A large scale ground mounted pv system changes the economics of a solar project in ways that catch installers out if they’ve only quoted residential rooftop work. The cost per watt drops as the system grows, but the structural engineering, foundation strategy, grid connection, and racking selection all shift with scale. Quote a 500 kW ground mount the way you’d quote a 10 kW rooftop and you’ll either lose the job or lose money on it.
This guide covers what actually changes as ground mounted solar power systems scale up, from 15 kW rural systems through to megawatt utility-scale arrays. We’ll walk through system sizing and economics, the structural and foundation decisions that matter at scale, how New Zealand’s grid-connection and consumption economics shape a project, and what to look for in racking built for large commercial projects.
Key takeaway
- Large scale ground mount economics improve with size: fixed costs spread across more kilowatts, so the cost per watt falls as the system grows.
- New Zealand has no STC-style upfront subsidy or feed-in tariff, so large commercial solar economics run on self-consumption against high retail power prices, plus commercial tax depreciation.
- Foundation strategy and structural engineering are the biggest cost and timeline levers on large arrays, not the panels or racking hardware.
- Racking with greater engineering spans reduces the number of posts and foundations per array, which cuts material cost and install time at scale.
- The Nova Ground Mount System is engineered for large scale projects, with ZAM-coated steel, 10° to 30° tilt, and both ground screw and concrete ballast foundations.
What counts as a large scale ground mounted pv system?
- Large scale ground mount economics improve with size: fixed costs spread across more kilowatts, so the cost per watt falls as the system grows.
- New Zealand has no STC-style upfront subsidy or feed-in tariff, so large commercial solar economics run on self-consumption against high retail power prices, plus commercial tax depreciation.
- Foundation strategy and structural engineering are the biggest cost and timeline levers on large arrays, not the panels or racking hardware.
- Racking with greater engineering spans reduces the number of posts and foundations per array, which cuts material cost and install time at scale.
- The Nova Ground Mount System is engineered for large scale projects, with ZAM-coated steel, 10° to 30° tilt, and both ground screw and concrete ballast foundations.
A 15kw ground mount solar system or 20 kw ground mount solar system sits at the small end. These are common for large rural properties, farms, and small businesses. A 15 kW array often ends up ground-mounted specifically because it needs 75 to 90 square metres of space that the available roof can’t provide. From there, systems scale up through mid-size commercial (100 kW), large industrial (250 kW and up), and utility-scale (1 MW and above).
The reason the band matters is that almost everything about the project (economics, grid connection, structural engineering, export limits) changes as you move up. A ground mounted pv system isn’t just a bigger version of the one below it.
System sizing and economics at scale
The single most important economic fact about large scale solar is that cost per watt drops as the system grows. Fixed costs (design, site setup, grid application, mobilisation) get spread across more kilowatts. A small commercial array carries a higher per-kilowatt cost than a large industrial one, and the gap is significant across the range from 20 kW to 250 kW and beyond.
Two caveats specific to New Zealand. First, ground mount costs more than rooftop for the same capacity, because the civil works, foundations, excavation, and mounting structure add cost that a roof install doesn’t carry. Second, and this is the big one for anyone comparing against Australian figures, New Zealand has no STC-style upfront subsidy. A comparable system carries a higher sticker price here than across the Tasman. What makes the numbers work is not a rebate but New Zealand’s high retail electricity prices: every kilowatt-hour the site consumes on-site is a kilowatt-hour it doesn’t buy at retail rates.
For a full breakdown of ground mount project costs across scales, see our guide to ground mount solar cost for installers.
| System size | Typical use case | What changes at this scale |
|---|---|---|
| 15 kW | Large rural home, small business; often ground-mounted for space | Standard grid connection; single-phase export limits may apply |
| 20 kW | Small commercial: farms, workshops, retail | Three-phase connection; lines company export approval |
| 100 kW | Mid-size commercial and industrial | Distributed generation approval under EA Part 6; export limits often negotiated |
| 250 kW+ | Large industrial, agricultural | Self-consumption economics dominate; export often capped by the lines company |
| 1 MW+ | Utility-scale | Grid connection agreement, PPA, and Electricity Authority processes |
Why self-consumption, not subsidy, drives New Zealand economics
This is the detail that catches out installers who’ve studied the Australian market. Australia has a hard incentive threshold at 100 kW (STCs below, LGCs above). New Zealand has no national rebate, feed-in tariff, or STC-style scheme at all. The economics run on a different engine entirely.
