Commercial Solar Calculator — IRR, NPV & Payback for 10–500 kW Systems | Solar Proof
Commercial & Industrial
Just a home? Use the residential calculator (5–20 kW · 25-yr net savings) →

The Commercial Solar Calculator for serious capex decisions.

Built for facility managers, finance teams and CFOs evaluating a 10–500 kW rooftop solar project. Get IRR, NPV, payback period, peak-demand reduction and STC/LGC eligibility in under 60 seconds — then request a tailored commercial quote.

IRR & NPV Peak-demand reduction STC / LGC eligibility 3-phase aware CO₂ reporting

Your business & site

01

Used for solar-resource lookup

~6 m² needed per kW of solar

Electricity usage

02
Monthly electricity bill $3,500
$500$10,000$20,000+
My bill is higher — enter exact amount →
Consumption between 9am – 3pm 75%

Drives self-consumption rate. 75% is typical for offices/factories.

"TOU + Demand" lets us model peak-demand reduction savings.

Site & system options

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Prefer STC upfront discount (cap at 99 kW) Most installers recommend staying just under 100 kW so the rebate comes off your invoice — typically much better than LGC monetisation over 5 years at current spot prices.
Already have solar on site? We'll size around your existing system and recommend top-up + battery

DC capacity of the panels on your roof

Include a new battery Federal Cheaper Home Batteries Program rebate applied automatically

Commercial-grade lithium. Federal rebate caps at 50 kWh usable.

For sizing context only — not used in financial calc.

Your results

Fill in the form and click Calculate commercial ROI

You'll see IRR, NPV, payback, peak-demand reduction and STC/LGC eligibility — plus a one-click commercial quote request.

How commercial solar economics differ from residential

A commercial solar project is a capex decision, not a household purchase. CFOs evaluating a 30 kW office rooftop or a 250 kW manufacturing array care less about "year-1 savings" and more about IRR, NPV, payback period, and peak-demand reduction. The Solar Proof commercial calculator surfaces all four, alongside the technical sizing details your installer will quote against.

Commercial tariffs are also structurally different. A residential customer typically pays a single retail rate near 34 c/kWh; a business pays roughly 22–28 c/kWh on energy plus a per-kVA demand charge on TOU+demand tariffs. Solar reduces both the energy and demand components — and the demand-charge saving is often the largest single line item for a high-load commercial site.

Daytime usage profile matters too. Where a residential household self-consumes only ~35% of generation, an office running 9–5 self-consumes 70–85%. That changes the maths: more energy is offset at the retail rate (high value) and less is exported at the feed-in tariff (low value). Our calculator lets you dial this in directly.

STC vs LGC: what your system size means for rebates

Australia treats small-scale and large-scale renewable systems under two different certificate schemes. The calculator flags which one applies to your sizing:

Under 100 kW — Small-scale Technology Certificates (STCs). A deemed up-front incentive calculated as postcode rating × system size × deeming years. Typically passed through by your installer as a point-of-sale discount (~$300–$400 per kW installed depending on postcode and install year). See our STC Calculator for an exact count.

100 kW and over — Large-scale Generation Certificates (LGCs). Paid on actual generation: one LGC per MWh, traded at variable prices (recently $30–$50). LGCs accrue each year for the eligible life of the project rather than being deemed up front. Most commercial buyers monetise LGCs via an annual sale or aggregator.

The system size at which it makes financial sense to cross the 100 kW threshold depends on your roof area, load profile and tariff. The calculator surfaces both sides so you can see the trade-off in your specific numbers.

Peak-demand reduction — the under-counted saving

On a typical commercial TOU+demand tariff, your monthly bill has three components: energy use (c/kWh), peak demand (per kVA, measured as the highest sustained draw in the billing period), and a fixed supply charge. Solar reliably attacks the first; for many sites, it also significantly reduces the second.

The amount of peak-demand reduction depends on the overlap between your solar generation curve and your site's peak-demand curve. For most daytime-running businesses the overlap factor is around 50–70%; we use 60% as a mid-range default. A 100 kW AC solar inverter, at a power factor of 0.9 and 60% peak overlap, will reduce billed kVA by roughly 54 kVA — a saving that compounds with rising network charges every year.

If your business operates 24/7 (e.g. cold storage, hospitality, healthcare), a battery can shift that benefit into night and shoulder periods. The calculator's battery toggle models this within the federal Cheaper Home Batteries Program rebate framework.

Commercial solar calculator FAQ

How is the commercial solar calculator different from the residential one?

It models system sizes from 10 kW to 500 kW with commercial-grade cost assumptions, applies a commercial electricity tariff (~25 c/kWh vs ~34 c/kWh residential), uses commercial-typical self-consumption profiles (70–85% vs ~35% residential), and reports IRR and NPV in addition to payback — the metrics CFOs and finance teams use when approving capex.

When does my system get STCs vs LGCs?

Systems with a nominal capacity of less than 100 kW are eligible for Small-scale Technology Certificates (STCs). 100 kW and larger systems use Large-scale Generation Certificates (LGCs), which are paid on actual annual generation rather than a deemed up-front amount. The calculator flags which scheme applies to your sizing.

What about peak-demand reduction?

For TOU + demand-charge tariffs (very common for businesses) the peak-demand component of your bill can be substantial. Solar reduces peak demand when generation overlaps your peak usage — typically ~60% overlap for daytime-running businesses. The calculator estimates the kVA reduction; your retailer's actual demand-charge formula determines the dollar saving.

How accurate is the IRR / NPV?

Indicative only. The calculator assumes 3% annual electricity inflation, 0.5%/year panel degradation, 10% discount rate for NPV, and a 25-year economic life. Real-world figures depend on your tariff, financing structure, depreciation treatment, and any state/local rebates. Always confirm with a written commercial quote.

Does it model batteries?

Yes — toggle the battery option and we model a commercial-grade lithium battery at $750/kWh installed, with the federal Cheaper Home Batteries Program rebate applied (capped at the 50 kWh usable maximum). For larger industrial battery storage, request a tailored quote.

More free Solar Proof tools

The commercial calculator pairs well with our other free tools — from STC counts to product comparisons:

For homeowners

Residential Solar Calculator

5–20 kW systems. Postcode-accurate savings, payback period and 25-year net savings.

STC & Battery Calculator

Exact STC count by postcode + the federal Cheaper Home Batteries Program rebate.

Product Directory

2,800+ panels, inverters and batteries from 270+ brands — datasheets included.

All Free Tools

Interval data report, invoice creator, STC calculator and more.
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