Photovoltaic plants in mountainous regions include many different design considerations than solar projects in lower lying locations. A case study from SolarMax provides an example of how failing to taking environmental considerations into account can result in a project not achieving its rated output.
Alan Beale, Solarmax USA
Imagine that you have a customer who wants to install a PV power plant at an altitude of 2,000m. You have entered all of the necessary data in your planning tool and designed the plant accordingly. All of the apparent parameters have been taken into account and correctly implemented. And yet the plant is not producing the expected yields. Why?
Peter, an experienced solar installation professional, found himself in this situation as he worked on a solar project in the Swiss Alps 2,000m above sea level. The plant included 16 strings, each with 13 solar modules connected to 4 SolarMax 15MT2 string inverters. The problem, however, was that even on sunny days, the solar power facility failed to achieve the rated output power of 15kW. It only produced 13kW.
Since Peter was not aware of having made any errors during the installation, he contacted the SolarMax hotline and questioned the functionality of the installed string inverter. After a comprehensive fault analysis and installation inspection by the SolarMax technical sales support team, it proved possible to identify the source of the fault: The plant was not designed taking into consideration important environmental factors associated with high locations.
The Problem
PV power plant in high locations should be slightly undersized due to environmental factors such as high solar radiation and low temperatures. But since this was not done, the MPP voltage range was only put to limited use, and the PV generator voltage only moved in the lower range. Furthermore, the lower voltage was partially below the minimum MPP voltage of 430V, which is necessary for the rated output power operations of the string inverter. Since the upper MPP voltage was also quite low due to the lengths of the strings, it was not possible for the installed string inverters to operate in the rated output power range, even during high levels of irradiation and high cell temperatures. For these reasons the plant had never operated in the rated output power range, which meant that it was unable to achieve an optimum power output yield.
The Solution
Peter changed the project design, arranging the 208 modules onto 8 strings with 18 modules per string and 4 strings with 16 modules each to solve the problem. The SolarMax 15MT2 string inverters were replaced with SolarMax 15MT3 inverter models. The inverters were replaced because of the broader MPP range of the latter. While the MPP range of the 15MT2 is between 430V and 750V, the range of the 15MT3 is between 320V and 750V. This range is decisive for the fact that the inverter can be used within its actual capacity. Before the correction, the voltage was so low that it was situated outside of the MPP range, which prohibited it from reaching the maximum output so it resulted in yield losses.By increasing the number of modules per MPP tracker, Peter was able to increase the voltage so that it was possible for the string inverter to operate in the rated output power range.
Most everyday solar installations are not at such extreme altitudes, so contractors may not know to be aware of the special design considerations required. Not realizing this can add significant time and cost to the project. Over 25 years, if the plant in the example had gone on producing 15kW instead of 13kW, it would have meant a loss of about $155,000.This example also shows that planning tools are not always reliable. The planning software that Peter used did not show any anomalies or signs that the plant could not run in line with expectations.
Here are some tips to prevent losses in yields due to incorrect installations:
- Training/Further Education: The many products on the market have exceptionally different device attributes and complex functionality. For this reason, seek manufacturer training to properly use their products.
- Technical Sales Support: Take advantage of manufacturer with questions and problems regarding the installation before and after the conclusion of the contract and the delivery of the devices and accessories. The support team employees have detailed knowledge of the different devices and can help you in finding direct solutions to any problems.
- Tools: The plant dimensioning is generally based on the complex calculation of a tool which aims to optimize the planning procedure. Depending on the functional scope, this is only of limited suitability for special installations. In cases where there is any doubt it is recommended to take the advice of product specialists in good time to identify any possible errors and to rectify them immediately.
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