Solar LED street lights may vary in size (wattage and depend on the required lux), ranging from 4Wp to 100Wp.
The battery size should be one of the main concern in regard to the average time of the operation. The solar panel(s) should be able to charge the batteries in the 9–13 hrs of daylight. (The number of hours the light stays on is dependent on your geographical location, seasonal lighting and Weather conditions availability.)
You can power the lights of upto 15Wp ratings with convenient Li-ion batteries which can be charged in 5–6 hrs roughly. For ratings >15Wp, Lead-Acid batteries are employed due to the costing issues.
Generally, a 18W Solar street light with an average of 1700 lumen output could be operated with a 75–100 AH battery for an operating time of 12–14 hours when fully charged by using a 70 or 80 Wp solar panel (~17.5 V, 3.5 Amps).
Coming back to the original question: at least 50% lower energy consumption than Sodium fixture of the same rating.