Solar Panel Installation: How Many Panels Do I Need?

How to Size a Solar System

Start with your annual electricity usage in kilowatt-hours (kWh). Check your utility bills --- the average Australian home uses 6,000-8,000 kWh per year, while the average US home uses about 10,500 kWh.

Divide your annual usage by the peak sun hours for your location (multiplied by 365). For example, Brisbane receives about 5.2 peak sun hours per day. A home using 7,000 kWh per year needs: 7,000 ÷ (5.2 × 365) = 3.7 kW system.

Divide the system size by the wattage of individual panels. Modern residential panels produce 370-425 watts each. A 3.7 kW system needs: 3,700 ÷ 400 = about 10 panels.

Roof Space Requirements

A standard residential solar panel measures roughly 1.7m × 1.0m (5.5 × 3.3 feet), covering about 1.7 square metres (18 sq ft) per panel.

A 10-panel system needs approximately 17 square metres (180 sq ft) of unshaded roof space. North-facing roofs (in Australia) or south-facing roofs (in the US) produce the most energy.

Shading from trees, chimneys, or neighbouring buildings can significantly reduce output. Even partial shading on one panel can reduce the output of an entire string. Modern micro-inverters or power optimisers help mitigate this.

Solar Panel Costs in 2026

In Australia, a 6.6 kW system (most popular residential size) costs $5,000-$9,000 after the federal STC rebate. Premium panels and micro-inverters sit at the higher end.

In the United States, a 6 kW system costs $12,000-$18,000 before the 30% federal tax credit, bringing the net cost to $8,400-$12,600.

Battery storage adds $5,000-$15,000 depending on capacity. A 10 kWh battery (like the Tesla Powerwall) typically costs $10,000-$13,000 installed and covers overnight usage for most households.

Payback Period and Savings

The typical payback period for solar in Australia is 3-5 years thanks to high electricity prices ($0.25-$0.35/kWh) and generous feed-in tariffs in some states.

In the United States, payback periods range from 6-10 years depending on state incentives, utility rates, and net metering policies. States like California, Massachusetts, and New York offer the best returns.

After payback, solar panels continue generating free electricity for another 15-20 years. Most panels come with 25-year performance warranties, guaranteeing at least 80% of original output.

Solar also increases home value. Studies show homes with solar sell for 3-4% more on average, adding $15,000-$30,000 to the value of a typical home.

Understanding Your Electricity Usage First

Before sizing any system, pull twelve months of electricity bills and find your annual kilowatt-hour (kWh) usage. The average US home uses roughly 10,000 to 11,000 kWh per year, but yours could be far higher with electric heating, a pool pump, or EV charging. Sizing to your actual usage is the foundation of a good system.

Note the seasonal pattern too. A home with heavy summer air conditioning has a very different profile from one with electric winter heat. This affects whether a system that offsets 100% of annual usage will actually cover your highest-demand months.

If you plan to add an electric vehicle, a heat pump, or a pool in the next few years, size the system for that future load now. Adding panels later often means a second permit, a second crew mobilization, and a second inspection, which raises the per-watt cost of the expansion.

Net Metering, Incentives, and the Federal Tax Credit

The economics of solar depend heavily on incentives. The federal residential clean energy credit has historically returned a significant percentage of system cost as a tax credit, and many states, utilities, and municipalities add their own rebates. Always confirm the current credit amount and eligibility before signing a contract.

Net metering rules determine what your utility pays for excess power your panels send back to the grid. Full retail net metering makes solar far more valuable than arrangements that pay a low wholesale rate for exports. Check your utility's current policy, as these rules change.

Battery storage changes the math again. Batteries let you use your own solar power at night and provide backup during outages, but they add substantial cost. Whether they pay off depends on local rates, time-of-use pricing, and how much you value backup power.

Buying, Leasing, or Financing Your System

Paying cash delivers the best long-term return because you own the system and claim all incentives directly, but it requires the largest up-front outlay. A solar loan spreads the cost over time and still lets you own the panels and claim the tax credit, though interest reduces total savings.

Leases and power purchase agreements (PPAs) require little or no money down, but the third-party owner claims the incentives and you simply buy the power or rent the equipment. These deals can complicate a future home sale, so read the transfer terms carefully.

Whatever the path, get at least three quotes, confirm the installer's licensing and warranty terms, and make sure the production estimate is based on your actual roof, shading, and orientation rather than a generic figure.

Frequently Asked Questions

How many solar panels do I need for a house? A typical home needs 15 to 25 panels to offset most of its electricity, depending on usage, panel wattage, and local sun hours. A 6 kW system using 400-watt panels is 15 panels.

How much roof space do I need? Plan on roughly 17 to 20 square feet per panel, so a 20-panel system needs about 350 to 400 square feet of unshaded, well-oriented roof.

What is the payback period for solar? With incentives and full net metering, many homeowners see payback in 6 to 10 years, after which the power is essentially free for the remaining 15-plus years of panel life. Use our solar panel calculator to estimate system size and savings for your usage.

Roof Condition, Orientation, and Shading

Solar panels last 25 years or more, so the roof beneath them should have comparable life left. Installing on an aging roof means paying to remove and reinstall the array when the roof is replaced. If your roof is more than about 10 to 15 years old, reroof first.

Orientation and tilt drive production. In the northern hemisphere, south-facing roofs produce the most, with east and west facing somewhat less, and north-facing roofs generally unsuitable. A good installer models your specific roof planes rather than assuming an ideal.

Shading is the silent production killer. Even partial shade from a chimney, vent, or tree on a few panels can drag down a whole string's output unless the system uses microinverters or power optimizers. A proper site assessment maps shading across the day and seasons.