Powering IoT soil, plant, and environmental systems
The installation of any sensor will often require additional power; whilst sensors and nodes will contain rechargeable batteries, to recharge these there needs to be an additional power supply.
ICT International devices can be powered by an external power source (SFM1x, SFM1, PSY1, HFD8). This can be:
- 20-volt Solar panel
- CH24 Power Supply
- 12 or 24 v battery
ICT International Nodes can be powered by a 20-volt solar panel.
The information here is for the following sensors, instruments, and devices:
- All SFM1x Sap Flow Meter versions
- All IoT Nodes (except S-Node)
- PSY1 Psychrometer
- SFM1 Sap Flow Meter
- HFD8 Heat Field Deformation Sap Flow Meter
- Other instruments/devices that can be powered by a 20-volt solar panel
Solar panel
All ICT International nodes and devices are supplied with integrated batteries; however, these are only for short term power supply. These batteries are charged by integrated solar regulators, based on Maximum Point Power Tracking (MPPT), that manage the voltage and amperage from the solar panel to the battery. These are optimised to work with 20-volt solar panels.
However, when installing nodes or devices, the location of solar panels must be taken into consideration. This is covered in the Solar Panel Installation section below.
CH24 Power Supply
The CH24 Power Supply is a 20-volt DC power supply that can be connected to either 240-volt or 110-volt AC. This is the ideal solution for powering either single or multiple ICT International (SFM1x, PSY1, SFM1, HFD8) instruments in a laboratory setting.
The design of these ICT International Instruments is such that they are not polarity sensitive, and can be daisy chained together. This allows one CH24 Power Supply to power multiple instruments simultaneously using the bus plugs on the end caps to provide continual power to the instrument.
When there is not an option of installing a solar panel or using the CH24 Power Supply, an alternative is to use a 12-volt battery (or 2x 12-volt batteries in series), and either charge on a frequent basis or exchange for a charged battery.
ICT International tested this solution on the SFM1x, and found a 12-volt, 26 amp/hour (Ah) battery was able to reliably provide up to 19 days of power before the battery had discharged to a 50% state of charge. With a 24-volt, 18AH solution, the run time was found to be 21 days. However, this was harder to achieve on a repeated experiment, potentially due to the different voltages in the two batteries.
The recommended solution from ICT International is to use a single 12-volt battery of at least 26 Ah, and change (or charge) the battery every 14 days. This will provide a reliable power supply that is easy to manage.
When installing solar panels the following must be considered:
- Daytime sunlight availability (duration)
- Shading
- Angle of solar panel(s)
- Power requirement of device
When these are considered and managed together, the installation will be successful. ICT International has installed solar panel systems with many of their instruments and devices, and have built up a wide range of experience and solutions.
Basics of solar power
The sun will provide approximately 1,000 watts per square meter; a 10-watt solar panel (the default size ICT International use for nodes) is 190mm x 315mm, or 0.06 square meters. This has the potential to capture 60W of power; however, that is in perfect conditions. When there is any shading, then the solar panel is less able to convert the solar radiation into power, and subsequently charging is reduced.
Maximising solar power in low light
When ICT International has installed measurement solutions in areas where there is low light transmission (such as below a forest canopy) then an up-sized solar panel (10W to 20W, for example) is used. This provides an increase in power, even if the panel is shaded to 50%.
However, when this is still insufficient, then a second solar panel is installed, and angled to different position. This requires connection via an extension cable, and the introduction of diodes to ensure that the charge is sent to the device. Please contact ICT International for further information on this.
Installation tips
In the northern hemisphere, direct the solar panel to the south. In the southern hemisphere, direct the solar panel to the north.
To install a solar panel correctly, a simple approximation of the angle that the panel can be made using the latitude of the site. For example, Armidale, NSW is at 30°30′S 151°39′E. The latitude is 30°, and therefore setting the panels at an angle of 30° from the horizontal will provide good performance for much of the year in a clear space.
When there is shading likely of the solar panel, and if it is practicable, then changing the solar panel angle during the summer (to a flatter angle, in the case of Armidale to 20° for example), and during the winter (to a more vertical angle, e.g. 65°) will increase the solar radiation captured.
Importantly, local knowledge can be used to determine exact installation angles; if there are frequent afternoon storms, then bias the solar panel to the east to capture more morning sun. If there is an increase (or decrease) in shading during the day as the sun moves across the sky, position the solar panel so that it captures the most sun.
Consider using extended solar cables to enable the solar panel to be placed in a (more) optimal position if the solar panel is not able to power the instrument sufficiently when close to the instrument or device.
