how do correct stackoverflow Exception at the "get" part of the code

It looks like you're having a recursion in your code. The

return Total;

Actually calls the Total getter again and this calls it again and so on.

In order to store the value you should have a backing variable which you would use internally in the class. So something like:

class appliance
       {
double soln1,soln2,soln3...soln20;

private double _total;

public double Total {

         get {
               return this._total;
                  }

          set {
  this._total=soln1+soln2+soln3......soln20;
                  }
             }

However, the setter looks a bit odd since you set the value based on other variables than what is passed to the property. Re-check that the code is as required or should you use

set {
    this._total=value;
        }