Key Takeaways
- Default loss coefficients can mislead real production by 15%.
- Cold Voc and hot Vmpp extremes must be calculated in string design.
- A weather station must be planned during the design phase.
- Annual 0.5-0.7% degradation must be included in the 25-year ROI model.
Solar power plants are long-lived infrastructure investments. Mistakes made during the design phase turn into recurring losses over the 20-25 year operating life. This article serves as a critical checklist for both investors and EPC contractors.
Mistake 1: Using Wrong Loss Coefficients
Using the default loss coefficients in PVsyst or similar simulation tools is a common mistake. Soiling loss, cable losses and transformer losses are specific to each site. A simulation made without site-specific meteorological data and a measurement campaign can mislead real production by 8-15%.
Mistake 2: Ignoring Minimum Voltage in String Design
On winter mornings, cold weather raises the panels' open-circuit voltage (Voc). If this value exceeds the inverter input voltage limit, it damages the equipment. On summer afternoons, panel temperature rises and voltage drops, possibly falling below the inverter startup threshold. Both extreme scenarios must be accounted for in string design.
Mistake 3: Deploying Without Planning a Weather Station
Local irradiance measurement is essential to truly calculate the plant's PR value. At plants built without a planned weather station, in performance disputes the EPC contractor or investor cannot produce any real data.
Mistake 4: Thinking About Monitoring System Cabling Afterward
Planning the cable routes of the SCADA and monitoring system independently of the panel roof layout is a cost trap. Cabling added later means both a safety risk and additional investment.
Mistake 5: Keeping the Inverter Ratio Too Low
Keeping the DC/AC ratio high (oversizing) to cut costs leads to inverter clipping loss. On a summer afternoon, production exceeding the inverter capacity is cut. The optimal DC/AC ratio must be simulated according to the site and tariff.
Mistake 6: Ignoring the Reactive Power Terms in the Grid Connection Agreement
Distribution companies impose increasingly strict terms on the reactive power compensation capacity of PV plants. Analyzing the inverter technical specifications and compensation need before the connection agreement is mandatory.
Mistake 7: Neglecting the Long-Term Degradation Curve
Panel manufacturers usually guarantee an annual power degradation of 0.5-0.7%. Building a 25-year ROI model without accounting for this degradation can overstate the real revenue in the investment's final 10 years by 10-15%. The annual PR trends in the SolarTools monitoring system prove whether the real degradation matches expectations.
Frequently Asked Questions
Which is the best meteorological data source for design simulation?
NASA POWER, Solargis and PVGIS are reliable free sources. However, for the most accurate result, a measurement campaign of at least 1 year on site is recommended.
Is there a generally accepted value for the DC/AC ratio?
For Turkey, the typical value is between 1.10 and 1.25; however, the optimal ratio should be determined by simulation according to the tariff structure and load curve.
When should the monitoring system installation be planned?
During the construction drawing phase; cable routes, panel locations and power supply should be included in the EPC scope. The cost of adding it later can increase 3-5 times.
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