further cos φ deviates from 1.0, the greater the reactive power component – and the more expensive operation becomes.
Quadrant Diagram & Performance Triangle
Reactive power is generated by inductive and capacitive components in an electrical circuit.
Reactive power is always generated when electrical energy is not only converted into work, but is first temporarily stored in electric or magnetic fields. This happens through two physical phenomena:
Inductive reactive power
Inductive loads - for example Electric motors, transformers, compressors, or ventilation systems – generate a magnetic field. The voltage leads the current by up to 90° (phase shift). This phase shift is the most common cause of reactive power in commercial operations.
Capacitive reactive power
Capacitive loads like Capacitors, long cable routes, or compensation systems generate capacitive reactive power. Here, the current leads the voltage. Capacitive reactive power can be used specifically to compensate for inductive reactive power.
Motto:
- Inductive reactive power: Current “lags” behind voltage → positive sign (+Q)
- Capacitive reactive power: Current “leads” voltage → negative sign (−Q)
- Both types strain the grid, but they cancel each other out.
Why is reactive power a problem for companies?
Reactive power does no work, but it loads lines, transformers, and measuring devices just like usable active current. This results in three specific disadvantages:
Higher electricity costs due to reactive power charges
Many network operators charge from a Power factor below 0.9 a so-called Reactive power surcharge. The monthly reactive energy amount (in kvarh) is billed separately. For medium-sized industrial companies, these costs can quickly amount to several thousand euros per year.
2. Overload of Power and Transformers
Since apparent power is transported through lines – not just active power – cables, fuses, and transformers are strained more than actually necessary. This leads to higher transmission losses (heat losses in the lines) and can, in extreme cases, lead to overloads.
3. Limited Network Capacity
High reactive power shares occupy transmission capacity in the grid, which is then no longer available for real power. Companies that want to fully utilize their grid connection capacity are therefore particularly reliant on a high power factor.
How is reactive power measured?
Reactive power is contributed by Energy meter at the grid connection point measured, which record both active energy (kWh) and reactive energy (kvarh). Modern meters in the field of grid usage measurement can display both values separately and thus form the basis for billing by the grid operator.
Key figures on your electricity bill:
- cos φ (Power factor): Verhältnis von Wirkleistung zu Scheinleistung. Zielwert: > 0,9
- KVARh (Reactive Energy): The actual amount of reactive power consumed in the billing period
- Reactive power price: Rate per kVARh charged by your grid operator for exceeding the minimum power factor
Practice Tip: Check the power factor
- Request your last 12 months' meter readings from the grid operator or check your annual bill.
- Is your power factor (cos φ) consistently below 0.9? Then an on-site reactive power measurement is worthwhile.
- Simple measuring devices (power analyzers) provide reliable measurements for just a few hundred euros.
Compensate reactive power: Reduce costs
The targeted reduction of reactive power is called reactive power compensation. Inductive reactive power is partially or completely offset by capacitive reactive power – the power factor increases, and reactive power costs decrease.
1. Capacitor banks (stationary compensation)
The classic solution: Capacitor banks are installed centrally or decentrally in the plant and supply capacitive reactive power. Step regulators automatically adjust the switched-on capacity to the current demand. This solution is cost-effective and often pays for itself within 1-3 years at a medium reactive power demand.
2. Active Filters and Static Var Compensators (SVCs)
Active compensation systems are suitable for installations with highly fluctuating reactive power demand (e.g., welding systems, presses). They react to load changes in milliseconds and can also reduce harmonics in the grid.
3. Inverters for PV systems and battery storage
Modern inverters can Provide or absorb reactive power – without additional hardware. PV systems from 135 kW are even obliged according to VDE-AR-N 4105 to provide reactive power for grid support. Through Grid forming with grid-forming inverters meet regulatory requirements and can contribute to compensation internally.
More information on this can also be found in the article: Reactive current for PV systems
Reactive Power and Grid Stability: The Overall Economic Dimension
Reactive power is not only a business administration issue but also a macroeconomic one. With the growing share of decentralized generation facilitiesPhotovoltaics, wind power) the reactive power provision is shifting from central power plants to the operators' own facilities.
Consequences for companies: Who is both producer and consumer – for example, through their own solar power system and a Battery storage – has the ability to manage reactive power internally, thereby meeting both grid costs and grid operator requirements.
Network operators may increasingly demand that large commercial consumers actively contribute to reactive power support in the future. Those who install the appropriate technology now will not only be well-positioned in terms of cost but also regulatorily prepared.
Conclusion: Actively manage reactive power – reduce costs, support the grid
Reactive power is not an academic niche topic, but a tangible cost factor for industrial and commercial enterprises. Those who know their power factor and actively improve it not only save money, but also protect their own infrastructure and contribute to grid stability.
Three core messages:
- Measurements Check your current power factor (cos φ) and the reactive energy costs on your electricity bill.
- Compensate Stationary capacitor banks or active filters are the direct way to reduce costs.
- Integrate If you operate a PV system or a battery storage system, you use their inverters for integrated reactive power control.
Would you like to know your current reactive power share and what is worthwhile for your business? CUBE CONCEPTS offers you free and non-binding advice through the Callback service.
Frequently Asked Questions about Reactive Power (FAQ)
What is the difference between reactive power and real power?
Active power (P) performs actual work – meaning heat, motion, or light. Reactive power (Q) is only used to build up electrical and magnetic fields and oscillates unused between the generator and consumer. Active power is measured in Watts (W), and reactive power is measured in volt-amperes reactive (var).
From when does the grid operator charge for reactive power costs?
Most grid operators charge for reactive power if the power factor (cos φ) permanently drops below 0.9. The exact threshold and price per kvarh vary depending on the grid operator and grid level. Check your electricity bill or grid usage statement.
What does cos φ = 0.9 mean?
A power factor of 0.9 means that 90% of the apparent power is available as usable active power. The remaining 10% is reactive power. This is the standard minimum requirement set by utility companies. The goal should be a value as close to 1.0 as possible.
Can a photovoltaic system be used for reactive power compensation?
Yes. Modern inverters in modern PV systems can both generate and absorb reactive power. According to VDE-AR-N 4105, PV systems with a capacity of 135 kW and above are even legally required to provide reactive power for grid support. For businesses, this offers the opportunity to compensate for internal reactive power demands directly via the inverter.
How quickly does a reactive power compensation system pay for itself?
This depends on the current reactive power share and the costs of the system. With a cos φ permanently below 0.85 and a medium-sized operation with a connected load of 500 kW, payback periods of 1-3 years for stationary capacitor banks are realistic. Active compensation systems, due to higher investment costs, tend to pay for themselves in 3-7 years.
Is reactive power the same as reactive current?
Fast – but not quite. Reactive power is the portion of current that belongs to reactive power. Reactive power (Q) results from the product of voltage and reactive current. In common usage, these two terms are often used interchangeably, but the distinction is technically correct: reactive current describes the current flow, and reactive power describes the physical result.