How Many Solar Panels Do I Need to Run a House?

If you are wondering how many solar panels do I need to run my house, the short answer for a US home is roughly 10 to 20 panels. But the real answer depends on three things: how much electricity you use, how much sun your roof gets, and the wattage of the panels you choose. This guide walks you through the exact calculation step by step, with three worked examples (clearly labeled as illustrative), and explains how roof space, shading, and orientation change the number.

How is the number of solar panels calculated?

The standard formula used across the solar industry is simple division:

Daily electricity use (in watt-hours) / peak sun hours / panel wattage = number of solar panels

This formula comes from solar.com’s 2026 sizing guide, and SolarReviews uses a close variant: (monthly kWh / monthly peak sun hours) / panel output. Both do the same job: they match your consumption to what a system of a given size can produce at your location (solar.com, solarreviews.com).

Let us work through each variable.

How much electricity do you use?

Find your usage in kWh, not dollars, on your electricity bills. Add up at least 12 months and divide by 12 to get your average monthly usage, or by 365 for daily usage. The EIA reports that the average US household uses 10,791 kWh per year, which equals 899 kWh per month or about 30 kWh per day (via solar.com). A bill of 900 kWh per month is a useful planning number for a typical home.

Usage varies a lot by state: solar.com notes average daily use of about 18 kWh in Hawaii versus 40 kWh in Louisiana. So always start from your own bills. If you plan to buy an electric car, add a pool, or switch heating to a heat pump, add that future usage now, since sizing for it later is more expensive.

How many peak sun hours does your roof get?

A peak sun hour is one hour when sunlight intensity averages 1,000 watts per square meter (1 kW/m2). It is not the same as hours of daylight: a place with 10 hours of daylight might only get 4 to 5 peak sun hours because morning and evening sun is weak.

In the US, average peak sun hours range from over 5.75 per day in the Southwest to less than 4 per day in the northernmost states (solar.com). SolarReviews publishes regional monthly totals that you can divide by 30 for daily figures: Southwest 198 to 228, Southeast 152 to 179, Midwest 122 to 152, Northeast 122 to 149, and Northwest 152 to 198 peak sun hours per month. As a concrete example, a 400-watt panel produces about 90 kWh per month in Arizona but only about 36 kWh per month in Alaska (SolarReviews).

Half of the US gets less than 4.5 peak sun hours per day and half gets more, so 4.5 is a reasonable national-average assumption for rough math.

What panel wattage should you assume?

A solar panel’s wattage is how much power it produces per peak sun hour. Residential panel ratings range from 250W to 450W, and 400W is the most popular rating based on solar.com’s sales data, offering a good balance of output and price per watt. A typical 400-watt monocrystalline panel produces about 2 kWh per day (SolarReviews).

If your roof space is limited, higher-wattage panels let you hit the same system size with fewer panels. In the UK, a standard 400W panel produces around 300 kWh per year (Green Central, greencentral.co.uk).

How many solar panels for a small, medium or large home?

Here are three illustrative worked examples. Assumptions are stated up front: 4.5 peak sun hours per day, 400W panels, 365 operating days, and a goal of 100 percent electricity offset (before roof and shading limits). These are planning numbers, not quotes.

Small home: 400 kWh per month. Daily use is about 13.3 kWh (13,300 watt-hours). 13,300 / 4.5 / 400 = 7.4, so round up to 8 panels, a system of about 3.2 kW. This matches SolarReviews’ table, which shows 8 panels for a 1,000-square-foot home with a $77 monthly bill.

Medium home: 900 kWh per month. Daily use is about 30 kWh (30,000 watt-hours), the US average. 30,000 / 4.5 / 400 = 16.7, so round up to 17 panels, a system of about 6.8 kW. SolarReviews puts the average home at 15 to 19 panels, and solar.com’s FAQ gives 13 to 19 panels for the average US home.

