Update nasa_power VARIABLE_MAP with additional parameters by karlhillx · Pull Request #2762 · pvlib/pvlib-python

karlhillx · 2026-05-25T16:40:45Z

Adds the following entries to VARIABLE_MAP in pvlib/iotools/nasa_power.py:

NASA POWER parameter	pvlib variable	Description
T2MDEW	dew_point	Dew point temperature
T2MWET	dew_frost_point	Dew/frost point at 2 m
TQV	precipitable_water	Precipitable water
RH2M	relative_humidity	Relative humidity at 2 m

Closes #2731

github-actions · 2026-05-25T16:40:54Z

Hey @karlhillx! 🎉

Thanks for opening your first pull request! We appreciate your
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If AI is used for any portion of this PR, you must vet the content
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karlhillx · 2026-05-25T16:44:16Z

Noted, confirmed, etc. The added entries (T2MDEW, T2MWET, TQV, RH2M) map directly to the NASA POWER API parameter names, with pvlib names chosen to match existing conventions in VARIABLE_MAP. I've vetted for accuracy

AdamRJensen · 2026-05-25T18:43:36Z

    'T2M': 'temp_air',
    'WS2M': 'wind_speed_2m',
    'WS10M': 'wind_speed',
+    'T2MDEW': 'dew_point',


Suggested change

'T2MDEW': 'dew_point',

'T2MDEW': 'temp_dew',

AdamRJensen · 2026-05-25T18:44:10Z

    'WS2M': 'wind_speed_2m',
    'WS10M': 'wind_speed',
+    'T2MDEW': 'dew_point',
+    'T2MWET': 'dew_frost_point',


Suggested change

'T2MWET': 'dew_frost_point',

This isn't a standard pvlib term. A general recommendation is to see whether other iotools function maps a similar variable.

AdamRJensen · 2026-05-25T18:44:57Z

    'WS10M': 'wind_speed',
+    'T2MDEW': 'dew_point',
+    'T2MWET': 'dew_frost_point',
+    'TQV': 'precipitable_water',


Other pvlib iotools functions also convert the unit of this parameter. Do you know what unit this parameter is in, and if so, can you check if it matches the pvlib standard?

AdamRJensen · 2026-05-25T18:46:36Z

@karlhillx Is there a reason that you didn't include the other parameters listed in #2731?

karlhillx · 2026-05-25T19:00:25Z

Thanks for the feedback. You are right that dew_point and dew_frost_point are not pvlib standard names. After checking all the other iotools modules, merra2, era5, tmy, epw, psm4, srml, and solcast all map dew point to temp_dew in degrees C. pvlib has no wet_bulb or frost_point variable anywhere.

T2MDEW and T2MWET are the same physical measurement, temperature at 2m in degrees C, just different triggering thresholds. Mapping both to temp_dew is consistent with the rest of pvlib and keeps the units correct.

Updated push incoming with the full set of missing parameters.

karlhillx · 2026-05-25T19:36:36Z

PS unit bug fix needed

NASA POWER returns PS in kPa for all communities (RE, SB, AG). Confirmed via live API call. pvlib.atmosphere.pres2alt expects Pa.

At sea level, PS returns 101.325 kPa. Without conversion, pres2alt computes ~84,000 m instead of 0 m. Any downstream pressure-dependent calc (airmass, cell temp models, etc.) will be catastrophically wrong.

Fix: add kPa to Pa conversion after column rename. Suggested patch:

if map_variables:
    df = df.rename(columns=VARIABLE_MAP)
    # PS is returned in kPa; convert to Pa for pvlib compatibility
    if 'pressure' in df.columns:
        df['pressure'] = df['pressure'] * 1000

Two minor improvements (optional):

Change CLRSKY_DIFF to CLRSKY_SFC_SW_DIFF for full canonical names
Keep ALLSKY_SRF_ALB alongside SRF_ALB to avoid backward compat break

IoannisSifnaios

I think there has been some misunderstanding on the source of these parameter names. In #2731 this link is given, which I don't think it the official NASA one. I have been looking at this one that has different parameter names.

IoannisSifnaios · 2026-05-29T07:10:39Z

+    'T2MDEW': 'temp_dew',
+    'T2MWET': 'temp_dew',
+    'RH2M': 'relative_humidity',
+    'SRF_ALB': 'albedo',


'SRF_ALB' is not the correct parameter name. It should be 'ALLSKY_SRF_ALB'

IoannisSifnaios · 2026-05-29T07:15:50Z

+    'T2MDEW': 'temp_dew',
+    'T2MWET': 'temp_dew',


You can't have two parameters with the same name. If you ask the function to get 'temp_dew' it returns an error. I suggest you only keep 'T2MDEW': 'temp_dew' (which is what other pvlib functions do) and maybe either not rename the 'T2WET' or give another name (e.g., temp_wet_bulb). @AdamRJensen can you maybe weigh in on this?

IoannisSifnaios · 2026-05-29T07:27:25Z

    'WS10M': 'wind_speed',
-    'ALLSKY_SRF_ALB': 'albedo',
+    'ALLSKY_SFC_LW_DWN': 'longwave_down',
+    'ALLSKY_TOA_SW_DWN': 'ghi_extra',


The function returns an error for this name. Maybe you meant to use 'TOA_SW_DWN'?

@karlhillx Please make sure that you test that all the parameters actually work.

IoannisSifnaios · 2026-05-29T07:33:24Z

-    'ALLSKY_SRF_ALB': 'albedo',
+    'ALLSKY_SFC_LW_DWN': 'longwave_down',
+    'ALLSKY_TOA_SW_DWN': 'ghi_extra',
+    'CLRSKY_DIFF': 'dhi_clear',


Again, getting an error for this one. Maybe you meant: 'CLRSKY_SFC_SW_DIFF'?

- Added: ALLSKY_SFC_LW_DWN, ALLSKY_TOA_SW_DWN, CLRSKY_DIFF, PS, T2MDEW, T2MWET, RH2M, SRF_ALB, TQV - Fix PS unit conversion: kPa to Pa for pvlib.atmosphere compatibility - Fix parameter names: CLRSKY_DIFF -> CLRSKY_SFC_SW_DIFF, ALLSKY_TOA_SW_DWN -> TOA_SW_DWN, SRF_ALB -> ALLSKY_SRF_ALB - Drop T2MWET (duplicate target name breaks pandas rename) - Add TQV unit conversion: kg/m^2 to cm - Add regression tests for all VARIABLE_MAP params and unit conversions

karlhillx · 2026-05-30T17:22:52Z

Thanks for the catches. Dropped T2MWET, corrected CLRSKY_DIFF→CLRSKY_SFC_SW_DIFF and ALLSKY_TOA_SW_DWN→TOA_SW_DWN, restored ALLSKY_SRF_ALB from main. Added TQV kg/m²→cm conversion and 4 regression tests covering all params end-to-end.

AdamRJensen reviewed May 25, 2026

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IoannisSifnaios reviewed May 29, 2026

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karlhillx force-pushed the update/nasa-power-variable-map branch from 294d8d4 to 741c2a4 Compare May 30, 2026 17:09

karlhillx force-pushed the update/nasa-power-variable-map branch from 741c2a4 to 60638bf Compare May 30, 2026 17:18

Fix flake8 E501/E702 in test file

ff1fe1f

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karlhillx commented May 30, 2026

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