That is already a thing and it’s called concentrated solar power. Basically aim a shit load of mirrors at a target to heat it, run some working fluid through the target and use that to make steam to turn a turbine. There are a few power plants that use it but in general it has been more finicky and disruptive to the local environment than traditional PV panels would be.
Given the egotistical nature of the Goauld I wouldn’t put it past them to have a sort of “gentleman’s agreement” to keep war mostly ground based to help limit the ability of the jaffa to rebel. We never see any Goauld weaponry that can track its target for instance. Everything just shoots in a straight line until it hits something. They want “war” to be up close and messy to help control their subjects. Given that, air defense as we understand it would defeat the purpose of fighting in the first place for them.