How Much Energy Does a Solar Panel Produce?
A typical 440 W panel makes about 1.5 to 2 kWh a day — roughly 550 to 800 kWh a year — in decent sun. But that "440 W" is a lab number, measured under perfect light at 25°C. What a panel really produces depends on sun hours, the technology, how it's angled, how hot it gets, and above all shade, where even a sliver can cost far more than its share. The tools below show why.
The nameplate watt is a lab figure — see what's left after the real world.
Shade is the big one not shown here — see the demo below.
The gap between the lab figure and the real one is the whole story. Swap the cell technology and watch the heat loss change; turn the panel east and watch the orientation cost climb. Then meet the loss the breakdown doesn't show — shade — in the demo lower down.
The short answer
In round numbers, a modern 400–500 W panel produces about 1.5–2.5 kWh a day, 45–75 kWh a month, and 550–900 kWh a year — the spread driven mostly by sunshine. The arithmetic is simple: rated watts × peak sun hours × a performance ratio of roughly 0.8 (heat, wiring, inverter and dirt losses). The rated wattage itself comes from Standard Test Conditions — 1000 W/m², a 25°C cell, and AM1.5 light — which your roof almost never matches. Everything below is the difference between that lab and your roof.
Panel type: what it changes
Counter-intuitively, technology barely changes energy per watt — a 440 W panel is 440 W whether it's PERC or HJT. What it changes is how many watts fit on your roof, and how the panel behaves over a hot day and a long life. Efficiency sets the area: 2026 modules run about 20–21% for mono PERC, 22–24% for TOPCon, and up to ~25% for HJT — and one extra efficiency point is roughly four fewer panels on a 10 kW system. TOPCon, developed at Germany's Fraunhofer Institute in 2013, overtook PERC as the dominant residential cell in 2024 with about 65% of production.
The bigger real-world levers are temperature and degradation. A panel loses power as it heats, and the temperature coefficient says how fast: about −0.35%/°C for PERC, −0.30% for TOPCon, and −0.26% for HJT. On a roof where cells hit 60°C, that's the difference between losing ~12% and ~9% to heat — which is why HJT wins in hot climates. N-type cells also age more gently, degrading roughly 0.25–0.40%/year versus 0.45–0.55% for PERC. Bifacial panels add a different trick: a glass back that harvests reflected light for a 5–20% rear-side gain over bright ground (concrete reflects ~30%, white gravel ~50%) — a real bonus on a ground mount, marginal on a dark rooftop.
Tilt, orientation & heat
Where you point a panel is worth more than which panel you buy. Facing the equator at a tilt near your latitude is the peak; turn it east or west and you lose roughly 10–20%, though an east-west split usefully spreads output across the morning and afternoon instead of piling it onto noon. Lay it dead flat or stand it too steep and you give up another ~10%. This is just the cosine effect — power falls off with the angle between the panel's face and the sun.
Heat is the quiet thief. Panels are rated at a 25°C cell, but a cell in full summer sun sits 25–30°C above the air around it, so a 35°C afternoon can mean a 60°C+ cell and a 10–15% haircut on output exactly when the sun is strongest. The flip side is the bonus nobody expects: cold, bright winter days are superb for panels, often beating mild ones. The explorer above lets you feel both — push the temperature up and watch the daily figure sink.
Shade & the inverter that fixes it
Shade is the one loss wildly out of proportion to its size, and it's the reason solar design is hard. Because cells are wired in series, the weakest cell throttles the current of the whole chain — like a single kink in a hose. A panel defends itself with bypass diodes (usually three), which switch a shaded cell-group out of the circuit to stop it overheating — but doing so removes that entire third of the panel. The result: a panel that's only 5% shaded can lose around 30% of its output, and shade falling across two of its three substrings can cost ~60%.
Now wire several panels into one string inverter and the shaded panel doesn't just lose its own output — it drags the series, so the sunny panels can't all run at their own best point. The fix is module-level power electronics: microinverters (Enphase) give every panel its own inverter, and power optimizers (SolarEdge, Tigo) give every panel its own DC tracker — either way each panel finds its own maximum and the shaded one is quarantined. In shaded installations that lifts output by roughly 8–17% a year, and adds per-panel monitoring as a bonus. Modern half-cut cells and smarter tracking have softened the old "one shaded panel kills the string" rule, but a roof with trees or a chimney shadow all day is still the textbook case for going module-level. Drag the shade across the panel below and switch the wiring to watch it happen.
A string of 8 panels; the third one falls into shade.
On one string inverter, the shaded panel both loses its own output and drags the series, so the sunny panels can’t all run flat-out. Even a small shadow costs more than its share.
And it fades, slowly
Whatever a panel makes on day one, it makes a little less each year. Modern modules degrade about 0.4–0.5% a year (less for N-type), so a panel still produces roughly 88–92% of its original output after 25 years — the basis of the standard 25-year performance warranty. Day to day, keep an eye on soiling and snow: even a thin film of dust or a dusting of snow can shave 5–15% until it's cleared or slides off. For the full arc, see how long solar panels last.
The watt stopped being the whole story
For years buyers chased the biggest number on the box. But the industry has quietly moved the contest from the cell to the system. Efficiency keeps climbing — PERC gave way to TOPCon, HJT is pushing past 25%, and perovskite-silicon tandems in the lab are already over 33%, hinting at panels that one day shrug off heat and squeeze far more from the same roof. Meanwhile the real gains on a typical house come from electronics and placement: a shaded roof with microinverters can beat a sunnier one wired naively.
So "how much does a panel produce" is becoming less a hardware spec and more a design question — orientation, temperature, shade and the brains attached to each module. Get those right and the watt looks after itself. The next number worth knowing is the one that turns kWh into a system size: how many watts a panel is.
Common questions
Game: panel facts
Five quick rounds on what really drives a panel's output.
Microinverters help shaded roofs by…
Method & sources
- Output — rated W × peak sun hours × performance ratio (~0.8); rating measured at STC (1000 W/m², 25°C cell, AM1.5). NREL PVWatts methodology.
- Cell tech (2026) — module efficiency PERC ~20–21%, TOPCon ~22–24%, HJT up to ~25%; temperature coefficient HJT ~−0.26, TOPCon ~−0.30, PERC ~−0.35 %/°C; N-type degrades ~0.25–0.40 vs PERC ~0.45–0.55 %/yr (SurgePV; a1solarstore; Clean Energy Reviews). TOPCon developed at Fraunhofer ISE, 2013; ~65% of 2024 production.
- Bifacial — 5–20% rear gain by ground albedo (grass 0.20, concrete 0.30, white gravel 0.50).
- Shading — even 5% shade ≈ 30% panel loss; two substrings ≈ 60% (bypass-diode behaviour, USPTO 9,502,897). MLPE lifts shaded-system output ~8–17%/yr (Aurora Solar; Clean Energy Reviews). Microinverters (Enphase), optimizers (SolarEdge, Tigo).
- This is a simplified planning model, not engineering design — model your roof with NREL PVWatts or PVGIS.
More solar & energy answers
The number on the box is what a panel could do — sun, heat, angle and shade decide what it will.