added function to compute useful power and spectral efficiency for multi-junction STPV

Author: FoleyLab

wptherml/stpvlib.py

@@ -11,6 +11,25 @@
 k=1.38064852e-23
 
 
+''' An idealized efficiency figure of merit with a numerator 
+    that is proportional to short circuit current and a denominator proporitonal
+    to incident power... the light-source can be thermal emission or can be solar.  '''
+def multi_spectral_efficiency(lam, light, lbg1, lbg2):
+    ### upper-bound of light-source
+    upper = np.amax(lam)
+    ### integrand for PV 1
+    num_integrand_1 = light * lam/lbg1
+    ### integrand for PV 2
+    num_integrand_2 = light * lam/lbg2
+    ### numerator 1
+    numerator_1 = numlib.Integrate(num_integrand_1, lam, 1e-9, lbg1)
+    ### numerator 2 
+    numerator_2 = numlib.Integrate(num_integrand_2, lam, lbg1, lbg2)
+    ### denominator
+    denominator = numlib.Integrate(light, 1e-9, upper)
+    
+    return numerator_1, numerator_2, denominator
+    
 ### Trial objective function for multi-junction STPV with a single emitter!
 def jsc_multi(lam, TE, eps_pv1, eps_pv2, T_pv1):
     upper = np.amax(lam)

wptherml/wpml.py

@@ -701,6 +701,19 @@ def filter_grad(self):
     ### Normal versions first - no explicit dependence on angle
 
     ### Spectral Efficiency - see Eq. 4 in Jeon et al, Adv. Energy Mater. 2018 (8) 1801035
+    ''' method for multi-junction stpv devices!  Provide the light-source and the band-gap wavelengths
+        of the first and second PVs, it will return the useful power density of the first and
+        second PVs along with the incident power density! '''
+    def multistpv_se(self, light, lbg1, lbg2):
+        output = stpvlib.multi_spectral_efficiency(self.lambda_array, light, lbg1, lbg2)
+        self.pv1_useful_power_val = output[0]
+        self.pv2_useful_power_val = output[1]
+        self.pv1_spectral_efficiency_val = output[0]/output[2]
+        self.pv2_spectral_efficiency_val = output[1]/output[2]
+        self.spectral_efficiency_val = (output[0]+output[1])/output[2]
+        return 1
+            
+    
     def stpv_se(self):
         self.spectral_efficiency_val = stpvlib.SpectralEfficiency(self.thermal_emission_array, 
                                                                   self.lambda_array,