The questions
worth asking first.

Installed cost usually falls between roughly $1.40 and $1.90 per watt for commercial-scale rooftop work, so a 100 kWp array typically lands somewhere between $140,000 and $190,000 before tax treatment. Smaller systems cost more per watt; large simple roofs cost less. Ground mounts and canopies cost more again because of the steel, foundations and civils.

Those are planning numbers, not a quote. Switchboard upgrades, roof strengthening, long cable runs, difficult access and consent requirements all move the figure, which is why we survey before pricing.

For a site with strong daytime load, an unshaded roof and a reasonable retail rate, simple payback commonly lands in the five-to-nine-year range, with the array warranted for thirty. Sites with low daytime use, heavy shading or a tight export limit take considerably longer.

The single biggest driver is self-consumption. Electricity you use as it is generated is worth your full retail rate including lines charges and GST; electricity you export is worth a fraction of that. A system sized to your load beats a bigger system sized to your roof.

There is no national feed-in tariff and no direct cash rebate for solar in New Zealand. What exists instead is a stack of financial supports that businesses can use together:

• Investment Boost. Introduced in Budget 2025, this allows a 20% upfront tax deduction on the cost of qualifying new assets available for use from 22 May 2025, in addition to normal depreciation on the remaining cost base.
• Depreciation. Solar generating equipment is depreciable property for tax purposes.
• Bank green lending. Most major New Zealand banks offer discounted finance for qualifying energy projects.
• EECA programmes. The Energy Efficiency and Conservation Authority runs targeted co-funding, though several programmes have closed or changed since Budget 2025 — availability needs checking at the time you apply.

We are not tax advisers. Confirm the treatment of any specific project with your accountant and check current programme status with EECA directly.

Buy-back rates are set by your electricity retailer, not by the government, and they vary widely. As a rule they sit well below what you pay to import, which is exactly why sizing to self-consumption matters more than maximising generation.

Rates and structures change, so it is worth asking your retailer for their current commercial buy-back terms before you finalise the array size — and worth asking two or three others at the same time.

A 640 W module measures 2382 × 1134 mm, so about 2.7 m² each. Allowing for walkways, setbacks and plant, budget roughly 5.5 to 7 m² of usable roof per kilowatt installed. A 100 kWp array therefore needs somewhere around 550 to 700 m² of clear, well-oriented roof.

Flat roofs with tilt frames need more area again because of row spacing to avoid self-shading.

In the southern hemisphere north-facing is optimal, but east and west arrays are far from useless — they produce less at midday and more at the shoulders of the day, which can actually match some load profiles better. South-facing planes at any meaningful pitch are generally not worth it.

Shading matters more than orientation. A single vent, flue or neighbouring building shading part of a string can cost far more than a suboptimal angle.

A bifacial module converts light striking the rear face as well as the front. The modules we specify have a bifaciality of 80% ±5%, meaning the rear face is 80% as efficient as the front when it receives light.

The gain depends entirely on what is underneath. On a light-coloured roof, gravel, concrete, a sealed carpark or pasture, the extra yield is real and worth designing for. On a dark membrane roof with modules mounted flush, it is close to zero. We model it site by site rather than assuming a blanket uplift.

Usually not, at least at first. On most commercial and rural sites the daytime load absorbs the majority of generation without any storage at all, and batteries add substantial capital cost for a marginal improvement in return.

Storage makes sense when you have a genuine resilience requirement — milk that will spoil, a coolstore that cannot warm, a process that cannot stop — or when your tariff has demand charges or a large evening peak worth shifting. We design the system battery-ready so you can add storage later without redoing the switchboard.

Modules carry a 12-year product warranty and a 30-year linear output warranty, guaranteed at no less than 87.4% of nameplate in year 30. Inverters are the shorter-lived component, typically with a 10-year warranty and often replaced once over the array’s life — something the financial model should account for from day one.

Maintenance is light but not zero: an annual electrical inspection, torque checks on clamps and fixings, thermal imaging of connections, and cleaning where soiling or bird activity justifies it. The critical item is monitoring, so an offline string gets noticed in days rather than at the next annual bill.

It depends on the installation. Many roof-mounted arrays on existing buildings are exempt, but ground mounts, carpark canopies and other structures generally require consent, and some roof installations do too depending on added load, the building and the council.

We identify the consent path during design rather than discovering it mid-build, and we manage the application where one is needed.

Connecting generation to the network is governed by Part 6 of the Electricity Industry Participation Code. We lodge a distributed generation application with your lines company — Vector across most of Auckland — who assess the connection and confirm any export limit that applies.

Network response times vary and can be the long pole in the programme, which is why we lodge as soon as the design is fixed rather than waiting for equipment to arrive.

They can limit it. On a constrained feeder your lines company may cap how much you are permitted to inject, or require zero export. That does not stop the project — it changes the optimal array size and means we design in export limiting or zero-export control at the inverter.

Because self-consumed energy is worth more than exported energy anyway, an export limit is usually less damaging to the business case than owners expect. It is a reason to size to load, not a reason to walk away.

It can, if the fixings and detailing are wrong. We select mounting systems appropriate to the cladding — including non-penetrating options where the roof warranty demands it — and detail penetrations so they stay watertight.

Where a manufacturer’s warranty is still live, tell us early and we will work to their requirements. Separately: if your roof has under about ten years of life left, replace it first. Removing and reinstating an array to re-roof underneath it is expensive.

Grid-tied electrical work in New Zealand must be carried out by an electrical worker registered with the Electrical Workers Registration Board, holding the appropriate registration class and endorsement for the work. On completion you should receive a Certificate of Compliance and an Electrical Safety Certificate.

Ask any installer — including us — for the registration details of the person who will actually be doing your work. It is a reasonable question and a good filter.

A standard grid-tied system shuts down. Anti-islanding protection is a mandatory safety requirement under AS/NZS 4777.2, so that the array cannot energise a line that a network crew believes is dead.

If you need power through an outage, that requires a hybrid inverter with battery storage and a backup circuit, designed in deliberately. It is a different system and a different budget — worth doing where an outage costs you real money, and worth skipping where it does not.