For an off-grid dehumidification system, you have two or three choices that I can think of. One is to install additional power panels to support the additional load of a "standard-type" electric refrigeration-based dehumidifier, and purchase the most efficient version of that type that you can.
The most likely alternative, which I'm not aware of being commonly available "pre-built" though it's possible that it's out there and I'm not aware of it, is to use solar heat to dry a desiccant, and then switch that desiccant into the airspace to be dried (either by switching airflow over fixed desiccant containers, or by physically moving it.) You would generally want to have at least 2 sets of desiccant, so that one set can be dried while another is absorbing water. This is fairly amenable to DIY implementation. It may need to be quite large to keep up with any significant drying load.
An outlier, which is more likely to be seen in a "commercial" or fairly large-scale offgrid setup would be to use an absorption refrigeration loop driven by solar heat to generate the "cold" for dehumidification (and possibly also for other refrigeration purposes) - the complexity of which typically makes it impractical and/or hazardous for a one-family sized situation. By the time you've gone through all that's required, option 1 looks inexpensive, normally, even though this has the potential to be more efficient in conversion of sun to cold; it's a complex and not very common setup, which can leak, has typically noxious chemistry (ammonia) and needs maintenance.