Update of UpdateMy sincere apologies for having posted sh*t earlier about the OEM discs thickness.
Here is what I think are the correct information about the rear disc brake.
Status Quo of my rear brake discAfter 75,000 km I still have the original disc and are using my 3rd pair of pads (1st was OEM, then the red ones from Brembo).
Thickness measured at eight places is still well over 4.7 mm (minimum thickness is 4.5 mm as you can see stamped on the disc), so I assume the OEM disc was 5 mm.
I am an avid user of the rear brake, e.g. using it for stability in downhill curves with the throttle open, so I think it can be said that for most of us it should be a long time until a replacement disc is necessary.
Replacement discsWhen searching for replacements I found out that the rims of our bikes are made by Italian company named Marchesini who are also supplying to other brands, most prominently for the 2008 Ducati Desmoseidici RR, a 188 HP limited edition bike. When you search the web for pictures, you can easily identify the rear brake disc being the same as on our Energicas by its unique design.
Main dimensions:
Diameter: 240 mm
Hole diameter: 125 mm
Centering diameter: 107 mm
Number of holes: 5
Hole diameter: 8.5mm (for M8 screws)
1. Brembo no. 68B40768
Thickness: 4 mm
Comment: Note that this is a thin one. I could not find any other matching Brembo disc with a higher thickness.
2. NG Brakes (Spain) no. NG1052
Thickness: 4 mm
Comment: Also a thin disc, maybe for racing. I tried to purchase this disc in Germany but the official distributors denied having it on stock. Maybe one has to contact the Spanish HQ.
3. EBC Brakes (Great Britain) no. MD618
Thickness: 5 mm
Comment: EBC Brakes (Great Britain) offers variations:
MD618 plain design, carbon steel
MD618C contoured, stainless
MD6181C contoured, carbon steel, gold plated
MD6181CX waved, stainless
MD6181D plain, stainless
4. Braking Brakes (Germany) no. DC04RID
Thickness 5 mm
Comment: Wave design
Issue of disc thicknessMost probably the thickness of the original disc was 5 mm with minimum of 4.5 mm.
Question is whether the thinner Brembo is safe to be used as replacement.
The OEM caliper has the Brembo part no. 920B85293 (thanks to Matthias (most) for this info!).
Replacement for EVAs according to the Brembo catalogue is a Brembo P2-RS84 with parts no. 120B27810. This caliper is made for discs with 5 mm and minimum 4.5 mm and thus probably would not be safe for use with a 4 mm disc.
Though that thinner disc could be used with a more sophisticated 4-piston caliper GP2-SS no. 120A44110 (for approx. 550 EUR).
SummaryAvailable discs with 4 mm thickness are most probably not safe to be used with the original caliper. Currently EBC seems to be the right source to get a replacement disc if needed. Best matching type would be the MD618.
First, let me wish a happy winter solstice, whatever other name you may have for it 
You might remember from some of my posts that the absence of information about the rear disc nagged me for a long time. So I took the opportunity of a major maintenance (change of sprockets and chain) to dismount the original disc and took some measurements.
After some research on the web, I found the Brembo 68B40768 to be fitting.
It’s also a fit for older Ducatis. Only difference to the original disc mounted on the Ribelle is the thickness. While the original one had 4.5 mm, the 68B40768 has only 4.0 mm.
Do you think that could be an issue?
UPDATE April 2025:
Found more alternatives:
NG Brakes (Spanish manufacturer) No. NG1052 (4 mm thickness).
EBC (UK manufacturer) MD618 (5 mm th.).
BRAKING (German manufacturer) No. DC04RID (5 mm th.).