100kW Commercial Solar: What It Costs and What It Returns
A 100kW solar system is the point where commercial solar stops being a utility bill reduction and starts being a capital asset with a return you can put in front of a board. It is also the last system size that qualifies for the upfront federal rebate, which makes it a genuinely important number rather than just a round one.
Here is what a 100kW system costs in Brisbane, what it generates, what it returns, and who it actually suits.
What a 100kW commercial solar system costs
A 100kW system installed in Brisbane runs to approximately $62,000 after the instant asset write-off. That covers roughly 240 Tier-1 415W panels and a 100kW industrial grid-tie inverter, plus mounting, cabling, switchboard work and commissioning.
For context against the smaller tiers we install:
| System size | Estimated cost | Annual saving | Typically suits |
|---|---|---|---|
| 30 kW | $22,000 | up to $7,800 | Small offices and retail |
| 50 kW | $34,500 | up to $13,500 | Warehouses and factories |
| 100 kW | $62,000 | up to $28,000 | Large-scale industrial sites |
Note that cost does not scale in a straight line. Doubling from 50kW to 100kW adds about 80% to the price, not 100%, because the fixed costs — design, approvals, scaffolding, project management, the crew being on site at all — spread across more panels. Larger systems are cheaper per kilowatt, which is one reason it rarely pays to undersize.
The figures above assume the instant asset write-off applies. Eligibility and thresholds change between financial years, so confirm your position with your accountant before treating the after-tax number as final.
What a 100kW system generates
Brisbane has one of the better solar resources of any Australian capital. A well-oriented, unshaded 100kW system here will generally produce in the region of 140 to 150 MWh a year — roughly 380 to 410 kWh on an average day.
That is a generalisation, and the spread around it is wide. Orientation, roof pitch, shading from adjacent buildings or plant equipment, panel soiling and the summer heat derate all move the number. A north-facing array on a clean warehouse roof sits at the top of that range. A split east–west array on a shaded inner-city site sits well below it.
East–west splits are not automatically worse, incidentally. They flatten the generation curve across the day rather than peaking at noon, which often matches a business load profile better than a north-facing array does.
What it returns, and how quickly
At the top of the range, a 100kW system saves up to $28,000 a year. Against $62,000 installed, that is a payback inside two and a half years, and commercial payback across our installs generally lands between 2.4 and 3.2 years.
The reason for that range is the single most important thing to understand about commercial solar: the return depends on how much of your generation you use on site, not on how much you generate.
Electricity you consume yourself offsets your retail tariff — the full rate you pay per kilowatt hour. Electricity you export earns a feed-in tariff, which for commercial customers is a fraction of that. A business consuming 90% of its own generation and one consuming 50% will see very different returns from identical systems on identical roofs.
This is why any credible commercial proposal starts with your interval data rather than your roof. The meter data tells us what your load actually looks like hour by hour, which determines the right system size and the payback figure you can rely on.
The 100kW threshold matters more than people expect
One hundred kilowatts is the cut-off for small-scale technology certificates. At or below 100kW, a system is eligible for STCs — claimed upfront and applied as a discount to your installed price. That is the rebate already reflected in the figures above.
Above 100kW, systems move into large-scale generation certificates instead. LGCs are created annually based on actual generation rather than paid upfront, which changes the shape of the investment: less capital relief on day one, an ongoing revenue stream afterwards, and more administration to claim it.
Neither is better in the abstract. But it does mean the economics either side of 100kW are not a smooth curve, and a system specified at 105kW without that being a deliberate decision is usually a mistake. If your load genuinely justifies more than 100kW, it is worth modelling both a 99kW system and the larger option properly before committing.
Who a 100kW system actually suits
A 100kW array needs roughly 500 to 550 square metres of usable roof. In practice it suits:
- Manufacturing and processing sites running plant through the day, where load is high and steady and self-consumption is naturally close to 100%
- Cold storage and food processing, where refrigeration load runs continuously and peaks with ambient temperature — which is also when solar output peaks
- Large warehouses and distribution centres with substantial roof area and daytime picking, packing and charging loads
- Multi-tenanted commercial buildings where common-area and HVAC load runs through business hours
It suits sites with high daytime consumption far better than sites with high total consumption. A business using most of its power overnight will get a poor return from a large array without storage, however big its bill.
Grid connection and approvals in South East Queensland
A system of this size requires network approval from Energex before installation, and the application process is a real part of the project timeline rather than a formality. Depending on your location and the capacity available in the local network, approval can come with export limiting conditions — a cap on how much you are permitted to send back to the grid.
Export limiting is less painful than it sounds for a site with strong daytime self-consumption, because you were not relying on export revenue anyway. It matters a great deal for a site that expected to export heavily. Either way, it is something to establish early, because it can change the optimal system size.
Getting a number you can actually use
The figures in this article are indicative, and they are honest indicative figures rather than headline ones. But no article can tell you what your site will return, because that depends on your roof, your load profile and your tariff.
What we do is read your interval data against your current tariff, design to your actual consumption pattern, and give you a fixed-price proposal setting out system size, projected generation, expected offset against current consumption, and a payback calculation built from your numbers rather than an average.
If you want to see what that looks like for your site, see our commercial solar service or read the full commercial cost breakdown. For an overview of commercial returns across system sizes, our guide to commercial solar costs, ROI and payback in Brisbane covers the wider picture.
