I am attempting to model a solar hot water collector in combination with a low temperature WaterHeater:Mixed, which has no auxiliary heating.

What I've noticed is that the simulation starts with the hot water tank above 60 degC. This leads to a number of hours at the beginning of the simulation where the tank is providing heating while the solar hot water system is not collecting enough heat to actually provide any heating.

Is there a way to initialize the WaterHeater:Mixed at a prescribed temperature in OpenStudio/EnergyPlus? Can I use a design day or schedule to start the tank at a low temperature and ramp?