QUESTION:

Is their a relationship between and/or way of converting Solar Heat Gain Coefficient and g-value (the euro version of SHGC) ?

ANSWER:

Yes.

SHGC = SC x 0.87

or

SHGC = SC x 0.86

...depending on which text you read.

where; SC = Shading Coefficient
and, SHGC = Solar Heat Gain Coefficient

For a couple of external online references, have a look at: Solar Heat Gain Coefficient (SHGC) FAQs