Just finished brewing a M Dunkel and I revised my boiling procedures in response to this thread.
I reduced my boiloff percentage to under 10% by covering the kettle to almost 100%. I had been covering the kettle by about 1/2 to 2/3, but my boil loss percentage was on the order of 1 gal/hr. That was too much. I knew I had to implement change.
So with the lid barely cracked, I quickly found that I needed to reduce the power. I had been boiling with a mild rolling action with the power modulator set at 45%. I had to turn the setting down to 20% to get the same rolling with the cover on. So, there is a big energy savings with the cover on. I did find that its important to keep your face away from the kettle when checking the boil! Steam is hot!!!
I did boil the last 15 min uncovered to help assure that DMS was boiled out and to meet my 10% volume loss goal. I'll bump that down to 8% in the future if this approach seems to work well.
These were changes that I needed to do. We'll see if they improve or degrade the beer.