There is a very useful water heater calculator online here:
http://processheatingservices.com/water-heating-time-calculator/
I assume if you’re working with US gallons then 200 gal = 757 litres.
55F to 120F = 12C to 49C (and wanting to raise the temp by 37C).
a 5.5kW element would achieve this rise in 356 mins, using around 32.6kwh of energy and in just a shade under 6 hours.
What size is the PV array you currently have installed?
What kW rating is the immersion element?
Do you need the water heated up by a certain time?
Have you made provision for legionella prevention? (my rule of thumb is heat the tank to 60C (140F) once a week for one hour). Your local legislation may vary on this.