<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def cloud_cover_to_irradiance(self, cloud_cover, how='clearsky_scaling', **kwargs):
 """ Convert cloud cover to irradiance. A wrapper method. Parameters cloud_cover : Series how : str, default 'clearsky_scaling' Selects the method for conversion. Can be one of clearsky_scaling or liujordan. **kwargs Passed to the selected method. Returns ------- irradiance : DataFrame Columns include ghi, dni, dhi """


        how = how.lower()
        if how == 'clearsky_scaling':
            irrads = self.cloud_cover_to_irradiance_clearsky_scaling(
                cloud_cover, **kwargs)
        elif how == 'liujordan':
            irrads = self.cloud_cover_to_irradiance_liujordan(
                cloud_cover, **kwargs)
        else:
            raise ValueError('invalid how argument')

        return irrads