I wanted to share The Sun Exchange with this community.
They trade in both Rands and Bitcoin and focuses on projects which are outside the commercial realm such as schools. It merges the idea of building wealth where one can sponsor a solar cell where thereafter, one can generate a rental income on your sponsored solar cells.
Forbes had an article on them sometime back;
I am not sure if the projects would qualify for the GBCSA Net Zero Carbon offset schemes.
As an additional benefit, by owning solar cells, one can also register to be an energy producer on the SolarCoin website to earn the SolarCOin cryptocurrency (not that cryptocurrencies are doing great lately) 
[Disclaimer: This is purely for information sharing purposes - not for promotional or endorsement purposes]