How Much Solar Power Can My Roof Generate in New Zealand?

As solar energy grows in popularity, many Kiwi homeowners wonder: how much solar power can my roof generate? The answer depends on a handful of factors—where you live, your roof’s size and orientation, the type of panels you choose, and whether any shade falls across your tiles. Let’s break it down into simple steps so you can get a ballpark figure for your own home.

Estimating Output per Kilowatt

In New Zealand, each kilowatt of quality solar panels typically produces about 3.5 to 4.5 kWh of electricity per day, depending on region and season. That adds up to around 1,300–1,650 kWh per year for every kilowatt installed. So, if you fit a 5 kW system (roughly 15–18 standard panels), you can expect around 17.5–22.5 kWh each day on average—enough to cover most daytime household needs.

Location & Sunlight Availability

Different regions in Aotearoa get varying amounts of sun. In summer, places like Northland and Nelson see up to 6 peak sun hours per day, while Southland might get closer to 4 hours. Peak sun hours are a handy way to convert the sun’s intensity into energy potential: more hours of strong sun means more kilowatt-hours generated.

Roof Size, Orientation & Tilt

Your roof’s usable area limits how many panels you can install. A typical solar panel occupies about 1.7 m² and delivers 300–400 W. On a 20 m² north-facing section tilted at about 30°—the sweet spot here—you could fit around 12 panels (3.6 kW), generating roughly 12.6–16.2 kWh per day in good conditions. East- or west-facing installations will yield slightly less (10–20 percent lower), but still make a solid contribution.

Panel Efficiency & System Losses

Modern panels boast efficiencies between 15 and 22 percent, meaning that portion of the sun’s energy becomes electricity. Higher-efficiency panels squeeze more power from the same space but often come at a premium. Don’t forget to allow for system losses—wiring, inverter conversion and occasional dirt—typically 15–25 percent of your raw output. A good rule of thumb is to multiply your theoretical yield by 0.75 to get a realistic figure.

Shading & Obstructions

Even small shadows—say from a gutter, skylight or nearby tree—can reduce panel output by 5–30 percent, depending on your inverter setup. It helps to map morning, midday and afternoon sun angles or use a simple online shading tool before finalising your design. Trimming branches or repositioning panels can go a long way toward keeping your system running at full tilt.

Next Steps

For a precise estimate tailored to your roof, Solar Hub uses satellite mapping and historical sunlight data. Just share your address and a few months of power bills, and you’ll get a custom design showing exactly how much sunshine your home can capture. Take control of your energy future and find out today!