Commercial Solar ROI Calculator

The Commercial Solar ROI Calculator is a free, no-signup tool built for Kiwi business owners, farmers, and commercial property managers who want a straight answer to one question: "Does solar actually pay back on my building?" You plug in your annual power spend, your roof or ground area, your commercial tariff, and your load profile (when you actually use electricity). The calculator then runs the numbers including the IRD 20% Investment Boost, standard depreciation, and a realistic commercial buy-back rate, and gives you a payback period, internal rate of return, and 25-year net benefit. It is built for ballpark clarity before you sign anything, not for tax filing. For the precise figures on your specific site, you still want a vetted installer quote, but this tool tells you whether the conversation is worth having.

What This Calculator Does

Most commercial solar conversations in New Zealand start with a salesperson's spreadsheet, which is a problem. Their job is to sell you a system; ours is to help you work out whether the maths makes sense before anyone walks onto your site.

This calculator models your specific situation using NZ-relevant inputs: your commercial tariff structure, your load profile (daytime-heavy operations like dairy sheds, irrigation, packhouses, workshops, and offices all behave very differently), and the available tax benefits. It gives you four headline numbers:

• Estimated system size (kW) suitable for your roof or paddock area
• Simple payback period in years
• 25-year net benefit after all costs and tax effects
• Internal rate of return (IRR) so you can compare against other capital projects

You will not get a precise quote. You will get the clarity to decide whether to spend an hour with an installer.

What You'll Need to Get the Most Out of It

Five minutes of prep makes the results twice as useful. Grab these before you start:

• Your last 12 months of power bills, or at least an annual kWh figure and total spend. If your billing is seasonal (irrigation, hort, dairy), this matters a lot.
• Your current commercial tariff structure: c/kWh for energy, fixed daily charges, and any time-of-use windows. Genesis, Mercury, Contact, Meridian, and Ecotricity all structure commercial deals differently.
• Approximate roof area or ground area available, in square metres. A back-of-napkin estimate (length x width) is fine.
• Roof orientation: north-facing is best, east/west loses around 10-15%, south is usually a no-go unless ground-mount is on the table.
• Your operating hours: when do you actually pull power? A dairy shed at 5am and 3pm has a different solar story to a packhouse running 9-to-5 in summer.

If you do not have your tariff details handy, your retailer's commercial team can email a current rate schedule within a day.

How It Works (In Plain English)

The calculator runs four layers of maths and stacks them together.

Layer 1: Generation modelling. Based on your region (we use NIWA solar irradiance data for the relevant zone) and roof orientation, we estimate how many kWh your system will generate per year per kW installed. Northland and Marlborough sit at the high end; Southland and Otago lower, but still very viable.

Layer 2: Self-consumption vs export. This is where load profile matters. A dairy farm with morning and afternoon milking might self-consume 50-65% of generation. A weekday-only office might self-consume 70-80%. A weekend-shut warehouse might only self-consume 30%. Self-consumed power is worth your full retail commercial rate (often 22-32 c/kWh including network charges). Exported power earns the commercial buy-back rate, typically much lower.

Layer 3: Tax effects. Commercial solar on a business asset qualifies for the IRD 20% Investment Boost (where applicable to your business structure and asset class) plus standard depreciation. We model both at your effective company tax rate to give you the true after-tax cost.

Layer 4: 25-year cash flow. We compare "do nothing and keep buying power" against "install solar, save power, claim tax benefits, sell exports". The difference, discounted appropriately, is your net benefit and IRR.

What We Do With Your Information

Nothing you do not explicitly ask us to do. Full stop.

The calculator runs in your browser. We do not require an email address, phone number, or business name to use it. Your inputs are not stored on our servers unless you choose to save your results by emailing them to yourself (optional, never required).

If you decide to take the next step and request matched quotes via our Get Quotes page, we share only what you provide on that form with up to three vetted installers in your region. We earn a referral fee if you proceed. We never sell your data, we never share it with anyone outside the matched installers, and we never put you on a marketing list. That is the deal.

Why You Can Trust This Tool

We built this calculator because the existing options in the New Zealand market are either installer-built (and naturally optimistic) or overseas tools that assume foreign tax credits and incentive schemes, none of which apply here.

The methodology draws on:

• EECA solar performance data and commercial energy guidance
• NIWA regional solar irradiance datasets
• IRD guidance on the Investment Boost and depreciation schedules for plant and equipment
• Electricity Authority tariff and network data
• Published commercial buy-back rates from Genesis, Mercury, Contact, Meridian, Octopus Energy NZ, and Ecotricity (reviewed regularly through our Solar ROI Calculator data pipeline)

NZ Solar Centre is independent. We do not sell panels, install systems, or own a stake in any installer. Our business model is referral fees from vetted installers when readers request quotes, which means our incentive is to give you accurate information so you trust us enough to come back. That is the entire model.

The calculator's assumptions are reviewed quarterly. Buy-back rates, finance rates (including the ASB rural solar finance options), and tax settings change, and so does the tool.

Frequently Asked Questions

How accurate is the calculator?

Within roughly 10-15% of a properly engineered installer quote, assuming your inputs are accurate. The biggest sources of error are self-consumption percentage (load profile) and roof shading, neither of which a calculator can perfectly model without a site visit.

Does it include the 20% Investment Boost?

Yes. When you tick "this is a business asset", the calculator applies the IRD 20% Investment Boost to the deductible cost in year one, plus straight-line depreciation thereafter. If you are unsure about eligibility, read our explainer on the IRD 20% Investment Boost for commercial solar or check with your accountant.

Will it work for a dairy farm or irrigator?

Yes. There is a preset load profile for dairy sheds (twice-daily peaks) and one for irrigation (heavy summer daytime). For a deeper dive on dairy specifically, see our guide on solar for dairy farms, milking sheds, and irrigation.

What if I'm leasing the building?

The calculator can still estimate the energy savings, but the tax benefits depend on who owns the asset. If you lease, you typically need landlord consent and either a power purchase agreement or a clear depreciation arrangement. Worth a conversation with your accountant before you commit.

Does it account for battery storage?

The base calculator focuses on solar PV alone, since most commercial sites get the strongest ROI from grid-tied solar without batteries. There is an optional "add battery" toggle that models lithium iron phosphate (LiFePO4) storage if your load profile makes it worthwhile, typically sites with significant after-hours consumption or demand charges.

Do I need to give my email to see results?

No. Results display on-screen immediately. Emailing yourself a PDF copy is optional.

What happens if I request quotes after using the calculator?

You'll be matched with up to three vetted installers in your region. They contact you within a few working days. You're under no obligation to proceed with any of them. We get paid only if you choose to engage. Your data is never sold or shared beyond those three installers.

Can I use this for a school, marae, or community building?

The energy modelling works fine, but the tax assumptions will not apply the same way. For not-for-profit and public sector buildings, treat the "tax benefit" output as zero and look at the simple payback figure instead. EECA has specific funding pathways for community buildings worth exploring.

What to Do Next

Use the calculator. If the numbers look promising (most commercial sites in NZ now show payback inside 5-7 years with the Investment Boost included), the logical next step is two or three matched quotes so you can compare real-world specs and pricing.

If you want broader context on the commercial side first, our Commercial and Rural Solar in NZ pillar covers the full picture: financing, tax, sector-specific case studies, and what to look for in a commercial installer.

If you are a residential customer who landed here by accident, head to our residential Solar ROI Calculator instead. The maths and the tax treatment are quite different.