Commercial Solar ROI Calculator

This calculator works out the real return on a commercial solar system for your business, including the two things most generic tools quietly ignore: the 20% Investment Boost deduction introduced in Budget 2025, and ordinary depreciation on the rest of the asset. For a typical commercial installation, those tax mechanics can pull the effective net cost down meaningfully in year one, which is often the difference between a payback near 8 to 9 years and one closer to 5 to 6 years. Punch in your roof or ground area, your daytime load, and your commercial tariff, and you get a grounded estimate of capital cost, annual savings, after-tax payback, and lifetime return, using current MBIE and Electricity Authority figures rather than guesswork.

What this tool does for your business

Residential solar maths is fairly simple. Commercial solar is not, because three things change the answer that a home calculator never touches: your tax position, your load profile, and your commercial tariff structure.

A business buying a solar system can usually claim the new 20% Investment Boost as an immediate deduction on the asset, then depreciate the remaining 80% under the normal regime. If your business is paying tax at the 28% company rate, that first-year deduction has real cash value. We fold that straight into the payback calculation so you see the after-tax number, not a misleading sticker figure.

We also size the system to your daytime electricity use, because a commercial system that exports half its output to the grid at a low buy-back rate earns far less than one sized to be consumed on site during business hours.

What to have handy before you start

You'll get a far better estimate with a few real numbers in front of you. Dig out:

• A recent power bill (ideally 12 months of usage). We want your annual kWh and, critically, your per-kWh rate including lines and levies, not just the headline energy price.
• Your daytime load pattern. Roughly what proportion of your power gets used between about 8am and 5pm? A factory or dairy shed running all day is very different from an office that empties at 5pm.
• Usable roof or ground area in square metres. As a rule of thumb, every 1kW of panels needs about 5 to 6 square metres of unshaded space.
• Your region or network. Sun hours and lines charges both vary by location.
• Your tax position. Whether you're a GST-registered company on the 28% rate, a trust, or a sole trader changes the deduction maths.

Don't have all of it? That's fine. The tool uses sensible NZ defaults so you can still get a ballpark, then refine it later.

How it works, in plain English

Under the bonnet, the calculator runs four linked steps.

1. It sizes the system to your space and your load

From your available area it works out the maximum array you could fit, then checks that against your actual daytime consumption. There's no point installing 100kW if you can only use 40kW during daylight and your buy-back rate is modest. We bias the recommendation toward self-consumption, because power you use yourself is worth your full retail rate, while exported power earns only the buy-back rate your retailer offers.

2. It estimates generation using real NZ sun data

Annual generation is modelled on NIWA solar irradiance figures for your region. A well-oriented system in Blenheim, Nelson or Central Otago will out-generate the same system on the West Coast by a noticeable margin, and the tool reflects that rather than using one flat national number.

3. It calculates capital cost using current installed pricing

Commercial systems benefit from economies of scale. Where a small residential job sits around $1.70 to $2.00 per watt installed (per MBIE and installer pricing through 2025), larger commercial arrays commonly land lower per watt because the fixed costs spread across more panels. We apply a commercial pricing band by system size.

4. It applies the tax mechanics, then works out payback

This is the part the home calculators skip. The tool applies the 20% Investment Boost as a first-year deduction, depreciates the remaining capital cost, and converts those deductions into a cash benefit at your tax rate. It then nets that against the upfront cost to produce an after-tax payback period and a lifetime return over the 25-year-plus life of the panels.

If you want the detail on how the Investment Boost itself works, including the eligibility conditions and how the deduction is claimed, we walk through it properly over here: the IRD 20% Investment Boost for commercial solar.

The one thing most businesses get wrong

Here's the insight worth more than the rest of the page combined: for commercial solar, your tariff structure usually matters more than your roof.

Many commercial connections pay demand charges or capacity charges on top of per-kWh energy. Solar trims your energy charge, but it does very little for a demand charge unless it's shaving your actual peak. Two identical businesses with identical roofs can get wildly different paybacks purely because one is on a flat energy tariff and the other is on a time-of-use or demand-based commercial tariff.

This is also why a milking shed often pencils out beautifully while an office struggles. The shed's biggest loads (vacuum pumps, milk cooling, water heating) run during daylight, so almost every solar kWh is self-consumed at full retail value. We dig into that specific case in our piece on solar for dairy farms, milking sheds and irrigation. The tool asks for your daytime load proportion precisely because it's the lever that moves your return the most.

