Low production in summer: diagnosis of temperature, MPPT, and shading
Quick summary: When it is hot, the panel working voltage (Vmp) drops, sometimes the inverter limits power (clipping), and shading may occur. With these quick checks, you will know what is happening and how to improve.
Actions in 5 minutes
- Measure the panel temperature with a laser thermometer (IR). If it is 60–75 °C, it is normal for the Vmp to drop and produce less.
- Open the inverter app (logger) and see if the power remains flat at the equipment's maximum: that is clipping.
- Check for shading at midday and in the afternoon, and for dirt on the lower edge of the panels.
- Record the open-circuit voltage (Voc) and the maximum current (Isc) per string in the DC panel, always with lockout and tagout (LOTO).
- Take action: clean, rearrange strings, adjust equipment limits, or consider a larger unit if clipping is constant.
Symptoms and probable causes
| Symptom | Probable causes | Priority |
|---|---|---|
| Produces less at midday when hot | Heat ↓ Vmp (operating voltage), the equipment may fall outside its range | High |
| “Flat” power graph at maximum | Inverter limitation (clipping) due to nominal power | Medium |
| One string performs worse than another | Partial shading, dirt, loose connector, or bypass diode activated | High |
| Rapid rises/drops in tracking | Outside the tracking range (MPPT window), adjustment/firmware or DC protection triggered | Medium |
Decision diagram (diagnosis in 10–15 min)
Start here according to your symptom:
- If power stays flat at the inverter's maximum → this is clipping. Need more peak energy? Consider increasing equipment power or adjusting the design.
- If production drops with heat → measure panel temperature (IR). Above 60 °C, Vmp drops. Check that the string voltage does not fall below the equipment's minimum operating voltage (MPPT window).
- If a string underperforms → look for shading and dirt, and check connectors. Clean, retighten, and compare again.
- If the tracking “shakes” → update firmware, check DC fuses/SPD, and ensure the configured operating range is correct.
Detailed step-by-step (with simple measurements)
-
Measure Voc/Vmp/Isc (key numbers):
- Voc (open-circuit voltage) per string, with DC isolated (LOTO): should be close to “number of panels × panel Voc” adjusted for temperature.
- Vmp (operating voltage) in the app: in high heat it can drop by 10–18% compared to a cool day.
- Isc (max current): rises slightly with strong sunlight; large differences between strings indicate shading or connection issues.
- Visual inspection and tightening: check for shading (12:00–14:00 and 18:00), dirt on the lower edge, and hot spots if you have thermography. Retighten the DC combiner terminals to the torque specified by the manufacturer.
- DC protections: check fuses per string and the status of the surge protection device (SPD). If the indicator is tripped or blackened, it needs to be replaced.
- Equipment (inverter/controller): check the operating range (MPPT window) and current limits per input in the datasheet. Update firmware and compare a cool day vs a hot day in the app.
Tools and reference values
- Multimeter and DC clamp meter, laser thermometer (IR), MC4 connector wrench.
- Simple rule: in high heat, Vmp drops; in cold, Voc rises. Design to operate within the equipment's range in both cases.
Safety and best practices
- Cut and lock out (LOTO) before touching the panel.
- Use PPE, respect polarity and cable cross-sections, and use original connectors.
- No live Isc without the correct procedure.
When to call a technician
If you smell burning, there are recurring hot spots, the SPD trips frequently, the inverter shows persistent alarms, or you see damaged connectors/cables.
Recommended products and spare parts
- MPPT Charge Controllers — Wide operating range • Better tracking in heat
- DC protections (fuses + SPD) — Safety and continuity
- Accessories and connectors — Reliable connections and low voltage drop
Frequently asked questions
How do I distinguish heat from clipping? If the power stays “flat” at the inverter's maximum, it's clipping. If it drops when the panel temperature rises, it's heat.
Do I need to change the inverter? Only if clipping is frequent and you need that peak energy. Sometimes it's enough to adjust the design and clean.
What should I do about seasonal shading? If possible, remove/trim the obstacle. If not, reconfigure the strings to reduce the impact during key hours.
How often should I clean? In areas with dust/pollen, once a month in summer. Record the date and compare production before/after.
Downloadable checklist
- [ ] Measure panel temperature (IR) at noon
- [ ] Record Voc/Vmp/Isc per string and compare
- [ ] Clean lower edge and check for shading
- [ ] Check equipment operating range and clipping events
- [ ] Check fuses, SPD, and tighten connections
- [ ] Update firmware and compare cool vs hot days
Low production in summer: temperature, MPPT, and shading diagnosis guides you step by step with clear language to improve your system's performance.
Questions about your case? Write to us and we will guide you with your measurement data.
