However, what is puzzling me is when I input a solar irradiance higher than the default (1000 W/m^2), the electrical efficiency drops instead of rises. Theoretically, since the solar cell is receiving more energy, shouldn't the electrical efficiency also rise? Is there a parameter in the model that I should also adjust in response to the higher solar irradiance to offset this? Any help would be much appreciated. Here is my parameter as reference:
%% Load parameters ------------------------------------
load.R = 4.5; %Resistance. With default parameters, 4.5 Ohm is approximately optimal for maximum electrical power extraction
%% Solar panel parameters ------------------------------
% Initial temperatures [K]
panel.initial.Tg0 = 295; %Glass cover
panel.initial.Tpv0 = 295; %PV cells
panel.initial.Te0 = 295; %Heat exchanger
panel.initial.Tw0 = 295; %Water in the tank
panel.initial.Tb0 = 295; %Back cover
% Geometry
panel.geometry.Acell = 0.0225; %Area of a cell, [m^2]
panel.geometry.Ncell = 72; %Number of cells
% Optical properties
panel.optical.ng = 1.52; %Refractive index ratio glass/air
panel.optical.absg = 0.2; %Absorption coefficient of glass per unit length [1/m]
panel.optical.dg = 0.01; %Thickness of glass cover [m]
panel.optical.rpv = 0.15; %Reflection factor of PV cell
% Heat transfer properties
panel.heatTransfer.Ta = 295; %Temperature of ambient air [K]
panel.heatTransfer.Tsky = 290;%Temperature of sky (for radiative heat transfer) [K]
panel.heatTransfer.Mg = 4; %Mass of glass cover [kg]
panel.heatTransfer.Mpv = 0.2; %Mass of one PV cell [kg]
panel.heatTransfer.Me = 15; %Mass of heat exchanger [kg]
panel.heatTransfer.Mb = 5; %Mass of back cover [kg]
panel.heatTransfer.Cg = 800; %Specific heat of glass [J/kg/K]
panel.heatTransfer.Cpv = 200; %Specific heat of PV cell [J/kg/K]
panel.heatTransfer.Ce = 460; %Specific heat of heat exchanger [J/kg/K]
panel.heatTransfer.Cb = 400; %Specific heat of back cover [J/kg/K]
panel.heatTransfer.epsg = 0.75; %Emissivity of glass
panel.heatTransfer.epspv = 0.7; %Emissivity of PV cell
panel.heatTransfer.hga = 10;%Free convection coefficient between glass and ambient air [W/m^2/K]
panel.heatTransfer.hgpv = 20; %Free convection coefficient between PV cells and glass [W/m^2/K]
panel.heatTransfer.hba = 10;%Free convection coefficient between back cover and ambient air [W/m^2/K]
panel.heatTransfer.ke = 130;%Thermal conductivity of heat exchanger [W/m/K]
panel.heatTransfer.Le = 0.04;%Thickness of heat exchanger [m]
panel.heatTransfer.kins = 0.1;%Thermal conductivity of insulation layer [W/m/K]
panel.heatTransfer.Lins = 0.03;%Thickness of insulation layer [m]
% PV cell electrical properties
panel.pv.Isc = 8.88; % Short-circuit current, Isc [A]
panel.pv.Voc = 0.62;% Open-circuit voltage, Voc [V]
panel.pv.Is = 1e-6; % Diode saturation current, Is [A]
panel.pv.Is2 = 0; % Diode saturation current, Is2 [A]
panel.pv.Iph0 = 8.88;% Solar-generated current for measurements, Iph0 [A]
panel.pv.Ir0 = 4000;% Irradiance used for measurements, Ir0 [W/m^2]
panel.pv.ec = 1.5; % Quality factor, N
panel.pv.N2 = 2; % Quality factor, N2
panel.pv.Rs = 0; % Series resistance, Rs [Ohm]
panel.pv.Rp = inf ; % Parallel resistance, Rp [Ohm]
panel.pv.TIPH1 = 0; % First order temperature coefficient for Iph, TIPH1 [1/K]
panel.pv.EG = 1.11;% Energy gap, EG [eV]
panel.pv.TXIS1 = 3;% Temperature exponent for Is, TXIS1
panel.pv.TXIS2 = 3;% Temperature exponent for Is2, TXIS2
panel.pv.TRS1 = 0;% Temperature exponent for Rs, TRS1
panel.pv.TRP1 = 0;% Temperature exponent for Rp, TRP1
panel.pv.Tmeas = 25; % Measurement temperature [degC]
%% Pipe parameters ----------------------------------------
pipe.length = 5; % Pipe length [m]
pipe.area = 0.0007; % Cross-sectional area [m^2]
pipe.Dh = 0.03; % Hydraulic diameter [m]
pipe.length_add = 1; % Aggregate equivalent length of local resistances [m]
pipe.roughness = 15e-6; % Internal surface absolute roughness [m]
pipe.Re_lam = 2000; % Laminar flow upper Reynolds number limit
pipe.Re_tur = 4000; % Turbulent flow lower Reynolds number limit
pipe.shape_factor = 64; % Shape factor for laminar flow viscous friction
pipe.Nu_lam = 3.66; % Nusselt number for laminar flow heat transfer
%% Tank params -------------------------------------------
tank.Volmax = 0.25; % Maximum tank capacity [m^3]
tank.Atank = 0.3; % Tank cross-sectional area [m^2]
tank.Voltank0 = 0.1; % Initial volume in the tank [m^3]
tank.Ttank0 = 295; % Initial temperature in the tank [K]
tank.Lins = 0.05; % Insulating layer thickness [m]
tank.kins = 0.1; % Thermal conductivity of insulation layer [W/m/K]
tank.hta = 10; % Free convection coefficient between tank and ambient air [W/m^2/K]
%% Pump flow input params --------------------------------
pumps.mdot_int = 0.02; % Internal circuit mass flow rate [kg/s]
pumps.mdot_dem = 0.005; % Demand mass flow rate (to the sink) [kg/s]
pumps.mdot_sup = 0.005; % Supply mass flow rate (from the source) [kg/s]
And for my output:
****** Efficiency Calculation *********
Total input energy from the sun in the period: 43.7928 kWh
Average input energy from the sun per day: 14.5976 kWh/day
Total electrical energy supplied to the load: 0.51956 kWh
Average electrical energy supplied per day: 0.17319 kWh/day
Total absolute thermal energy in the water supplied to the user: 34.4859 kWh
Total absolute thermal energy in the water extracted from the source: 16.498 kWh
Total used thermal energy (sink - source): 17.9879 kWh
Average used thermal energy per day (sink - source): 5.996 kWh/day
Electrical efficiency: 0.011864
Thermal efficiency: 0.41075
Total efficiency: 0.42261
***************************************
It just seems that an electrical efficiency of 1.2% is too low for a solar irradiance of 4000 W/m^2. Maybe someone with more electrical expertise can make sense of this code.
