How Solar Energy Monitoring Works

Every grid-tied solar system already reports something. The inverter app shows a generation figure, a daily total, maybe a lifetime number. It is genuinely useful, and it is also only a third of the picture.

Monitoring fills in the rest: what the house is drawing, which direction power is flowing at the meter, and how much of what the roof makes actually gets used on site. Here is the mechanism, from the clamp on the cable to the number on the phone.

What the inverter knows, and what it cannot

An inverter measures its own output. It knows how much DC arrived from the array and how much AC it pushed into the building's wiring. That is all it can see, because that is all that passes through it.

What it cannot see is where that AC went. Once power leaves the inverter it joins the rest of the household supply, and from there it either gets consumed by something in the house or flows back out to the grid. The inverter has no visibility of either. Two houses with identical generation can have completely different bills, and nothing in the inverter app would distinguish them.

That gap is exactly why a system can generate to specification and still leave the bill barely moved — the subject of why your solar system isn't cutting your bill.

The measurement: current transformers

A current transformer, universally shortened to CT, is a ring of magnetic material with a coil wound round it. Pass a live conductor through the middle and the alternating current in that cable induces a proportional, much smaller current in the coil. Measure the small one and you know the large one.

The important property is that nothing has to be cut. A split-core CT hinges open, clips around an existing cable and closes again. No conductor is broken, no connection is disturbed, and the measurement is galvanically isolated from the circuit being measured.

Where the clamps go

Placement is what turns raw current readings into meaningful quantities. On a typical solar home, clamps go on the cable from the inverter, and on the incoming supply from the grid. Additional clamps can go on individual heavy circuits.

• On the inverter's output, a clamp measures generation
• On the incoming grid supply, a clamp measures the net flow — which runs in both directions
• On a heavy circuit such as an air conditioner or geyser, a clamp isolates that load on its own

Direction matters here. A CT on the grid main sees current whether the house is importing or exporting, so the device has to distinguish the two rather than simply totalling them.

Why voltage is measured too

Current alone does not give you power. Power is the product of voltage, current and power factor, so the monitor also takes a voltage reference from the supply. On a single phase installation that is one reference; on three phase it is three, one per phase.

Both are measured as true RMS rather than assumed from a peak, which matters because household loads are increasingly non-linear. Switch-mode supplies, LED drivers and inverter-driven compressors draw current in a shape nothing like a clean sine wave, and a measurement that assumes one will be wrong.

Turning measurements into the four numbers that matter

From those inputs the device derives the quantities you actually care about. Generation is what the inverter clamp reads. The grid clamp gives import when flow is inbound and export when it is outbound. Consumption is then arithmetic: what the house used is what it generated, plus what it imported, minus what it exported.

That last figure is the one no single meter reads directly, and it is usually the most useful. It is what makes self-consumption calculable — the share of your generation that you used yourself rather than sending away.

Getting the data off the wall

Measurement is continuous; reporting is periodic. The device commissions onto the home's 2.4 GHz Wi-Fi and streams readings to a cloud platform, where they are stored, aggregated and served back to the app.

Two details matter more than they sound. Time synchronisation over NTP, with a real-time clock holding time through a power cut, means a reading taken during an outage still lands on the correct timestamp rather than corrupting the day's data. And over-the-air firmware updates mean a device installed today can gain capability later without anyone revisiting the site.

What the data lets you do

• See self-consumption as a percentage, and watch it change when you move a load into daylight
• Catch an underperforming array by comparing this month against the same month last year
• Identify the always-on load that runs all night, which is the floor under every bill
• Verify that a change you made actually did something, rather than assuming it did

What it does not do

Worth being straight about the limits. A whole-home monitor with clamps on the mains tells you what the house is drawing, not which appliance is drawing it. Disaggregating individual appliances from a single aggregate signal is an inference, not a measurement, and it is only reliable for large distinctive loads. If you want a specific circuit measured, clamp that circuit.

Accuracy also has a class. Class 1 means measurement within one percent under defined conditions; Class 2 within two. That is fine for understanding behaviour and finding waste, and it is not the same thing as a utility revenue meter — nor is it intended to be.