Simscape Model Error - Residual norm too large

Hello,

I'm trying to create a model of a solar power system in Simscape. Therefore I wrote an Simscape Component modelling a solar panel. But always when I try to execute my model, I get the following error message:

Initial conditions solve failed to converge. ...Nonlinear solver: failed to converge, residual norm too large. ......Here is the set of components with unconverged equations:

'Simscape_Solar_Module/Solar Panel' Equation location is: 'C:/Users/paschmal/Matlab/Example1/+Electrical/solar_panel.ssc' (line 51)

I hope somebody could help me with this problem?

Thanks a lot!

if true
  % code
component solar_panel
  nodes
      p = foundation.electrical.electrical; % +:top
      n = foundation.electrical.electrical; % -:bottom        
  end
  variables
      I = {0, 'A'};
      V = {0, 'V'};
  end
  inputs
      E = {1000, 'W/m^2'}; % E:top
  end
  outputs 
      V_o ={0, 'V'}; % V_o:bottom
      I_o ={0, 'A'}; % I_o:bottom
  end
  parameters
      I_sc = {6.46, 'A'};     % Kurzschlussstrom
      V_oc = {65.3, 'V'};     % Leerlaufspannung
      R_s = {1e-2, 'Ohm'};    % Reihenwiderstand
      R_p = {100, 'Ohm'};     % Parallelwiderstand
      N = 1.5;                % Qualitätsfaktor (1 <= m <= 2)
  end
  parameters(Access=private)
      E_0 = {1000, 'W/m^2'};  % Bestrahlungsstärke STC
      V_t = {25.7, 'mV'};     % Temperaturspannung
      i_0 = {0, 'A'};
  end
  function setup
      through(I, p.i, n.i);
      across(V, p.v, n.v);
  end
  equations
      if abs(V) < V_oc
          let
              I_ph = I_sc*E/E_0;
              V_d = abs(V) + abs(I)*R_s;
              I_s = (I_sc-V_oc/R_p)/(exp(V_oc/(N*V_t))-1);
              I_d = I_s*(exp(V_d/(N*V_t))-1);
              I_p = V_d/R_p;
          in
              I == I_ph - I_d - I_p;
          end
      else
          I == i_0;
      end
      V_o == V;
      I_o == I;
  end
end

end