What Size Solar System Do I Need? kW & Panel Count Chart (2026)

By Serhii Dovzhenko, Solar & Energy Storage Specialist · Updated October 28, 2026 · Prices checked October 28, 2026 · Data verification: Adsec.ca

The size of a solar system is the total wattage of its panels (the array), in kilowatts (kW), and you can work it out from one number on your electric bill. Get that right and the panel count, roof space, inverter and battery follow.

This guide gives you the formula, a kW chart by monthly electricity use, a panel-count chart, the roof space each size needs, and how off-grid sizing differs from grid-tied. At the end are seven complete kits from 1.2 kW to 14.4 kW that are in stock and active on October 28, 2026, with store prices before any promo code. Looking for a portable power station instead of a roof system? Our solar generator sizing guide covers watts, Wh and surge.

1. The 3-step solar sizing formula

System size (kW) = yearly kWh / (peak sun hours x 365 x 0.75)

1. Find your yearly use. Add up the last 12 months of kWh on your utility bills (most utilities show a 12-month graph). No history? Multiply one month by 12, but pick an average month, not a heating or cooling peak. The US average was 865 kWh a month in 2024 according to the EIA - about 10,400 kWh a year.
2. Find your peak sun hours. A peak sun hour is one hour of full-strength sunlight (1,000 W per square meter). Most of the US gets 3.5-6 a day averaged over the year: roughly 3.5-4 in the Pacific Northwest and the Northeast, 4-4.5 in the Midwest and mid-Atlantic, 4.5-5 in the Southeast and Texas, and 5.5-6.5 in the desert Southwest. For your exact address, NREL's free PVWatts calculator gives a site-specific figure.
3. Apply a real-world factor. Panels rarely deliver their nameplate rating: heat, wiring, inverter losses, dust and imperfect tilt typically cost 20-25%. We use 0.75, which is cautious; a well-oriented, unshaded south-facing roof often does slightly better.

Worked example: a home using 900 kWh a month (10,800 kWh a year) in Ohio at about 4.2 peak sun hours needs 10,800 / (4.2 x 365 x 0.75) = 9.4 kW. The same home in Arizona at 6 sun hours needs 10,800 / (6 x 365 x 0.75) = 6.6 kW. Location changes the answer by 40% or more, which is why a single "average system size" is only a starting point.

Installers call the same idea a production ratio (yearly kWh per watt of panels); in the US it usually falls between 1.1 and 1.6.

2. Solar system size chart by monthly electricity use

The chart sizes for 100% of yearly use. Under net metering that is usually the target. Where your utility pays little for exported power, a system covering 60-80% of use, plus a battery to store midday surplus, often pays back faster than a bigger array.

Planning to add load?

Size for the next five years, not the last twelve months. Common additions and their rough yearly use:

• Electric vehicle: about 3,000-4,000 kWh a year for 12,000 miles (roughly 0.25-0.33 kWh per mile) - add 2.5-3.5 kW of panels at 4 sun hours.
• Heat pump replacing gas heat: 3,000-6,000 kWh a year depending on climate and house size.
• Heat-pump water heater: about 1,000-1,500 kWh a year (a standard electric tank uses 3,000-4,000).

Buy an inverter with spare solar input now rather than replace it later - every kit below accepts more panels than it ships with.

3. How many solar panels do I need?

Panels = system size in watts / panel wattage, rounded up. A 9 kW system is 9,000 / 450 = 20 panels of 450 W, or 23 panels of 400 W.

*Panel area only, based on a 450 W panel of about 23 sq ft (75 x 45 in). Allow extra for fire-code setbacks from ridges and edges, vents and skylights - usable roof is often only 60-70% of the total. Daily output uses the 0.75 factor.

Higher-wattage panels mean fewer panels and fewer mounting points, but they are larger and heavier (a 590 W bifacial panel is close to 90 in long), so check your rafter layout and whether one person can handle them on a roof.

