Solar Panel Efficiency Loss: 10 Causes and Fixes in Antalya

Solar panel efficiency loss rarely comes from one big fault. More often it is heat, soiling, shading, connection losses and inverter limits stacking up. If your system in Antalya produces less than expected, the right approach is not to guess the cause but to work through measurement and elimination. In this article we go through the 10 most common causes, how to recognise each one and how to fix it.

First, know the expected output

To say "output is low" you need a reference. According to the European Commission's PVGIS tool (PVGIS 5.3, 14 percent system loss, optimum tilt, south-facing), the annual specific yield in central Antalya is about 1,656 kWh/kWp. The monthly value is 99 kWh/kWp in December and 168 kWh/kWp in July. So lower output in winter is usually not a fault, just shorter sunshine duration. According to Turkish State Meteorological Service (MGM) data, average daily sunshine is 4.8 hours in December and 11.7 hours in July.

As an example, you can calculate the PVGIS-based monthly expectation for a 5 kWp system. Real output deviates from this value from year to year depending on weather; the goal is not to match it exactly but to notice a persistent deviation that you cannot explain.

The expected values in the table are calculations made by multiplying the PVGIS figures by 5; they are not a guaranteed output.

A more reliable method is the "performance ratio" approach: you compare actual output with the output expected from the irradiation that fell on the panel surface in the same period. Many monitoring platforms do this automatically. If the ratio stays low for several weeks, the problem lies with the system, not the weather. If the ratio drops suddenly and recovers after rain, think of soiling; if the decline is gradual and does not recover, think of degradation or a connection loss.

Another important distinction is between "low output" and "zero output". If there is no production at all, the cause is most likely a grid outage, an inverter shutdown or a tripped fuse. With a partial drop, several of the ten causes in this article usually act together; finding and fixing a single cause is often not enough, so you need to rule them out one by one.

Environmental causes of solar panel efficiency loss (1-4)

1. High cell temperature

Panel power output falls as temperature rises. In Antalya, the average maximum temperature in July is 34.2 °C. A calculation using the NOCT approach gives a cell temperature of about 65 °C at 34 °C ambient and 1000 W/m² irradiance. In that case the loss relative to STC is about 12 percent for a TOPCon panel with a Pmax coefficient of -0.30 %/°C, and about 13.6 percent for a PERC panel at -0.34 %/°C (calculation, not measurement). The fix: leave enough air gap behind the panel and choose a product with a low temperature coefficient. Installations pressed against a hot roof covering without ventilation make this loss bigger, so the height of the mounting system and the rail spacing should be considered at the design stage.

2. Soiling

Most of Antalya's rainfall comes between November and February; in July and August the number of rainy days per month is about 0.5. Dust, pollen and salt build up through the summer. The symptom: output rises noticeably after rain. The fix: solar panel cleaning and tracking with monitoring data.

3. Shading

A chimney, an air-conditioner outdoor unit, a neighbouring building, a tree or even bird droppings on the roof can disable a whole cell string. If the shadow repeats at the same hour every day, you will see a "notch" in the production curve. For details, see our article on the effect of shading on solar panels.

4. Wrong tilt and orientation

PVGIS values apply to a south-facing system at the optimum tilt (33° for central Antalya). East-west layouts, or low-tilt systems on a flat roof, produce less than this reference over the year. That is not a fault but a design choice; still, expectations should be set accordingly. We explained how roof tilt and orientation affect output in solar panel tilt and orientation in Antalya.

Electrical and hardware causes (5-8)

5. Cell cracks and hot spots

Mechanical impacts such as transport, stepping on panels during installation or hail can create micro-cracks in a cell. A crack creates a heating point and the panel loses power. This damage, invisible to the eye, is revealed by thermal camera panel inspection.

6. Connector and cable losses

A loose, oxidised or incorrectly crimped DC connector increases resistance, causing both loss and heating. A typical sign is one string delivering lower current than the others. On the coast, for example in Kemer and Alanya, humid and salty air can speed up connector oxidation; this is why connectors and cable entries should be checked by eye and by measurement during maintenance visits.

7. String mismatch and panel degradation

If panels of different power or different age are connected in the same string, the weak panel drags the array down. Natural degradation is a separate matter: the TommaTech TT605-144TN10 datasheet gives a performance warranty of 99 percent in year 1 and 87.4 percent in year 30, which means a decline of about 0.4 percent per year (calculation). In NREL's 2012 literature review, the median degradation of field modules is 0.5 percent per year. So a sudden, large drop within a few years cannot be explained by "normal ageing".

8. Inverter faults

Insulation faults, overheating or grid-related interruptions can make the inverter reduce or stop production. For details, see our article on inverter faults and solutions.

System and measurement causes (9-10)

9. Grid conditions and inverter curtailment

In hours when grid voltage is high, the inverter may reduce its power or disconnect for protection. This is seen especially around midday, in areas where many generators are connected to the same line. Warnings such as "grid voltage high" on the monitoring screen indicate this; to solve it, measurements are made together with the distribution company.

10. Monitoring, meter and expectation errors

Sometimes the problem is not in production but in measurement: a wrongly installed current transformer, a communication drop or a wrongly entered system size makes the monitoring screen show low data. Comparing the bidirectional hourly meter with inverter data eliminates misleading results. There is also the expectation error: mistaking the low winter output, which is normal according to PVGIS, for a fault.

Quick matching from symptom to cause

The table below helps you match the symptom you see on the monitoring screen with a probable cause. Use it to narrow your first suspicion rather than as a definitive diagnosis.

Step-by-step diagnosis method

Handling solar panel efficiency loss systematically saves time. The order we recommend is:

1. Take the PVGIS value for the same month and the same period of the previous year as your reference.
2. Look at the daily production curve on the monitoring screen; if there is a notch, think shading; if it is cut flat, think inverter limiting.
3. Compare the strings with one another; if only one string is low, a connector, a panel or a crack is suspect.
4. Note the fault log and warnings on the inverter screen.
5. Check visually for soiling and shading, looking only from ground level or with safe access.
6. If the problem persists, contact a qualified team for current, voltage and thermal measurements on the DC side.

Climbing onto the roof, touching the DC cable or opening panel connections is dangerous; the DC line is live whenever there is daylight. Do not do these things yourself.

When should you call a service team?

You need service if solar panel efficiency loss recurs clearly in the same weather conditions, if a single string keeps lagging, if the inverter keeps giving the same error, or if you notice discolouration or a smell around a connector or junction box. Solar Nexo provides survey and technical support in Antalya with a 24/7 support approach; even if your system was installed by another company, you can request a technical check through our contact page.

Conclusion

The way to solve solar panel efficiency loss is to first know what normal output is, then rule out causes, starting with environmental effects such as heat and soiling and moving on to hardware issues such as connections and the inverter. Keeping in mind that the winter-summer difference in Antalya is about 40 percent according to PVGIS (99 kWh/kWp in December, 168 in July) prevents unnecessary alarms. For persistent, unexplained deviations, a qualified team that takes measurements is the fastest solution.

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