# in ModelChain
    def __init__(..., singlediode_calcparams_model=None)
        # calls setters
        self.singlediode_calcparams_model = singlediode_calcparams_model

    @property
    def singlediode_calcparams_model(self):
        return self._singlediode_calcparams_model

    @singlediode_calcparams_model.setter
    def singlediode_calcparams_model(self, model):
        if model is None:
            self._singlediode_calcparams_model = self.infer_singlediode_calcparams_model()
        elif isinstance(model, str):
            model = model.lower()
            if model == 'desoto':
                self._singlediode_calcparams_model = self.calcparams_desoto
            elif model == 'pvsyst':
                self._singlediode_calcparams_model = self.calcparams_pvsyst
            else:
                raise ValueError(model + ' is not a valid calcparams power model')
        else:
            self._singlediode_calcparams_model = partial(model, self)

    def infer_singlediode_calcparams_model(self):
        params = set(self.system.module_parameters.keys())
        if set([desoto_params_list]) <= params:
            return self.calcparams_desoto
        elif set([pvsyst_params_list]) <= params:
            return self.calcparams_pvsyst
        else:
            raise ValueError('could not infer calcparams model from '
                             'system.module_parameters')

    def calcparams_desoto(self):
        self.singlediode_params = self.system.calcparams_desoto(self.effective_irradiance,
                                          self.temps['temp_cell']))
        return self

    def calcparams_pvsyst(self):
        self.singlediode_params = self.system.calcparams_pvsyst(self.effective_irradiance,
                                          self.temps['temp_cell']))
        return self

    def singlediode(self):
        # removed call to self.system.calcparams_desoto
        # removed assignment to self.desoto

        self.dc = self.system.singlediode(*self.singlediode_params)

        self.dc = self.system.scale_voltage_current_power(self.dc).fillna(0)

        return self