Is there a maximum recommended distance between the panels and the tank?

To minimize heat losses, it is recommended that you reduce not only the distance between the panels and the tank as much as possible, but also between the tank and the different taps in the house. But there is no particular average distance to abide by:

• For a high temperature application with DN16 multilayer piping, a fluid leaving the panels at 50°C with an outside temperature of 20°C will lose 1.2 W of thermal power per meter of pipe. Over 10 meters, it will lose 12 W. Over 20 meters, it will lose 24 W. The thermal production at this temperature is 404 W (with an insulated Spring panel). The energy loss over 10 meters is therefore 3%; over 20 meters it is 6%. These losses are acceptable.
  
  
• For a low temperature pool-type application with PVC-C piping, a fluid leaving the panels at 30°C with an outside temperature of 10°C will lose 3.2 W of thermal power per meter of pipe. Over 10 meters, it will lose 32 W. Over 20 meters, it will lose 64 W. The thermal production at this temperature is 794 W (with a non-insulated Spring panel). The energy loss over 10 meters is therefore 4%; over 20 meters it is 8%. These losses are also acceptable.