What do you mean by solarpunk being a reality? That is really important as solarpunk is utopian and that somewhat litterally means no place. So you have to draw the line of what makes a country solarpunk enough to count. That basicly is a question of what your values are. Anyway some of my ideas are:

First of all technically speaking there is a massive problem of providing a high quality of life and no breaking planetary boundaries. Basicly rich countries provide the quality of life for nearly everybody, but break planetary boundaries, whereas poor countries do not break planetary boundaries, but do not provide a high quality of life. I really like the Happy Planet Index, which basicly takes how long a good a persons life is and divides its by the enviromental footprint. The regions which do the best in it are Latin America and then a bit worse is Europe. However some Asian countries do well as well. However those places are also more likely to just reform to the point of decent sustainability, as the cliff is not as bad.

If you want to see new organizational systems, you have to look at the most disadvantaged places in the current system. So places like Rojave and Zapatistas in Mexico are examples of that. However Subsaharan Africa is propably the most likely place for other new systems being born, given the current situation. If you have little to loose, taking risks is just a prudent move. So Europe for example is not going to try something like that at all.