For a commercial ground mount in New Zealand, the value comes from three places. First and biggest is self-consumption: New Zealand has some of the higher retail electricity prices in the developed world, so every unit the business uses on-site during daylight displaces expensive grid power. Second is the retailer buy-back rate for exported surplus, typically in the 8 to 17 cents per kilowatt-hour range depending on the retailer, well below the retail price, which is exactly why self-consumption matters more than export. Third is commercial tax treatment: businesses can depreciate the solar asset and deduct interest, which materially lowers the real cost of the system.
The practical design consequence is that a large New Zealand commercial ground mount should be sized to the site’s daytime load, not to the available land. An oversized array that exports most of its generation at 8 to 17 cents is far less valuable than a right-sized array that offsets retail power. Grid connection and export also get more involved as the system grows: distributed generation above certain thresholds needs approval under the Electricity Authority’s Part 6 distributed generation rules, and the local lines company sets export limits that can cap how much surplus a large array is allowed to send back.
Nova’s field notes: size to the load, not the land
The most common sizing mistake we see on New Zealand commercial ground mounts is sizing to the available paddock rather than the site’s actual daytime consumption. Because there’s no subsidy rewarding raw system size and export buy-back rates are low, a big array that pushes most of its output onto the grid at 8 to 17 cents per kilowatt-hour is a poor investment compared to a right-sized array that offsets power the business would otherwise buy at full retail.
Before finalising the system size on a large commercial quote, get the site’s interval consumption data and model the self-consumption rate at different array sizes. Show the client where the returns flatten out. The right answer is usually the array that maximises self-consumption, plus a modest export margin, not the biggest array the land can hold. Sizing to the load is how New Zealand commercial solar quotes are won.
Structure and foundations are the real cost levers at scale
On a residential rooftop, the mounting hardware is a small fraction of the job. On a large ground mount, the structure and foundations become one of the biggest cost and timeline drivers. This is where installers make or lose margin on large projects.
Foundation strategy drives the timeline
The two foundation types (concrete ballast footings and ground screws) behave very differently at scale. Concrete needs 7 to 14 days to cure before structural loading, which on a large array can add weeks to the build. Ground screws are load-bearing immediately, which is why large commercial developers paying interest on construction finance tend to favour them where soil conditions allow. On a 500 kW array, the difference between a foundation type that lets you build continuously and one that forces a two-week cure window is real money. New Zealand’s varied soils, volcanic in the central North Island, rocky in the South Island, peat in low-lying areas, mean the foundation decision changes from site to site.
Engineering spans reduce post and foundation count
Here’s a large-scale factor that installers often overlook: the span between structural supports. A racking system engineered for greater spans needs fewer posts and fewer foundations to cover the same array area. On a large ground mount, that translates directly into fewer excavations or pile drives, less material, and faster installation. The Nova Ground Mount System is engineered with greater spacing spans than many competing systems, which is a meaningful advantage on large commercial projects where post and foundation count multiply quickly across the array.
Wind, seismic, and structural certification scale with exposure
Large arrays present a large surface to the wind, and structural demand under AS/NZS 1170.2 grows as the project scales and the site’s wind zone increases. New Zealand adds seismic design under NZS 1170.5, which matters more as the structure gets larger. For large projects in exposed or seismically active areas, the racking supplier must provide engineering documentation certifying the system for the specific wind zone, seismic classification, and terrain category. Our guide to the best solar ground mount system for New Zealand conditions covers the structural specifications that matter most.
What to look for in racking for large scale projects
Not all ground mount racking is built for scale. Five things separate a system that performs on large commercial projects from one that only makes sense for small arrays.
Greater engineering spans
As covered above, wider spans between supports mean fewer posts and foundations per array. On large projects, this is one of the biggest levers on both material cost and install time. Ask any supplier for their maximum span figures and compare them directly.
Foundation flexibility as standard
Large sites rarely have uniform soil, and New Zealand’s geology varies enormously across short distances. A racking system that supports both ground screw and concrete ballast foundations lets the installer adapt to soil variation across a big site without changing suppliers or product lines.
Corrosion resistance for a 25-year asset
Large commercial arrays are long-term assets, and corrosion failure across hundreds of structural members is expensive to remediate. Zinc Aluminium Magnesium (ZAM) coated steel offers significantly better corrosion resistance than standard galvanised steel, which matters in New Zealand where most large sites are within reach of coastal salt air.
