It is tough to solo a kin/elec defender ( who have a damage boosting power and a strong heal ), so I would say very...
@Unthing ... Mostly on Union.
Defenders are not soloers.
Now offenders on the other hand... 
Myself I soloed a FF/NRG offender to L35, however this was pre-ED, and the knockback in energy has great synergy with FF, don't think FF/elec makes a decent offender, especially post-ED.
Aye FF/Energy was a good soloer pre ED. Now though it's kinda painful mainly I've found because of reduced sniper damage.
The Smoking Demon
Ash/Tar Corruptor
Union
@The Smoking Demon
How tough will it be to solo a FF/Elec defender?