The Solar System Cost & ROI Calculator

This calculator tells you what solar would actually cost on your roof and how many years it takes to pay for itself, using real New Zealand numbers rather than a salesperson's best-case fantasy. Plug in your location, your roof, and your current power bill, and you'll get an honest estimate: a fully installed 5kW system in 2025 runs roughly $9,000 to $13,000 (around $1.70 to $2.20 per watt, per MBIE and current installer pricing), and for a household with decent daytime use, payback typically lands somewhere between 7 and 12 years. The tool exists to give you that number before anyone tries to sell you one.

What this does for you

Most online solar calculators are built by companies that want to sell you panels. They quietly assume you'll use every kilowatt-hour your roof produces, that your buy-back rate is generous, and that nothing ever goes wrong. Reality is messier, and the gap between the rosy estimate and your actual saving is where a lot of Kiwi homeowners get burned.

Our calculator is built the other way around. It starts from your real bill, applies the lines charges that actually exist on your network, and uses conservative self-consumption assumptions so the payback number you see is one you can trust. If anything, we'd rather under-promise. A nice surprise beats a nasty one when you've spent eleven grand.

What to have handy before you start

You'll get a far better estimate if you grab a few things first. None of it is hard to find.

• A recent power bill (ideally a winter one and a summer one). We need your average monthly spend and, if you can see it, your daily usage in kWh and your per-unit rate.
• Your location or postcode. This sets your sun hours and, crucially, your lines company, which changes the maths more than most people realise.
• Your roof direction and pitch. Roughly which way the main roof faces (north, east, west) and whether it's steep or shallow. A guess is fine; a site visit refines it later.
• A rough sense of when you use power. Home all day? Out until 6pm? This one input moves your payback by years.

How it works, in plain English

The tool runs three layers of calculation, and we're happy to show you all of them.

1. How much your roof will generate

We take your location and roof orientation and apply solar generation figures derived from NIWA sunshine-hour data. This is where local reality bites. A north-facing roof in Blenheim or Central Otago (Marlborough and the lower South Island get genuinely excellent clear-sky winter sun) will out-generate the same panels on a west-facing roof in cloudier Auckland or the West Coast. The calculator bakes that in rather than using a flat national average.

2. What that generation is actually worth to you

This is the part the sales calculators fudge. Every unit of solar power is worth two completely different amounts depending on what you do with it:

• Power you use yourself is worth the full retail rate you'd otherwise pay, often 28 to 38 cents per kWh depending on your retailer and region.
• Power you export to the grid only earns your buy-back rate, which from most retailers sits well below retail. Buy-back rates move around, so we point you to live figures rather than freezing a number that dates.

Because of that gap, two identical houses next door to each other can have wildly different payback periods. The one where someone's home running the heat pump, washing machine and dishwasher during daylight gets full value. The one that's empty until 6pm exports most of its generation for buttons. The calculator asks about your usage pattern precisely because it matters this much. If you want to dig into how export pricing works, we go deep on it here: the dynamic tariff and buy-back engine.

3. The bit nobody else shows you: your network's lines charges

Here's the genuinely hard-to-find insight. Your payback isn't just about generation and buy-back. It's shaped by how your lines company structures its charges, and they differ enormously across the country.

Networks like Vector (Auckland), Orion (Christchurch and Canterbury), Wellington Electricity, Aurora Energy (Dunedin and Central Otago) and Unison (Hawke's Bay) each split their pricing differently between fixed daily charges and variable per-kWh charges. Where a big chunk of your bill is a fixed daily line charge, solar can't touch that portion no matter how much you generate. Where the variable component is high, every self-consumed unit saves you more.

The calculator adjusts for your network's charging structure, which is why our payback figure for a Christchurch home can differ from an Auckland home with an identical system and identical bill. Most tools quietly ignore this. We think it's one of the most important numbers in the whole equation.

How this neutralises the margin games

Solar quotes are not standardised, and that's deliberate. The most common way a homeowner overpays is by judging a quote on the headline system size and the promised "savings" rather than the installed cost per watt and a realistic payback.

By giving you an independent installed-cost range and an honest payback before you talk to anyone, this tool changes the conversation. When an installer quotes you, you'll already know:

• Whether their price per watt sits in the fair range or well above it.
• Whether their savings claim assumes unrealistic self-consumption.
• Whether the payback they're promising matches the maths for your actual network and usage.

You don't need to become an expert. You just need a trustworthy number in your back pocket so the negotiation starts on your terms. If a quote's payback is years rosier than ours, ask them to show their working on self-consumption and buy-back. A good installer will happily walk you through it. A dodgy one will get vague.

