Solar Panels kWh Calculator
Free solar panels kWh calculator for Australia. Enter your monthly kWh use, target offset, and panel wattage to see system size, panel count, and bill savings — calibrated to BoM and Clean Energy Council standards.
Prepared by the Solar Calculator HQ editorial team. Review our formula, source and limitation standards.
Solar Panels kWh Calculator
How to use this calculator
This tool sizes a solar system from the kWh number on your electricity bill — the opposite direction of a production calculator. Enter six values and it returns required system size in kW, panel count, daily/monthly/annual production, offset achieved, and year-1 bill savings:
- Monthly electricity use (kWh) — average from your last 12 months of bills. AER’s 2026 average is 542 kWh/month (6,500 kWh/year).
- Target offset (%) — how much of your bill you want to eliminate. 90% is standard without a battery; 110%+ if you have storage.
- Peak sun hours per day — Australian average is 4.5. BoM Solar Resource Maps show exact values: Darwin 5.7, Brisbane 4.9, Perth 5.4, Sydney 4.4, Melbourne 4.0, Hobart 3.6, Adelaide 4.7.
- System efficiency (%) — leave at 78%. CEC Design Guidelines default for Australian rooftop installations.
- Panel wattage (W) — STC nameplate. 2026 Australian standard is 440–510 W (Q CELLS Q.PEAK DUO ML-G11+, Jinko Tiger Neo, REC Alpha Pure-RX).
- Electricity rate (A$/kWh) — your blended residential retail rate. AER DMO 2025-26 averages 33–36c/kWh; flat tariff varies by state and time of use.
The formula
annual_need_kWh = monthly_kWh × 12
target_kWh = annual_need_kWh × (offset / 100)
required_array_W = target_kWh × 1000 / (PSH × 365 × derate)
panel_count = ceil(required_array_W / panel_W)
actual_array_W = panel_count × panel_W
daily_production = actual_array_W × PSH × derate / 1000
year1_savings = min(annual_production, annual_need) × rateThe savings figure assumes self-consumption — exported kWh earn the FiT, which is much lower than retail. The savings calculator handles the dual-stream model.
A worked example for the AER average household at 90% offset:
- Need: 542 × 12 = 6,504 kWh per year
- Target: 6,504 × 0.90 = 5,854 kWh
- Required array: 5,854 × 1000 / (4.5 × 365 × 0.78) = 4,575 W
- Panel count: ceil(4575 / 440) = 11 panels
- Actual array: 11 × 440 = 4,840 W (4.84 kW)
- Daily production: 4840 × 4.5 × 0.78 / 1000 = 17.0 kWh
- Annual production: 17.0 × 365 = 6,200 kWh (95% offset)
- Year-1 savings at 34c/kWh: A$2,108
System size by household consumption
Using 4.5 peak sun hours, 78% derate, 440 W panels, 90% target offset:
| Monthly kWh | Annual kWh | System kW | Panels | Daily kWh | Year-1 savings* |
|---|---|---|---|---|---|
| 400 | 4,800 | 3.52 | 8 | 12.36 | A$1,469 |
| 542 | 6,504 | 4.84 | 11 | 17.00 | A$1,990 |
| 700 | 8,400 | 6.16 | 14 | 21.62 | A$2,571 |
| 900 | 10,800 | 7.92 | 18 | 27.80 | A$3,305 |
| 1,200 | 14,400 | 10.56 | 24 | 37.07 | A$4,406 |
| 1,500 | 18,000 | 13.20 | 30 | 46.34 | A$5,508 |
*At 34c/kWh blended residential rate. State FiT not included.
What changes the result
Peak sun hours by capital city
BoM 2026 Solar Resource Maps confirm:
- 3.4 kW in Darwin at 5.7 PSH (8 panels)
- 4.0 kW in Perth at 5.4 PSH (10 panels)
- 4.4 kW in Brisbane at 4.9 PSH (10 panels)
- 4.6 kW in Adelaide at 4.7 PSH (11 panels)
- 4.84 kW in Sydney at 4.5 PSH (11 panels)
- 5.4 kW in Melbourne at 4.0 PSH (13 panels)
- 6.0 kW in Hobart at 3.6 PSH (14 panels)
Same 6,504 kWh/year household, same 90% target offset.
