The sun is such an energy source. Thus, solar energy IS renewable (yes, even if in about 5 billion years of time, the sun will start to die).
However, when we hear someone talk about renewable energy, many of us also mix in the idea of sustainability that a power source can be used long-term without any serious consequences to the earth.
Many have raised this question of sustainability over the last 30 years, calling out the intensive manufacturing process which uses and produces fairly toxic chemicals. In addition, recent accidents at solar cell manufacturing plants have raised global awareness of the dangers of chemical spills and accidents at these factories.
First off, lets state the obvious: solar is, of course, renewable. Photovoltaic solar panels transmit the suns light into electricity with no effect on how much sunlight well have in the future. 100 years from now, it doesnt matter if we have 100 solar panels or 1 million it wouldnt affect the amount of sunlight we receive in the slightest (despite recent reports that some believe otherwise).
However, a 2015 report from Clean Energy Action, a clean energy advocacy group based in Boulder, Colorado, found that the EIAs findings were based on outdated data and that they didnt distinguish between coal that is economically viable to mine and coal that is too deep and difficult to mine (and therefore cannot be counted as future supply).
One thing though is certain: A finite amount of coal exists and if we continue using it, one day it will be gone. Its nice to know that, with solar energy, this will never be a problem.
Silicon (the 8th most prevalent element in the universe) is the basic building block of solar cells and what translates the sunlight into electricity. To obtain pure silicon like solar panels require, manufacturers start with quartz and, through several intensive procedures, refine it into pure silicon. During this refining process, both carbon dioxide and sulfur dioxide are released into the air, but at such low levels they cant do much harm.
In response, China (who produces half of all PV panels worldwide) in 2011 introduced more stringent rules around recycling these chemicals during the manufacturing process setting a requirement that 98.5% of silicon tetrachloride to be recycled. Awareness around this issue is also steadily rising, due to news coverage of the high profile spills, as well as the work from the Silicon Valley Toxics Coalition, a nonprofit dedicated to tracking emissions during the panel manufacturing process. They annually release a Score Card that assigns solar manufacturers a sustainability score.
Its also important to keep in mind that the solar industry isnt the only player in the energy world that has accidents. In 2014, an undiscovered leak in a tank at a chemical storage facility in West Virginia allowed 10,000 gallons of 4-methylcyclohexane methanol, a chemical used to purify coal before use in a power plant, into the Elk River outside Charleston and then made its way into the citys water treatment center. The governor of West Virginia declared a state of emergency and warned 300,000 residents to not drink, cook, or bathe in the water.
In regards to the chemicals used during the manufacturing process, proper handling and care could prevent the majority of accidents (and in some cases poor decision making) that have cropped up over the last 10 years. And by properly recycling solar panels, we can save and reuse many of the metals and minerals that are incorporated into solar panels.