Using the details you provide — such as your location, roof orientation, household electricity use, number of solar panels and optional battery storage — the calculator estimates your potential savings, payback period, and emission reductions.

Results are indicative only and depend on real-world factors such as regional pricing differences, exact solar design details future electricity prices. To keep the tool simple, several assumptions are applied (outlined below).

Energy Consumption

If your electricity use isn’t known, the calculator uses average household consumption for your region, based on the Electricity Authority’s Residential Consumption League Table (2024).

Solar Generation

Expected annual generation is calculated using regional PV output data from The Global Solar Atlas, adjusted for roof direction and tilt using OpenSolar modelling.
Panel performance is assumed to degrade by 1% in the first year and 0.375% per year thereafter.

Self-Consumption

Self-consumption — how much of your solar energy you use directly — depends on your household’s energy profile and whether you include a battery.
This is estimated using regression analysis on OpenSolar models for a range of system sizes.

Solar System Cost

System installation cost is based on an average of $2.27 per watt, and batteries at $1,250 per kWh, as reported in the 2024 My Solar Quotes annual survey.

Electricity Cost

Electricity price assumptions are drawn from national datasets and industry guidance:

• Daily fixed charge: $1.20 per day (Electricity Authority regional power price modelling)

• Import tariff: A flat $0.34 per kWh (MBIE Electricity Price Modelling)

• Inflation rate: 3.5% per year (as per SEANZ Fair Pricing Assumptions)

• Export rate: flat $0.12 per kWh, not adjusted for inflation (also as per SEANZ Fair Pricing Assumptions)

These inputs are used to estimate bill savings and the financial payback period.

Emissions

Considering upfront emissions — materials, manufacturing, and transport through to disposal/recycling — is an important part of responsible solar design. Yet, accurate estimates for these embodied emissions are difficult to find in a New Zealand context. The goal isn’t just to install solar, but to design systems that genuinely account for their full lifetime environmental impact.

Solar reduces emissions by lowering the amount of electricity you draw from the national grid. Although Aotearoa New Zealand’s grid is largely renewable, fossil fuel generation is still used during periods of high demand.

Grid electricity emissions are based on Ministry for the Environment’s Measuring Emissions: A Guide for Organisations (2025).

The upfront emissions are determined using per-kW and per-kWh emission factors derived from a life-cycle assessment of SolarZero’s large-scale virtual power plant (VPP) systems conducted by researchers at Victoria University of Wellington:

Pimentel Pincelli I, Hinkley J, Brent A. Life cycle assessment of a virtual power plant: Evaluating the environmental performance of a system utilising solar photovoltaic generation and batteries. Renewable Energies. 2024; 2(2). doi:10.1177/27533735241285428

By combining upfront emissions with operational savings, the calculator estimates both the upfront carbon footprint of the system and its emissions payback period — the time required for avoided grid emissions to offset the system’s manufacturing footprint.

It is worth noting that you cannot ‘payback’ emissions, so sizing a system correctly and using high quality components to ensure longevity is very important.

Component Lifetimes

The calculator assumes the following equipment lifetimes:

• Panels: 30 years

• Inverter: 15 years (replacement cost ≈ $2,500)

• Battery: 15 years (replacement cost ≈ $1,250 per kWh)