Large home: 1,600 kWh per month. Daily use is about 53.3 kWh (53,300 watt-hours). 53,300 / 4.5 / 400 = 29.6, so round up to 30 panels, a system of about 12 kW. SolarReviews’ table shows 27 panels for 1,600 kWh per month and 34 for 2,000 kWh per month using 400W panels, which lines up closely with this math.

Always round up, not down: an undersized system leaves part of your bill on the table, while a slightly oversized one covers seasonal dips.

How do roof space and shading change the answer?

Your roof, not your math, may decide the final number.

Roof space. A typical residential panel needs about 17 to 18 square feet of roof (SolarReviews shows a 7.6 kW installation covering about 334 square feet, and 10 panels needing 177 square feet). In metric terms, plan for about 2 m2 per panel (Green Central). So the 30-panel example above needs roughly 530 square feet, while 17 panels need about 300 square feet. Vents, chimneys, and skylights eat into usable space too.

Roof orientation and pitch. In the US, south-facing roofs tilted 30 to 45 degrees are ideal for maximum production (SolarReviews). East- or west-facing roofs still work but produce less, so you may need a few extra panels to reach the same output.

Shading. Trees, neighboring buildings, and chimneys cut production. Shade on even part of a panel can drag down a whole string of panels, which is why installers run shade analyses before quoting. If shading is unavoidable, you may need more panels elsewhere on the roof, or fewer panels in the shaded area.

Utility limits. Many US utilities cap residential systems at about 120 percent of a home’s annual usage, so you cannot always install extra panels just to sell more power back (SolarReviews). And where net metering pays less than the retail rate, or is unavailable, it can make more financial sense to size for your daytime usage and add a battery rather than maximizing panel count.

Going off-grid changes everything. A grid-tied system uses the grid as backup at night, so 17 panels can offset 1,000 kWh per month. Fully off-grid, the same usage needs about 17 panels plus at least three 13.5 kWh lithium-ion batteries to cover nights and cloudy days (SolarReviews). Off-grid sizing is a separate job and always needs professional design.

How can you get your exact number?

Do the manual math above with your own bills, then verify with a proper tool. Enter your address, your average monthly kWh, and your panel wattage preference into TheSolarCost solar panel calculator to get an exact system size and panel count for your roof, before you request installer quotes.

---

FAQs: How many solar panels do I need?

How many solar panels does it take to run a house?

The average US home needs 13 to 19 panels of 400W each to fully offset annual electricity use (solar.com), or 15 to 19 panels (SolarReviews). Your number depends on your kWh usage, local peak sun hours, and panel wattage: daily kWh divided by peak sun hours divided by panel wattage.

Is 10 kW enough to run a house?

In many cases, yes. The average US household uses about 30 kWh per day, which can be offset by a 5 to 8.5 kW system depending on sun exposure (solar.com). A 10 kW system using 400W panels is 25 panels, which covers most homes well beyond the average.

Can I run my house on solar only?

During the day, yes, and with net metering your daytime surplus earns credits that cover your nighttime grid use. To run entirely on solar with no grid connection at all, you need battery storage sized for your night loads and cloudy days (SolarReviews).

Do I need more panels if my roof faces east or west?

Often yes. South-facing roofs at 30 to 45 degrees are ideal in the US; other orientations produce less per panel, so you typically need a few extra panels to generate the same annual kWh (SolarReviews).

How much roof space do 20 solar panels need?

How many solar panels do I need for a 3-bed home? How many solar panels you need depends on usage. A typical 3-bed home using 900 kWh/month needs about 17 panels of 420W. To work out how many solar panels you need, divide daily kWh by peak sun hours and panel wattage.

About 353 square feet for 400W panels, or roughly 17 to 18 square feet per panel (SolarReviews). A 7.6 kW system of about 19 panels covers around 334 square feet, which is roughly 20 percent of an average residential roof.

Last reviewed: 11 October 2026

By TheSolarCost Editorial Team