According to viewtopic.php?t=48429 , it used to sayProduce more than 10 GJ per hour using solar panels
And was changed when nuclear was added.Produce more than 10 GJ per hour without the use of Steam
However, the new text is not clear. A simple calculation (and test) shows that running 100 solar panels for an hour (with radars to use the power) grants the achievement. But what if you also have a steam engine? In that case, you are indisputable "Produc[ing] more than 10 GJ per hour using solar panels", but the achievement does not trigger.
Producing 10GJ solar power in one network, while a steam engine is in another network, triggers the achievement. Is that on purpose?
One way to solve the ambiguity is to change the achievement formulation to
Produce more than 10 GJ per hour using only solar panels