As a heads up, while the change I said worked in 1.11.2, it may not work now.

Redstone Flux is it's own thing now and as such the Interface we need has changed. Functionally it's the same however.

We need to ensure that the following is in the build.gradle

repositories {
    maven {
        name = "CoFH Maven"
        url = "http://maven.covers1624.net"
    }
}

dependencies {
    deobfCompile "cofh:RedstoneFlux:1.12-2.0.0.1:universal"
}

and update the @Optional.Interface to the following

@Optional.Interface(iface = "cofh.redstoneflux.api.IEnergyReceiver", modid = "redstoneflux")

i've pushed this change to the 1.12 branch

As one more rider to this issue, we need to remove the old RF API and imports. Ran into that while testing out the GUI stuff