Get latitude & longitude from address geopandas

I have a csv of about 100 million logs. Where one of the column is address and I am trying to get latitude and longitude of the address. I want to try something like mentioned in the Solution , But the solution given is arcGIS and that is a commercial tool. I did try google API that has limit of 2000 entries only.

What is next best alternative to get address's Lat & Long into the large dataset.

Input: The column Site is the address from the City Paris

start_time,stop_time,duration,input_octets,output_octets,os,browser,device,langue,site
2016-08-27T16:15:00+05:30,2016-08-27T16:28:00+05:30,721.0,69979.0,48638.0,iOS,CFNetwork,iOS-Device,zh_CN,NULL
2016-08-27T16:16:00+05:30,2016-08-27T16:30:00+05:30,835.0,2528858.0,247541.0,iOS,Mobile Safari UIWebView,iPhone,en_GB,Berges de Seine Rive Gauche - Gros Caillou
2016-08-27T16:16:00+05:30,2016-08-27T16:47:00+05:30,1805.0,133303549.0,4304680.0,Android,Android,Samsung GT-N7100,fr_FR,Centre d'Accueil Kellermann
2016-08-27T16:17:00+05:30,,2702.0,32499482.0,7396904.0,Other,Apache-HttpClient,Other,NULL,Bibliothèque Saint Fargeau
2016-08-27T16:17:00+05:30,2016-08-27T17:07:00+05:30,2966.0,39208187.0,1856761.0,iOS,Mobile Safari UIWebView,iPad,fr_FR,NULL
2016-08-27T16:18:00+05:30,,2400.0,1505716.0,342726.0,NULL,NULL,NULL,NULL,NULL
2016-08-27T16:18:00+05:30,,302.0,3424123.0,208827.0,Android,Chrome Mobile,Samsung SGH-I337M,fr_CA,Square Jean Xxiii
2016-08-27T16:19:00+05:30,,1500.0,35035181.0,1913667.0,iOS,Mobile Safari UIWebView,iPhone,fr_FR,Parc Monceau 1 (Entrée)
2016-08-27T16:19:00+05:30,,6301.0,9227174.0,5681273.0,Mac OS X,AppleMail,Other,fr_FR,Bibliothèque Parmentier

The address with NULL can be neglected and also can be removed from the output.

The output should have following columns

start_time,stop_time,duration,input_octets,output_octets,os,browser,device,langue,site, latitude, longitude

Appreciate all the help, Thank you in advance!!

import csv
from geopy.geocoders import Nominatim

#if your sites are located in France only you can use the country_bias parameters to restrict search
geolocator = Nominatim(country_bias="France")

with open('c:/temp/input.csv', 'rb') as csvinput:
    with open('c:/temp/output.csv', 'wb') as csvoutput:
       output_fieldnames = ['Site', 'Address_found', 'Latitude', 'Longitude']
       writer = csv.DictWriter(csvoutput, delimiter=';', fieldnames=output_fieldnames)
       writer.writeheader()
       reader = csv.DictReader(csvinput)
       for row in reader:
            site = row['site']
            if site != "NULL":
                try:
                    location = geolocator.geocode(site)
                    address = location.address
                    latitude = location.latitude
                    longitude = location.longitude
                except:
                    address = 'Not found'
                    latitude = 'N/A'
                    longitude = 'N/A'
            else:
                address = 'N/A'
                latitude = 'N/A'
                longitude = 'N/A'

            #here is the writing section
            output_row = {}
            output_row['Site'] = row['site']
            output_row['Address_found'] = address.encode("utf-8")
            output_row['Latitude'] = latitude
            output_row['Longitude'] = longitude
            writer.writerow(output_row)