the requirements to power supply for a portable machine (as your example, grascutter) are comparable to those for automotives, with some differences of course.
There are a few options to have direct power production from renewable energy sources like solar or wind power.
Direct solar power could be an idea if the machine is not bound to certain working hours. For example, an autonomous grascutter could just cut gras whenever solar power is available.
Direct wind power is questionable for such type of machine. The same is true for geothermal, tidal and so on.
If you don't want to use direct renewable energy, you will have to include some energy storage. For electrical power from renewable sources, batteries can be used. You can also use biomass in different types, which is also some kind of stored energy. Or you use chemicals produced with renewable power, like (green) hydrogen or synthetic fuels. There is lots of literature to energy storage systems...