⚠️

Why panels don't charge as they should — 7 causes and solutions

90%fixed without replacement
−30%from dirt
−50%from shading
7main causes
🔎 Problem Statement

The system is installed, but there is no generation — what is the reason

Batteries don't charge fully, the inverter shows low performance, and the bills haven't decreased as expected — one of the most common complaints from solar system owners.

Good news: in 90% of cases, the cause can be fixed independently or with a specialist's help without major expenses. You just need to know where to look.

Total-Energo specialists perform full diagnostics of solar systems — from thermal imaging to inverter data analysis.

7 causes in this article

1Dirt on panels

2Shading from trees and buildings

3Incorrect angle or orientation

4Natural panel degradation

5Inverter / controller issues

6Oxidation of contacts and connectors

7Panel overheating in heat

⚡ How to know if the station is underperforming

Before looking for the cause — make sure the problem actually exists. Here are the red flags:

Inverter shows power below 70–80% of nominal on a clear sunny day

Batteries do not charge to 100% even after a full sunny day

Monthly generation is lower than promised upon purchase

Sharp drop compared to the same month last year

−30% From dirt

if not washed for 1+ year

−50% From shading

one panel limits the whole row

−15% From overheating

on hot +35°C days

90% Solved

without replacing equipment

🔧 Detailed breakdown

Select a cause — find the solution

👇 Click on a cause — see its impact and what to do
0% 25% 50% 75% 100% Normal 100% 💧 Dirt on panels Losses: up to −30% of generation ✅ Solution: wash with a soft brush and clean water

💧 Dust, bird droppings, and leaves — the most common cause. Wash the panels 2–4 times a year, especially after dust storms.

📋 All 7 causes

Full description of each — and exactly what to do

💧
Dirt on panels
⬇ up to −30% generation
Dust, bird droppings, poplar fluff, leaves — all this blocks sunlight. Especially critical is spot contamination: even a small spot of bird droppings on one cell can "drag down" the performance of a whole row due to bypass diodes.
✅ Wash 2–4 times a year with a soft brush and clean water. Never wash with hot water in the heat — a sharp temperature drop can damage the glass.
🌳
Shading from trees and buildings
⬇ up to −50% or more
Trees grow, neighbors build new superstructures — shading that was not taken into account during installation may appear a year later. Because of the series connection of the panels, one shaded panel limits the entire row.
⚠️ Trim branches regularly. For serious shading — install power optimizers so that each panel works independently.
🧭
Incorrect angle or orientation

 

⬇ up to −20% generation
Ideal for Ukraine is south, 30–35°. But there's a nuance: in winter the sun is low, so a steeper angle (45–60°) gives better results in November–February. A roof facing east or west means minus 10–15% per year. More details.
✅ Change the angle twice a year for adjustable mounts. With unfortunate roof orientation — optimizers will partially compensate for losses.
📉
Natural panel degradation
⬇ 0.5–2% per year
All solar panels gradually lose efficiency — it's physics. High-quality ones (JA Solar, Longi, Canadian) degrade by 0.5%/year, cheap analogs — up to 2%/year. After 10 years, a high-quality panel gives 95%, a cheap one — only 80–85%.
ℹ️ Compare generation with the first months of operation (data in the inverter's memory). A drop of >10% in a year is a warranty case.
⚙️
Problems with the inverter or controller
⬇ from −10% to full stop
The inverter is the heart of the system. Typical problems: overheating due to poor ventilation, outdated firmware, incorrect MPPT settings, damage after a thunderstorm. Even perfect panels will yield zero with a faulty inverter.
🔧 Check the error log and the temperature around the inverter. Update the firmware. If there are error codes — straight to the service center.
🔌
Oxidation of contacts and MC4 connectors
⬇ from −5% to stopping a row
MC4 connectors oxidize over time, especially with poor-quality installation without waterproof connectors. An oxidized contact increases resistance, lowers current, and can cause the cable to heat up.
🔧 Visual inspection of accessible connectors. Do not disassemble MC4 yourself — a special tool is required. Thermal imaging diagnostics will show the problem exactly.
🌡️
Panel overheating in heat — surprising, but normal
⬇ up to −15% on the hottest days
Solar panels have a negative temperature coefficient: typically −0.35% for every degree above 25°C. In summer, panels heat up to 60–70°C — power drops by 12–16%. This is why generation is lower than expected on the sunniest days.
✅ Ensure a ventilation gap between the panels and the roof of at least 10–15 cm — this reduces the temperature of the panels by 5–10°C.
📊 Brief summary

All 7 causes: losses and difficulty to fix

# Cause Typical losses Difficulty
1 💧 Dirt on panels 10–30% ✅ Easy — wash
2 🌳 Shading from trees / buildings 20–50%+ ⚠️ Medium
3 🧭 Incorrect angle or orientation 5–20% ⚠️ Medium
4 📉 Natural degradation 0.5–2%/year ℹ️ Normal process
5 ⚙️ Inverter problems 10–100% 🔧 Needs a specialist
6 🔌 Oxidation of MC4 contacts 5–30% 🔧 Needs a specialist
7 🌡️ Overheating in heat 10–15% ✅ Gap under panels
🛠️ Step-by-step diagnostics

How to correctly find the cause — algorithm

1
 
Check the app or inverter display
It contains detailed generation statistics and error codes. Compare current power with nominal power for the current time of day and cloudiness.
2
 
Inspect the panels visually
Check for dirt, shading, and visible damage. Wipe a small area — if the rag gets dark, it's time to wash.
3
 
Compare generation with last year
Data for the exact same months. A normal drop is up to 1–2% per year. More than 15% — there is a problem that needs to be found.
4
 
If the cause is not obvious — thermal imaging diagnostics
An inexpensive procedure that will pinpoint exactly where the problem is: a defective panel cell, an oxidized contact, or a faulty bypass diode — without any dismantling.

✅ Can be done independently

Wash panels from dirt and dust. Trim tree branches casting shadows. Change the tilt angle on adjustable mounts. Check the inverter firmware version and update it via the app.

🔧 Needs a specialist

The inverter displays error codes or won't start

One panel or row generates significantly less than others

Generation dropped by more than 15–20% over a year

Suspicion of damage after a thunderstorm or strong wind

Cables or connectors feel hot to the touch

✅ Summary

Prevention is better than repair

Minimum annual maintenance plan

Washing panels in spring after dust storms
Washing in summer — in July-August during heavy dusting
Clearing leaves and snow in autumn and winter
Trimming trees growing towards the panels
Comparing monthly generation with the previous year
Checking the inverter error log once a quarter
Thermal imaging diagnostics every 2–3 years
Monitoring ventilation around the inverter in summer

⚠️ Don't wait until it gets worse

A solar station is a long-term investment that requires minimal but regular maintenance. Timely diagnostics extends the lifespan of the system and restores full performance. A delayed problem usually costs more.

Total-Energo — diagnostics and maintenance of solar stations

We will perform a full inspection of your system: from visual examination and inverter data analysis to thermal imaging diagnostics of the panels. We will find the problem and fix it quickly.

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