Minimizing Problems with Wasps on Weather Stations

Weather stations can suffer damage or the data can be altered due to pests. Pest issues include anything from Elk rubbing the velvet off their antlers against a station, cattle bumping and damaging a station while grazing, vandalism, bird droppings on light sensors, ice buildup, and wasp nests. Each of these issues can reduce data quality and each has many possible solutions.

Wasps can be a problem for many reasons. In addition to an unpleasant human interaction, wasps like to build nests in confined spaces such as in gill-type temperature shields. These nests block airflow and cause elevated temperature readings. Several steps can reduce wasp nests. First, we have found that plugging all open tubes reduces nests in the end of the cross arms We have found that the short vinyl caps from either http://stockcap.com or http://www.caplugs.com work well to fit snugly over ends of cross arms. If the caps are a bright color, this has the added benefit of high visibility to prevent head bumps. Another effective method to plug tube openings is to put closed-cell foam inside the hollow cavities of cross arms.

Once possible nest locations are reduced, it helps to use spray repellent. Some sprays kill wasps and the residue will linger and prevent wasps from returning. Gill radiation shields can even be sprayed with repellent. While this residue can be washed off with moisture, it still helps.

We have used traps to reduce wasp populations around a station. Traps use an attractant to lure in and trap wasps. This is an effective longer-term solution instead of – or in addition to – spray repellents.

Passive, gill-type temperature shields provide a cavity in which wasps like to build nests. We have found that MetSpec temperature shields have reduced numbers of wasp nests, apparently because the gaps that wasps would use to enter the shield are smaller, making it more difficult, for them to enter. Wasps do not like to build nests in areas that are windy. In our experience, wasps never build nests in aspirated temperature shields.

Getting good data goes far beyond sensor and product selection. Ongoing maintenance, such as checking a gill shield for a wasp nest, is critical to gathering good data. We consistently remind our customers that ensuring sensors are mounted correctly, leveled when needed and cleaned periodically go a long ways to getting better measurements.

Seth Humphries
Product Development Scientist

Extreme Weather Conditions

I thrive in harsh weather conditions, especially extreme cold. One year at the end of June, I did some work in Houston. It was 38 C (~100 F) and felt like 100 %RH outside but in the confined environment where I was working it was about 49 C (~120 F) and felt like 200 %RH. Another time, while helping a local scout troop, I set up an orienteering course near the head waters of the Missouri river in temperatures well below -18 C (~0 F). I have even commuted to work on my bike in temperatures below -29 C (-20 F). As humans, we can adapt and survive such conditions but can the sensors and instruments on which we depend also survive?

When discussing survivability of equipment in extreme environments many factors must be considered that do not affect operation at room temperature. Perhaps the largest factor is a mismatch in coefficients of thermal expansion between materials. For example, aluminum has a larger coefficient of thermal expansion than stainless steel. Two parts that fit tightly at room temperature may not fit tightly at -30 C. This fact can be used to create tight fits between two rings, an inner one of aluminum and an outer of stainless steel. When submerged in liquid nitrogen, they will fit easily but once brought back to room temperature the fit may not be tight enough to create a water tight seal.

While this method creates a tight seal, often materials will contract differentially creating a gap between them in which water might condense. After several freeze/thaw cycles two pieces formerly bonded can separate.

We continuously test our pyranometer sensors on the roof top of our building and have many years of experience in this environment. We continually monitor their output and compare them to primary standard reference sensors.

Our pyranometers were designed with color in mind. In cold environments, the sun warms the head causing frost and snow to melt off the sensor more quickly. You might expect that this black color would be an issue in blazing Death Valley type heat. However, the heads only get to about 12 C above ambient air, in conditions with almost no wind and at peak solar intensity. We have also tested the temperature dependence of the pyranometer. At extreme hot and cold temperatures, the sensors vary by less than 5%.

Our temperature sensors are also highly water resistant. We used ST-100 temperature sensors in warm (60 C), mild brine solution for 2 months. We then did 30 days of accelerated aging tests (3 hour cycling from -20 to 60 C). These sensors still meet specification.

We tested our SB-100 barometric sensor both indoors and outdoors. We compared it against a more accurate and more expensive Setra pressure sensor, model #276, for 4 months. Inside our building, the largest error measured was < 0.03 kPa. Outside in a weather proof box, near ambient temperatures, the largest error was < 0.2 kPa. This SB-100 provides a very low cost, accurate sensor for weather stations.

Comparison of two Apogee SB-100 pressure sensors (one inside, one
outside) with a Setra Model #276 pressure sensor (inside). The plots are
absolute pressure (kPa), pressure difference (kPa) with reference to the
Setra sensor, and outdoor temperature (Celsius) for more than 140 days
over a wide range of outdoor temperatures.

Our quantum sensors are used in a wide variety of applications. In fact, some of our customers use our quantum sensors to monitor lights in salt water tanks for coral growth. They are repeatedly submerged and often left in the bottom of tanks; they continue to perform.

Our sensors survive, not by chance, but by design. When our building was being constructed one of the beams was a few feet too long. Rather than let that go to waste, we built a sign out of it that now hangs above our employee break area. It is inscribed with a tag line under our logo that says: "built to last". Our sensors weather the worst.

