Solar and your carbon footprint in Perth: how much CO2 does solar actually save?

Perth's electricity grid — the South West Interconnected System (SWIS) — is powered predominantly by gas, coal, and a growing share of renewables. The grid's carbon intensity determines how much CO2 your household avoids by generating solar rather than drawing from the network.

For Perth solar owners, the environmental case is strong. Here's the actual maths.

Perth grid carbon intensity

The SWIS grid's carbon intensity is approximately 0.67 kg CO2 per kWh of electricity consumed.

This figure reflects the current generation mix in the SWIS: Synergy's coal plants (Muja, Bluewaters), gas peakers and base load, and a rapidly growing share of solar, wind, and battery storage from the Renewable Energy Zone (REZ) build-out.

The 0.67 kg/kWh figure is an annual average. It varies through the day:

• Midday: Significantly lower during peak solar generation hours across the SWIS — distributed rooftop solar and utility-scale solar plants push the carbon intensity down toward 0.3–0.4 kg/kWh on sunny days.
• Evening peak: Higher as solar generation drops and gas peakers ramp up to meet demand.
• Overnight: Moderate, mainly baseload gas and coal.

For calculating solar's CO2 savings, the average of 0.67 kg/kWh is the right figure to use.

How much CO2 does a Perth solar system avoid?

Annual CO2 savings by system size:

| System size | Annual generation (Perth est.) | CO2 avoided/year | Equivalent | |---|---|---|---| | 3kW | 4,500 kWh | 3,015 kg (3.0 tonnes) | ~12,000 km driven in a petrol car | | 5kW | 7,500 kWh | 5,025 kg (5.0 tonnes) | ~20,000 km driven | | 6.6kW | 10,000 kWh | 6,700 kg (6.7 tonnes) | ~27,000 km driven | | 10kW | 14,500 kWh | 9,715 kg (9.7 tonnes) | ~39,000 km driven |

Comparison references:

• Average Australian petrol car: ~0.25 kg CO2/km (Oz-average small car). A 6.6kW system avoids the equivalent of driving 26,800 km/year.
• One return economy flight Sydney–London: approximately 3.5–4.5 tonnes CO2-equivalent (depends on carbon accounting method).
• A 6.6kW Perth solar system avoids roughly 1.5–2 return flights to London per year.

Over a 25-year system life (accounting for 0.5%/year panel degradation), a 6.6kW system avoids approximately 155–165 tonnes of CO2.

Panel embodied carbon and payback

Solar panels have embodied carbon — the CO2 emitted during their manufacture, transport, and installation. This is most relevant when asking whether solar is "actually green" or just shifts emissions from electricity generation to manufacturing.

Typical embodied carbon for a 6.6kW system:

• Solar panels (silicon manufacturing, framing): approximately 2,000–3,500 kg CO2 total for the system
• Inverter and mounting hardware: approximately 200–500 kg CO2
• Installation and transport: approximately 100–200 kg CO2
• Total: approximately 2,300–4,200 kg CO2

Carbon payback period:

At Perth's grid intensity (0.67 kg CO2/kWh) and a 6.6kW system generating 10,000 kWh/year:

• Annual CO2 avoided: 6,700 kg
• Embodied carbon: 2,300–4,200 kg
• Carbon payback period: 4–8 months

Within less than a year, the system has "repaid" its manufacturing carbon. Every subsequent year is a net reduction.

This compares very favourably with Perth's grid: the SWIS burns coal and gas continuously with no payback period — every kWh from the grid emits 0.67 kg CO2 with no offsetting benefit.

Solar export and CO2: what does DEBS export do?

When you export electricity to the grid, you're displacing generation that would otherwise come from a fossil fuel plant. The carbon saving per kWh exported is approximately the same as per kWh self-consumed — 0.67 kg CO2/kWh — because grid carbon intensity applies to both import and export.

The financial benefit of self-consumption (33c saved) is much larger than the financial benefit of export (2c earned), but the environmental benefit is similar per kWh. Self-consuming solar has the same carbon impact as exporting it — you avoid importing grid electricity either way.

WA's energy transition: the grid is getting greener

The SWIS is undergoing rapid decarbonisation. Commitments and projects in progress as of 2026:

• Collie coal plant retirement: Muja A/B units closed; Collie Power Station retirement scheduled. Coal's share of SWIS generation is declining.
• Renewable Energy Zone (REZ) projects: Large-scale solar farms in the mid-west and battery storage projects are adding significant zero-emissions capacity.
• Distributed rooftop solar: Perth's residential solar uptake is among the highest in the world by per-capita installed capacity. On sunny days, rooftop solar accounts for 30–50% of SWIS daytime generation.

As the grid decarbonises, the CO2 savings from rooftop solar will gradually decrease — not because solar is less beneficial, but because the grid itself is cleaner. The highest CO2 saving from rooftop solar occurs now, while the grid is still carbon-intensive.

Implication: Installing solar now locks in high-CO2-displacement benefit for the system's 25-year life, even as the grid cleans up. Early adopters of solar have already avoided significantly more CO2 per kWh than the same system installed in 2030 will avoid.

The EV multiplier

If you add an electric vehicle charged from home solar, the carbon savings multiply:

A petrol car averaging 10L/100km emits approximately 0.23 kg CO2/km. An EV charged from Perth's grid (0.67 kg/kWh, at 5km/kWh) emits 0.134 kg CO2/km — roughly half the petrol car. Charging the same EV from solar-generated electricity (0 kg CO2/kWh): 0 kg CO2/km.

The EV + solar combination at Perth's grid intensity achieves near-zero transport emissions for city driving, compared to 0.23 kg/km for petrol.

CO2 intensity figure of 0.67 kg CO2/kWh represents the SWIS average based on WA's current generation mix and is consistent with Australian government published data for the WA grid. This figure changes annually as the generation mix evolves. Embodied carbon estimates are based on published lifecycle assessment data for crystalline silicon solar panels; actual values vary by manufacturer, module type, and supply chain.