Why Are My Solar Panels Producing Less Than Expected? (12 Causes and Fixes)

You opened your monitoring app, or maybe you got your annual true-up bill from the utility, and the numbers don’t add up. The salesperson promised one figure. What you’re seeing is lower. Now you’re staring at the screen wondering whether something is broken, whether you got sold a bad system, or whether you’re just imagining it.

Here’s the good news: in most cases, the cause is something specific and identifiable — and often something you can fix yourself or get fixed quickly. Solar panels that produce “less than expected” usually aren’t a mystery. There are about a dozen real reasons it happens, and we’re going to walk through every one, starting with the most common.

Before we dive in, it’s worth confirming your system is actually running at all. If you haven’t already, read our guide on [LINK: How to Tell If Your Solar Panels Are Actually Working] — it’ll help you rule out a total outage before you start hunting for a partial one.

Now, the 12 causes, roughly in order of how often they’re the culprit.

1. Shading (the most common cause by far)

Shade is the number one reason healthy solar systems underproduce. And the frustrating part is that shade changes over time. The tree that was a sapling when you installed your panels five years ago is now tall enough to throw a shadow across your roof every afternoon. A neighbor built a second story. A new rooftop vent, satellite dish, or chimney is casting a shadow you never noticed.

Here’s the part that surprises most people: with a traditional string inverter system, shade on even a single panel can drag down the output of every panel wired together in that “string.” The panels are connected in series, like old Christmas lights — one weak link pulls down the whole chain. So a little shadow on one corner of one panel can cost you far more than you’d expect.

Systems with microinverters (one small inverter per panel) or power optimizers handle shade much better, because each panel operates independently. One shaded panel doesn’t drag down its neighbors.

What to do: Walk outside and look at your roof at different times of day — morning, noon, and late afternoon. Note any new shadows. Trimming an overhanging branch is often the single highest-return fix you can make. If shade is unavoidable and you have a string system, ask your installer whether optimizers can be retrofitted.

2. Dirty Panels and Soiling

Solar panels are glass. Glass gets dirty. Dust, pollen, tree sap, bird droppings, and general grime build up over time and physically block sunlight from reaching the cells underneath.

In rainy climates, rain rinses most of this away on its own. But in dry, dusty regions — think the Southwest, or anywhere with a long dry season — soiling can cost you 15 to 25 percent of your output before you even notice. That’s a huge, invisible loss.

What to do: This is one of the easiest fixes on the list. In many cases a garden hose from the ground, on a cool morning or evening, is enough to rinse off loose dirt. For stubborn buildup or hard-to-reach roofs, hire a professional panel cleaning service — they’re inexpensive and do it safely. Never climb onto a wet, sloped roof yourself. A clean panel can recover most of that lost 15-25 percent immediately.

3. Normal Panel Degradation

Solar panels don’t last forever at 100 percent, and they’re not supposed to. Every panel slowly loses a little capacity each year. The good news is that “a little” really is little.

According to analysis from kWh Analytics, the median degradation rate is about 1.09 percent per year. That means a 5-year-old system should be producing roughly 5 percent less than it did brand new. That’s completely normal and expected — it’s even baked into your manufacturer’s warranty.

What is not normal is a sudden, sharp drop. If your system lost 10 percent of its output in its second year, that’s not degradation — that’s a problem (likely one of the other causes on this list). Degradation is slow and gradual. Sudden drops mean something else is going on.

What to do: Compare this year’s production to last year’s, adjusting for weather. A 1-2 percent annual decline is healthy. A double-digit drop is a red flag worth investigating.

4. Inverter Problems

Your inverter is the unsung workhorse of your solar system — it converts the DC power your panels make into the AC power your home uses. It’s also the component most likely to fail, because it works hard every single day.

Here’s the lifespan reality: a central string inverter typically lasts 10 to 15 years, while microinverters last 20 to 25 years. If your system is around the decade mark and production is dropping, the inverter is a prime suspect.

The quickest check costs nothing: look at the status light on your inverter (it’s usually a box on the side of your house or in the garage). A steady green light generally means everything’s fine. A red or amber light, or blinking, signals a fault.

