Solar for small businesses in Perth: a practical assessment

Small businesses in Perth — retail, hospitality, trades, professional services, light industrial — face electricity tariffs and demand charges that can significantly affect operating costs. Solar systems for commercial premises operate under different rules than residential, but the financial case is often compelling.

Commercial vs residential electricity costs in Perth

Residential (Synergy A1): 33.26c/kWh supply charge + ~$1.11/day

Business tariffs (Synergy):

• L1 (Small business, under 50MWh/yr): 35.4c–44.2c/kWh + demand charge component
• T2–T5 (Medium business): complex tariff structures with time-of-use, demand charges (per kW of peak demand), and capacity charges
• Energy WA (formerly Verve): for large industrial customers — not relevant to typical SMEs

Commercial electricity in Perth is typically 10–35% more expensive per kWh than residential before demand charges, and significantly more when demand charges apply.

What makes commercial solar different

Export limits: Commercial premises on single-phase connections face the same 5kW export limit as residential. Three-phase connections allow up to 30kW export for certain tariff classes. For larger commercial systems, export limiting or self-consumption focus is often required.

Demand charges: Many commercial Synergy tariffs include a demand charge — a monthly charge based on your peak power draw (kW) in a short window (typically 15–30 minutes). Solar reduces consumption, but a brief peak demand event (starting an AC system, running multiple pieces of equipment simultaneously) can still trigger a high demand charge. Battery storage that limits peak demand can be valuable in demand-charge scenarios.

Self-consumption is more valuable: When commercial tariffs are 40–50c/kWh, the value of self-consuming solar generation is higher than residential (at 33.26c/kWh). A 100kWh/day commercial system consuming 80% of its generation on-site is displacing 80kWh × 44c = $35.20/day in electricity purchases.

Depreciation and tax treatment: Business owners can claim depreciation on solar system assets. Under the Instant Asset Write-Off (subject to ATO thresholds and eligibility criteria), the full system cost may be deductible in the year of installation. This significantly improves the after-tax payback for businesses paying corporate or business income tax. Consult your accountant for your specific situation.

GST: Solar installation for business use is generally GST-creditable. A $25,000 system + 10% GST = $27,500 gross; if you're registered for GST, you claim back the $2,500 GST, making the net cost $25,000. This is different from residential solar (residential consumers can't claim GST input credits).

System sizing for small business

Key principle: size to consumption, not to roof space.

Commercial premises that operate 7am–6pm on weekdays have excellent solar alignment — peak generation coincides with operating hours. A system sized to meet 70–90% of daytime operating load maximises self-consumption.

Example: retail shop (500sqm, split AC, lighting, POS, refrigeration)

• Average consumption: 150–250kWh/day (operating days)
• Daytime generation needed: approximately 70% of 200kWh average = 140kWh
• System required: approximately 30–40kW (depending on roof orientation and tilt)
• This is a commercial-scale system requiring commercial-grade inverters and installation

Example: trades business (office + workshop, 100sqm)

• Average consumption: 30–60kWh/day
• System: 10–15kW covers most daytime operating load
• Residential-scale inverters possible (depending on connection)

Weekend-closed businesses: If the business is closed weekends, weekend solar generation exports at DEBS rates (residential connection) or at commercial export rates (if applicable). This reduces overall financial benefit on generation that can't be self-consumed. Size to weekday daytime consumption rather than total system generation.

Cost guide for small business systems

| System size | Approximate installed cost (2026 Perth) | |---|---| | 6.6kW (residential-scale, small office) | $7,000–$11,000 | | 10–15kW (small commercial) | $12,000–$20,000 | | 20–30kW (medium commercial) | $22,000–$40,000 | | 50kW+ (larger commercial) | $45,000–$90,000+ |

STCs apply to commercial systems — the rebate scales with system size. For systems over 100kW, Large-scale Generation Certificates (LGCs) apply instead of STCs.

ROI assessment framework

For a small business assessing solar:

1. Get 12 months of electricity bills — calculate annual spend and average consumption by month
2. Identify daytime vs evening consumption split (most business electricity is daytime — good for solar)
3. Obtain a system quote with generation estimate and self-consumption modelling
4. Model the after-tax payback (include depreciation benefit with your accountant)
5. Compare to cost of finance if borrowing (business loans at current rates vs electricity cost savings)

Typical result for well-suited small business:

• Pre-tax payback: 4–7 years
• After-tax payback (with instant asset write-off): 2.5–5 years
• 20-year NPV: significant positive return on investment at current electricity prices

What to check when getting commercial quotes

• Is the installer CEC-accredited for commercial systems?
• Is the equipment commercial-grade (Tier 1 panels with 30-year warranty, commercial inverters)?
• Does the quote include Western Power commercial connection approval (ACUP application for systems over 30kW)?
• Is production monitoring included (important for verifying performance and claiming GST/depreciation)?
• Does the quote include an estimated self-consumption rate? How was this calculated?

BillWise is designed for residential analysis, but the principles — understanding your consumption before sizing a solar system — apply equally to commercial decisions. For complex commercial solar modelling, work with a CEC-accredited commercial solar designer.