The honest limits of this estimate

We'd rather you trust the number than be wowed by it, so here's what the tool cannot do:

• It can't see your roof. Shading from neighbouring buildings, plant rooms, vents, or pitch and orientation all affect output. A site visit refines this.
• It models a typical tariff, not your exact contract. If you're on a negotiated large-customer rate or have demand charges, your real figure needs your actual bill.
• Tax outcomes depend on your circumstances. The Investment Boost and depreciation have eligibility conditions. Confirm the treatment for your specific entity with your accountant before you commit.
• It assumes no battery unless you add one. Storage changes the maths, sometimes for the better with demand charges, sometimes not.

Treat the output as a solid, well-grounded estimate to decide whether solar is worth a serious look for your business. It is not a quote.

What happens with your information

Plainly: the calculator runs in your browser. You can get your estimate without handing over a single contact detail.

If you choose to go further and ask us to line up quotes, here's exactly how that works. We pass your details to up to three installers we've vetted ourselves, and only those three. We do not sell your information to a pool of random companies, we do not add you to marketing lists, and you'll never get a wall of cold calls because your number got passed around.

How are we funded? When an installer we've referred wins your work, they pay us a referral fee. You pay nothing for the introduction, and the fee doesn't get loaded onto your quote. We only make money when the match actually works for you, which keeps us honest about who we put in front of you. You're never under any obligation to proceed.

Why you can trust the numbers

Every figure in the tool traces back to a named New Zealand source:

• Generation uses NIWA regional solar irradiance data.
• Installed pricing bands reflect MBIE data and current NZ installer quoting through 2025.
• Tariff and buy-back assumptions draw on published rates from NZ retailers and Electricity Authority market data.
• Tax mechanics follow the Investment Boost and depreciation rules as set out by IRD.

We update the assumptions as rates move. It's free to use because our job is to help you make a good decision; the business model only works if you trust us, and trust comes from accurate numbers, not optimistic ones.

Frequently Asked Questions

Is the calculator really free?

Yes. There's no charge to use it and no charge to receive quotes. We're paid a referral fee by installers only if you go ahead with one we've matched you to, and that fee is never added to your price.

Do I have to give my contact details to get an estimate?

No. The estimate runs without any personal information. You only share details if you decide you want quotes.

How accurate is the payback figure?

It's a well-grounded estimate based on real NZ sun data, current pricing and the tax rules. The two things that can shift it are your exact tariff (especially if you have demand charges) and your roof's shading and orientation. A site visit and your real bill tighten it up.

Does it really include the 20% Investment Boost?

Yes. It applies the Investment Boost as a first-year deduction and depreciates the remaining cost, then converts those deductions to a cash benefit at your tax rate. Confirm the exact treatment for your entity with your accountant, since eligibility depends on your circumstances.

Will my business cover its whole power bill with solar?

Almost certainly not, and any installer who promises that is overselling. Solar offsets your daytime usage; you'll still draw from the grid at night and on dull winter days. The aim is a strong return on the portion you can realistically displace, not a zero bill.

What if I'm on a network with demand charges?

That changes the maths, sometimes significantly. Solar alone often does little for a demand charge unless it shaves your actual peak, which is where battery storage can earn its keep. Flag your tariff type in the inputs and treat the output as conservative until your real bill is reviewed.

Is this useful for a farm rather than a building?

Very much so. The tool handles both roof and ground-mount area. Farms often have excellent daytime self-consumption from irrigation and shed loads, which tends to produce strong returns. If finance is part of the picture, it's worth understanding the rural lending options, which we cover in our piece on ASB rural solar finance.

How is the commercial tool different from the home one?

The home version doesn't model company tax, the Investment Boost, depreciation, or commercial tariffs. If you're a homeowner, you'll get a better answer from our residential solar cost and ROI calculator instead.

What to do next

Run your numbers through the tool, then sense-check them against the bigger picture before you talk to anyone. Our overview of commercial and rural solar in New Zealand covers the system choices, the tariff traps and the tax detail in full, so you walk into any installer conversation knowing exactly what good looks like.

A sensible order of play: get your ballpark estimate here, pull together 12 months of your actual usage and your real per-kWh rate, have a quick word with your accountant about how the Investment Boost lands for your entity, then get a couple of proper quotes off the back of a site visit. That sequence keeps you in control and stops you signing anything before the numbers are solid.