switch to non-normalized temp coeffs

Author: kandersolar

pvlib/ivtools/sdm/desoto.py

@@ -421,9 +421,9 @@ def fit_desoto_batzelis(v_mp, i_mp, v_oc, i_sc, alpha_sc, beta_voc):
     i_sc : float
         Short-circuit current at STC. [A]
     alpha_sc : float
-        Short-circuit current temperature coefficient at STC. [1/K]
+        Short-circuit current temperature coefficient at STC. [A/K]
     beta_voc : float
-        Open-circuit voltage temperature coefficient at STC. [1/K]
+        Open-circuit voltage temperature coefficient at STC. [V/K]
 
     Returns
     -------
@@ -447,6 +447,10 @@ def fit_desoto_batzelis(v_mp, i_mp, v_oc, i_sc, alpha_sc, beta_voc):
        IEEE Trans. Sustain. Energy, vol. 7, no. 2, pp. 504-512, Apr 2016.
        :doi:`10.1109/TSTE.2015.2503435`
     """
+    # convert temp coeffs from A/K and V/K to 1/K
+    alpha_sc = alpha_sc / i_sc
+    beta_voc = beta_voc / v_oc
+
     # Equation numbers refer to [1]
     t0 = 298.15  # K
     del0 = (1 - beta_voc * t0) / (50.1 - alpha_sc * t0)  # Eq 9

pvlib/pvarray.py

@@ -423,9 +423,9 @@ def batzelis(effective_irradiance, temp_cell,
     i_sc : float
         Short-circuit current at STC. [A]
     alpha_sc : float
-        Short-circuit current temperature coefficient at STC. [1/K]
+        Short-circuit current temperature coefficient at STC. [A/K]
     beta_voc : float
-        Open-circuit voltage temperature coefficient at STC. [1/K]
+        Open-circuit voltage temperature coefficient at STC. [V/K]
 
     Returns
     -------
@@ -447,9 +447,6 @@ def batzelis(effective_irradiance, temp_cell,
        (taken from the De Soto model)
     3. estimating the MPP, OC, and SC points on the resulting I-V curve.
 
-    The ``alpha_sc`` and ``beta_voc`` temperature coefficient parameters
-    must be given as normalized values.
-
     At extremely low irradiance (e.g. 1e-10 Wm⁻²), this model can produce
     negative voltages.  This function clips any negative voltages to zero.
 
@@ -461,15 +458,18 @@ def batzelis(effective_irradiance, temp_cell,
 
     Examples
     --------
-    ...           'alpha_sc': 0.00046, 'beta_voc': -0.0024}
     >>> params = {'i_sc': 15.98, 'v_oc': 50.26, 'i_mp': 15.27, 'v_mp': 42.57,
+    ...           'alpha_sc': 0.007351, 'beta_voc': -0.120624}
     >>> batzelis(np.array([1000, 800]), np.array([25, 30]), **params)
-    {'p_mp': array([650.0439    , 512.99195952]),
-     'i_mp': array([15.27      , 12.23049227]),
-     'v_mp': array([42.57      , 41.94368864]),
-     'i_sc': array([15.98     , 12.8134032]),
-     'v_oc': array([50.26      , 49.26532905])}
+    {'p_mp': array([650.0439    , 512.99199048]),
+     'i_mp': array([15.27      , 12.23049303]),
+     'v_mp': array([42.57      , 41.94368856]),
+     'i_sc': array([15.98    , 12.813404]),
+     'v_oc': array([50.26      , 49.26532902])}
     """
+    # convert temp coeffs from A/K and V/K to 1/K
+    alpha_sc = alpha_sc / i_sc
+    beta_voc = beta_voc / v_oc
 
     t0 = 298.15
     delT = temp_cell - (t0 - 273.15)

tests/ivtools/sdm/test_desoto.py

@@ -95,15 +95,15 @@ def test_fit_desoto_sandia(cec_params_cansol_cs5p_220p):
 
 
 def test_fit_desoto_batzelis():
-              'alpha_sc': 0.00046, 'beta_voc': -0.0024}
     params = {'i_sc': 15.98, 'v_oc': 50.26, 'i_mp': 15.27, 'v_mp': 42.57,
+              'alpha_sc': 0.007351, 'beta_voc': -0.120624}
     expected = {  # calculated with the function itself
-        'alpha_sc': 0.0073508,
-        'a_ref': 1.7257631194825132,
-        'I_L_ref': 15.985408869737098,
-        'I_o_ref': 3.594300567343102e-12,
-        'R_sh_ref': 389.4378389153357,
-        'R_s': 0.1318159287478395
+        'alpha_sc': 0.007351,
+        'a_ref': 1.7257632483733483,
+        'I_L_ref': 15.985408866796396,
+        'I_o_ref': 3.594308384705643e-12,
+        'R_sh_ref': 389.4379947026243,
+        'R_s': 0.13181590981241956,
     }
     out = sdm.fit_desoto_batzelis(**params)
     for k in expected:

tests/test_pvarray.py

@@ -118,8 +118,8 @@ def test_huld_errors():
 
 
 def test_batzelis():
-              'alpha_sc': 0.00046, 'beta_voc': -0.0024}
     params = {'i_sc': 15.98, 'v_oc': 50.26, 'i_mp': 15.27, 'v_mp': 42.57,
+              'alpha_sc': 0.007351, 'beta_voc': -0.120624}
     g = np.array([1000, 500, 1200, 500, 1200, 0, nan, 1000])
     t = np.array([25, 20, 20, 50, 50, 25, 0, nan])
     expected = {  # these values were computed using pvarray.batzelis itself
@@ -148,8 +148,8 @@ def test_batzelis():
 
 
 def test_batzelis_negative_voltage():
-              'alpha_sc': 0.00046, 'beta_voc': -0.0024}
     params = {'i_sc': 15.98, 'v_oc': 50.26, 'i_mp': 15.27, 'v_mp': 42.57,
+              'alpha_sc': 0.007351, 'beta_voc': -0.120624}
     actual = pvarray.batzelis(1e-10, 25, **params)
     assert actual['v_mp'] == 0
     assert actual['v_oc'] == 0