Solar Charging Trials during COVID19

Solar Charging Trials - in COVID Times.

It is August 2020 in Melbourne, Australia. We haven't been allowed to travel any distance for many weeks now, so there's no sailing trials permitted for hobbyists. So no chance to test the new sail, or the new LoRa telemetry system now installed on Voyager 2.0.

This allows time to start looking ahead to Voyager 3.0, which will be a scaled up version of Voyager 2.0 at 2m LOA, and about 0.5m in beam.

The intention of Voyager 3.0 is that it has a large enough deck space to accommodate enough solar cells to allow for missions of indefinite duration. Currently the battery capacity of Voyager 2.0 is about 80 to 120 hours (4 or 5 days). The Wingsail battery life is about 200 hours (8 days).

The Solar Cells in use are the Sunpower C60 cells. These are a light weight and flexible (within limits) and can be sliced up. They can provide over 3A at around 0.5V in direct sun. I'm currently slicing them into thirds, which can yield around 1A at 0.5V per cell in direct sun, and of course when connected in series, the three cells can yield 1.5V at 0.5A.

The image below shows a typically test set up for working out the basic parameters of the charging setup.

Preliminary Test Set up for assessing Cell Quantity and Charging Circuits

In order to evaluate different Solar Charging arrangements in the real world, I commenced with the Wingsail by pressing into service the failed (overweight) WingSail #2. This was kitted out with 4 third size slices of Sunpower C60 Cells in conjunction with the LTC3015 Step up DC-DC converter charging a single 18650 Li-ion cell. The load is the current Wingsail Controller board, but without the Bluetooth module, which was replaced with an Ebyte LoRa module instead. The Wingsail Controller was programmed with software primarily intended to read 3 sets of Voltages and currents and transmit them to a monitoring station.

Mock up of the Voyager Wingsail and electronics for trialing Solar Charging

It will be necessary to place cells on both sides of the sail.

The current Wingsail (without Solar Charging) has two 18650 cells. It is expected that only one cell will be required once solar charging is used. This will partially offset the increased weight due to solar cells (but not by much).

The test rig charging circuits and the the test rig software  are still being adjusted, but the aim is to monitor the operation of the solar charged Wingsail over a period of a month or so.

During this time, we'll start on a mock up of the deck of  the future Voyager 3.0 and set up a solar charging test rig for her.

This is part of the ongoing development of a low cost autonomous oceangoing sailing drones, utilising a self-trimming wingsail. This is the Voyager series of sailing drones.