100% working example. It saves battery life greatly, but ESP can still operate (except wifi)..

Esp8266 wifi radio off and on again

extern "C" {
  #include "user_interface.h"
}   
void turnWifiOn() 
{
    if(MAIN_DEBUG) DEBUG_OUTPUT.println(E("WiFi Radio: Turning ON"));
    wifi_fpm_do_wakeup();
    wifi_fpm_close();
    wifi_set_opmode(STATION_MODE);
    wifi_station_connect();
    yield();
}

#define FPM_SLEEP_MAX_TIME 0xFFFFFFF
void turnWifiOff() 
{
    if(MAIN_DEBUG) DEBUG_OUTPUT.println(E("Diconnecting client and wifi"));
    // client.disconnect();
    wifi_station_disconnect();
    wifi_set_opmode(NULL_MODE);
    wifi_set_sleep_type(MODEM_SLEEP_T);
    wifi_fpm_open();
    wifi_fpm_do_sleep(FPM_SLEEP_MAX_TIME);
    yield();
}