The system incorporates steam power when there is a spike or when power is non-optimal.
Long story short when the yellow(Mains power) is low it doesn't supply enough water and causes the light's to turn on
The idea would be to hook this up to your offshore pumps for your Steam grid then connect your steam grid to your main Grid.
The less water in the system the better the system functions to a point i have about 15 in there and it seems very responsive if you want it to kick in slower just add more water you can also tune it with the arethmetic combinators.
My system currently resets to normal after Power production > Power consumption.
Normal state
Pump Array A @ max power pump faster then Pump Array B @ 100% power
Failed State
Pump array A @ X% power pump slower then Pump Array B @ 100% power
Note: you need liquid in the system to get it to work so connect a offshore pump then disconnect after a 1 or 2 seconds.(Unless you want to tune it for higher amounts of water or you want a delay before the system triggers your steam power grid)
Version 2.1 Blueprint
Legacy
Version 1.3 Pic
Version 1.3 Blueprint