admitance12=(5000./(400^2))*(1-I*Tan[ArcCos[0.8]])

admitance23=(2000./(400^2))*(1+I*Tan[ArcCos[0.7]])

admitance13=(6000./(400^2))*(1-I*Tan[ArcCos[0.5]])

cisla={0.0234*I-I*(0.0125/(Sqrt[3]))+I*(0.0375/(Sqrt[3])),-I*0.0128+I*(0.0312/(Sqrt[3]))-I*(0.0375/(Sqrt[3])),I*0.065-I*(0.0312/(Sqrt[3]))+I*(0.0125/(Sqrt[3]))}

C12=C12/.Solve[cisla[[1]]==I*314*C12,C12]
C13=C13/.Solve[cisla[[3]]==I*314*C13,C13]

L23=L23/.Solve[cisla[[2]]==((-I)/(314*L23)),L23]

plocha=2.;
PSluncenaMetrCtverecni=1000;
fi=80°;
PelNaMetrCtverecni=300;
sigma=5.66*(10^(-8));
epsilon=0.9;
TObloha=5+273;
TZem=20+273;
alfa=17;
TVzduch=15+273;

PSlunce=PSluncenaMetrCtverecni*plocha*Cos[fi];
Pel=PelNaMetrCtverecni*plocha*Cos[fi];
PSalaniDoOblohy=sigma*epsilon*plocha*((T^4)-(TObloha^4));
PSalaniZeme=sigma*epsilon*plocha*((T^4)-(TZem^4));
PKonvekce=alfa*2*plocha*(T-TVzduch);
Teplota=T/.Solve[PSlunce==Pel+PSalaniDoOblohy+PSalaniZeme+PKonvekce,T][[4]]

Print["Teplota je ",Teplota-273,"°C"]