Size your system
Find it on your bill. US average is about 900 kWh/month.
Sets your peak sun hours (state average).
Editable — use your installer's PVWatts figure if you have one.
Sun hours, derate, and why installers oversize slightly.
Why your utility's policy changes the math.
The honest math, including the 2026 tax credit change.
Frequently asked
How many solar panels do I need for a 2,000 sq ft home?
Home size doesn't decide it — your kWh usage does. A home using 10,800 kWh/year needs roughly 6–8 kW (15–20 panels at 400W) depending on sun hours. Enter your actual bill above for your number.
What is a peak sun hour?
One hour of sunlight at 1,000 W/m² intensity. Arizona averages about 6.5 per day; Washington about 3.8. It bundles daylight length, angle, and cloud cover into one number installers actually use.
Can I install solar myself to save money?
DIY kits exist and cut labor cost, but permits, interconnection, roof work, and electrical code make professional install the norm for grid-tied homes. This calculator can't replace an electrician.
Is the federal solar tax credit still available in 2026?
No — for homeowner-owned systems. Section 25D ended for systems placed in service after December 31, 2025 (One Big Beautiful Bill Act, IRS FS-2025-05). Leased systems may still qualify for commercial credits through the leasing company.
Worked example: sizing a system from a real bill
Take a home that uses 900 kWh a month, or 10,800 kWh a year, in a state averaging 5.0 peak sun hours a day. The sizing math runs in three steps. First, divide annual use by sun hours and days: 10,800 divided by (5.0 times 365) gives about 5.9 kW before losses. Second, divide by the derate factor of about 0.80, which covers inverter losses, wiring, heat, dust, and panels that never quite hit their nameplate rating: 5.9 divided by 0.80 gives about 7.4 kW. Third, divide by panel wattage: 7,400 watts divided by 400-watt panels gives 19 panels, rounded up. That same home in Arizona at 6.5 sun hours needs only about 5.7 kW and 15 panels, while in Washington at 3.8 sun hours it needs about 9.7 kW and 25 panels. Location matters more than house size, which is why every sizing answer starts with your bill and your state, not your square footage.
What a system this size costs in 2026
At the SEIA and Wood Mackenzie Q2 2026 national average of $3.36 per watt installed, the 7.4 kW system above costs about $24,900 before any state or utility incentive. There is no federal residential credit to subtract for homeowner-owned systems placed in service in 2026, so the price on the contract is much closer to the price you actually pay than it was in 2024 or 2025. Cost per watt falls as systems get bigger, because permitting, design, and interconnection fees are mostly fixed: a 4 kW system often prices near $3.60 per watt, while a 12 kW system can come in near $3.10 per watt. Roof complexity moves the number too. A simple single-story asphalt roof is the cheapest case; steep pitches, tile, multiple roof planes, and a panel upgrade for an older electrical service each add cost. Get the cost per watt in writing on every quote so you can compare installers on the same basis.
Roof space, orientation, and the mistakes that shrink output
Nineteen 400-watt panels need roughly 350 to 400 square feet of clear, unshaded roof once setbacks and walkways are included. South-facing roof at a tilt near your latitude is the ideal case. East and west-facing arrays typically produce 10 to 20 percent less over the year, and north-facing sections in most of the US produce too little to be worth the hardware. The three mistakes that cost homeowners the most output are sizing from square footage instead of actual usage, ignoring future loads such as an electric vehicle or a heat pump that will raise usage after the system is sized, and accepting a design that places panels behind afternoon tree shade to keep the layout tidy. If your usage is about to change, size for the usage you will have, not the usage on last year’s bills, and ask the installer for a shade analysis in writing before you sign.