Electric vehicles are finally becoming mainstream, but BMW is celebrating their 40th anniversary of building the eco-friendly automobile.

BMW is celebrating their 40th anniversary of building electric vehicles.

Things kicked off at the 1972 Olympic Games when BMW introduced two 1602 Electric prototypes. Essentially a proof of concept, the vehicles were equipped with a 43 HP (32 kW) electric motor and twelve 12V lead-acid batteries. This enabled the models to accelerate from 0-50 km/h (31 mph) in 8 seconds, hit a top speed of 100 km/h (62 mph) and travel approximately 30 km (19 miles) on a single charge.

A few years later the company introduced the BMW LS Electric in 1975. Equipped with regenerative brakes and an onboard charger, the model featured a 23 HP (17 kW) electric motor and ten 12V batteries. This enabled the prototype to accelerate from 0-50 km/h (31 mph) in 11.4 seconds, hit a top speed of 65 km/h (40 mph) and travel approximately 30 km (19 miles) on a single charge.

In the early 80's, BMW began developing the 325iX Electric. Equipped with sodium-sulphur (NaS) batteries, which had an energy density three times greater than lead-acid batteries, the 325iX offered the first glimpse at a feasible electric vehicle. It had a 30 HP (22 kW) electric motor which enabled the car to accelerate from 0-50 km/h (31 mph) in 9 seconds, hit a top speed of 100 km/h (62 mph) and travel up to 150 km (93 miles) on a single charge.

Encouraged by the results of the 325iX Electric, BMW began developing its first purpose-built electric vehicle. Originally unveiled at the 1991 Frankfurt Motor Show, the E1 concept featured aluminium construction and a lightweight plastic exterior. Power was provided by a sodium-sulphur battery which powered an electric motor that developed 43 HP (32 kW). It enabled the model to accelerate from 0-50 km/h (31 mph) in 6 seconds, hit a top speed of 120 km/h (75 mph) and travel up to 150 km (93 miles) on a single charge.

Shortly thereafter, BMW unveiled the 325 electric which used sodium-nickel chloride batteries. This change, along with the addition of a powerful 61 HP (45 kW) electric motor, enabled the model to run from 0-50 km/h (31 mph) in 6 seconds, hit a top speed of 135 km/h (84 mph) and travel up to 150 km (93 miles) on a single charge.

In more recent years, BMW has offered the MINI E and the BMW ActiveE. While they were only available in limited quantities, they helped pave the way for the upcoming i3 that will enter production in late 2013.

Gallery: BMW celebrates 40 years of building electric vehicles