SR05-D1A3-PV manual v1801 58/83
Another way to improve measurement reliability is to introduce redundant sensors.
• the use of redundant instruments allows remote checks of one instrument using the
other as a reference, which leads to a higher measurement reliability.
• in PV system performance monitoring, in addition to instruments measuring in the
plane of array, horizontally placed instruments are used for the measurement of
global radiation. Global irradiance data enable the user to compare the local climate
and system efficiency between different sites. These data can also be compared to
measurements by local meteorological stations.
7.3 Speed of repair and maintenance
Dependability is not only a matter of reliability but also involves the reaction to
problems; if the processing time of service and repairs is short, this contributes to the
dependability.
Hukseflux pyranometers are designed to allow easy maintenance and repair. The main
maintenance actions are:
• replacement of desiccant
• replacement of cabling
For optimisation of dependability a user should:
• design a schedule of regular maintenance
• design a schedule of repair or replacement in case of defects
When operating multiple instruments in a network Hukseflux recommends keeping
procedures simple and having a few spare instruments to act as replacements during
service, recalibrations and repair.
7.4 Uncertainty evaluation
The uncertainty of a measurement under outdoor or indoor conditions depends on many
factors, see paragraph 1 of this chapter. It is not possible to give one figure for
pyranometer measurement uncertainty. The work on uncertainty evaluation is “in
progress”. There are several groups around the world participating in standardisation of
the method of calculation. The effort aims to work according to the guidelines for
uncertainty evaluation (according to the “Guide to Expression of Uncertainty in
Measurement” or GUM).
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