title: Heat Regeneration in Dymola/Modelica
body: <p>I want to build a system which consists of solar thermal collectors and ground source heat exchanger. I have a whole season weather data, which is connected with solar thermal collectors. I want to see how much heat will be released during the whole season from solar collectors to the ground by ground source heat exchanger respectively borehole, and the increased ground temperature by heat release.</p>
  <p>Although I have the same number of unknowns and equations, the singularity error comes up.</p>
  <p>Is there any missing process element?</p>
  <p><img src="https://i.stack.imgur.com/TSIcB.png" alt="Screenshot of model" /></p>