It is common usage today to use the word 'alternative energy' when discussing renewable energy. The unfortunate thing about this is that it infers that renewable energy is the poor cousin of energy derived from coal or nuclear fuel.
As both coal and nuclear are clearly unsustainable (in my understanding of the meaning of that word*), I would hope that in the not too distant future the use of renewable energy will outstrip the use of non-renewable energy (eg fossil fuels and nuclear energy) and at that point renewable would clearly no longer be the alternative, but would have become the mainstream energy source.
Even if the description of renewable energy as 'alternative energy' may technically be correct at this juncture I much prefer to be forward thinking and decline from using the word 'alternative' when talking about renewable energy.
In the same light, when we install a grid-interactive solar power system we are required to install a warning sign that reads: 'Warning - dual supply. Isolate both normal and solar supplies before working on the switchboard.' This again is showing a clear bias towards the grid supply which in this case is powered mostly by coal-fired power stations.
I live in a solar powered household and in my view the solar power is my normal supply. To show a less biased attitude I would prefer the wording: '... Isolate both grid and solar supplies ...' which would also mean that the signs won't be dated when renewable energy becomes the mainstream energy source.
* I must note that some organisations such as the Business Council for Sustainable Energy (BCSE) have defined the word 'sustainable' as anything that reduces greenhouse gas emissions. Using this definition, coal mining, coal fired power stations and fossil fuel powered vehicles can be made to look sustainable and allows the BCSE to give the highest producers of greenhouse gas emissions the tick of approval to allow them to look green.