System sizing

Panel count for a net-zero home

Net-zero means your system produces as much as you use over a full year. Enter your annual usage and see the exact panel count that gets you there, plus room for future growth.

Your numbers

1 Project details Optional
Shown on your exported report. Leave blank to skip.
2 Your annual usage
Add up 12 months of bills, or check your utility's online usage history.
Covers panel degradation and planned electrification. An EV adds about a third of an average home's usage, so scale the buffer to your own numbers.
3 Your location and equipment
Check NREL's PVWatts for your address. Most of the US ranges from 3.5 to 6 hours.
Most home panels quoted in late 2025 were 400 to 460 watts, according to EnergySage's marketplace data.
4 Derate factor
Accounts for inverter loss, wiring loss, dust, and temperature derate combined.

How it works

Three steps to net-zero

Step 1

Total your real annual usage

Pull 12 months of actual bills rather than estimating from a single month, since net zero is judged on the full year, not the sunniest one.

Step 2

Decide whether to size for today or tomorrow

A system sized exactly at 100% of today's usage degrades below that over time and won't cover an EV or heat pump added later. Check the oversizing for a future EV calculator if that's on your horizon.

Step 3

Confirm your net metering policy supports the target

Full-retail net metering makes 100% offset straightforward. Reduced-export policies change the math, sometimes favoring a smaller system or one paired with a battery. If your utility instead caps system size outright, the net metering cap tool works backward from that limit.

What net-zero really means for sizing

Annual balance, not monthly balance

A net-zero system doesn't produce exactly what you use every day, or even every month. It produces a surplus in sunny months and a deficit in darker ones, with net metering crediting the summer surplus against the winter shortfall, though what happens to a leftover balance at the annual true-up varies by utility. What matters for a net-zero target is the full year adding up, not any single billing cycle, and the annual kWh output estimator turns your location into the yearly production figure that balance depends on.

Why your net metering policy changes the target

Where every kWh you export credits at the same rate you'd otherwise pay to import it, 100% annual offset is the straightforward, cost-effective target. Under newer reduced-export policies, covered directly by the net billing vs net metering comparison, exported power earns less than retail value, which can make a smaller system, or one paired with a battery that keeps more of your production on site, the better choice. The right answer depends on your export rate and when you use power, so check your utility's current rules before treating 100% as the default.

Why sizing for today's usage often falls short

Solar panels lose a little output every year. NREL's compendium of photovoltaic degradation rates found median degradation of 0.5 to 0.6% a year for crystalline silicon modules, so a system sized to exactly match today's usage produces about 95% of it a decade from now. A planned EV or heat pump makes current usage the wrong baseline entirely: an EV alone adds about a third of an average home's annual consumption, a load the future EV oversizing calculator sizes directly. A home battery behaves differently, since the future battery calculator shows it adds mainly round-trip losses, and the 110% offset tool covers a general growth buffer.

What a realistic panel count looks like

The average US home uses about 10,800 kWh of electricity a year, according to EIA. For a home using 10,500 kWh with 400-watt panels and a 0.80 derate, that works out to about 15 panels at 6 peak sun hours, 20 at 4.5, and 26 at 3.5, a spread wide enough that running your own numbers matters more than any single average. If a partial offset suits your utility's export rules better, the 90% offset tool models that directly.

Questions

Frequently asked

Net-zero means your system produces as much energy over a full year as your home consumes, not that your bill is zero every single month. Summer surplus offsets winter shortfalls through net metering, so the annual total is what matters, not the month-to-month balance.

Yes, significantly. Where every exported kWh credits at the full retail rate, 100% annual offset is the natural target. Under reduced-export policies, sizing below 100%, or adding a battery to use more of your output on site, may make more sense, and the right balance depends on your export rate and when you use power.

Often yes. Panels degrade at a median of 0.5 to 0.6% a year, so a system sized at exactly 100% of today's usage produces about 95% of it after a decade. A 10% buffer roughly absorbs 20 years of that decline, and an EV adds about a third of an average home's usage, so plan for it separately if one is coming.

It depends heavily on your consumption, local sun hours, and panel wattage. A home using 10,500 kWh a year with 400 watt panels needs about 15 panels at 6 peak sun hours, 20 at 4.5, and 26 at 3.5, assuming a 0.80 derate.

Related tools

Keep sizing your system

Panel count for 90% offset Panel count for 110% offset Oversizing for a future EV Oversizing for a future battery Solar panel calculator System size for a net metering cap limit System size by annual kWh usage All system sizing tools