TSLA

Automotive manufacturers are required to sell a certain amount of Zero Emission Vehicles in certain regions like the US or Europe. Manufacturers that are not able to produce the required amount are allowed to buy surplus credits from other manufacturers, to avoid being fined. Tesla, being the largest EV manufacturer in the world has plenty of these credits to sell

Energy generation means Solar PV (photovoltaic) in the case of Tesla. The company bought SolarCity in 2016, the largest residential solar installer in the US at the time

After the acquisition, they stopped door-to-door sales (which was the cornerstone strategy of SolarCity) and focused only on selling solar through Tesla showrooms and their website. This, combined with resources being reassigned to the automotive side to support the Model 3 ramp at the time led to a serious decline in solar deployments

Elon Musk introduced the Solar Glass Roof product not long after the SolarCity acquisition, but volume production did not start until late 2020, which also did not help the deployment numbers

From early 2021 Tesla solely sells its solar pruducts bundled with their home battery, the Powerwall and vice versa. Based on Musk's comments on the 21Q1 earnings call, this decision was made mainly to simplify solar deployments, as this way, solar and batteries are always installed in the same configuration. Also with this, all Tesla energy deployments can be part of a VPP (Virtual Power Plant)