Wow such a policy could only be thought up by folks deeply sympathetic with the fossil fuels industry it seems to me.
I wonder how they will react when it becomes clear that the world economy is actually very dishonest by not reflecting the physical effect of us using the energy of the sun, as we should, like all of nature.
The Joules added to the economy from sunlight are as real as any from fossil fuels, but unlike fossil fuels, no Joules need to be given in exchange.
In the case of oil, it took literally millions of years of Joules from sunlight to create it, but we sacrifice those to gain the power needed to get us to the shops for groceries, for example.
In other words, our net output by using fuel created by nature for all things, is reduction of Joules, replacing those by pollution.
Yet the Joules from sunlight can be used by us to create human made fuels like hydrogen, again for nothing in return, with no pollution, which even generates no pollution in its combustion, in fact even produces oxygen like the trees do.
So there we see incredibly valuable physical product being added to the economy, whether it is used to create hydrogen for all industry, or to heat some panels on the roof of your parents house makes no difference, the Joules are added at no cost after installation, and should be recognised as valuable product.
So instead of being taxed, your parents should be rewarded, by the continuous issuance of money reflecting the valuable product they added to the economy, per Austrian Economics ideals.
Ironically, if instead of putting their surplus energy back into the grid, they were generating some valuable cryptocurrency tokens, they would be getting such a reward...