Estimate the number of electric vehicle charging stations in the US.

clarifying questions:

1. Are we focusing on individually owned EV charging or commercial or public charging stations? - Anywhere you can charge a EV car
2. Are these privately owned EV charging stations in a household in the US 
3. and publicly available charging stations such as at work, malls etc. Is that correct? - Yes.

• Formula: Total US household EV chargers  + total public EV chargers  = total charging stations in the US.
• Total household EVC  = households that own solar+ households that don't own solar(1M)
• Total public EV charger  = chargers at the rental apartment(included in the 1M above) + chargers at the workplace
• Total US population 300M, 100M households 80% own a car, 5% is EV.
• Total 4M EVs
• Avg 4% of households own solar 
  • Total households in the US that own a solar= total household 100M * 0.04%= 2.5M households
• Total households in the US that own an EV charger= 50% of total solar owners = 2.5M* 0.5% = 1.25M
• total 4M EVs exists, 1.25M owners charge it at home using solar, let's assume rest charge them using electricity, or EVs at rental apt = 2.75M * .04%= 1M EVs
• 10M employers in the US, 1% of them offer EV charging stations, 100K EV charging stations. assuming there are avg 5 charging stations per employer = 500K EVC

I'll first start with some clarifications. (*EV = electric vehicles)

a. Do we want to estimate the number stations with exclusive EV charging bunks or hybrid stations as well. (lets assume for now, interviewer asks us to go with exclusive EV charging stations only).
b. I'd like to align on electric vehicles in general. So electric vehicles run on rechargeable elctric batteries which once charged generally run for 8hrs straight or 500 miles. Does this seem reasonable? (lets say interviewer say all good)

I'll take a top down approach. Lets consider US is spread across ~4M Sq, miles.

Next lets divide the US total area into 3 buckets and assume that the charging stations will be proportional to EV usage:

a. States with high EV usage: like CA, NY, WA, NV etc.. Lets say 30% of US has high EV usage, so these states will likely have more EV charging stations.

b. States with no EV usage: like ND,SD, WY, TN etc.. Lets say 40% of US has no electric vehicles and hence no EV charging stations are established yet.

c. States with low to medium EV usage: like OH, TX, IL, GA, FL, WY etc.. Lets say remaining 30% of US has average EV usage, so lets assume the charging stations will be proportional to EV usage. 

Further, lets divide the area into urban (downtown, tech areas, city centres) and rural(suburbs and country side).

i. In states with high EV usage, its likely that city limits have expanded due to growing prospects of living conditons, employments, salary etc(like bay area, san jose etc.). So lets assume of the total area, urban is 50% and rural is 50%. As the EV usage is high, lets say there is 1 EV charging station per 50 sq miles in urban while  1 EV charging station per 250 sq miles in rural.

ii. In states with low to medium EV usage, lets assume of the total area, urban is 30% and rural is 70%. In this case, as the EV usage is average and cold vary across states, lets say there is 1 EV charging station per 100 sq miles in urban and in rural areas.

Now lets calculate: (per discussion above 60% of US total area has EV usage and hence EV charging stations exist. We have assumed that states without usage of EVs have no charging stations.)

(High EV usage Urban) + (High EV usage Rural) + 

(Average EV usage Urban) + (Average EV usage Rural) +

{30%*4M*50%*(1/50)} + {30%*4M*50%*(1/250)} + {30%*4M*30%*(1/100)} + {30%*4M*70%*(1/100)}

= {1.2M/100} + {1.2M/500} + {1.2M*(3/1000)} + {1.2M*(7/1000} 

= 12000 + 2400 + 3600 + 8400 = 26,400 EV charging stations

We previously assumed that states without high EV usage do not have EV charging stations at all.. But in reality population with EVs could travel to states without high EV usage. And although not all of the states could have EV charging stations established, some popular tourist destinations, Inter-state highways etc. could have them. So we could add ~600 to the total number and say that there are approximately 27,000 EV charging stations in USA. Which sounds reasonable. 

Hybrid stations:

Initially, we did not consider hybrid stations which are generally gas stations with 1 or 2 EV charging points in addition. If we need to add this to our estimate, we can do the following calculation. Lets say there is 1 gas station every 5 sq. miles across US. 

Hybrids may not be common in states without EV usage, so we can minus 40% of the US total area from this calculation. Similarly states with low to medium usage might also have exclusive stations (gas or EV). We can exclude the other 30% as well. 

We can expect hybrid stations in urban and rural areas in the states with high EV usage. Urban, so as to provide convenience to users and expand business and in some rural areas it'll make sense to have a hybrid gas stations instead of having EV charging exclusively.  Urban has exclusive stations too, so lets say 2% of the traditional gas stations have hybrid stations and 3% of the rural areas have hybrid stations. We have considered urban and rural area % to be equal in states with high EVs. So to add the Hybrid stations we will do the below calculation:

{1.2M*50%*(1/5)*(2%)} + {1.2M*50%*(1/5)*(3%)} = 6000 hybrid stations

Including Hybrid stations, we will have a total of 33K EV charging stations. Seems quite reasonable!