Installing solar PV can reduce the amount of active energy drawn from the grid while changing how reactive energy is billed. A company may therefore pay less for active energy yet see a new or higher reactive energy charge on its distribution invoice. This does not automatically indicate a fault with the panels or inverter. The cause can only be established by comparing readings at the metering point with PV operation and the facility’s loads.
Does solar PV cause reactive energy charges?
PV panels alone do not automatically trigger an additional charge. Billing depends on reactive energy exchanged at the revenue metering point and the rules applicable to the customer. However, three different effects may arise after the system is commissioned:
- active energy drawn from the grid falls while inductive reactive energy consumption remains close to its previous level;
- the inverter adjusts reactive power according to its selected control mode and voltage conditions;
- at low load, capacitive reactive energy becomes apparent, for example due to cables, filters or incorrect operation of existing power factor correction equipment.
These effects can overlap. Comparing only the total monthly charges before and after PV installation is therefore insufficient to attribute the difference to the PV system.
Why does tgφ increase after PV starts operating even though the machines run as before?
Active power P [kW] describes the rate at which energy is transferred to perform work, produce heat and support other processes. Reactive power Q [kvar] describes the periodic exchange of energy associated with electric and magnetic fields between the installation and the grid. When inductive reactive energy is billed, the tgφ ratio is important: it is calculated from the reactive and active energy drawn during the same billing period or time band.
A PV inverter primarily supplies active energy to the installation. If the facility’s loads still require roughly the same amount of inductive reactive energy while self-consumption of PV reduces active energy drawn from the grid, the ratio of the two quantities may increase.
Assume that the following quantities are measured on the grid side of a facility over comparable billing periods:
| Indicator | Before PV commissioning | After PV commissioning |
|---|---|---|
| Active energy drawn from the grid | 10 MWh | 5 MWh |
| Inductive reactive energy drawn from the grid | 3 Mvarh | 3 Mvarh |
| tgφ = reactive energy / active energy | 0,30 | 0,60 |
In this simplified example, the quantity of reactive energy has not increased. Instead, the denominator—active energy drawn from the grid—has fallen. With a contractual tgφ₀ of 0.4, a value of 0.60 indicates that the billing threshold for inductive consumption has been exceeded. The table illustrates the mechanism; it does not calculate an invoice charge. In a real installation, Q may also change, while aggregation and charging rules depend on regulations, the tariff and the metering configuration.
If the installation exports active energy to the grid during some periods, do not mechanically insert a negative P into this ratio. Check the directions of energy flow, meter registers and the billing rules applicable to that metering point.
What exactly is charged for in Poland in 2026?
As at 23 October 2026, the rules for billing reactive energy drawn beyond the contractual limit in Poland are based on Section 52 of the Polish Minister of Energy’s Regulation of 3 September 2026 (Journal of Laws 2026, item 1182), in force since 5 September 2026. It distinguishes excessive inductive reactive energy consumption, inductive consumption without active energy consumption, and capacitive reactive power. These charges apply to customers supplied from medium-, high- and extra-high-voltage networks; low-voltage customers may also be subject to them.
For inductive consumption, the reference is the contractual tgφ₀ ratio. If it is not specified in the relevant documents, the Polish regulation provides a value of 0.4. Capacitive reactive energy does not benefit from the same 0.4 allowance: the regulation refers to energy fed in above the level corresponding to tgφ = 0. The amount charged also depends on voltage level, the quantity of energy billed, the reference price and the applicable tariff provisions.
The current provision is available in Poland’s Electronic Journal of Laws – Journal of Laws 2026, item 1182. For an individual company, its contract and the applicable distribution system operator tariff must also be checked. The Polish Energy Regulatory Office (URE) publishes information on approved distribution tariffs for 2026.
How do the PV inverter and the facility’s electrical installation affect reactive power?
Inverter settings can change Q
An inverter does not have to operate at a constant power factor (cosφ) of 1. Depending on its model, configuration and the operator’s requirements, it may control reactive power through a fixed cosφ, a cosφ(P) curve, a Q(U) function or a specified Q setpoint. The Fronius Reactive Power Mode documentation illustrates the available control modes and parameters.
This distinction matters: a change in Q after PV commissioning does not prove that the inverter is malfunctioning. It may be performing a required voltage-support function. Before anyone adjusts its settings, the equipment documentation, grid-connection conditions and requirements of the relevant distribution system operator (OSD in Poland) must be compared. Reactive power control should not be disabled solely to obtain a more favourable invoice reading.
Cables, filters and existing compensation also matter
At low load, the capacitive effect of cables and filters may become more apparent at the billing meter. A separate issue is a capacitor bank sized for the facility’s previous operating profile. If compensation stages remain switched on despite lower demand for inductive reactive power, the system may become overcompensated.
Useful information in such cases includes the history of compensation-stage switching, controller settings, current-transformer locations and a diagram showing how PV is connected relative to the existing compensation system. We discuss the general selection and assessment of equipment separately in our article on reactive power compensation.
Night-time charges do not prove the inverter operates at night
If capacitive reactive energy appears after dark, first check energised cables, filters, the transformer and compensation operation at low load. Not every inverter can supply reactive power after PV electricity generation has stopped. Special solutions do exist—for example, the manufacturer’s SMA Q at Night function for certain equipment series—but this feature must not be assumed for every installation.
How can you tell whether PV really caused the increase in charges?
