I run a 10gal electric keggle that's pipelined. I mash the next batch while boiling.
I just run multiple batches in a day times (up to 6). it's either a one whole day, or 2 day affair.
As a reference point I use 2 3000 watt elements in my kettle.
However, I usually don't ramp them up to full power. I aslo have them controlled with some SSRs.
Hope that helps.