Reactive Power Support from Solar Inverters India

Every DISCOM in India has a power factor clause in its tariff schedule. Maintain power factor above your tariff’s threshold and you pay the base rate. Drop below it (as many factories with induction motors do) and the surcharge appears on every bill, month after month. A solar inverter with reactive power support capability can compensate for the lagging reactive demand of inductive loads during daylight hours, eliminating or reducing the penalty without buying a dedicated power factor correction panel.

Direct answer. Reactive power support allows a solar inverter to supply VARs alongside real power, improving the facility’s power factor at the metering point. Whether and how much reactive support is required depends on your connection and your DISCOM’s interconnection agreement. The Reactive Power Compliance Test defines the four steps an EPC must complete to demonstrate compliance.

For EPC teams designing C&I solar installations at factories, schools, or hospitals, reactive power capability is a specification requirement, not an optional feature. Failing to address it results in either a DISCOM interconnection objection or a continued power factor penalty after the solar system is commissioned.

What Reactive Power Is: VARs, Power Factor, and Why It Costs Money

Understanding reactive power starts with the distinction between real power and apparent power. Real power (measured in kW) is the energy converted to useful work, heat, motion, light. Apparent power (measured in kVA) is the total power demanded from the grid, including both real power and the reactive component that oscillates back and forth between source and load without doing useful work.

Power factor is the ratio of real power to apparent power: PF = kW / kVA. A perfect system has PF = 1.0, meaning all apparent power is real power. An inductive system (a factory full of motors) has PF of 0.7–0.85, meaning 20–30% of the apparent power drawn from the grid performs no useful work.

The reactive power component (measured in kVAR, kilovolt-ampere reactive) flows back and forth in the cables, transformers, and switchgear, heating them without delivering energy to the load. DISCOMs incur infrastructure cost to deliver this reactive current, which is why they penalise facilities that maintain poor power factor.

kVAR per 100 kW = 100 × tan(arccos(power factor)).

62 kVAR. The reactive power a 100 kW load draws at a 0.85 power factor (100 × tan(arccos 0.85)), compared with 33 kVAR at 0.95. Your DISCOM’s tariff order decides what that gap costs you, so read its power factor clause.

Why C&I Buyers Care: The Penalty Arithmetic

The financial case for reactive power correction from the solar inverter rests on three numbers: the current power factor penalty, the cost of dedicated power factor correction equipment, and the inverter’s reactive power headroom at typical solar generation levels.

If the building’s inductive load demand is 150 kVAR during the same hours, the inverter can supply all of it, eliminating the daytime power factor deficit and with it the associated penalty on daytime consumption.

The alternative is a dedicated automatic power factor correction (APFC) panel, which you would price from a dated quote for your kVAR size. If the solar inverter can supply that reactive power for free during solar hours, the APFC panel becomes smaller or unnecessary.

Grid Connectivity Requirements: Reactive Power by Plant Size

The requirement depends on your connection voltage, plant size and the rules your DISCOM applies, so confirm it in writing before you design. The CEA connectivity regulations{target=“_blank” rel=“noopener”}, your SERC’s supply code and the DISCOM’s interconnection agreement are the documents to read. This guide does not quote size thresholds as law; the pattern below describes how requirements typically scale.

Smaller Systems

Many DISCOMs accept the inverter operating at unity power factor, and some do not require a reactive power demonstration at interconnection. Voluntary reactive power support, where the inverter allows it, can still help a facility’s power factor.

Mid-Size Systems

The DISCOM may specify the operating mode in the interconnection agreement, often a fixed power factor (cos phi) mode with a stated power factor range at the point of common coupling. Read the figure from your agreement.

Large Systems

Larger plants are more likely to be required to provide reactive power support in automatic modes. The inverter may need to implement:

• Q(U) droop control: Reactive power adjusted automatically as a function of grid voltage deviation from set-point.
• AVR (Automatic Voltage Regulation) mode: The inverter actively maintains a target voltage at the point of common coupling by adjusting reactive output.
• Remote set-point capability: The DISCOM load dispatch centre may need to adjust the reactive power set-point remotely via SCADA or a direct communication link.

EPC teams handling utility-scale or large C&I installations must address all three requirements in the protection and control design. Failing the reactive power capability test during DISCOM commissioning inspection is a common delay cause at this scale, which is why reactive power mode selection belongs in the commercial solar design phase, not retrofitted at commissioning.

Active vs Passive Reactive Power Correction: Solar Inverter vs Capacitor Bank

The traditional approach to power factor correction is a passive capacitor bank, fixed or automatic (APFC). Capacitors supply lagging reactive power by generating leading reactive current, compensating for the lagging current drawn by inductive loads.

Solar inverters with reactive power capability represent an active approach: the inverter’s power electronics can synthesise reactive current of any magnitude and phase angle within its rated kVA capability, responding dynamically to load changes.