Fast, repeatable installation
On a large array, every minute saved per module compounds across thousands of modules. Pre-fabricated holes, single-bolt rail clamps, module clamps with integrated earthing pins, and minimised component count all reduce on-site time. In a market where skilled installer labour is in short supply, install efficiency is often the difference between a profitable project and a marginal one.
Engineering and technical support
Large projects involve soil reports, structural calculations, wind and seismic certification, and grid connection paperwork. A racking supplier with a responsive engineering team reduces the risk of costly rework and helps installers navigate the complexity that comes with scale. On a large commercial project, this support is worth more than a small saving on hardware.
Nova’s field notes: quote the whole system, not just the panels
The most common mistake we see on large commercial ground mount quotes is under-costing everything that isn’t panels and inverters. On a rooftop job, the balance-of-system cost is modest. On a large ground mount, the civil works, foundations, structural steel, trenching, and grid connection can rival or exceed the cost of the modules themselves.
When you scope a large ground mount, build the quote from the ground up: geotechnical survey, foundation type and count, structural racking, trenching and cabling, grid connection, and commissioning. The projects that go wrong are almost always the ones where the installer treated the ground mount like a rooftop job with longer legs. It isn’t.
Build smarter large scale ground mount projects with Nova
At Nova, we’ve spent more than 15 years designing solar mounting systems that make installers’ lives easier and large projects more profitable. The Nova Ground Mount System is built around our “less is more” philosophy: fewer components, greater engineering spans, single-bolt rail clamps, module clamps with integrated earthing pins, and pre-fabricated holes for tilt from 10° to 30°. It supports module sizes up to 2190 x 1150mm in portrait orientation, both ground screw and concrete ballast foundations, and comes in Zinc Aluminium Magnesium coated steel for superior corrosion resistance. The system is snow load rated, structural stability tested, and corrosion resistance tested. It installs up to 30% faster than traditional ground mount systems, is backed by a 25-year warranty, and is supported by a technical team that works with you from soil report to commissioning.
Whether you’re quoting a 20 kW rural ground mount or scoping a multi-megawatt commercial array, speak to the Nova technical team for project-specific support, or explore the NOVA Ground Mount System specifications in detail.
Frequently asked questions
How much land does a large scale ground mounted pv system need?
As a rule of thumb, a ground mounted pv array needs roughly 1.5 to 2 hectares per megawatt of capacity, depending on panel efficiency, row spacing, and tilt angle. A 100 kW system needs roughly 1,500 to 2,000 square metres. Row spacing matters at scale: rows need enough gap to avoid inter-row shading, which increases with tilt angle and latitude. Steeper tilt means more shading and more land per watt.
At what size should I switch from rooftop to ground mount?
It’s driven by available roof space and site conditions, not a fixed system size. A 15 kW system often needs ground mounting because it requires 75 to 90 square metres of unshaded, well-oriented roof that many sites don’t have. For commercial sites with large, simple roofs, rooftop can make sense well above 100 kW. Ground mount wins when roof space is limited, roof condition is poor, or the site has spare land and the client wants optimal orientation and tilt.
Are there any subsidies for large commercial solar in New Zealand?
No. New Zealand has no STC-style upfront subsidy, no feed-in tariff, and no national rebate for solar. Commercial solar economics run on self-consumption against high retail electricity prices, retailer buy-back rates for exported surplus (typically 8 to 17 cents per kilowatt-hour), and commercial tax depreciation on the asset. This is why sizing a system to the site’s daytime load, rather than to the available land, is the key to a strong return.
What’s the payback period on a commercial ground mount system in New Zealand?
Most well-sized commercial solar systems in New Zealand see payback in the region of 5 to 10 years, depending on electricity prices, self-consumption rate, and the site’s load profile. Despite the higher upfront cost without a subsidy, high retail power prices do the heavy lifting that a rebate does in other markets. Payback is most favourable when the site consumes most of its generation on-site during daylight hours.
Does Nova supply racking for utility-scale ground mount projects?
Yes. The Nova Ground Mount System scales from small rural arrays up to megawatt-scale commercial and utility projects using the same engineered components. The greater engineering spans, foundation flexibility, and fast installation design are specifically valuable at scale, where post count, foundation count, and install time multiply across the array.
