Solving Equations with inputs from an Excel file

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rammah nagi
rammah nagi 2019-7-23
评论： Alex Mcaulley 2019-7-24
Hi, I am modelling a solar panel and I am struggling to get a solution for the Tpv shown in the code. When I use a single value for Ta there are no problems in finding an exact solution. However when I get the Ta to be read from the excel sheet (column 8, 24 rows) it returns me with no solutions (In the workspace Tpv is defined as "0x1 sym"). I have pasted my model below, any help would be greatly appreciated.
Hi, I am modelling a solar panel and I am struggling to get a solution for the Tpv shown in the code. When I use a single value for Ta there are no problems in finding an exact solution. However when I get the Ta to be read from the excel sheet (column 8, 24 rows) it returns me with no solutions (In the workspace Tpv is defined as "0x1 sym"). I have pasted my model below, any help would be greatly appreciated.
%% Energy balance Top layer
fileName1 = '1Day.xlsx';
numData1 = xlsread(fileName1);
Ta = numData1(:,8);
EtaG = 0.88; %emissivity of glass
Sigma = 5.67*10^-8; %stefan boltsman constant
Tsky = 0.0552.*Ta.^(1.5);
Tg = Ta + 10;
qsky = EtaG*Sigma.*(Tg.^4-Tsky.^4); %heat flux loss between sky and glass
Vw= numData1(:,12);
hwind = 4.5+2.9.*Vw;
qwind = hwind.*(Tg-Ta);
kair = 0.025;
eag = 0.005;
Etapv = 0.9;
syms Tpv
eqn1 = qsky + qwind == (Sigma .* (Tpv.^4 - Tg.^4)) / (1 / Etapv + 1/EtaG - 1) + (kair / eag) .* (Tpv - Tg);
Tpv= solve(eqn1,Tpv);

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Alex Mcaulley
Alex Mcaulley 2019-7-23
I suspect you have an overdetermined system (1 variable and 24 equations). Probably you want this:
%% Energy balance Top layer
fileName1 = '1Day.xlsx';
numData1 = xlsread(fileName1);
syms Tpv Ta Vw
% Ta = numData1(:,8);
EtaG = 0.88; %emissivity of glass
Sigma = 5.67*10^-8; %stefan boltsman constant
Tsky = 0.0552.*Ta.^(1.5);
Tg = Ta + 10;
qsky = EtaG*Sigma.*(Tg.^4-Tsky.^4); %heat flux loss between sky and glass
% Vw = numData1(:,12);
hwind = 4.5+2.9.*Vw;
qwind = hwind.*(Tg-Ta);
kair = 0.025;
eag = 0.005;
Etapv = 0.9;
eqn1 = qsky + qwind == (Sigma .* (Tpv.^4 - Tg.^4)) / (1 / Etapv + 1/EtaG - 1) + (kair / eag) .* (Tpv - Tg);
Tpv = solve(eqn1,Tpv);
res = double(subs(Tpv,{Ta,Vw},{numData1(:,8)',numData1(:,12)'})) %Where each column of res contains the solutions for each pair of values (Ta,Vw)
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rammah nagi
rammah nagi 2019-7-23
Say I wanted to use the values obtained from Tpv in another equation
qrpv= (Sigma * (res.^4 - Tg.^4)) / (1 / Etapv + 1/EtaG - 1);
qrpv1 = double(subs(qrpv,{Ta,Vw},{numData1(:,8)',numData1(:,12)'}));
Would this be the way to go about it?
Alex Mcaulley
Alex Mcaulley 2019-7-24
Well, the correct way to do this is doing the substitution at the end (keeping the symbolic variables):
qrpv= (Sigma * (Tpv.^4 - Tg.^4)) / (1 / Etapv + 1/EtaG - 1);
qrpv1 = double(subs(qrpv,{Ta,Vw},{numData1(:,8)',numData1(:,12)'}));

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