Analyse the same electricity metering point (PPE in Poland) throughout. Start with invoices from before and after PV commissioning, followed by the active and reactive power profiles recorded by the metering system. If detailed Q data are unavailable, they may need to be obtained from the operator or measured temporarily on site.
| Signal in the data | Possible interpretation | What to compare |
|---|---|---|
| During PV generation hours, active energy drawn from the grid falls while inductive reactive energy consumption stays similar | An increase in tgφ due to a changed ratio, without an increase in reactive energy drawn | P and Q for matching intervals, plus PV generation |
| Q changes with voltage or inverter output | Operation of the inverter’s Q control function | Inverter logs, Q(U)/cosφ(P) settings, voltage |
| Capacitive Q occurs at night and on weekends | Cables, filters or overcompensation at low load | Compensation-stage status, night-time loads, circuits that remain energised |
| Charges rise after changes to production, lighting or automation | A factor unrelated to PV or the combined effect of several changes | Production schedules, upgrade dates, before-and-after measurements |
| Active energy is exported to the grid | Billing may involve different directions of energy flow | Meter quadrants and registers, the DSO’s data aggregation method |
Data worth collecting
- Invoices and billing terms: several months before and after PV commissioning and, where seasonality is significant, comparable periods from the preceding year where possible. Record inductive and capacitive reactive energy separately, including quantities, rates, time bands and the relevant PPE. Our guide to analysing an electricity distribution invoice can help identify these items.
- P/Q profile at the metering point: ideally, synchronised 15-minute data with import and export directions. Check register definitions and the sign convention. Where loads fluctuate rapidly, a resolution finer than 15 minutes may be needed to diagnose controller behaviour.
- PV generation and inverter settings: actual generation using the same timestamps, the cosφ/Q operating mode, any Q(U) settings, and logs of events and operating limits.
- Actual facility loads: shift schedules, shutdowns, night operation, switching of major loads, process changes and upgrade dates.
- Compensation diagram and condition: stage ratings and number, controller logic, transformer locations, switching mode and the equipment’s condition after PV was connected.
Next, compare similar days and hours, taking account of facility output, season, temperature and PV generation. When analysing billing meters, establish whether active and reactive data relate to the same interval and the same energy-flow directions. If the results remain ambiguous, plan measurements at the common connection point and selected outgoing circuits.
For a broader diagnosis of power quality parameters, such as voltage and harmonics, the methods in IEC 61000-4-30:2025 may be relevant. This standard does not replace the operator’s billing rules, nor does every suspected Q charge justify a full assessment of all power quality parameters.
What can be improved without buying a new compensation unit?
The order of action depends on which effect measurements have confirmed.
| Confirmed cause | Possible next step | Important limitation |
|---|---|---|
| Change in tgφ mainly caused by reduced active energy import from the grid | Assess the P/Q balance and existing control; examine possible setting options | The tgφ value alone does not establish the appropriate equipment rating |
| The inverter changes Q according to the active control mode | Check configuration against the documentation, design and DSO requirements | Changes must be made only by authorised personnel without breaching grid requirements |
| The existing capacitor bank overcompensates at low load | Check the controller, thresholds, current transformers and stage switching | Do not disconnect protection devices or stages without assessing the consequences for the installation |
| Capacitive Q persists and is not caused by incorrect settings | Assess a reactor-based or active compensation design | Selection requires load profiles, grid conditions and harmonic analysis |
| There are no significant charges, but the P/Q profile has changed | Set up monitoring and a review point after PV acceptance | Not every change in a parameter justifies investment |
For a PV installation, upgrading reactive power compensation should account for normal production hours as well as night shifts, weekends and shutdowns. Equipment sized solely for the daytime peak Q may perform poorly at minimum load. If a larger installation is still at the planning stage, the reactive energy assessment should be combined with a design-stage comparison of import and generation profiles relevant to industrial solar PV.
What should be checked at handover and after several months of PV operation?
Record the following in the commissioning report or an internal checklist:
- inverter P/Q control settings and the DSO requirements on which they are based;
- the location of active and reactive energy metering and how flow directions are recorded;
- the behaviour of the existing capacitor bank, reactors or active compensator at high and low PV generation;
- the P/Q profile on a working day, during a shutdown and after dark;
- the planned date for comparing initial invoices with the pre-commissioning period;
- how the effect of any configuration change will be verified, separately for inductive and capacitive reactive energy.
Evaluate results using data from comparable operating conditions. A lower charge in one month may reflect a different production schedule rather than a lasting improvement in control. After changes to settings or compensation equipment, check the P/Q profile and subsequent bills.
When reactive energy charges rise after installing PV
From an auditor’s perspective, the first step is to distinguish two questions: did the quantity of reactive energy itself change after PV installation, or did the relationship between Q and active energy drawn from the grid change most? Only then should you determine whether the cause lies in inverter settings, existing compensation, facility loads or metering.
If you would like to define the scope of further diagnostics, describe the installation and send the available invoices from before and after PV commissioning. P/Q profiles, generation data, inverter settings and information about night-time loads will also help. These allow us to determine whether configuration checks, additional measurements or a redesign are needed. A broader review of business expenditure may also combine this work with electricity cost optimisation.
Sources
- Polish Minister of Energy’s Regulation of 3 September 2026, Journal of Laws 2026, item 1182, Section 52 – the basis for reactive energy billing rules in Poland.
- Polish Energy Regulatory Office – approval of tariffs for 2026 – information on operators’ tariffs.
- Fronius, Reactive Power Mode settings manual – examples of model-dependent Q control modes.
- SMA, Q at Night – technical documentation – an example of a dedicated night-time function available on selected inverters.
- IEC 61000-4-30:2025, power quality measurement methods – the standard’s scope for selected power quality parameters.
