Powering remote and wireless devices with solar panels
Banner offers stand-alone powering solutions designed for wireless instrumentation applications. Deploying them appropriately requires understanding a few basic solar power concepts.
In those situations where wired power isn't available or practical, solar panels can supply industrial wireless devices increasing the range and efficiency of your wireless sensor network. Banner says its FlexPower Solar Supply provides power for continuous wireless sensing and monitoring applications in a compact, plug-and-play package.
The FlexPower Solar Supply includes solar panel, controller, and rechargeable battery pack. It is designed to provide continuous power for 4-20 mA sensors if minimum conditions are met. These units assume that the sun is only available at specific times and may not be available at all if weather conditions are poor. The general design assumption is to size the elements to perform even in the worst-case scenario. Therefore, each unit's battery pack is able to power the load for a specific time span known as an autonomy period.
Autonomy is a measure of how long the assembly will supply power without sunlight. Autonomy depends on the load and battery capacity, but it is also affected by battery temperature. In this case, a fully charged battery will supply 350 mW with 10 days of autonomy. Ten days of 100% autonomy means that the battery is able to carry the load through 10 days of darkness or 20 days with only half the required sunlight, or insolation.
Insolation is the amount of solar radiation falling on an area per unit time and is measured in kWh/m2. Insolation can be characterized as an equivalent number of hours of direct sunlight per day required to maintain a desired load. Powering a typical 4-20 mA transmitter with a continuous supply of 350 mW requires minimum insolation of 1 kWh/m2 per day, which is roughly equivalent to 80 minutes of direct sunlight during the winter. (This level is available anywhere south of the arctic circle, so most of North America qualifies.)
Consequently, a single FlexPower Solar Supply can supply a continuously powered 4-20 mA, two-wire transmitter at 13V and power a wireless transmitter such as the Banner DX80 FlexPower Node for continuous sensor operation. Even with a 20 mA transmitter signal, the battery provides about 10 days of autonomy. Locations with exceptionally poor insolation rates can be supplemented with a larger battery pack.
-Edited by Peter Welander, process industries editor, PWelander@cfemedia.com
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