Isn't their role to be spammed in the middle of a power stall or raid on one's base to take advantage of huge available factory build power to save one's economy? That's what I do with them:
http://pa-db.com/compare?u1=solar_drone&u2=solar_array I think the usage of Icarus is to make the energy without the placement under the ground. It is just like the solar array. The solar array is less effective than the T2 power plant, but it is still worth using since it saves the space of your planet, especially for the small plant. I think the Icarus is similar to the solar array. The Icarus is less effective than the T1 power plant. T1 power plant creates 600 energy per second, while the Icarus with the same metal can only create 560 energy per second. But the Icarus doesn't cost you a placement under the ground. And the Icarus is available in T1 factory rather than T2 or orbital factory. Please note the power efficiency per metal of T1 air factory and the T1 fabricator. T1 air factory takes 45 energy per metal, while T1 vehicle fabricator takes 63.6 energy per metal. To get 600 energy/sec income, a T1 power plant needs at least 400 * 63.3 = 25440 energy. On the other hand, 3.2 Icakus need 400 * 45 = 18000 energy. This may save much energy! There is also an interesting fact that Icarus is more cost effective than the solar array in metal comparison. The price of solar array is 1800 metal which is equal to 14.4 Icarus, but the solar array creates only 2500 energy per second, while 14.4 Icarus create 2520. When should you make Icarus? In early game, once you find out that there is no other opponent on your planet. Then you can build this little power plant until you get enough energy but short for metal. The Icarus takes more metal but less energy to build, so it can help the player in early game which is usually short for the energy. After you get enough energy but short for metal, try to build the T1 power plant instead. In middle game, T2 power plant is much more efficient than Icarus, So you should use T2 power plant in middle game. In the late game, player may need to save the space of the planet. And the stationary power plant takes fabricator to walk and build. In this period, player can choose the Icarus to replace the solar array, while it is under the risk of enemy T2 fighter which may come and sweep your power. Of course, if the system contains a gas giant, you will only build jig rather than any other power plants in the late game.
I am still not sure whether the Icarus is a practical unit in 1vs1 situation. I feel it is a very risky choice in early game, but I did see the Uber rank player uses them. In custom game with multiple planet, I can scout the planet by firefly. Once I comfirm there is no enemy on my planet, I can use Icarus safely.
It's also a comparably safe bet if you want to turtle on a plateau where building space is limited and bombers already are your worst threat so AA is something you are going to build either way. Just order them to hold fire and not to roam, and to assist a factory or any other structure, and they will be more than happy to stack en mass.
Fighters have lots of HP, Icarus do not. So... having Icarus in your base, enemy fighters fly over all your AA, kill all the Icarus really quick, fly away with 1/2 HP. You cannot protect those things easily. Even if you're on your own on a planet, an enemy with half a brain will send 1 T2 fighter and take out all your power super quick :/ Surprised we're not seeing PTEs with buffs to this unit yet. We know it sucks by now.
