code: def global_horizontal_irradiance(self):
          
          analysis_period = AnalysisPeriod(timestep=self.timestep,
                                           is_leap_year=self.is_leap_year)
          header_ghr = Header(data_type=GlobalHorizontalIrradiance(),
                              unit='W/m2',
                              analysis_period=analysis_period,
                              metadata=self.metadata)
          glob_horiz = []
          sp = Sunpath.from_location(self.location)
          sp.is_leap_year = self.is_leap_year
          for dt, dnr, dhr in zip(self.datetimes, self.direct_normal_irradiance,
                                  self.diffuse_horizontal_irradiance):
              sun = sp.calculate_sun_from_date_time(dt)
              glob_horiz.append(dhr + dnr * math.sin(math.radians(sun.altitude)))
          return HourlyContinuousCollection(header_ghr, glob_horiz)
docs: Returns the global horizontal irradiance at each timestep.