How many solar panels do I need for a 1,500 kWh per month home?

At Kansas City's 5.18 peak sun hours (PVWatts' annual print, rounded to two decimals) with standard 400W panels, a 1,500 kWh-per-month home needs about 31 panels, which is a 12.4 kW system. That count falls in sunnier regions and rises in cloudier ones: the same home in Phoenix needs closer to 24 panels. Three things you set on this calculator move the number the most, namely your monthly usage, your local sun hours, and the panel wattage you pick. Stepping up to 450W or 500W modules cuts the count noticeably (28 or 25 panels).

Does the number of solar panels change depending on where I live?

Yes, and the swing is large: Seattle needs about 71% more panels than Phoenix (24 against 14 for an 874 kWh month, the 2025 U.S. residential average, at 3.98 and 6.66 peak sun hours), and Phoenix needs about 42% fewer than Seattle. Peak sun hours run from 3.98 in Seattle to 6.66 in Phoenix (PVWatts' annual prints for those two points), so a home that needs 18 panels at Kansas City's 5.18 sun hours needs about 14 in Phoenix and 24 in Seattle. Sunlight, not just the size of your bill, sets the panel count. Always use your own location's sun-hour figure rather than a national average.

How many solar panels does it take to offset 100% of my electricity?

Size the array so its yearly production matches your yearly use, which is your monthly bill times 12. Because panel counts round up to whole panels, the result usually lands a few percent above 100%, giving a small cushion. Grid-tied homes with net metering can bank summer surplus as credits that cover winter shortfalls, which is what makes a full annual offset realistic. To see when a system you have priced pays for itself, enter its cost and annual production in our solar ROI calculator .

Should I add panels for an electric car or a heat pump?

Yes. Big new loads change the math, so add their yearly energy to your bill figure before you calculate. A typical electric car driven 12,000 miles a year uses about 3,000 to 4,000 kWh, roughly 250 to 330 kWh a month, which can add about 6 to 7 panels on its own at Kansas City's sun hours. A cold-climate heat pump can add even more in winter. Size for the home you will have in a year rather than today's bill, because adding panels later often means a second permit and inverter work.

How Many Solar Panels? - For Your Home

6 min read

Wondering how many solar panels it takes to power your house? This calculator answers it from the one number you already have: your monthly electricity use in kilowatt-hours, straight off your utility bill. Enter that with your local peak sun hours and a panel size, and it returns the panel count, the system size in kilowatts, and roughly how much of your bill the array offsets. It is built for grid-tied homeowners; if you are instead sizing an off-grid or RV system to a daily watt-hour load, the watt-hour tool linked below fits better.

Home solar sizing banner: 874 kWh a month, the 2025 US average use, needs 18 panels of 400W for a 7.2 kW system.

Start With the Number on Your Bill

Find your monthly kWh. Your electricity bill lists the kilowatt-hours you used. Take a recent bill, or average the last 12 months to even out summer and winter swings. The 2025 U.S. residential average is 874 kWh a month (EIA-861 Historical State Data).
Pick the month you want to cover. To offset your highest-use month (summer AC or winter heating), use that month's kWh. Grid-tied homes with net metering can instead size to the annual average and let credits balance the year.
Account for changes coming. An electric car adds roughly 3,000 to 4,000 kWh a year (about 250 to 330 kWh per month). A heat pump or pool pump adds more. Fold those into your figure before sizing.
No bill yet? For a new build or addition, our kWh calculator turns appliance wattages and run times into a monthly kWh figure.

Solar panel count by monthly electricity use and region, from 500 to 1,500 kWh in Phoenix, Kansas City and Seattle. — A sunnier location can cut the panel count by more than a third: a 1,000 kWh per month home needs 16 panels in Phoenix but 27 in Seattle.

The Same Home Needs More Panels in Seattle Than Phoenix

Two identical homes with identical bills can need very different panel counts, because sunlight is not spread evenly across the country. Peak sun hours (the daily hours of full-strength sun a location receives) range from 3.98 in Seattle to 6.66 in Phoenix (NLR's PVWatts annual prints for those two points at latitude tilt, roof mount, rounded to two decimals). A Phoenix roof gathers two-thirds more energy per panel than a Seattle roof of the same size.

That is why panel count tracks your address as much as your usage. An 874 kWh-per-month home, the 2025 U.S. residential average (EIA-861), needs roughly 18 panels at Kansas City's 5.18 sun hours, about 14 in sunny Phoenix, and 24 in cloudy Seattle. Pull your own location's sun-hour figure from NLR's PVWatts rather than trusting a national number, then enter it above.

Panels Needed by Monthly Bill and Region

Use this as a quick reference before you run your own numbers. Counts assume 400W panels, PVWatts' 14% default loss, its 96% default inverter efficiency and the cell-temperature factor 302 / 320 = 0.944; your exact figure depends on your bill and local sun. Phoenix 6.66, Kansas City 5.18 and Seattle 3.98 are PVWatts' annual prints at each point, rounded to two decimals.

