Terms

Every figure on Rafter is an estimate from our model. That includes generation, savings, payback, system size and price. It is not a quote, an offer or financial advice.

Real results depend on things we can't see, such as your roof's condition, wiring, shading, your power plan and how you use power. An installer would need to check your home before giving you a price. Get your own advice before you spend money.

These are the main assumptions behind every estimate, with their sources.

• Sunshine. 10 years of hour-by-hour weather for your location (2014-2023) from PVGIS, including hills on the horizon. If PVGIS can't be reached, we use a simpler model and say so.
• Your roof. Measured from LINZ LiDAR where we can, or estimated from the building outline. Panels keep a 0.45 m gap from roof edges.
• Power prices. We start from 34c a kWh, including GST. Where MBIE's Quarterly Survey of Domestic Electricity Prices (February 2026) has a figure for your area, we scale this to match. Time-of-use plans are examples, not a retailer's real plan.
• Daily charge. $2.07 a day including GST. That's the most a low-user plan can charge from 1 April 2026, under the Low Fixed Charge regulations. Solar doesn't change it, so it doesn't change your savings. We use it to work out your power use from a bill amount.
• Solar you sell back. 12.5c a kWh. That's the middle of retailers' standard buy-back rates listed on Consumer NZ's Powerswitch in September 2026. Those rates ran from 8c to 18c, excluding GST.
• System price. A typical NZ installed price for the system's size, including GST, from EECA: $8,500 for 3 kW, $11,500 for 5 kW, $20,000 for 10 kW. We draw straight lines between these. A battery adds $1,000 per kWh, from EECA's examples. Installers' prices vary. On an installer's own page, the price uses that installer's prices for their panels, inverter, installation and batteries.
• Self-consumption. Hour by hour, we match your solar output against a typical NZ pattern of home power use, scaled to your yearly use. Solar you use yourself saves what you would have paid for that power. Solar you don't use is sold back. A battery stores spare solar for later. We don't know your real pattern of use, so this is an estimate too.
• Your power use. From your bill or yearly use if you give it. Otherwise 7,000 kWh a year for a typical home, or 2,600 kWh plus 1,300 kWh per person. These are our typical figures, not measurements.
• Losses. We take off 14% for wiring, dirt and other losses, which is PVGIS's standard figure. The inverter is 96.5% efficient. Hot panels make less power, and we allow for that. Shading from trees and buildings is modelled from LiDAR where we can, with a 2% allowance for what it can't show. Otherwise we allow 5%.
• Degradation. Panels lose 0.5% of their output each year. This is the median rate found in NREL's review of field studies (Jordan and Kurtz, 2013).
• Price escalation. We assume power prices rise 2% a year. Real prices may rise faster or slower.
• Payback and lifetime. Payback is when savings add up to the price. We count savings over 25 years, and judge a battery over 12 years. We don't include interest, maintenance or replacing the inverter.
• CO₂ avoided. 0.0787 kg CO₂-e for each kWh of solar, the average for NZ grid power in 2025 (Ministry for the Environment).

• Elevation (LiDAR), aerial photos, building outlines, addresses and property boundaries: Toitū Te Whenua Land Information New Zealand (LINZ). Sourced from LINZ. CC BY 4.0. Some LiDAR surveys are licensed to LINZ by councils, who are named with each survey.
• Aerial basemap: LINZ Basemaps, © Toitū Te Whenua LINZ, CC BY 4.0. See the LINZ copyright statement.
• LiDAR point clouds for the same surveys, served by OpenTopography. CC BY 4.0.
• Solar data: PVGIS © European Communities, 2001-2026, from the EU Joint Research Centre. Reused with acknowledgement.
• Address search and some building outlines: © OpenStreetMap contributors, under the Open Database Licence. Address search by Photon (komoot).
• Prices and factors: EECA (system prices), MBIE (power prices), Consumer NZ Powerswitch (buy-back rates), the Low Fixed Charge regulations (daily charge) and the Ministry for the Environment (emissions). We use their published figures; they don't endorse Rafter.

We work hard to make our estimates useful, but we don't promise they are accurate, complete or right for your home. The data we use can be out of date or wrong.

As far as the law allows, we are not liable for any loss from using Rafter or relying on its estimates. This includes lost savings and money spent on a solar system.

Nothing in these terms limits your rights under the Consumer Guarantees Act 1993 or the Fair Trading Act 1986, or any other right the law says can't be limited.

We may change these terms. The date at the top shows the latest version. New Zealand law applies.

Questions? Email hello@rafter.co.nz. See also our privacy notice.