Plug-in solar payback calculator
Pick your city, the size of kit and what you pay for power. The answer is an estimate from the assumptions listed under it, so change any of them to match your home.
An estimate from the stated assumptions, not financial advice. Your roof, shade, bill and habits change the answer.
Not yet, expected around mid-2027, no date set: follow it on the tracker. The calculator works the same today as it will on launch day; only the kit prices will be real then.
What the answer rests on
- Kit size starts at 800 W, the inverter limit in Germany and the UK. New Zealand has set no limit yet.
- Price starts at $1,500, the figure Labour's SolarSaver page and MySolarQuotes both give for a two-panel kit (Labour, MySolarQuotes). Nothing is on sale here yet.
- Sun comes from PVGIS, the European Commission's solar model, for panels facing north, scaled down to NIWA's measured sun in each city (1991-2020) where NIWA's stations saw less (PVGIS, NIWA). It allows 14% for the inverter, cables and dirt. Shade from trees, a neighbour or the balcony above isn't in it.
- Power price starts at 35c a kWh. MBIE's 42.1c national average for August 2026 (MBIE) includes daily charges, which solar doesn't cut, so we start lower. Use the per-kWh rate on your bill.
- Self-use starts at 70%. HTW Berlin's simulator puts an 800 W kit at 61 to 88% in homes using 3,000 to 5,000 kWh a year (HTW Berlin). Lower it if nobody is home in the day.
- Buy-back starts at 0c, because nobody has said plug-in kits will be paid for spare power. Retailers pay rooftop owners about 8 to 17c a kWh (MySolarQuotes).
- No price rises, no wear on the panels, no interest on the money. It's a simple payback, not a forecast.
Every city with the same kit
An 800 W kit at $1,500, 70% used at home, 35c a kWh. The sunniest cities aren't always the quickest: the further south, the less a railing-hung panel loses against a tilted one, because the sun sits lower.
| City | kWh a year, tilted | Saved a year | Payback, tilted | Payback on a railing | Average bill c/kWh |
|---|---|---|---|---|---|
| Auckland2,121.8 sunshine hours a year | 1,095 | $268 | 5.6 yrs | 8.7 yrs | 41.3Vector Auckland |
| Hamilton2,033.8 sunshine hours a year | 1,070 | $262 | 5.7 yrs | 8.8 yrs | 39.8WEL Networks |
| Tauranga2,401.5 sunshine hours a year | 1,138 | $279 | 5.4 yrs | 8.3 yrs | 45.0Powerco Tauranga |
| Wellington2,094.1 sunshine hours a year | 1,080 | $265 | 5.7 yrs | 8.6 yrs | 37.2Wellington Electricity |
| Nelson2,497.1 sunshine hours a year | 1,128 | $276 | 5.4 yrs | 7.9 yrs | 38.4Nelson Electricity |
| Christchurch2,128.4 sunshine hours a year | 1,066 | $261 | 5.7 yrs | 8.2 yrs | 38.6Orion |
| Dunedin1,775.5 sunshine hours a year | 961 | $235 | 6.4 yrs | 8.9 yrs | 42.5Aurora Dunedin |
| Invercargill1,764.6 sunshine hours a year | 976 | $239 | 6.3 yrs | 8.7 yrs | 39.0Electricity Invercargill |
Sun from PVGIS and NIWA, read 21 October 2026; bills from MBIE's survey of 15 August 2026, whole bill over 8,000 kWh a year, incl. GST.
How it works it out
Power a year = kit size in kW × the city's kWh per kW. Saved a year = the share you use × your power price, plus the rest × any buy-back rate. Payback = price ÷ saved a year. With the defaults in Christchurch that is 0.8 × 1,332 = 1,066 kWh, of which 70% saves $261 a year, so $1,500 takes 5.7 years.
Get one email the day it is legal
We watch the Ministry for Regulation, the Electricity Authority and the Beehive every week. When plug-in solar is legal, or the standard it needs is published, we write once with what changed and which kits qualify.
More guides
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What plug-in solar is
One or two panels, a small inverter and a cable to a normal socket.
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Why it is banned now
A 2012 prohibition notice and one clause in AS/NZS 4777.1.
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Cost and savings
Kit prices overseas, what NZ sellers expect to charge, and payback by city.
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Plug-in batteries
What a battery adds, what it costs, and what the rules say so far.
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Renters and body corporates
Why this matters most to people who can't put panels on a roof.
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Plug-in or rooftop
Size, price, payback and who each one suits.
Sources
- PVGIS 5.3, PVGIS-ERA5 database (2005-2023), European Commission Joint Research Centre.
- Climate normals 1991-2020: sunshine hours and daily global radiation, NIWA.
- Quarterly Survey of Domestic Electricity Prices, 15 August 2026, MBIE, 15 August 2026.
- Stecker-Solar-Simulator, HTW Berlin.
- Solar power buy-back rates NZ, MySolarQuotes, 16 October 2026.
- SolarSaver, Labour Party.
- What's all the hype about plug-in solar (aka balcony solar)?, MySolarQuotes, 17 August 2026.