Wat is the carbon footprint of the production of solar panels?

Ref 4: http://news.nationalgeographic.com/news/energy/2014/11/141111-solar-panel-manufacturing-sustainability-ranking/

How Green Are Those Solar Panels, Really?
As the industry grows, so does concern over the environmental impact.
By Christina Nunez, National Geographic

Fabricating the panels requires caustic chemicals such as sodium hydroxide and hydrofluoric acid, and the process uses water as well as electricity, the production of which emits greenhouse gases. It also creates waste. These problems could undercut solar’s ability to fight climate change and reduce environmental toxics.

A study released in May by Northwestern University and Argonne National Laboratory found that the carbon footprint of a panel from China is twice that of one from Europe, because China has fewer environmental standards and more coal-fired power plants.

China has already seen a backlash. Panel manufacturer Jinko Solar, for example, has faced protests and legal action since one of its plants, in the eastern province of Zhejiang, was accused of dumping toxic waste into a nearby river.

Solar manufacturers in the United States are subject to both federal and state rules that dictate, for example, how and where they can dispose of toxic wastewater. In Europe recent regulations mandate the reduction and proper disposal of hazardous electronic waste.

Right now, solar panel recycling suffers from a chicken-or-egg problem: There aren’t enough places to recycle old solar panels, and there aren’t enough defunct solar panels to make recycling them economically attractive.

It would be difficult to find a PV module that does not use at least one rare or precious metal, because they all have at least silver, tellurium, or indium.

The source of that energy, which is often coal, he added, determines how large the cell’s carbon footprint is.