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A plant installs photovoltaics. The bill drops, as planned. A few months later, a new line appears: reactive energy charges.
Nothing is broken. It’s just arithmetic.
☀️ PV reduces the active energy you buy from the grid (the energy that does the actual work).
⚙️ But your motors and other inductive loads (transformers, welders, furnaces…) still need the same reactive energy: the energy that magnetizes them but does no useful work.
📐 The grid allows reactive energy up to one third of active energy. Beyond that, you pay.
A simplified example:
Before PV: you draw 300 units of active and 100 of reactive. That’s right at the limit, so no penalty.
After PV covers 40% of your load: you draw 180 of active, still 100 of reactive. Reactive is now over half of active, so you cross the limit and the penalty appears.
Same machines, same behavior. Only the solar plant changed.
Why reactive energy is a cost, even when the penalty looks small
The line on the bill is only the receipt, not the real cost:
🔥 Reactive current still flows through cables, breakers and the transformer, and losses grow with the square of the current.
🔧 Hotter cables and stressed machines age faster.
🏗️ Transformer capacity is sized in kVA, so reactive energy occupies headroom you’ve already paid for. You find out when you want to add a production line or expand the PV plant.
Where it goes wrong after a PV installation
The power factor correction was sized before the PV plant, and nobody recalculated it. Or the CT of the correction controller sits downstream of the inverter connection point, so it no longer sees what is exchanged with the grid. The result: too few capacitor steps, or too many, and reactive energy flowing into the grid, which is also charged.
Without monitoring, you discover this in the invoice, one quarter later.
With monitoring, you see it in days.
This is where an Electrex energy monitoring system makes the difference:
📊 Active and reactive energy and power factor are measured at the connection point and on the main loads, so the balance is visible before the bill arrives.
🕒 Interval data lets you compare behavior before and after the PV commissioning.
🚨 Built-in relays and alarm thresholds flag when the power factor drifts, for example if a capacitor step stops working.
🔌 Multiple communication ports (Modbus RTU/TCP, Ethernet) feed the same data to your SCADA, EMS or cloud platform, with no walled gardens.
🧩 Process and environmental data in the same system help you correlate the power factor with machine behavior.
Commissioning a PV plant should include re-checking the power factor correction. Monitoring makes that check continuous instead of a one-off.
Is your power factor correction still the one you had before the PV plant?
📩 Want to see how Electrex monitoring is deployed through our certified partners? Book a call with me (form here below).
Contact me to schedule a call! I will be glad to answer any questions you may have.
About us
Since 1993 Electrex designs, develops, manufactures and markets, Made in Italy, instruments and software for energy management and control.
The Electrex solutions are used in the Energy Efficiency and Energy Automation applications, for the industrial, commercial, public, civil, and renewable energy sectors allowing a rapid return on investment.
The solutions provided up to now allow the management of over 530,000 measuring points and more than 960,000 points are controlled via Energy Automation applications.
Electrex, one of the first companies to operate in these sectors, has acquired over the years a considerable experience and competence that few other companies can claim to have. With over 40% of the staff dedicated to R & D, we demonstrate our strong commitment to innovation and continuous improvement in order to anticipate the needs of our customers.
