diff --git a/pvmismatch/pvmismatch_lib/pvmodule.py b/pvmismatch/pvmismatch_lib/pvmodule.py
index 3c557c0..1e9e1d3 100644
--- a/pvmismatch/pvmismatch_lib/pvmodule.py
+++ b/pvmismatch/pvmismatch_lib/pvmodule.py
@@ -171,11 +171,11 @@ def __init__(self, cell_pos=STD96, pvcells=None, pvconst=PVconstants(),
         self.cellArea = cellArea  #: [cm^2] cell area
         if pvcells is None:
             # faster to use copy instead of making each object in a for-loop
-            # use copy instead of deepcopy to keey same pvconst for all objects
+            # use copy instead of deepcopy to keep same pvconst for all objects
             # PVcell.calcCell() creates new np.ndarray if attributes change
             pvcells = PVcell(pvconst=self.pvconst)
         if isinstance(pvcells, PVcell):
-            pvcells = [copy(pvcells) for _ in xrange(self.numberCells)]
+            pvcells = [pvcells] * self.numberCells
         if len(pvcells) != self.numberCells:
             # TODO: use pvexception
             raise Exception(
@@ -235,21 +235,56 @@ def setSuns(self, Ee, cells=None):
         """
         if cells is None:
             if np.isscalar(Ee):
-                for pvc in self.pvcells:
+                new_pvcells = range(self.numberCells)  # new list of cells
+                old_pvcells = dict.fromkeys(self.pvcells)  # same as set(pvcells)
+                for cell_id, pvcell in enumerate(self.pvcells):
+                    if old_pvcells[pvcell] is None:
+                        new_pvcells[cell_id] = copy(pvcell)
+                        old_pvcells[pvcell] = new_pvcells[cell_id]
+                    else:
+                        new_pvcells[cell_id] = old_pvcells[pvcell]
+                self.pvcells = new_pvcells
+                pvcell_set = old_pvcells.itervalues()
+                for pvc in pvcell_set:
                     pvc.Ee = Ee
             elif np.size(Ee) == self.numberCells:
-                for pvc, Ee_idx in zip(self.pvcells, Ee):
-                    pvc.Ee = Ee_idx
+                self.pvcells = copy(self.pvcells)  # copy list first
+                for cell_idx, Ee_idx in enumerate(Ee):
+                    self.pvcells[cell_idx] = copy(self.pvcells[cell_idx])
+                    self.pvcells[cell_idx].Ee = Ee_idx
             else:
                 raise Exception("Input irradiance value (Ee) for each cell!")
         else:
             Ncells = np.size(cells)
+            self.pvcells = copy(self.pvcells)  # copy list first
             if np.isscalar(Ee):
-                for cell_idx in cells:
-                    self.pvcells[cell_idx].Ee = Ee
+                cells_to_update = [self.pvcells[i] for i in cells]
+                old_pvcells = dict.fromkeys(cells_to_update)
+                for cell_id, pvcell in zip(cells, cells_to_update):
+                    if old_pvcells[pvcell] is None:
+                        self.pvcells[cell_id] = copy(pvcell)
+                        self.pvcells[cell_id].Ee = Ee
+                        old_pvcells[pvcell] = self.pvcells[cell_id]
+                    else:
+                        self.pvcells[cell_id] = old_pvcells[pvcell]
             elif np.size(Ee) == Ncells:
-                for cell_idx, Ee_idx in zip(cells, Ee):
-                    self.pvcells[cell_idx].Ee = Ee_idx
+                # Find unique irradiance values
+                # TODO possible "cleaner" alternative by grouping cells into tuples that match the set irradiance
+                # E.g: pvsys.setSuns({X: {Y: {'Ee': (0.33, 0.99), 'cells': [(2, 3), 17]}}})
+                cells = np.array(cells)
+                Ee = np.array(Ee)
+                unique_ee = np.unique(Ee)
+                for a_Ee in unique_ee:
+                    cells_subset = cells[np.where(Ee == a_Ee)]
+                    cells_to_update = [self.pvcells[i] for i in cells_subset]
+                    old_pvcells = dict.fromkeys(cells_to_update)
+                    for cell_id, pvcell in zip(cells_subset, cells_to_update):
+                        if old_pvcells[pvcell] is None:
+                            self.pvcells[cell_id] = copy(pvcell)
+                            self.pvcells[cell_id].Ee = a_Ee
+                            old_pvcells[pvcell] = self.pvcells[cell_id]
+                        else:
+                            self.pvcells[cell_id] = old_pvcells[pvcell]
             else:
                 raise Exception("Input irradiance value (Ee) for each cell!")
