RFTools Power Relay
The Power Relay allows you to control how much RF to output based on a redstone signal. In its GUI you can set the amount of RF/tick to give in case redstone signal is off and also in case redstone signal is on. Typically you would use 0 in case the redstone signal is off and some other value in case the redstone signal is on. You can use this in combination with the RF Monitor to turn off a portion of your RF network in case power is low. For example, to turn off ore processing machines.
You can craft this block with the following recipe:
Here is a screenshot of the user interface:
