As an experiment, I tried minimizing just the first term of your expression and got a useful error message
In[51]:= NMinimize[{(E1[6.5] - tsd1[[1]])^2, a > 10 && b > 20}, {a, b}]
During evaluation of In[51]:= NMinimize::nnum: The function value (96.4742 +Sqrt[86916. -Sqrt[7.55438*10^9+Times[<<2>>]]]/(2 Sqrt[2])+Sqrt[86916. +Sqrt[7.55438*10^9-3.97633*10^6 Plus[<<2>>]]]/(2 Sqrt[2]))^2 is not a number at {a,b} = {11.9186,21.6635}.
During evaluation of In[51]:= NMinimize::nnum: The function value (96.4742 +Sqrt[86916. -Sqrt[7.55438*10^9+Times[<<2>>]]]/(2 Sqrt[2])+Sqrt[86916. +Sqrt[7.55438*10^9-3.97633*10^6 Plus[<<2>>]]]/(2 Sqrt[2]))^2 is not a number at {a,b} = {11.9186,21.6635}.
During evaluation of In[51]:= NMinimize::nnum: The function value (96.4742 +Sqrt[86916. -Sqrt[7.55438*10^9+Times[<<2>>]]]/(2 Sqrt[2])+Sqrt[86916. +Sqrt[7.55438*10^9-3.97633*10^6 Plus[<<2>>]]]/(2 Sqrt[2]))^2 is not a number at {a,b} = {11.9186,21.6635}.
During evaluation of In[51]:= General::stop: Further output of NMinimize::nnum will be suppressed during this calculation.
Out[51]= NMinimize[{(-1739.3 +
a (179.376 - 8/5 b Cos[(43 \[Pi])/180]) +
1/(2 Sqrt[
2]) (\[Sqrt](a^2 (222.029 + (7.51018 +
32/65 Sqrt[3] b Sin[(17 \[Pi])/180]) (12.1941 +
16/65 Sqrt[3]
b (Sqrt[3] Cos[(17 \[Pi])/180] +
Sin[(17 \[Pi])/
180]))) - \[Sqrt](a^4 (222.029 + (7.51018 +
32/65 Sqrt[3] b Sin[(17 \[Pi])/180]) (12.1941 +
16/65 Sqrt[3]
b (Sqrt[3] Cos[(17 \[Pi])/180] +
Sin[(17 \[Pi])/180])))^2 -
4 a^4 (-47.7013 +
7.51018 (7.51018 +
32/65 Sqrt[3]
b Sin[(17 \[Pi])/180])) (-89.1844 + (12.1941 +
16/65 Sqrt[3]
b (Sqrt[3] Cos[(17 \[Pi])/180] +
Sin[(17 \[Pi])/180])) (6.00082 + 13/(2
\!\(\*SubscriptBox[\(17\), \(\[AliasDelimiter]\)]\))))))) +
1/(2 Sqrt[
2]) (\[Sqrt](a^2 (222.029 + (7.51018 +
32/65 Sqrt[3] b Sin[(17 \[Pi])/180]) (12.1941 +
16/65 Sqrt[3]
b (Sqrt[3] Cos[(17 \[Pi])/180] +
Sin[(17 \[Pi])/
180]))) + \[Sqrt](a^4 (222.029 + (7.51018 +
32/65 Sqrt[3] b Sin[(17 \[Pi])/180]) (12.1941 +
16/65 Sqrt[3]
b (Sqrt[3] Cos[(17 \[Pi])/180] +
Sin[(17 \[Pi])/180])))^2 -
4 a^4 (-47.7013 +
7.51018 (7.51018 +
32/65 Sqrt[3]
b Sin[(17 \[Pi])/180])) (-89.1844 + (12.1941 +
16/65 Sqrt[3]
b (Sqrt[3] Cos[(17 \[Pi])/180] +
Sin[(17 \[Pi])/180])) (6.00082 + 13/(2
\!\(\*SubscriptBox[\(17\), \(\[AliasDelimiter]\)]\))))))))^2,
a > 10 && b > 20}, {a, b}]