What to do: Note what the light is doing and check your monitoring app for error codes. If you suspect inverter trouble, don’t open it or attempt repairs — call your installer or a licensed technician. For a deeper walkthrough, see [LINK: Is My Solar Inverter Failing?].

5. NEM 3.0 and Net Metering Changes

This one trips up a lot of people, especially in California. You look at your bill, see smaller savings, and assume the panels are underperforming. But here’s the key distinction:

Production (the kilowatt-hours your panels generate) and savings (the dollars you keep) are two different things.

Your utility can change how much it pays you for the power you export to the grid — and that changes your bill without your panels producing a single watt less. California’s shift to NEM 3.0 (the Net Billing Tariff) cut export credit rates dramatically. Same sunshine, same panels, same kilowatt-hours — but the dollars look different because the rules changed underneath you.

What to do: Look at the kWh produced in your monitoring app, not the dollar savings on your bill. If your kWh numbers are healthy but your savings shrank, your panels are fine — your rate structure changed. We cover this in detail in our guide to NEM 3.0 for existing owners.

6. Seasonal Variation

The sun is lower in the sky in winter, the days are shorter, and the weather is cloudier. Your panels respond accordingly. This isn’t a malfunction — it’s astronomy.

A system in a northern state producing 30 percent less in December than it did in June is behaving exactly as it should. Some homeowners panic when winter numbers come in low, then feel relief when summer arrives, not realizing both are perfectly normal.

What to do: Don’t compare December to June. Compare December to last December, and June to last June. Year-over-year, same-month comparisons are the only fair way to judge whether something has actually changed.

7. High Temperatures

This one feels backwards: more heat does not mean more power. Solar panels are rated at a cell temperature of 25°C (77°F), and they actually become less efficient as they get hotter.

For every degree above that rating, output typically drops by about 0.3 to 0.5 percent. On a blazing summer day, a rooftop panel in Phoenix can hit 70°C, which means it might lose 13 to 22 percent of its rated output right when the sun is strongest. It’s a real effect, it’s normal, and there’s not much you can do about it — but it’s worth knowing so you’re not alarmed by lower-than-expected midday numbers in a heat wave.

What to do: Nothing, really — this is physics. Just factor it into your expectations on very hot days. Properly installed panels have an air gap beneath them to help them shed heat, so as long as yours were mounted correctly, you’re already getting the benefit.

8. A Faulty Microinverter or Optimizer

If you have microinverters (Enphase) or power optimizers (SolarEdge), each panel reports its production individually. That’s great for diagnosing problems — because when one little unit fails, it silently takes its one panel offline while the rest keep humming. Your total output drops, but nothing looks dramatically “broken.”

The telltale sign: in your app, one panel shows zero or far lower production than all its neighbors, day after day, even in full sun. Healthy panels track closely together. One consistent outlier means a dead or dying microinverter/optimizer.

What to do: Open your monitoring app and look at the per-panel view. If you’re not sure how to read it, our guide on [LINK: How to Read Your Enphase/SolarEdge App] walks through exactly where to look. If one panel is clearly the odd one out, contact your installer — these components are usually under a long warranty.

Emporia Vue 3 home energy monitor — An independent home energy monitor like the Emporia Vue 3 lets you verify your total solar production separately from your installer’s app — useful for spotting discrepancies between what you’re actually generating and what the software claims.

9. Wiring and Connection Issues

Your system is held together by connectors and wiring, and over years of sun, heat, and weather, things can degrade. The small MC4 connectors that link panels can work loose. Rodents love to chew on rooftop wiring. Corrosion can creep into connections exposed to moisture. Any of these can cut production — sometimes a little, sometimes a lot.

This is not a DIY situation. We’ll say it plainly: do not touch your solar wiring, open any electrical enclosure, or work anywhere past your meter. Solar systems carry dangerous voltage even when the sun isn’t shining, and this is exactly the kind of work that requires training.