Monthly Use	Phoenix (6.66 sun hrs)	Kansas City (5.18)	Seattle (3.98)
500 kWh	8 panels	11 panels	14 panels
750 kWh	12 panels	16 panels	20 panels
1,000 kWh	16 panels	21 panels	27 panels
1,500 kWh	24 panels	31 panels	40 panels

The pattern is consistent: a sunnier location can cut your panel count by a third or more for the same electricity bill.

Worked Examples

Sizing a Phoenix Home From Its Power Bill

Context

A Phoenix household averages 1,100 kWh a month, driven by heavy summer air conditioning. Phoenix gets 6.66 peak sun hours (NLR's PVWatts print at latitude tilt, roof mount, rounded to two decimals). They want to cover the whole bill with standard 400W panels, PVWatts' default 14% losses, its default 96% inverter efficiency and the cell-temperature factor 302 / 320 = 0.944.

Calculation

Annual use = 1,100 × 12 = 13,200 kWh

Derate = 0.86 × 0.96 × 302 / 320 = 0.779 (rounded for display; the engine carries the exact product)

System needed = 13,200 / (6.66 × 365 × 0.779) = 6,969 W (the engine's figure at the exact factor)

Panels = 6,969 / 400 = 17.4, rounded up to 18 panels (7.2 kW installed)

Production = 7.2 × 6.66 × 365 × 0.779 = 13,637 kWh (the engine's figure at the exact factor), about 103% of usage

Interpretation

Eighteen 400W panels, a 7.2 kW system, cover the full 13,200 kWh in an average year with a 3% cushion from rounding up. Phoenix's high sun hours keep the count low; the same bill in a cloudier city would need several more panels.

Takeaway

In a high-sun region a typical home offsets its bill with a 7 to 8 kW array. Before ordering, confirm the roof holds 18 panels with the solar roof area calculator.

How Many Panels for a Gas-Heat Chicago Home

Context

A Chicago home uses 800 kWh a month; heating and hot water run on gas, so the electric bill is modest. Chicago averages 4.18 peak sun hours at latitude tilt (NASA POWER 2001-2020 climatology). Same 400W panels and factors.

Calculation

Annual use = 800 × 12 = 9,600 kWh

System needed = 9,600 / (4.18 × 365 × 0.779) = 8,076 W (the engine's figure at the exact factor; 0.779 is rounded for display)

Panels = 8,076 / 400 = 20.2, rounded up to 21 panels (8.4 kW installed)

Production = 8.4 × 1,188.8 = 9,986 kWh, about 104% of usage

Interpretation

Twenty-one panels land a little above the 9,600 kWh target. Chicago needs three more panels than Phoenix despite the smaller bill, purely because it gets about 37% less sun.

Takeaway

Cold-climate homes on gas heat often need fewer panels than all-electric homes in sunnier states, since usage matters as much as sunshine. If you later switch to a heat pump, recalculate with the higher kWh, and see why real output sits below nameplate in our solar panel output guide.

Frequently Asked Questions

Glossary

Peak Sun Hours (PSH)

The number of hours per day that sunlight averages 1,000 watts per square meter, the lab condition panels are rated at. A location with 5 peak sun hours gives each watt of panel roughly 5 watt-hours of daily production before losses. It is the single biggest reason two homes with the same bill need different panel counts.

Bill Offset

The share of your annual electricity use that solar replaces. A 100% offset means yearly production matches yearly consumption; net metering lets summer surplus cover winter shortfalls so the books balance over twelve months.

Derate Factor

The fraction of a panel's rated power that reaches your meter. This calculator multiplies three factors: PVWatts' default 14% system loss (0.86), its default 96% inverter efficiency (0.96) and the cell-temperature factor 302 / 320 = 0.944 from Trina's NOCT print, about 0.779 in all. A lower derate factor means more panels for the same offset.

Nameplate Wattage

The rating stamped on a panel, measured under standard test conditions. Real output sits below nameplate most of the time because of heat and imperfect sun angles, which is why sizing builds in a loss allowance instead of using the sticker number directly.

Sizing an off-grid cabin, van, or RV to a daily watt-hour load rather than a monthly bill? The solar panel calculator works in watt-hours and panel wattage instead.

The honest answer to how many solar panels you need is a small range, not a single number, because sun hours, panel wattage, and next year's loads all move it. Start from your real monthly kWh, use your own location's sun hours, and round up to whole panels. If keeping the lights on during outages matters as much as cutting the bill, you will also want storage, and our batteries for a solar system calculator sizes that side. Get the panel count right first, then build the rest of the system around it.

More Solar calculators

Browse all solar calculators: Panel output, battery bank sizing, charge time, and system design for off-grid, RV, and residential setups.

Last updated: October 19, 2026

Written and maintained by Dan Dadovic, Commercial Director at Ezoic Inc. & PhD Candidate in Information Sciences. On the energy side, Dan has hands-on experience with residential solar panel installation, DIY battery bank construction, off-grid power systems, wind power, and EV ownership/driving, all from building, maintaining, and operating his own systems.

Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.

Methodology reviewed by Doc. dr. sc. Damir Topić, Assistant Professor, FERIT Osijek.