Why Is My Solar Production Low?

"My production seems low" has about six common explanations, and they're worth working through in order — because the most likely ones aren't faults.

Step 1: Compare like with like

Before anything else: compare against the same month in a previous year.

Month-against-last-month is dominated by season and will mislead you. Same-month-last-year controls for that.

If you don't have a prior year, compare against the monthly figures in your original production estimate — not the annual total divided by twelve, which ignores seasonality.

See solar panel monitoring explained and solar production by season.

Step 2: Rule out weather and season

Season. Winter production is a fraction of summer in most locations — shorter days, lower sun angle. That's expected, not a fault.

Weather. A cloudy month produces less. Compare a full year rather than reacting to one month.

Heat. Panels produce less per hour of sun when hot, so a heatwave can reduce output despite abundant sunshine. See why solar panels produce less when hot.

If the shortfall is one month and the weather was poor, wait and watch.

Step 3: Check for physical obstruction

Snow. Complete coverage means near-zero output. Usually resolves as it slides or melts. See do solar panels work in winter.

Soiling. Dust, pollen, bird droppings and agricultural or industrial deposits accumulate. In regions with regular rain this largely self-manages; in dry regions it builds.

The signature is uniform low production across all panels — everything down together, no single outlier. See how to clean solar panels.

Debris. Leaves, branches or nesting material, particularly at panel edges and under the array.

Step 4: Look for shading changes

This one catches people because it develops slowly.

Trees grow. A branch that cleared the array three years ago may not now. Shading losses are disproportionate to the shaded area in series strings.

Seasonal sun angles shift. The sun's path is lower in spring and autumn than at midsummer, so an obstruction that casts no shadow in June may shade the array in October — same object, different angle.

New obstructions — a neighbour's extension, a new satellite dish, a chimney added.

The signature: a notch in the daily production curve at a consistent time of day, or one panel consistently down while others are fine.

See how shading affects solar panels.

Step 5: Check for equipment faults

With panel-level monitoring, this is straightforward: look for a module consistently below its identical neighbours under the same conditions. That's a failed panel, optimizer or microinverter.

With system-level monitoring only, you'll see the total is down and need help isolating it. Common faults:

• A string offline — total drops by a large step
• Inverter fault — check for error codes and see solar inverter troubleshooting
• A failed panel dragging its string
• A failed optimizer or microinverter
• A tripped breaker on the solar circuit
• Connection degradation — loose or corroded connections

A sudden step change points to equipment. A gradual decline points to shading, soiling or normal degradation.

Step 6: Consider whether the estimate was wrong

A different problem from a system that declined — and a common one.

If the system never met its estimate, check whether that estimate:

• Applied a system derate for inverter losses, wiring, temperature, soiling and mismatch
• Used location-specific irradiance data
• Modelled your actual orientation and tilt, per roof plane
• Incorporated a site-specific shading analysis
• Accounted for clipping, if the array is oversized relative to the inverter

Optimistic estimates are common, and an estimate without a stated derate is overstating production. See peak sun hours explained, solar system sizing mistakes, and choosing a solar installer.

Raise it with the installer, with monitoring data in hand.

Step 7: Normal degradation

Panels lose a small amount of output annually. Over years this is measurable; over months it isn't the explanation.

If production is down a few percent after several years, that's expected and warranted. If it's down substantially in one year, it isn't degradation. See how long do solar panels last and solar panel warranties explained.

Quick reference

What should you do about low solar production?

1. Compare same-month-last-year or against the monthly estimate
2. Check for snow, soiling and debris
3. Look at the daily curve shape for shading notches
4. Check panel-level data if available
5. Check for inverter error codes and the solar breaker
6. Look for new shading — walk outside at several times of day
7. Contact your installer with the data, not just an impression

That last point matters. "Production seems low" gets a different response than "October production is 30% below the same month for the previous two years, and panel 7 has been consistently below its neighbours since August."

The bottom line

Compare against the same month in a previous year before concluding anything — season, weather and heat explain a great deal. Then check for snow and soiling (uniform drop), shading changes (a notch in the daily curve, or one panel down), and equipment faults (a sudden step). And consider that the original estimate may simply have been optimistic, which is a different conversation with your installer.

Check expectations with the solar output calculator, revisit economics with the solar panel payback calculator, or read solar panel monitoring explained.