What to do: If your production has dropped and you’ve ruled out shade, soiling, and seasonal effects, a wiring or connection fault is a likely culprit — and it’s time to bring in a professional. A licensed solar technician can safely inspect connectors, test for faults, and check for rodent damage.

get a free inspection quote — If you suspect a wiring or connection issue, get a professional inspection from a certified installer rather than attempting any electrical diagnosis yourself.

10. A Monitoring App Glitch (Not a Real Problem)

Sometimes the panels are perfectly fine and the app is the problem. Monitoring systems rely on a small gateway device and a home internet connection to report data. When the internet hiccups, the gateway loses power, or the software glitches, your app can show zero production even though your system is generating normally.

This is one of the most common false alarms in all of residential solar. Before you assume the worst, rule out a reporting glitch.

What to do: First, check whether your home is still drawing solar power even though the app shows nothing (your electric meter or whole-home monitor can confirm this). Next, check that the circuit breaker for your solar system hasn’t tripped. Then try restarting the monitoring gateway — unplug it for 30 seconds and plug it back in, exactly like rebooting a router. Give it a few minutes to reconnect. Very often, the “outage” disappears and you’ve lost nothing but a few minutes.

11. The System Was Sold Too Small (or Oversold)

This is the hardest truth on the list. Sometimes the system is working flawlessly — it’s simply never going to hit the number you were promised, because that number was optimistic from the start.

It happens when the original quote assumed you’d use less electricity than you really do, or assumed more sunshine than your roof actually gets, or used best-case modeling to make the sale. The panels do exactly what they’re capable of; it’s just that “what they’re capable of” was always going to fall short of the glossy estimate.

What to do: Dig out your original proposal and find the estimated annual production in kWh. Compare it to what your system has actually produced over a full year (use your monitoring app’s annual total). If your real production roughly matches the technical spec of the equipment but falls short of the sales estimate, the hardware is fine — the estimate was inflated. From there, your options are to add more panels, add a battery to use more of what you make, or simply reset your expectations. It’s not a satisfying answer, but knowing it saves you from chasing a fault that doesn’t exist.

12. A New Battery Is Diverting Your Production

Did you recently add a home battery? If so, this might explain everything. Before the battery, your excess midday solar flowed out to the grid and earned you export credits. Now, that same excess power charges your battery first — so less of it reaches the grid, and your export credits drop.

Homeowners see smaller export numbers and assume production fell. It didn’t. The energy is simply going into your battery instead of to the utility, where you’ll use it yourself in the evening instead of buying expensive grid power. Your actual production is unchanged — only the destination of the electricity changed.

What to do: If your export credits dropped right after you installed a battery, that’s expected and usually a good thing — especially under NEM 3.0, where stored energy is worth far more than cheap midday exports. Check your total production in kWh (not just exports) to confirm your panels are still generating normally.

Quick Reference: All 12 Causes

#	Cause	DIY or Pro?	Urgency
1	Shading	DIY (trim branches) / Pro (optimizers)	Medium
2	Dirty panels / soiling	DIY (or cleaning service)	Low
3	Normal degradation	No fix needed	Low
4	Inverter problem	Pro	High
5	NEM 3.0 / rate changes	No fix (understand it)	Low
6	Seasonal variation	No fix needed	Low
7	High temperature	No fix needed	Low
8	Faulty microinverter / optimizer	Pro (warranty)	Medium
9	Wiring / connection issue	Pro (always)	High
10	App glitch (false alarm)	DIY (restart gateway)	Low
11	System sold too small	No quick fix	Medium
12	Battery diverting export	No fix (it’s working)	Low

The Bottom Line

If your panels are producing less than expected, work down this list from the top. Start with the free, easy checks — shade, dirt, seasonal timing, and app glitches account for a huge share of “underperformance” reports, and you can resolve them yourself in an afternoon. If you’ve ruled those out and your kWh production has genuinely dropped, the most likely hardware culprits are the inverter, a failed microinverter, or a wiring fault — and those are jobs for a licensed professional, never for you.

The most important habit: track your production in kWh, year over year, same month to same month. That single discipline will tell you, faster than anything else, whether you have a real problem or a normal variation.

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Last reviewed: June 2026 | solarschoice.com is an independent site — we are not affiliated with any solar installer or utility.