The solo 401k allows you to contribute $15,000, no matter what, plus 20% (as a sole proprietor, some corporation set-ups allow 25%) up to $44,000.
The SEP allows for 20 or 25% (same rules) up to $44,000, period.
So if you made $50,000.
Solo: $15,000 + (20% of $35,000) = $22,000, leaving you...