Using the CMP 11 Pyranometers to Measure the Irradiance During PV Projects in Chile

Chile’s geography covers at least seven key climatic subtypes ranging from alpine tundra and glaciers in the south to the driest desert in the world, the Atacama. Additionally, the country’s extreme topography results in the development of microclimates. The formation of a thick coastal fog called ‘Camanchaca’ in the morning at low altitudes close to the coast in the northern part of Chile is an example of the effects produced by microclimates. This is challenging from the perspective of a solar and wind energy developer.

Handling Uncertainty

At present, the input data provides the largest source of uncertainty for large-scale PV development. Since Chile has a limited number of ground stations with superior quality irradiation measurements, many developers are forced to use solar models and satellite data with very little validation. This causes high uncertainties in estimating the long-term solar resource.

This scenario necessitates the planning and execution of a high quality measurement campaign for reducing uncertainties and providing investors comfort in the accuracy of the solar plant yield. Mainstream Renewable Power is developing many solar projects in the country, totaling around 350MW. Hence, performing its own high quality solar radiation and meteorological measurements is the best approach of handling project risks to ensure the availability of high quality measured data to be confidently used in financial models for all of its projects. At its measurement stations (Figure 1), Mainstream uses two Kipp & Zonen CMP 11 pyranometers equipped with CVF 3 ventilation units for irradiation measurement.

Solar Radiation Measurement Station.

Figure 1. Solar Radiation Measurement Station.

Kipp & Zonen CMP 11 Pyranometers

The CMP 11 Pyranometer (Figure 2) employs the temperature compensated detector technology originally devised for the CMP 22 and delivers improved performance when compared to the CMP 6. It is ideally suited for meteorological networks and satisfies the demands for solar energy applications with its reduced response time of 1.66 seconds.

The CMP 11 Pyranometer.

Figure 2. The CMP 11 Pyranometer.

A waterproof socket covers the signature yellow signal cable, which is offered in a wide choice of lengths pre-wired to the waterproof plug. The integral bubble level is increased to the top of the housing and can be seen without the removal of the redesigned snap-on sun shield that also covers the connector (Figure 3). The connector with gold-plated contacts enables easy exchange and re-calibration and the screw-in drying cartridge is easily removable. Moreover, the replacement desiccant is provided in convenient refill packets (Figure 3).

The CMP 11 Pyranometer.

Figure 3. The CMP 11 Pyranometer.

The CMP 11 Pyranometer does not need any power as it supplies a low voltage of 0-20mV corresponding to the amount of incident radiation. The AMPBOX is the ideal solution in cases requiring a higher voltage level or a 4-20mA signal. Low tilt error, fast response time, and excellent linearity are the key features of this Secondary standard pyranometer.

Role of CMP 11 Pyranometers at Mainstream

Mainstream Renewable Power uses one pyranometer in the horizontal plane and the second one inclined in the same plane as the fixed panels (Figure 4). This includes some redundancy to the measurements and also enables minimizing the uncertainties in the transposition models employed. The CVF 3s ensure the reduction of suspect data caused by condensation and minimize the requirement for pyranometer cleaning owing to accumulated dust.

Global and Tilted irradiation.

Figure 4. Global and Tilted irradiation.

Mainstream also performs measurements of other atmospheric parameters, including temperature, humidity, wind speed, and wind direction. The regular maintenance of the equipment is ensured by Mainstream with local contractors who service each station several times a week. They clean the pyranometer domes and the solar panel that supplies power to the data logger and the ventilation units. They also monitor the CVF 3 inlet filters and the silica gel desiccant in the pyranometers once a month, to check whether they need to be replaced. They can download data in very remote areas to ensure Mainstream’s ability to perform regular checks of the measurements.

Mainstream knows that most of the locally operated ground stations do not comply with such stringent standards with respect to data quality and often do not have any form of maintenance record log. Hence, the accuracy and reliability of these datasets is often debatable as well as there is higher uncertainty in the measurements.

Conclusion

With the pyranometer of the highest accuracy and regular maintenance, Mainstream Renewable Power is able to collect quality datasets with the minimum uncertainty, which is crucial to successful solar project development.

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This information has been sourced, reviewed and adapted from materials provided by Kipp & Zonen.

For more information on this source, please visit Kipp & Zonen.

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