 

Seth Humphries
Product Development Scientist

Accelerated Aging

I work hard and take pride in doing good work: to always do my best. As I have come to be part of the Apogee family, I have noticed that my feelings of hard work and pride are commonly shared. I have seen others work on weekends, or late into the evenings to ensure that our products are both accurate, rugged and ship on time. Collectively, we want Apogee to sell the best products and have the best reputation.

One type of product in which we at Apogee take particular pride is our short-wave sensors; i.e. pyranometer and quantum sensors. These rugged, optical sensors can withstand harsh outdoor environments, submersion in salt water, and are vibration tolerant. Yet, this is not enough for us.

We perform accelerated aging tests on our sensors to provide confidence in their long-term stability. Accelerated aging tests cannot directly predict the product lifetime in the field, but they do provide assurance that the product is rugged enough to withstand expected operating conditions. Accelerated aging tests often involve high levels of UV light, high temperature and humidity, high vibration, or some combination of extreme conditions. In this case we used extreme temperature cycling. We cycled a group of sensors every three hours from -20 to 60 C (-4 to 140 F). After 3 months, and more than 350 temperature cycles, the sensors did not fail.


Although our sensors are rugged, we recommend periodically, minimally every year, checking the output of radiation sensors against the sun on clear days using our free Clearsky Calculator. The user enters the location of the sensor (longitude, latitude, time zone) as well as day of year and environmental conditions and an expected output of the sensor is calculated. The sky must be clear. Our experience is that the calculated radiation intensity is within 2% of the actual solar intensity. If it does not match, the user should re-clean and inspect the sensor and again check against the Clearsky Calculator. If it still does not match then please give us a call and we can help resolve issues and, if necessary, help you get it recalibrated.

We want to ensure that we have a sensor that will continue to operate whether continuously submerged, frozen in arctic conditions or heated under the tropical sun.

Seth Humphries
Product Development Scientist

Why silicon pyranometers are the best choice for monitoring solar photovoltaic panel efficiency

Sensors that measure the available solar energy, pyranometers, are an excellent way to monitor the performance of solar photovoltaic panels. They can indicate changes in panel efficiency over time (80% of initial output after 25 years for crystalline silicon) and indicate the need for panel maintenance.

Figure 1 Spectrum of light produced by the sun and received
on the surface through the atmosphere.
Source: wikibooks.org

There are two main types of pyranometers: Blackbody and silicon-cell. Blackbody pyranometers cost $1000 to $5000. Silicon pyranometers are about 10% of this cost.

Blackbody pyranometers use the thermoelectric effect to produce electricity when heated [Myers]. The detector surface has a uniform response to all wavelengths of the solar spectrum, which is defined as 280 to 2800 nm [Moore]. The sun-light incident on the detector heats the surface and a signal is generated that is proportional to the amount of light. This signal is calibrated to match the total integrated intensity of the solar spectrum.

Silicon pyranometers, on the other hand, use a silicon-based photodiode. These typically have a spectral response from about 300 to 1100 nm. Electricity is generated due to the photo-electric effect [Einstein] in the same manner that a solar panel produces electricity. Because of the spectral response, a silicon cell pyranometer subsamples the solar spectrum and its output is calibrated to match that of the entire integrated solar spectrum.

There are instances when the subsampling of a silicon based pyranometer does not accurately represent the entire solar spectrum of light coming through the atmosphere. When sunlight is filtered through the water vapor in clouds, partially-cloudy to overcast conditions, some of the infrared portion of the solar spectrum is reduced, which shifts the spectrum to the shorter wavelengths. This results in a signal from a silicon pyranometers that can be as large as 14% higher than the true total for solar radiation on heavily overcast days [Dupont].

Although blackbody pyranometers accurately measure the integrated total solar spectrum under overcast conditions, this intensity does not represent the radiation available for solar panel power production.

Since the spectral response of silicon-based pyranometers closely matches the spectral response of silicon-based solar panels [Dupont], silicon pyranometers provide better indication of the radiation energy available for conversion to electricity by the solar panel.

Thus using a silicon pyranometer will yield more accurate measurements of panel efficiency. Better measurements of panel efficiency will lead to improved understanding of changes in electrical output and solar panel response.

References
Myers DR, Stoffel TL, Reda I, Wilcox SM and Andreas AM. Recent Progress in Reducing the Uncertainty in and Improving Pyranometer Calibrations. J. Sol. Energy Eng. 124(1):44-51, Feb. 2002. DOI:10.1115/1.1434262

Moore CE, Minnaert MGJ and Houtgast J. The solar spectrum 2935 A to 8770 A. National Bureau of Standards Monograph, Washington: US Government Printing Office (USGPO), 1966.

Einstein A. On a heuristic point of view concerning the production and transformation of light. Annalen der Physik, 1905.

Dupont R, Siemer J, Hirsch M. How Much Sunlight? Photon: The Photovoltaic Magazine, 12:50-67, Dec 2010.

Seth Humphries
Product Development Scientist