I'm currently simulating a PV/T model , i started with this at first , and it keeps saying that my equations and variuables are unbalanced , so i tried to play with it , I'm new using MODELICA , I usually work on matlab / simulink

block PVT
extends Modelica.Blocks.Interfaces.SI2SO;
input  Real G=800 "radiance";
input  Real Ta      "temperature ambiante";
Real Tvext(start=293.15) "Temperature verre exterieur";
Real Tvint(start=293.15)  "Temperature verre interieur";
Real Tcel(start=293.15) "Temperature de la cellule ";
constant Real a = 273.15;
constant Real Vvent =3;
constant Real A_verre = 1.64;
constant Real Sigma = 5.670373e-8;
constant Real Epsilon_v = 0.88;
constant Real h_ca = 17.8 ;
constant Real Lambda_v = 1.05;
constant Real Sigma_v = 0.003;
constant Real mv_v = 2500;
constant Real c_v = 810;
constant Real Tau_verre = 0.95;
constant Real Lambda_cel = 148;
constant Real Sigma_cel = 0.002;
constant Real Alpha_cel = 0.9;
constant Real Acel = 0.87;
constant Real ccel = 700;
constant Real mv_Si = 2330;
constant Real Tciel=350;
output Real Qelec;


equation
Ta = (Tciel/0.0552)^(2/3);
algorithm
der(Tvext)  := ( (A_verre*G - Sigma*Epsilon_v*A_verre*(Tvext^4 - Tciel^4)) - (h_ca*A_verre*(Tvext - Ta)) - ((Lambda_v/Sigma_v)*A_verre*(Tvext - Tvint)))/((mv_v*A_verre*Sigma_v)*c_v);

der(Tvint) : = ( (A_verre*G*Tau_verre) + ((Lambda_v/Sigma_v)*A_verre*(Tvext - Tvint)) - ( (Lambda_cel/Sigma_cel)*A_verre*(Tvint - Tcel)))/((mv_v*A_verre*Sigma_v)*c_v);

der(Tcel) := ( ( A_verre*G*Tau_verre)*Alpha_cel + ((Lambda_cel/Sigma_cel)*A_verre*(Tvint - Tcel)) - (0.178*(1-0.00375*(Tcel -273.15 -25))*Acel*( G*Tau_verre)))/((mv_Si*Acel*Sigma_cel)*ccel);

Qelec := ( 0.178*(1-0.00375*(Tcel -273.15 -25))*Acel*( G*Tau_verre));

end PVT;

i keep getting this error :


[1] 19:32:03 Traduction Erreur
[PVT: 32:1-32:179]: Failed elaborate assignment for some unknown reason: der(Tvext) := 0.0001646090534979424 * G + (-8.213873646090535e-012) * (-15006250000.0 + Tvext ^ 4.0) + (-0.002930041152263375) * (Tvext - Ta) + (-0.05761316872427984) * (Tvext - Tvint). File a bug report and we will make sure this error gets a better message in the future.

[2] 19:32:03 Traduction Erreur
Error occurred while flattening model PVT