The honest limits of this estimate

We'd be no better than the sales calculators if we pretended this was the final word. It isn't. It's a strong, conservative estimate, and a proper site visit will sharpen it.

The tool can't see your specific shading (a single chimney, a neighbour's tree, a two-storey house to your north can knock real generation down). It can't measure your exact roof area or whether your switchboard needs upgrading, which is a real cost on older homes. It uses regional averages for sunshine, and your actual microclimate varies. And it assumes the system is well designed and well installed, which is exactly why the people who do the work matter.

Treat the number as your reality check, not your final quote. It tells you whether solar is worth pursuing on your roof and what a fair deal looks like. The site visit fills in the rest.

What happens to your information

This matters, so we'll be plain about it. Using the calculator does not hand your details to anyone. You can run the numbers as many times as you like without giving us your name, your email, or your phone number. There's no catch and no obligation.

If you separately decide you'd like actual quotes, that's a different, deliberate step you choose to take. We never quietly on-sell your details to a list of installers who then ring you at dinnertime. When you ask for quotes, we match you with installers we've vetted ourselves, and we tell you exactly who they are. Nothing happens behind your back.

Why you can trust the numbers

The calculator is free because it's the front door to a service that's funded by vetted installers, not by you. When you choose to get quotes and go ahead with an installer we've matched you to, that installer pays us a referral fee. You never pay more for using us, and the fee doesn't change the price you're quoted. We're upfront about that because it's the only honest way to run this.

The assumptions behind the tool are built from NIWA sunshine data, MBIE energy pricing and installed-cost data, published lines-company pricing schedules, and current retailer buy-back rates. Where figures move (buy-back rates, finance offers), we point you to live tools rather than baking in numbers that go stale.

If you want to sanity-check whether your power costs even support solar before you start, or you'd like to understand the terms an installer throws at you, the plain-English glossary of NZ solar terms is a good companion. And if you're weighing up financing the system, the green finance qualifier will tell you what's actually available to you.

Frequently Asked Questions

Is the calculator really free?

Yes, completely. You can run it as often as you like without paying anything or handing over your contact details. We're funded by referral fees from vetted installers when you choose to proceed, and that never adds to your price.

How accurate is the payback estimate?

It's a solid, deliberately conservative estimate built on NIWA sun data, MBIE cost data and your local lines-company pricing. It can't see your specific shading or roof condition, so a site visit will refine it. If anything, we'd rather the real result beat our estimate than disappoint you.

Do I have to give my email or phone number to use it?

No. The calculator runs without any personal details. You only share contact information if you separately decide you want quotes, and that's entirely your call.

Why does my location change the result so much?

Two reasons. Your region sets your realistic sun hours (Marlborough and Central Otago genuinely beat cloudier areas), and your lines company structures its charges differently, which changes how much solar actually saves you. We factor both in.

Why does it ask when I'm home during the day?

Because power you use yourself is worth far more than power you export. A household home and using appliances during daylight gets full retail value from its solar; an empty house exports most of it at a lower buy-back rate. This single factor can shift your payback by several years.

Will solar wipe out my power bill completely?

No, and be wary of anyone who says it will. A grid-connected home still pays fixed daily lines charges and buys power at night and through the low-sun winter months. Solar meaningfully reduces your bill; it doesn't erase it.

What's a fair installed price in 2025?

For a typical 5kW system, roughly $9,000 to $13,000 fully installed, or about $1.70 to $2.20 per watt, based on MBIE data and current installer pricing. Use that as your yardstick when a quote lands.

What happens if I decide I want quotes?

You take a separate, deliberate step and we match you with up to three installers we've vetted ourselves. We tell you who they are, there's no obligation to proceed, and we never sell your details to anyone else.

What to Do Next

Run your numbers and take the estimate as your reality check, not gospel. It tells you whether solar stacks up on your roof and what a fair price looks like before anyone gets you on the phone.

Once you've got that figure, here's the sensible order of play:

• Note your fair price. Around $1.70 to $2.20 per watt installed is your yardstick. Anything well above that needs explaining.
• Get real quotes to compare against your estimate. If a quoted payback is years rosier than ours, ask them to show their working on self-consumption and buy-back.
• Check the finance angle if you're borrowing. The green finance qualifier shows what's genuinely available to you.

That's how you make a smart solar decision without being sold to. If you'd like the bigger picture first, start with our main guide to solar in Aotearoa.