Where is the sun relative to my lunar rover?
If you like Python then see Skyfield; Observing from a Moon location which I believe will do exactly what you need! Also see for example this answer to Ephemeris for lunar body-centered body-fixed coordinates? written by Skyfield's author.

For example, you posted your question at 2020-04-20 15:21:36 UTC. Let's say your rover has just driven up to Surveyor III at 3° 0′ 58.03″ S, 23° 25′ 4.48″ W  (-3.01612°, -23.41791°) (read more about Surveyor III in How did Apollo-12 manage to land next to Surveyor-3? First “Space-Tourists”?)

At that moment the Sun was below the horizon. The output of the script below is

RA:  01h 54m 39.28s
Dec:  +11deg 45' 38.6"
alt:  -38deg 30' 34.6" degrees (below the horizon)
az:  265deg 50' 21.5" degrees around the horizon from north



  I can get the coordinates of the Earth-Moon barycenter using VSOP2013


factoids: VSOP is what PyEphem uses under the hood. It is currently in maintenance mode maintained by the same person who wrote Skyfield. 



#!/usr/bin/env python
# -*- coding: utf-8 -*-
# adapted from https://rhodesmill.org/skyfield/planetary.html

from skyfield.api import PlanetaryConstants, Loader

load = Loader('~/Documents/fishing/SkyData')  # avoids multiple copies of large files
ts = load.timescale(builtin=True)
t = ts.utc(2020, 4, 20, 15, 21, 36)

eph = load('de421.bsp')
earth, moon, sun = [eph[thing] for thing in ('earth', 'moon', 'sun')]

pc = PlanetaryConstants()
pc.read_text(load('moon_080317.tf'))
pc.read_text(load('pck00008.tpc'))
pc.read_binary(load('moon_pa_de421_1900-2050.bpc'))

frame = pc.build_frame_named('MOON_ME_DE421')
Surveyor_III = moon + pc.build_latlon_degrees(frame, latitude_degrees = -3.01612,
                                              longitude_degrees = -23.41791)

apparent = Surveyor_III.at(t).observe(sun).apparent()
ra, dec, distance = apparent.radec()
print('RA: ', ra)
print('Dec: ', dec)

alt, az, distance = apparent.altaz()
if alt.degrees &gt;= 0:
    print('alt: ', alt, 'degrees (above the horizon)')
else:
    print('alt: ', alt, 'degrees (below the horizon)')
print('az: ', az, 'degrees around the horizon from north')