Attention, the Yeti 150 charging input has a maximum charging power of 60 watts.
https://www.goalzero.com/shop... or
https://www.goalzero.com/media...
You can couple two Boulder 50s together. The necessary cables are available - see
https://www.goalzero.com/media...
But in the case of two coupled Boulder 50s, the specification of the Yeti 150 is exceeded. Even if the coupled solar panels do not effectively reach the summary power of 100 watts, one can expect 70 watts in good conditions, which would be too much.