Your solar production dropped. Check these first

Most production drops have a plain cause. Work through this list in order, from the sky to the meter to the glass, and you will usually find it before anyone climbs a ladder.

Is it really a drop?

Start here, because many “drops” are the calendar. Output on the Front Range swings hard between seasons. A clear day in December makes a fraction of what a clear day in June makes, because the sun is low and the day is short.

So compare like with like:

• The same month last year: not last month, and not your best day ever.
• Clear days with clear days: a cloudy week tells you about the clouds.
• Daily totals: not a single moment’s power reading.

If November this year looks like November last year, nothing has dropped. Our article on why winter output drops explains what normal looks like through the dark months.

Was it the weather?

Next, rule out the sky. A few patterns explain a lot of sudden dips:

• Cloud and storms: obvious in hindsight, easy to forget when you only see the monthly total.
• Smoke: a hazy week in late summer trims output, though distant smoke takes less than it looks. See what wildfire smoke does to your solar output.
• Snow: panels covered after a storm make little or nothing until it slides off.
• Upslope fog: a grey morning along the foothills can flatten the first half of a day.

Weather dips recover. If clear days after the weather look like clear days before it, you can stop here.

Is the app telling the truth?

Sometimes the panels are fine and the reporting is not. Monitoring data travels from your inverter or gateway, over your home internet, to the app. A new router, a power cut or a changed Wi-Fi password can break that chain.

• Flat zero for hours or days: often a reporting gap, not an outage.
• A gap that later fills in: the gateway stored data and caught up.
• Odd spikes after a gap: stored data arriving all at once.

The quickest check is your utility meter. On a sunny afternoon, if the meter shows the house exporting power while the app shows zero, the system is producing and the app is not hearing about it. Your installer can help reconnect the monitoring.

Does the system show a fault?

Look, but do not touch. Many inverters have a status light or a small display, and most apps show alerts or error codes.

• A fault light or error code: note it, photograph it, and call your installer.
• The inverter off or silent on a sunny day: call your installer.
• A panel or string at zero in the app: call your installer.

Faults are electrical, and electrical work belongs to your installer or a licensed electrician. We do not open junction boxes, reset equipment or rewire anything, and we would gently suggest you do not either.

Did anything change at the house?

Think back over the last few weeks. Work on the house can affect the system even when nobody touched the panels.

• Roof work: panels taken off and put back for reroofing may not have been reconnected fully.
• Electrical work: a new EV charger, a panel upgrade or a remodel can leave a breaker or disconnect off.
• A power cut: some systems need a manual restart afterwards.

If the drop lines up with any of these, call your installer first. They can confirm the system is back to how it should be.

Has something new cast shade?

Shade grows quietly. Trees keep growing every summer, and a branch that cleared the array last summer may not this summer. Low winter sun makes it worse: a tree well south of the house can shade the bottom row by mid-afternoon in December.

Other new shade is easy to miss because it is not on your roof:

• A neighbor’s addition or second story: casts long shadows in winter.
• A new satellite dish or vent: shades a corner every morning.
• Your own improvements: a new pergola, a grown-up hedge, a raised chimney cap.

Panel-level data makes shade easy to spot, because it repeats every clear day at the same hour. Our guide on how to read panel-level data shows what that pattern looks like.

Is something on the glass?

Now look at the panels themselves, from the ground, on a clear morning with binoculars.

• A slow slide over weeks: a film of pollen, dust or ash building on dry days.
• One panel or patch: a bird dropping, leaves or a cottonwood seed mat.
• The bottom row: a dirt line at the frame, or old snow holding on at the eave.
• Twigs or feathers at the edges: pigeons nesting under the panels, with droppings to match.

A slow, steady slide on clear days with no new shade and no change in season is the classic sign of soiling. That is the one cause on this list a wash can fix.

Did hail come through?

If the drop started after a storm, think hail. From May to August, Front Range hail can crack panel glass, bend frames and knock debris onto the array.

Look from the ground for a white, crazed web in the glass, a cracked corner or a bent frame. Do not climb up to check, and do not wash a cracked panel. Our article on what to check on your panels after hail has the full list, and a storm check gets you a photo report of every module from $119.

How big a drop matters?

Big and lasting matters. Small and brief usually does not. A method published in Solar Energy by researchers at UTS, UNSW and Diagno Energy gives a sensible yardstick. It flags major underperformance when output stays below 60% of expected for three non-cloudy days, and minor underperformance below 80% for seven days. The method was tested on 1,089 Australian PV systems.

In plain terms:

• Far below normal for three clear days: something is wrong. Act now.
• Somewhat below normal for a week of clear days: worth finding out why.
• A short dip that recovers: weather, shade, or a bird that has since moved on.

“Expected” is the tricky word. For most owners, the best expected value is the same clear-day period last year, adjusted for any new shade. Our guide to reading your solar app shows how to pull those figures out.

Who do you call for what?

Each cause has an owner, and it is not always us:

• Fault codes, dead inverters, panels at zero: your installer or a licensed electrician.
• Monitoring gaps: your installer, or the monitoring maker’s support line.
• Roof leaks or damaged flashing: a roofer.
• Hail damage you may claim: your insurer, ideally before repairs.
• Film, droppings, debris on the glass: a wash.
• Something you cannot name: a visual inspection with photos of every module.

We will always tell you which of these it is when we can see it. If it is not ours, we say so and point you to the right trade.

Can someone watch this for you?

Yes. With your permission and read-only access, our performance monitoring service reads your production every month and flags a drop that outlasts the weather. You get a short, plain note: what we see, the likely cause, and who should look at it.

Output watch is from $12 a month or $129 a year. It is the cheapest way to stop wondering whether a low month means anything.

Where to go from here

If you have worked down this list and the cause still is not clear, email us a screenshot of a few clear days from your app and we will give you a plain read. If the glass is the problem, put your figures into the output check to see what it is worth, and book a visit when it suits you.