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 Little Cayman (CCMI2) 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. |
Some obvious features of the above graph are as follows: initial buoy deployment was on October 23rd, 2013; the Main RH levels (red) ceased to fall below 20% on November 16th, 2013; there is a nine-month period when Main RH levels (red) remain strictly above 60% (January 17th - October 27th, 2014); there is a break in data lasting from the station's power failure (December 29th, 2014) until redeployment (March 12th, 2015); and there is a two-week period (April 30th - May 14th, 2015) during which there were no Met RH updates (green) because the Met logger's program stopped running (a situation believed to have been caused by excessive watchdog errors, indicating a potential programming/timing problem). Note that the station's annual maintenance operations took place October 14th - 29th, 2014, throughout which RH data continued to be collected.
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 the lifetime of Met junction box RH data from the Buccoo Reef, Tobago CREWS/CCCCC buoy 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) begins nicely stable and largely below 10% for about six months, a pattern which starts to be disrupted on April 10th, 2014. On June 6th, 2014 the pattern shifts significantly above 10% for the first time, and this increasing pattern becomes quite obvious on August 7th, 2014, which is the last Met RH report to fall below 10%. This only becomes worrisome on October 29th, 2014, the date of buoy redeployment after its annual maintenance operations, which also happens to be the Met RH's last report to fall below the 20% humidity threshold. Met RH values remain in the worrisome-but-not-alarming range (above 20% but below 50%) from October of 2014 to May of 2015, but following the two-week period of non-updates of Met RH data (i.e. beginning May 14th, 2015, see above) Met RH values are well into the >50% alarming range, with 97.2% of Met RH reports rising above 50% humidity. In the final 6 days of data examined in this report, in fact, all of the Met RH reports are above 90% humidity.
The Main RH numbers for this station are even more concerning. These numbers started low but spiked quickly. Less than one month after initial deployment the Main RH numbers rose above 20% and never recovered, beginning November 16th, 2013. Two months after that, on January 17th, 2014, the Main RH numbers rose above 60% humidity and remained there until the buoy's annual maintenance operations nine months later in October. Following those operations Main RH levels dropped slightly but remained at >50% humidity for 97.2% of the time.
These diagnostics indicate that there are presently serious humidity problems in both of the Main and Met junction boxes at this site, with the Main junction box problems being pretty much constant over the lifetime of the buoy to date and the Met junction box problems starting slow but becoming very serious over the last few months. Given that this is the site where junction box condensation was blamed for a very serious power failure, both of these humidity concerns should be attended to at the earliest possible opportunity.
Similar analyses have been conducted at this station's sister buoys located at Buccoo Reef, Tobago (BUTO1) and at Speyside / Angel's Reef, Tobago (ARTO1). 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 BUTO1 and at this link for ARTO1.
(signed)
Mike Jankulak
