TL;DR
- Typical Mackay commercial payback: 3-6 years.
- Retail/office: 4-5 yr. Workshop: 3.5-5 yr. Cold-storage: 3-4 yr with battery.
- Demand-charge reduction often adds 15-25% more savings vs kWh offset alone.
- GST reclaim + accelerated depreciation improve after-tax ROI further.
How commercial solar saves money — four levers
- Energy offset: kWh you don't buy at ~25-35c commercial rate.
- Demand-charge reduction: lowering your peak kW draw during utility-measured intervals.
- Export credit: feed-in tariff for surplus (currently 4-8c/kWh commercial).
- Tax: GST input credit + depreciation / instant asset write-off where applicable.
Worked examples (Mackay, April 2026)
| Business | System | Net cost | Annual savings | Payback |
|---|---|---|---|---|
| Cafe (Mackay CBD) | 40 kW | $38,000 | $8,500 | 4.5 yr |
| Medical practice | 60 kW | $56,000 | $12,800 | 4.4 yr |
| Engineering workshop | 100 kW | $92,000 | $24,500 | 3.8 yr |
| Cold-storage (100 kWh battery) | 150 kW + 100 kWh | $235,000 | $68,000 | 3.5 yr |
| Mining services camp | 200 kW + 200 kWh | $340,000 | $95,000 | 3.6 yr |
After-tax payback typically shortens another 8-15% depending on depreciation treatment.
The demand-charge lever most forget
Ergon commercial tariffs (e.g. Tariff 20/22/40) include a demand charge — typically $8-$25 per kW of peak 30-minute average measured monthly. A 100 kW solar system reduces midday peak demand by 40-70 kW on a clear day, saving $300-$1,500/month on demand alone before counting energy. Adding a modest battery locks in those savings on cloudy days too.
Financing and tax
- Cash purchase: simplest, fastest payback, captures all tax benefits.
- Commercial green loan: 0% or low-rate finance over 5-7 yr. Cashflow-positive from month 1 if savings exceed repayment.
- PPA / operating lease: no upfront capex, fixed c/kWh rate below grid price. Useful for tenants or businesses with capex constraints.
FAQs
What if I'm a tenant?
PPA (Power Purchase Agreement) models work well: the installer owns the system, you buy the output at a fixed rate below grid. Requires landlord consent.
Does solar affect building insurance?
Minor premium increase (usually < $200/yr). Notify insurer of system value and commissioning date.
Want a modelled payback for your NMI?
Free 48 h feasibility including demand-charge analysis and finance options.
Request feasibility