4. "8 kW kit" does not always mean 8 kW of panels

This is the most common mix-up we see. Solar kits are often named after the inverter - its maximum continuous output - not the array. An "8,000 W kit" can ship with 3.3 kW of panels; a "10 kW kit" with 5.4 kW. Both numbers matter, but they answer different questions:

• Array size (panel kW) decides how many kWh you produce - this is the number from the formula above.
• Inverter size (kW output) decides how many appliances run at once: well pump, AC compressor, range and dryer together. For off-grid and backup, size it to your largest simultaneous load plus motor surge.
• Battery size (kWh) decides how long you run after sunset or during an outage.

The table below lists in-stock kits by their real array size. "Est. kWh per month" uses 4.5 sun hours and the 0.75 factor.

Specs are from the manufacturer data on each product page. The SGH hybrid kits are also sold without panels if you already have an array or want to source panels locally.

5. Grid-tied vs off-grid sizing

Grid-tied (with or without battery): size the array on your yearly kWh, because the grid absorbs summer surplus and covers winter shortfall under net metering. Check your utility's rules first - some cap system size at 100-120% of past use, and the inverter must be UL 1741 listed for interconnection. A battery is optional and sized for backup or time-of-use savings; our whole-home battery backup cost guide covers that math.

Off-grid: there is no grid to bank surplus, so size for your worst month, usually December. In much of the northern US, December delivers 2-3 peak sun hours against a yearly average of 4. A cabin using 10 kWh a day in winter needs 10 / (2.5 x 0.75) = about 5.3 kW of panels, versus 3.3 kW for the yearly average. Off-grid batteries are sized for 1-3 days without sun (daily kWh x days / 0.9 usable), and a generator usually covers long cloudy spells. See our best off-grid solar kits guide for complete systems by home size.

6. Our picks by home size

7. Which size for which home?

Browse every size: 5 kW, 8 kW, 10 kW, 12 kW, 15 kW and 20 kW solar power systems, or all solar power kits.

8. What our customers ask

Sizing questions reach us by phone, text and email in a few repeating patterns (shared here without any personal details):

• "Is the 10 kW kit 10 kW of panels?" Buyers often search our store for a "10,000 W" kit and are surprised that the number is the inverter. We walk through array size, inverter size and battery separately, as in section 4.
• "I need about 20 kWh of storage - what fits my inverter?" Battery requests usually come with an existing inverter. The first question is voltage: most of what we stock is 48V, while some brands use high-voltage stacks, and they are not interchangeable.
• "How big do I need?" We send the Solar Kit Calculator first, then check the result against 12 months of bills and any EV or heat pump the customer plans to add.
• "Will I need a trailer?" Yes for most home-size kits: a 450 W panel weighs about 54 lb and a 20-panel kit ships on a pallet, so plan for freight delivery or a trailer pickup.

9. Cost, incentives and codes

The kits above run about $1,100-$1,800 per kW of panels with batteries included, before racking, permits and installation. For grid-tied systems, note that the 30% federal residential clean energy credit (Section 25D) ended for expenditures after December 31, 2025, so payback now depends on your utility rate, net-metering rules and any state or utility rebates (this is not tax advice). Prices in this guide are store prices checked October 28, 2026. One code per order: SAVE250 ($250 off $4,000+) and SAVE500 ($500 off $8,000+) apply to kits at these price levels, and ECO100 gives $100 off $1,500+. Black Friday pricing is tracked in our Black Friday solar deals hub.

Still unsure? Send us 12 months of usage and your ZIP code and we will size the array, inverter and battery for you - or start with our full off-grid solar power systems and hybrid solar inverters.

Serhii Dovzhenko, Solar & Energy Storage Specialist at Eco Solar Kits · LinkedIn

Serhii is based in Vancouver, BC, and works on product data, system sizing and buyer guides for Eco Solar Kits. He attends solar and energy storage industry conferences and is involved in the community of electricians in Vancouver, BC. Credit for the data verification in this guide goes to Adsec.ca.