Have a look at this survey:
http://www.nadler.com/public/DeRese_...ilplanes.p df

30% of pilots have had an engine failure.

Motorgliders require additional margins to be safe,
and many are not so reliable.

So far, my Antares 20E has not let me down,
but it is a motor-glider and I fly it always
such that the day when there is a problem,
I will have a pre-planned and safe out.

Hope this is helpful,
Best Regards, Dave "YO electric"