There is no need for mandatory international targets for nations renewable energy production.

Targets for renewable energy is impractical because it is unsustainable at this point of time. The current sources of renewable energy are hydro, solar, wind and geothermal. All these sources require significant technology to convert to electricity. Most nations with the potential to produce energy from these sources cannot afford or sustain the monetary input required to install these technologies on a large scale.

Also the extremely high costs of renewable energy make it an albatross's cross on the nations which might be forced to install it due to targets.

The
renewable energy sources are also not developed enough to completely replace coal. They can only reduce the need for coal based power to a certain extent.

One however feels the need to set targets for mandatory carbon sinks in proportion to the amount of power a country generates

Energy production is the prime cause of the problem of the burgeoning production of green house gases which is leading to climate change. If we are to tackle the problem of increasing carbon emissions, then a shift to renewable energy resources is a must. 
 
In the present scenario, when all the countries are passing the buck in terms of setting carbon reduction goals, the vision of mandatory renewable energy targets seems a far fetched dream. However, if the countries agree to such goals then it will indeed be the biggest achievement in climate change negotiations.  
 
In the present scenario we see that if there is no mandatory target for any project, then the governments take a step-motherly attitude to the topic. To ensure that the goals of greater renewable energy usage are fulfilled, the governments need to have mandatory goals no matter how lenient they are. Such goals will ensure that at least some progress is done and the projects do not go to the back burner.