The Reactive Power Compliance Test

This four-step framework defines how an EPC team should verify reactive power compliance before DISCOM commissioning inspection. Completing this test during pre-commissioning saves the delay of a failed inspection:

1. Baseline measurement: At the DISCOM meter, measure the existing power factor without solar inverter reactive support active. Record the worst-case (minimum) power factor during typical operating hours using a power quality analyser. This is the target condition the inverter must correct.
2. Inverter reactive capability confirmation: At the expected average solar generation level, calculate the available reactive power headroom. For a 100 kW inverter operating at 70 kW: available kVAR = √(100² − 70²) = 71 kVAR. Confirm this exceeds the reactive demand from step 1.
3. Mode configuration and testing: Configure the inverter’s reactive power mode per the DISCOM’s interconnection agreement (fixed PF, Q mode, or droop). Apply the configuration and measure the resulting power factor at the DISCOM meter under typical load. Confirm it meets the minimum power factor required by your DISCOM’s tariff or interconnection agreement.
4. Documentation package: Prepare the reactive power compliance documentation: inverter specification sheet showing kVA rating and reactive power capability, inverter settings screenshot showing the active reactive power mode, and the power quality report from step 3 confirming the achieved power factor. This package accompanies the commissioning application to the DISCOM, alongside the electrical and CEIG drawings already prepared for the interconnection submission.

Common Reactive Power Configuration Mistakes: What EPCs Get Wrong

Understanding the failure modes of reactive power configuration prevents commissioning delays and post-installation performance issues.

• Unity PF default left active: Most inverters ship with reactive power support disabled (unity PF mode). EPC teams that do not explicitly configure reactive power mode during commissioning leave money on the table and may fail the DISCOM’s reactive capability test where one is required.
• Over-correcting to leading PF: Supplying more reactive power than the load consumes shifts the facility’s power factor to leading (capacitive). Some DISCOMs penalise leading power factor as aggressively as lagging. Always size reactive support against the measured reactive demand, not the inverter’s maximum capability.
• Ignoring night hours: Solar inverter reactive support is unavailable after sunset. A C&I facility with significant inductive load at night requires a supplementary capacitor bank or STATCOM for round-the-clock compliance. A commissioning design that achieves 0.97 PF during the day and 0.82 PF at night will still incur partial monthly penalties.
• No reactive power in the monitoring data: Ensure the monitoring system logs kVAR output alongside kW generation. Without reactive power data, there is no way to verify the inverter is meeting its reactive set-point or diagnose when it is not.

See the solar inverter commissioning guide for the complete commissioning workflow, including how reactive power documentation fits into the DISCOM approval package. The harmonics and THD guide covers the related power quality topic of harmonic distortion.

Reactive Power and Harmonics: The Dual Power Quality Problem

Reactive power and harmonics are related but distinct power quality issues. Both affect C&I solar installations in India and both require attention during system design.

Reactive power affects the fundamental frequency (50 Hz) component of the current waveform, it is the phase displacement between voltage and current at 50 Hz. Harmonics are distortions at integer multiples of 50 Hz (100 Hz, 150 Hz, 250 Hz, etc.) generated by non-linear loads such as variable-frequency drives, UPS systems, and LED driver circuits.

Solar inverters affect both. A poorly controlled inverter can inject harmonic current into the grid alongside reactive power. The CEA connectivity regulations for distributed generation (2013, amended 2019) require harmonic current injection to stay within IEEE 519 limits. See the THD glossary entry for the definition.

Verify that an inverter’s reactive power mode does not increase harmonic injection: a combined power quality test is a sensible part of any large-plant commissioning protocol.

Monitoring Reactive Power: Why kVAR Data Matters

Reactive power support is only verifiable through monitoring data. An inverter that reports only kW generation gives no visibility into whether its reactive set-point is being met. EPC teams should confirm the monitoring platform captures:

• kVAR output: Reactive power supplied by the inverter, logged at 15-minute intervals minimum.
• Power factor at inverter terminals: The actual PF the inverter is operating at.
• Reactive set-point: The commanded reactive output, to distinguish between the inverter not meeting its set-point versus the set-point being configured incorrectly.
• kVA utilisation: What percentage of the inverter’s rated kVA is being used, to identify periods where the kVA limit constrains reactive output.

Many monitoring systems do not log reactive power by default, which leaves operators with no visibility into whether their power factor compliance is being maintained; check that yours does.

The solar inverter monitoring guide covers the full data architecture for inverter monitoring in India, including what parameters should be captured and how to set up alerts for power factor deviation.

Where Qbits Fits

• On-Grid Inverters: Review the current product families and exact-model documents against the project design and utility requirements.
• Hybrid Inverters: Review current QBH model documents and confirm the exact battery, firmware, PV, backup-output, transfer, communication, warranty and project requirements in writing.
• Solar Inverter Commissioning Guide: DISCOM approval workflow including reactive power documentation requirements.
• THD and Power Quality Guide: Related power quality specification for C&I installations.

Contact Qbits with the exact model, site inputs and documents relevant to the request. Confirm the responsible party, deliverable, fees and response time after submission.