         self.Imod, self.Vmod, self.Pmod, self.Isubstr, self.Vsubstr = self.calcMod()
diff --git a/pvmismatch/pvmismatch_lib/pvstring.py b/pvmismatch/pvmismatch_lib/pvstring.py
index 02b32ea..84c33b0 100644
--- a/pvmismatch/pvmismatch_lib/pvstring.py
+++ b/pvmismatch/pvmismatch_lib/pvstring.py
@@ -5,7 +5,7 @@
 """
 
 import numpy as np
-from copy import deepcopy
+from copy import copy
 from matplotlib import pyplot as plt
 # use absolute imports instead of relative, so modules are portable
 from pvmismatch.pvmismatch_lib.pvconstants import PVconstants, NUMBERMODS
@@ -30,7 +30,7 @@ def __init__(self, numberMods=NUMBERMODS, pvmods=None,
             # use deepcopy instead of making each object in for-loop, 2x faster
             pvmods = PVmodule(pvconst=self.pvconst)
         if isinstance(pvmods, PVmodule):
-            pvmods = [deepcopy(pvmods) for _ in xrange(self.numberMods)]
+            pvmods = [pvmods] * self.numberMods
             # reset pvconsts in all pvcells and pvmodules
             for p in pvmods:
                 for c in p.pvcells:
@@ -87,11 +87,23 @@ def setSuns(self, Ee):
 
         """
         if np.isscalar(Ee):
+            new_pvmods = range(self.numberMods)  # new list of modules
+            old_pvmods = dict.fromkeys(self.pvmods)  # same as set(pvmods)
+            for mod_id, pvmod in enumerate(self.pvmods):
+                if old_pvmods[pvmod] is None:
+                    new_pvmods[mod_id] = copy(pvmod)
+                    old_pvmods[pvmod] = new_pvmods[mod_id]
+                else:
+                    new_pvmods[mod_id] = old_pvmods[pvmod]
+            self.pvmods = new_pvmods
             for pvmod in iter(self.pvmods):
                 pvmod.setSuns(Ee)
         else:
+            self.pvmods = copy(self.pvmods)  # copy list first
             try:
                 for pvmod, cell_Ee in Ee.iteritems():
+                    pvmod = int(pvmod)
+                    self.pvmods[pvmod] = copy(self.pvmods[pvmod])
                     if hasattr(cell_Ee, 'keys'):
                         self.pvmods[pvmod].setSuns(**cell_Ee)
                     else:
@@ -100,9 +112,12 @@ def setSuns(self, Ee):
                         except TypeError:
                             self.pvmods[pvmod].setSuns(cell_Ee)
             except AttributeError:
-                Ee = Ee[0]
-                for pvmod in iter(self.pvmods):
-                    pvmod.setSuns(Ee)
+                # Ee was a list? just take first item in list
+                if len(Ee) > 1:
+                    raise TypeError('Irradiance, Ee, should be scalar or dict')
+                for mod_id, pvmod in enumerate(self.pvmods):
+                    self.pvmods[mod_id] = copy(pvmod)
+                    self.pvmods[mod_id].setSuns(Ee[0])
         # update modules
         self.Istring, self.Vstring, self.Pstring = self.calcString()
 
diff --git a/pvmismatch/pvmismatch_lib/pvsystem.py b/pvmismatch/pvmismatch_lib/pvsystem.py
index 857ea24..4f5a74a 100644
--- a/pvmismatch/pvmismatch_lib/pvsystem.py
+++ b/pvmismatch/pvmismatch_lib/pvsystem.py
@@ -5,7 +5,7 @@
 """
 
 import numpy as np
-from copy import deepcopy
+from copy import copy
 from matplotlib import pyplot as plt
 # use absolute imports instead of relative, so modules are portable
 from pvmismatch.pvmismatch_lib.pvconstants import PVconstants, NUMBERMODS, \
@@ -34,7 +34,7 @@ def __init__(self, pvconst=PVconstants(), numberStrs=NUMBERSTRS,
                               pvconst=self.pvconst)
         # use deep copy instead of making each object in a for-loop
         if isinstance(pvstrs, PVstring):
-            pvstrs = [deepcopy(pvstrs) for _ in xrange(self.numberStrs)]
+            pvstrs = [pvstrs] * self.numberStrs
         if len(pvstrs) != self.numberStrs:
             # TODO: use pvmismatch excecptions
             raise Exception("Number of strings don't match.")
