Performance and output

Output vs usage gap analyzer

Enter your annual output, annual usage, and location. See which months run a surplus, which run a deficit, and your annual net gap.

Your output and usage

1 Project details Optional
Shown on your exported report. Leave blank to skip.
2 Annual totals and location
Use your rated annual output, or the annual output estimator.
From your utility bills, or the household output calculator.
Sets how sharply output swings between summer and winter.

How it works

Three steps to your gap pattern

Step 1

Enter both annual totals

Use your system's rated annual output, or the annual output estimator, alongside your actual usage from utility bills or the household output calculator. A battery can close that gap by storing midday surplus for the evening, and the self-consumption battery size calculator sizes it.

Step 2

Set your location and load profile

Latitude shapes how much output swings between summer and winter, while your heating or cooling profile shapes when usage peaks.

Step 3

See where the two curves diverge

The analyzer maps both curves across the year and flags which months run a surplus, which run a deficit, and how they net out annually.

Understanding your surplus and deficit pattern

Why the annual totals can match while months don't

Output peaks in summer while usage often peaks in winter for heating-heavy homes or in summer for cooling-heavy homes, so the two curves rarely line up perfectly even when the yearly totals are close. This is normal and doesn't mean either number was calculated wrong. A DOE study of federal PV systems found an average energy ratio of 74.6%, a useful reference when comparing modeled output against actual household usage.

What a positive annual gap does and doesn't guarantee

Not necessarily does a positive annual gap mean you'll never pay a winter electric bill. A positive annual gap means your system produces more than you use over the full year, but if your utility doesn't roll over credits indefinitely, a big winter deficit can still show up as a bill even with a surplus on paper. Check your utility's net metering rules to see how credits carry over. The net billing vs net metering comparison explains why this rollover question depends heavily on which billing structure your utility actually uses.

What an all-deficit result means

An all-deficit result usually means the system is undersized for your usage, which is common in heating-heavy climates where winter usage climbs faster than winter output can keep up. If you're seeing this, revisit the household output calculator to check your target output against what your current system actually delivers.

How your heating and cooling load shapes the curve

A heating-dominant home uses the most electricity in the coldest months, which is exactly when solar output is lowest, while a cooling-dominant home uses the most in summer, closer to when output peaks. That's why a cooling-dominant home in a sunny climate often sees a much smoother gap pattern than a heating-dominant one further north. An EIA analysis of hourly electricity load confirms this same seasonal shape nationally, with total U.S. electricity demand peaking in summer afternoons and running lower and steadier through the winter months.

What to do with this result next

If your worst month runs a heavy deficit, compare it against the real-world vs nameplate gap calculator to rule out derating as a factor, or head back to the performance and output hub for related tools.

Questions

Frequently asked

Output peaks in summer while usage often peaks in winter for heating-heavy homes or in summer for cooling-heavy homes, so the two curves rarely line up perfectly even when the yearly totals are close.

Not necessarily. A positive annual gap means your system produces more than you use over the full year, but if your utility doesn't roll over credits indefinitely, a big winter deficit can still show up as a bill even with a surplus on paper.

An all-deficit result usually means the system is undersized for your usage, which is common in heating-heavy climates where winter usage climbs faster than winter output can keep up.

A heating-dominant home uses the most electricity in the coldest months, which is exactly when solar output is lowest, while a cooling-dominant home uses the most in summer, closer to when output peaks.

Related tools

Keep exploring your output

Household output calculator Annual kWh output estimator Monthly kWh output estimator Real-world vs nameplate gap Daily kWh output estimator Quick output estimator Capacity factor calculator All performance and output tools