State feed-in tariffs
The savings figure assumes 100% self-consumption. Australian households typically self-consume 30–40% of generation without a battery, 70–85% with one. Exported kWh earn the FiT:
- NSW Solar Boost (Origin): 11.4c/kWh first 14 kWh/day, then 7c
- Victoria ESC minimum: 4.9c/kWh (some retailers offer 12c+ on 12-month contracts)
- South Australia Tango: 12c/kWh
- Queensland Ergon Energy regional: 12c/kWh
- Queensland SEQ retailers: 6–8c/kWh
- WA Synergy DEBS: 10c/kWh peak (3-9pm), 2.75c off-peak
- Tasmania Aurora: 10.869c/kWh
- ACT ActewAGL: 9c/kWh
- NT Jacana: 9.13c/kWh
Source: AER + state regulator websites, April 2026. Battery storage time-shifts exports — a 10 kWh battery raises self-consumption to 75% on a typical 6.6 kW system.
Panel orientation and tilt
The reference case is north-facing at latitude tilt (33° in Sydney, 38° in Melbourne, 28° in Brisbane). Off-axis penalties (CEC Design Guidelines):
- East or west: 12–18% loss versus north
- South: 25–30% loss (avoid in residential design)
- Flat (0° tilt): 8–12% loss
Many Australian homes have east-west roof aligned with street frontage — split-array installs (panels on both pitches) lose only 5–8% versus a hypothetical north-facing equivalent and capture morning + afternoon load profiles better.
Soiling
Australian soiling losses (CEC + SunWiz fleet data 2026):
- Coastal humid (Sydney, Brisbane, Melbourne): 2–3% annual
- Inland dry (Adelaide, Perth, Canberra): 4–6%
- Rural dust (NSW Riverina, Central QLD, WA wheatbelt): 6–10%
- Bushfire-affected periods: spike to 15–25% during smoke events
The cleaning cost calculator walks through whether annual cleaning is economic for your postcode.
Why size from kWh, not from roof space
Roof-area sizing is the planning-stage shortcut. kWh sizing is what eliminates a bill. The Clean Energy Council 2026 best-practice guide confirms: kWh-driven sizing is the standard for any quote that meets the CEC New Energy Tech Consumer Code.
The right workflow:
- Sum 12 months of bills. Add projected load if you are buying an EV (3,500–4,500 kWh/yr at 15,000 km) or heat pump hot water (1,800 kWh/yr replacing gas, per Sustainability Victoria).
- Decide your offset target. Without battery: 90–110%. With battery: 100–130%.
- Run this calculator with local PSH from BoM.
- Sanity-check roof area: each 440 W panel needs ~2.0 sq m. A 6.6 kW system needs ~30 sq m of unshaded north-facing roof.
- Get CEC-accredited installer quotes — required for STC rebate eligibility under the Small-scale Renewable Energy Scheme.
Common mistakes
- Sizing under 6.6 kW because of “the rule”: 6.6 kW with a 5 kW inverter clears STC thresholds and stays inside DNSP export limits in most states. But if you use 8,000+ kWh/year, oversize the panels (10 kW DC) with a 5 kW inverter and the STCs still apply.
- Ignoring time-of-use tariffs: Most Australian states have rolled out smart meters. A flat 34c/kWh assumption overstates savings if you use ToU and most consumption is overnight (off-peak 18c). Match self-consumption to the tariff structure.
- Forgetting state battery rebates: NSW Peak Demand Reduction Scheme (≈$1,200 for 10 kWh), Victoria Solar Homes battery loan, WA Distributed Energy Buyback Scheme — these significantly change the optimal system + battery split.
- Using a single CEC-accredited quote: Get three. SunWiz Q1 2026 data shows a 25–35% spread between cheapest and most expensive quote for identical system specs in the same postcode.
Sources
- Bureau of Meteorology Solar Resource Maps — peak sun hours for any Australian location
- Clean Energy Council Design Guidelines 2026 — installation standards and AS/NZS 5033 compliance
- AER Default Market Offer 2025-26 — Australian residential kWh and tariff benchmarks
- SunWiz Australian Solar PV Q1 2026 — installation, performance, and pricing data
- Clean Energy Regulator postcode data — installation and STC certificate database
- AS/NZS 5033:2021 — installation and safety requirements for PV arrays