@@ -118,6 +118,8 @@ def setSuns(self, Ee):
                 pvstr.setSuns(Ee)
         else:
             for pvstr, pvmod_Ee in Ee.iteritems():
+                pvstr = int(pvstr)
+                self.pvstrs[pvstr] = copy(self.pvstrs[pvstr])
                 self.pvstrs[pvstr].setSuns(pvmod_Ee)
         self.Isys, self.Vsys, self.Psys = self.calcSystem()
         (self.Imp, self.Vmp, self.Pmp,
diff --git a/pvmismatch/tests/test_setsuns.py b/pvmismatch/tests/test_setsuns.py
index 73c0046..f11f9d4 100644
--- a/pvmismatch/tests/test_setsuns.py
+++ b/pvmismatch/tests/test_setsuns.py
@@ -7,6 +7,10 @@
 import numpy as np
 from nose.tools import ok_
 from pvmismatch.pvmismatch_lib.pvsystem import PVsystem
+import logging
+
+logging.basicConfig(level=logging.DEBUG)
+LOGGER = logging.getLogger(__name__)
 
 
 def test_basic():
@@ -48,3 +52,105 @@ def test_set_str_2():
     Ee = {1: .1}
     pvsys.setSuns(Ee)
     ok_(np.isclose(pvsys.Pmp, 29136.544447716446))
+
+
+def test_gh34_35():
+    pvsys = PVsystem()
+    # display unique id numbers
+    LOGGER.debug('\n*** unique id numbers ***')
+    LOGGER.debug('pvstrs:\n%r', set(pvsys.pvstrs))
+    LOGGER.debug('pvmods:\n%r', set([x for y in pvsys.pvmods for x in y]))
+    LOGGER.debug(
+        'pvcells:\n%r',
+        {hex(int(id(z))): z for y in pvsys.pvmods for x in y for z in x.pvcells}
+    )
+    # test strings references same object
+    assert pvsys.pvstrs[0] == pvsys.pvstrs[1]
+    # modules references same object
+    assert pvsys.pvmods[0][0] == pvsys.pvmods[1][1]
+    # cells reference same object
+    assert pvsys.pvmods[0][0].pvcells[0] == pvsys.pvmods[1][1].pvcells[1]
+
+    # test set suns on just string #2 
+    pvsys.setSuns({2: 0.88})
+    # display unique id numbers
+    LOGGER.debug('pvstrs:\n%r', set(pvsys.pvstrs))
+    LOGGER.debug('pvmods:\n%r', set([x for y in pvsys.pvmods for x in y]))
+    LOGGER.debug(
+        'pvcells:\n%r',
+        {hex(int(id(z))): z for y in pvsys.pvmods for x in y for z in x.pvcells}
+    )
+    # test other string not changed
+    assert (pvsys.pvstrs[0].pvmods[0].Ee == 1.0).all()
+    assert (pvsys.pvstrs[1].pvmods[1].Ee == 1.0).all()
+    # test all modules in string #2 changed
+    assert (pvsys.pvstrs[2].pvmods[0].Ee == 0.88).all()
+    assert (pvsys.pvstrs[2].pvmods[2].Ee == 0.88).all()
+    # test strings references same object
+    assert pvsys.pvstrs[0] == pvsys.pvstrs[1]
+    # modules references same object
+    assert pvsys.pvmods[0][0] == pvsys.pvmods[1][1]
+    # cells reference same object
+    assert pvsys.pvmods[0][0].pvcells[0] == pvsys.pvmods[1][1].pvcells[1]
+    assert pvsys.pvmods[2][0].pvcells[0] == pvsys.pvmods[2][2].pvcells[2]
+
+    # test set suns on just module #4 in string #2
+    pvsys.setSuns({2: {4: 0.75}})
+    # display unique id numbers
+    LOGGER.debug('pvstrs:\n%r', set(pvsys.pvstrs))
+    LOGGER.debug('pvmods:\n%r', set([x for y in pvsys.pvmods for x in y]))
+    LOGGER.debug(
+        'pvcells:\n%r',
