Solving Equations with inputs from an Excel file

2019 7 23
1 个回答
回答已采纳
更新时间：2019 7 24
6 次查看（30 天）

0 个投票

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);

请先登录，再回答此问题。

 采纳的回答

Alex Mcaulley
Alex Mcaulley 2019-7-23

0 个投票

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)

3 个评论
显示 1更早的评论 隐藏 1更早的评论

rammah nagi
rammah nagi 2019-7-23
编辑：rammah nagi 2019-7-23
Thank you for the help
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)'}));

请先登录，再进行评论。

更多回答（0 个）

类别

在 帮助中心 和 File Exchange 中查找有关 Introduction to Installation and Licensing 的更多信息

产品

版本

R2019a

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by