While browsing Thingiverse, a 3D model hosting site, I stumbled upon this. It’s a betavoltaic cell, meaning it generates electricity from a source of beta waves. In this case, beta waves are generated from a small vial of tritium gas. The beta waves excite phosphorous, coated on the vial, which powers a small array of solar cells. Tritium-fueled betavolatic cells can provide power without intervention for up to 20 years! I found some flaws in his design, though, so I’m designing my own.
The main problem with the design I found is that it uses extremely inefficient solar cells. The cells only have about 45% of their surface area as photovoltaic material, meaning the rest is wasted. The tritium vial puts out minimal light, so every photon counts. Furthermore, I wasn’t able to find a panel of the same size that would still fit, while using the full surface area. My design uses these. They aren’t much bigger, but have 5 times the power output, which is a colossal difference.
There is still research to do before maximum efficiency can be achieved.For example, at what light level do the solar cells perform most efficiently? The more panels are put in a betavoltaic cell, the less light each one gets. If their efficiency was perfectly linear, it would even out, and the betavoltaic cell would generate the same amount of power no matter the number of solar cells, so less solar cells would be better due to the reduced cost. However, this is the real world, and nothing is ever that perfect. Solar cells will have a peak efficiency at a certain light level. That peak efficiency determines the ideal number of cells.
The files to make your own can be found on my git server.