So the Valify robot lawnmower will have a solar panel on top of the body. I was browsing around the internet without any success finding what I needed. The sizes where wrong, the power was to low etc. So the best way to actually get what I need is to make a custom solar panel to fit the robot instead of finding one.
This is the first time for me, so it will be a learn by doing experience so this will be a series of blogs post until the finish product (internet will be my teacher, and maybe you have some input in the topic?)
So the robot runs on two 22.2V LiPo batteries. My LiPo charger allows me to run DC 11-18V with a charge current range: 0.1-7.0A. So I guess a good voltage to aim for is 18V because of the Solar panel ratings are calculated in bright direct sunlight. Conditions such as indirect sunlight, overcast and partial shade conditions will decrease the output.
So next questions, how will the layout look?
From the start, I thought I used two cells of 27V each in parallel. But when I only need 11-18V this layout will not be of any value. My space is limited to 600x170mm and depends on how much I can cut and shape the cells. I know a cell can be splitted, but I don’t know how they actually can be shaped. In my case I have a quite straight panel on top of the robot except the Scanse sweep sticking out on the top with a diameter of 50mm. Lets look and learn more about this later.
I decided to buy 300pcs of Polycrystalline Silicon mini Solar cells 0.12W 0.5V 0.24A 39x19mm (I bought extras) for this project. I bought small cells that are easy to install in different formations.
So the cells are rated at 0.12W 0.5V 0.24A. My aim is 18V (or should I maybe aim higher?)
In order to get a theoretical 18V from the cells I need 36 cells connected in serial.
The cells are 39x19mm. Making them perfect for a 4 column installation. With 4 columns, 9 rows are needed to retrieve 18V. The size for the first group of cells will be around 160x171mm. But how many of this group will fit on the robot? 600/171=3.50 groups. Quite perfect, around 3mm gap between each cell.
I am happy with the first layout, so lets move on calculating on what this cells can produce before making any changes too the layout. All cells in each group will be connected in serial and then the groups will be connected in parallel.
Cells are rated at 0.12W 0.5V 0.24A
So lets start of with the for one group in serial:
Serial connection: voltage = per solar panel voltage (U) * quantity(x)
Parallel connection: Current= per solar panel Current (I)*quantity(x)
Voltage unchanged= (U)
So with this 3 groups connected, I will be able to produce almost 13W. And what is 13 watts? Typical energy usage of the Nvidia Jetson TX2 is around 7.5 watts.
So in the next part I will look at the different alternatives for Backsheet, Encapsultant and glass/Plexiglass. I will have a week or two until the cells and wires arrive.
As always. Happy for feedback.