+        {hex(int(id(z))): z for y in pvsys.pvmods for x in y for z in x.pvcells}
+    )
+    assert (pvsys.pvstrs[0].pvmods[0].Ee == 1.0).all()
+    assert (pvsys.pvstrs[1].pvmods[1].Ee == 1.0).all()
+    assert (pvsys.pvstrs[1].pvmods[4].Ee == 1.0).all()
+    assert (pvsys.pvstrs[2].pvmods[0].Ee == 0.88).all()
+    assert (pvsys.pvstrs[2].pvmods[2].Ee == 0.88).all()
+    assert (pvsys.pvstrs[2].pvmods[4].Ee == 0.75).all()
+    assert pvsys.pvstrs[0] == pvsys.pvstrs[1]
+    assert pvsys.pvmods[0][0] == pvsys.pvmods[1][1]
+    assert pvsys.pvmods[0][0].pvcells[0] == pvsys.pvmods[1][1].pvcells[1]
+
+    # set just cells #0 and #2 in module #4 in string #2
+    pvsys.setSuns({2: {4: {'Ee': 0.66, 'cells': [0, 2]}}})
+    # display unique id numbers
+    LOGGER.debug('pvstrs:\n%r', set(pvsys.pvstrs))
+    LOGGER.debug('pvmods:\n%r', set([x for y in pvsys.pvmods for x in y]))
+    LOGGER.debug(
+        'pvcells:\n%r',
+        {hex(int(id(z))): z for y in pvsys.pvmods for x in y for z in x.pvcells}
+    )
+    assert (pvsys.pvstrs[0].pvmods[0].Ee == 1.0).all()
+    assert (pvsys.pvstrs[1].pvmods[1].Ee == 1.0).all()
+    assert (pvsys.pvstrs[1].pvmods[4].Ee == 1.0).all()
+    assert (pvsys.pvstrs[2].pvmods[0].Ee == 0.88).all()
+    assert (pvsys.pvstrs[2].pvmods[2].Ee == 0.88).all()
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[0].Ee == 0.66
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[1].Ee == 0.75
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[2].Ee == 0.66
+    assert pvsys.pvstrs[0] == pvsys.pvstrs[1]
+    assert pvsys.pvmods[0][0] == pvsys.pvmods[1][1]
+    assert pvsys.pvmods[0][0].pvcells[0] == pvsys.pvmods[1][1].pvcells[1]
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[0] == pvsys.pvstrs[2].pvmods[4].pvcells[2]
+
+    # set cells 3 and 4 to one irradiance and 5 to another. should only make two new cell objects
+    pvsys.setSuns({2: {4: {'Ee': (0.33, 0.99, 0.33), 'cells': (3, 4, 5)}}})
+    assert (pvsys.pvstrs[0].pvmods[0].Ee == 1.0).all()
+    assert (pvsys.pvstrs[1].pvmods[1].Ee == 1.0).all()
+    assert (pvsys.pvstrs[1].pvmods[4].Ee == 1.0).all()
+    assert (pvsys.pvstrs[2].pvmods[0].Ee == 0.88).all()
+    assert (pvsys.pvstrs[2].pvmods[2].Ee == 0.88).all()
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[0].Ee == 0.66
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[1].Ee == 0.75
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[2].Ee == 0.66
+    assert pvsys.pvstrs[0] == pvsys.pvstrs[1]
+    assert pvsys.pvmods[0][0] == pvsys.pvmods[1][1]
+    assert pvsys.pvmods[0][0].pvcells[0] == pvsys.pvmods[1][1].pvcells[1]
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[0] == pvsys.pvstrs[2].pvmods[4].pvcells[2]
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[3].Ee == 0.33
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[4].Ee == 0.99
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[5].Ee == 0.33
+    assert pvsys.pvstrs[2].pvmods[4].pvcells[3] == pvsys.pvstrs[2].pvmods[4].pvcells[5]
+