How many clean electric grid california (san francisco) figures are given for the Nissan Leaf?
create table table_23840623_4 (clean_electric_grid_california__san_francisco_ varchar, vehicle varchar, PRIMARY KEY (clean_electric_grid_california__san_francisco_))
select count(clean_electric_grid_california__san_francisco_) from table_23840623_4 where vehicle = "nissan leaf"