By way of example please see this post from the Little Cayman station log (including photos), which concludes that a "catastrophic power loss" was caused by "condensation" within the "solar panel junction box." To my knowledge there are no diagnostic RH sensors deployed in the solar panel junction boxes at any CREWS/CCCCC station but this serves as an important lesson about the damage that moisture incursion can have on station operations. In this case the Cayman station was nonoperational for 73 days and when redeployed it was found that communications with the WXT (Vaisala's 'Weather Transmitter') had failed, which may indicate another yet-undiagnosed effect of junction box condensation at that buoy.
The following graph shows the Buccoo Reef (BUTO1) diagnostic RH values plotted over the buoy's deployment lifetime to date (through June 9th, 2015). The red line is RH maxima as measured within the Main junction box and the green line is RH maxima as measured within the Met junction box.
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| Please click on this image to see it in larger form. |
The large gap in data is from when the station was entirely offline due to a power failure, from May 15th to August 11th, 2014. The highest spike in the Main RH (red line) occurred on November 13th, 2014, while the buoy was undergoing maintenance on land and was likely measured at a time that the junction box was open to the moist outside air.
Note that these data report only the maximum RH seen in a ten-minute period of those raw values collected every five seconds.
A natural question is how humid is too humid? I have heard it suggested that these junction box humidity maxima should not exceed 20%, and BUTO1's Met junction box RH data shows that this is an entirely attainable goal and can be regarded as a reasonable target. However, at what point should overly-high RH values prompt remedial intervention? I have for many years run CREWS programming tests inside my office which has had the side-effect of collecting a long-term dataset of indoor RH values, in an environment that is dry enough to prevent any damage from moisture or condensation. Based on these somewhat accidental datasets I would suggest that RH values up to 50% may be considered tolerable, but that prolonged measurements of diagnostic humidity in excess of 50% should be considered cause for immediate reparative action.
The story told by these data, then, is twofold: the Met junction box (green line) remains extremely dry throughout the buoy's lifetime, but the Main junction box (red line), despite starting out very dry, has grown more humid over time to the point where RH has remained between 60% and 80% since the November 13th, 2014 maintenance operation (with 99.1% of all reported values falling within this range during this period).
Based on our ad hoc standard, then, BUTO1's Main junction box started its deployment acceptably dry but humidities gradually increased until they began exceeding our targeted level of 20% after three months. We cannot know what the Main RH levels were like during the station's mid-2014 power failure but immediately upon resumption of operations the Main RH levels were alarmingly high and have remained strictly higher than 50% humidity in 98.5% of Main RH measurements reported since that time (August 11, 2014). Therefore this station can be said to have a persistent and long-lasting problem with moisture incursion into the Main junction box which should be attended to at the earliest opportunity. [This station's Met junction box, on the other hand, requires no humidity intervention whatsoever.]
Similar analyses have been conducted at this station's sister buoys located at Speyside / Angel's Reef, Tobago (ARTO1) and at Little Cayman, Cayman Islands (CCMI2). A pattern that is common to all three of these buoys is that the Main RH levels are all presently at alarming levels, after starting out acceptably low during initial deployment and increasing much more quickly than the Met RH levels do. This might suggest a design or construction problem with the moisture seals on the Main junction box, or a lack of clear deployment instructions regarding proper sealing of the junction boxes and the use of fresh desiccant.
The Met RH patterns at the three buoys range from BUTO1, where Met RH levels start low and stay low throughout the buoy's entire lifetime, to ARTO1, showing a mildly-increasing trend of Met RH levels that is not yet any cause for alarm, to CCMI2, where Met RH levels began low but increased quickly and are presently at levels that are alarmingly high. There does not seem to be any reason to suspect a systemic problem with the Met junction box design, construction, or deployment practices as there is in the case of the Main junction boxes.
The complete analyses for the other RH diagnostics, including graphs, may be found at this link for ARTO1 and at this link for CCMI2.
(signed)
Mike Jankulak