Calculator
What does this system actually save
A rough annual figure from system size and rate plan. It takes about fifteen seconds, and every assumption behind the number is written on this page rather than hidden in it.
Work the numbers
Enter a system size to see an estimate.
Estimate only. It assumes 4.5 sun-hours a day and an 80% system derate, and applies a blended utility rate rather than your actual bill. Real production depends on orientation, shading, equipment condition and weather; real savings depend on your rate plan, your usage pattern and your net metering programme. Check the figures against your own bill before relying on them.
What this number is, and what it isn't
An estimate is only useful if you know what went into it.
The production formula
System size × 4.5 sun-hours per day × a 0.80 derate × 365 days. That derate covers inverter losses, wiring, soiling and temperature.
The rates
Blended averages by plan, reviewed January 2026. Tiered assumes 70% within baseline; time-of-use assumes 70% of production offsets off-peak usage.
What it ignores
Shading, orientation, tilt, panel degradation, rate escalation and your actual consumption pattern. A south-facing unshaded array will beat this; a north-facing shaded one will not.
What it is not
It is not a quote, an appraisal, or a statement about what this system is currently producing. Only an inspection establishes that.
An estimate isn't a measurement
This calculator tells you what a system of that size should produce. It cannot tell you whether the system on that roof is producing anything at all — a system can look immaculate and be down an inverter. In a transaction, that difference is the whole question.
Working a weekend transaction? So are we
The office is open Monday–Friday 9am–6pm, but inspections run on weekends and requests are open around the clock. We'll call to confirm the date and time.
Requesting an inspection isn't a confirmed appointment — we'll contact you to confirm timing.