Companies send signal to satellite with plant energy sensor

Companies Plant-e and Lacuna Space have jointly developed a sensor that works entirely on plant energy. This sensor successfully sent a signal to a satellite in low Earth orbit. The project is supported by ESA.

The setup of Plant-e
and Lacuna Space

The set-up of both companies successfully sent a first message on November 20, 2019, the companies announced on Tuesday. A terrestrial connection was still used for this. After this, the entire set-up was moved to the roof of an office. At 9:00 AM on November 21, the first signal successfully came in via a satellite in low Earth orbit.

The sensor of Lacuna Space and Plant-E consumes about 0.075mW when sending the message via an antenna on Earth. When sending a satellite message, this is about 0.138mW. At the same time, the plant energy could provide enough energy to send messages every three hours via terrestrial networks.

The set-up of Lacuna Space and Plant-e. Image via Plant-e

For the time being, the sensor is a proof-of-concept, and is therefore not yet intended for large-scale use. According to the two companies, the system should eventually reduce the costs, maintenance costs, and environmental impact of IoT devices. For example, the sensor can be used in agriculture, in rice fields, or other areas with a lot of water in the ground, without the need for external power sources.

Lacuna Space previously made sensors for iot devices that can send signals to cubesats, but these needed a battery. However, the company has now started a collaboration with the Wageningen Plant-e. Plant-e produces a so-called plant microbial fuel cell, also known as a p-mfc, which converts the energy emitted by living plants into usable electricity.

The technology of Plant-e.
Image via Plant-e

Plants produce organic matter through sunlight. Some of this matter is used by the plant itself for growth, but not all of it. The rest is expelled from the roots. This residual matter is broken down by surrounding bacteria, releasing electrons and protons. The electrons are captured by a Plant-e anode, after which they flow through the wiring and function as usable electricity. This also requires a cathode, a positive pole; that’s where the protons end up. Energy continues to circulate through the wire in this way. The end result is CO2-negative electricity, because the plant continues to grow and thus stores CO2 at the same time.

The Plant-e and Lacuna Space set-up consists of a planter with a temperature sensor, a p-mfc, an energy harvester, a supercapacitor for the storage of reserve energy, and a Lacuna sensor that sends signals to a cubesat of Lacuna or an antenna on the ground, if it is close enough. The resulting data can be sent via satellite to a web interface at a ground station. For example, Lacuna Space currently uses Slack.

Lacuna Space uses sensors that transmit data via LoRaWAN. LoRaWAN is a media access protocol for wide-area networks. It is completely open source and can be used without licenses, allowing anyone to set up their own network with LoRaWAN. LoRaWAN uses channels with a bandwidth of 125kHz, 250kHz or 500kHz depending on the region or frequency plan. In any case, the network always uses the license-free sub-GHz radio frequencies. In Europe, the network operates on the 868MHz frequency. The communication is encrypted with 128-bit AES encryption. LoRaWAN requires very little power and also has a range of several kilometers. According to Lacuna Space, this makes it very suitable for sending data between different IoT devices.

Currently Lacuna has a single satellite in low Earth orbit. This is a compact cubesat, which has a receiver as payload. This receiver can pick up very weak signals from IoT devices, allowing data to be sent all over the world. This satellite of Lacuna is located at an altitude of about 500km.

According to Lacuna, it is already possible to cover the earth with a single satellite: the satellite passes over the sensor, after which data is received at the receiver. The satellite then orbits the Earth, while the Earth itself also orbits. This allows the satellite to provide the entire Earth with connectivity, with the caveat that this is not in real time. The satellite can only transmit data when it is near a ground station on Earth. The satellite can therefore transmit a signal a maximum of twice a day, with a waiting time of up to 12 hours. Incidentally, this is scalable with more satellites. This year, Lacuna plans to launch three more satellites. Provided they are each launched at the right time, the waiting time can, for example, be reduced to a maximum of three hours.