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What a typical-year load profile is, and why it matters

Most real energy audits are short. A power logger left in place for two weeks, a utility export covering one quarter — rarely a full, continuous year. But several useful questions ("what does this system look like integrated over 12 months?") genuinely need a full year to answer. A typical-year load profile is a synthetic 365-day, hour-by-hour demand shape built from your real, shorter audit, so those questions have something to work against — while being explicit the whole way through about which hours are real measurements and which are statistically synthesized.

Why not just repeat your audited days?

Simply looping a two-week audit fifty-two times over would understate how real demand varies — week to week, month to month, and even hour to hour on two otherwise-similar days. A system sized against an artificially smooth, repeating profile can look better on paper than it would against the real variability a site actually experiences.

How the extrapolation works

WattSketch follows HOMER Energy's documented synthetic-load-profile method: start from a baseline daily shape for each month (built from your own real, cleaned audit data — the same hour × day heatmap your Analyze screen already computes, not a generic assumption), then add two independent layers of randomness:

• Day-to-day variability — each synthetic day's total energy is scaled up or down from the baseline by a random factor.
• Hour-to-hour variability — within a day, the hour-by-hour shape is perturbed slightly around the baseline curve.
• Every synthetic day is then renormalized so its total energy matches its own target exactly — the randomness changes the day's shape, never silently drifts its total away from what was intended.

How strongly both layers of randomness are applied is controlled by a single Variability slider (0–100%). The underlying constants that translate that slider into actual day-to-day and hour-to-hour spread are WattSketch's own interaction choices, disclosed as such in the tool itself — not a sourced physical figure the way, say, a battery round-trip efficiency number is.

What stays real vs. what's synthesized

Every day you actually audited keeps its own real measured shape in the typical year — it isn't touched or replaced. Only the days you didn't audit are filled in synthetically, and the tool shows you plainly which is which, month by month, rather than blending the two together indistinguishably. You can also adjust month-to-month seasonal scaling yourself if you have reason to believe a month you didn't audit runs noticeably hotter, colder, or busier than your audited period would suggest, and download the full 8,760-row result to inspect exactly what was generated.

When you actually need this step

It's optional, and skippable — most of WattSketch's solar sizing only needs your real average daily energy use, which a short audit already gives you reliably. Reach for the typical-year extrapolation specifically when something you're looking at wants a genuine full-year shape: a full annual self-consumption/export picture month by month, or a year-round view of a battery or generator's behavior across every season, not just the one your audit happened to capture.

An honest limitation

A synthetic year is still a statistical estimate, not a measurement. If your business or site has a real, known seasonal pattern your audit didn't capture — a summer-only cooling load, a harvest-season production run — the automatic extrapolation won't know about it unless you tell it, via the manual seasonal scaling controls. Treat a typical year as a reasonable, inspectable estimate for planning purposes, not a substitute for actually metering a full year if the decision riding on it is a large one.