Musk's statement about Supercharger costs was made in May, 2013. The costs obviously reference U.S. stations at that time.
By the time a Supercharger station is starting construction, a significant portion of the costs are already in play. The equipment is already ordered and delivered. The number of supercharger plugs obviously affects the price. And the total project time can be as short as 3 months but more likely stretches from 6 months to a year. Tesla does not know beforehand how quickly a site can develop. Some happen right away. Others, like Greenville, SC, end up in limbo - the Superchargers equipment almost completely installed and the site was blocked from completion. As much as 80% of a Supercharger site cost is already spent before the ground is broken. The sites have gotten bigger... you can't ignore the additional costs just because it is inconvenient to your argument. The price difference between a 2 Supercharger, 4 plug site is different from a 6 Supercharger, 12 plug site. The price for some of the smaller 2 plug sites are actually quite high due to their location. Some have odd numbers, like 5, which means 3 Superchargers, 5 plugs. You have to apply a corrective factor there. You also ignore the fact that some stations have solar canopies and some have battery storage. You can't ignore those either. We also don't know how far in advance Tesla has to buy the various components or how they have to account for the deals that are part of this. For example, once a site owner signs the contract, there may be book value added right there even though the first permit hasn't been granted. We also don't know the payment arrangements - how much is contributed to book value as electricians and other labor is spent on developing the site. These are real costs that you can't ignore that go into the book value.
Let's assume that Musk's initial cost was given as a 3 Supercharger, 6 plug site that was common in 2013 as a starting base. In 2013, 4 Supercharger, 8 plugs sites are normal in the U.S.
You take the book value at the end of Q4 2013 of $25.6 million and divide against 64 open Supercharger sites. 2 of these sites have solar canopies, so the right number to even start with is 66. You don't take into account the number under construction. At the end of January, 2014, there were 87 Superchargers open. In other words, the 23 more Superchargers were in the last phases of construction. Easily 90+% of the costs of these Superchargers were already spent by the end of 2013. So 23 * 0.9 = 20.7. By the end of Q1, 2014, there were 96 open. That's an additional 9 and say 70% of those costs were already spent by the end of 2013. That's an additional 6.3. Then by the end of Q2, 2014, 125 were open. Let's say it's fair to add 50% of the costs for those 32 additional sites. That's another 16. So just with 6 months of sites under construction, we're looking at correcting the original 64 value you gave to 64 + 2 + 20.7 + 6.3 + 16 = 109. There are additional costs already incurred for sites beyond even the 6 months as some sites literally took 1 year to develop. But let's just round that 3 more. So 112. Remember, Tesla's original plan was for far more sites than what actually opened, so many more sites were under development (hence costs incurred) but the actual open stations lagged as those site selection, site owner agreements, permitting, and construction, and utility delays mounted.
The current global average of plugs per site is now 5.51 (2,419 / 439). However, in 2013 and the first half of 2014, most of the sites were full sized sites in the U.S. and Europe. Later in 2014 and now in 2015, we are diluted with a bunch of 2 plug Superchargers in France, UK, and Hong Kong/China. Most of the early sites are at least 4 plug but many more were 8 plug. Assuming most were 6 plug sites, but 2:1 ratio of 8 plug sites versus 4 plug sites, a corrective factor of about 20% is about right for the actual number of plugs per site for the Superchargers installed and under various phases of construction at the end of 2013. Therefore, 112 * 1.2 = 134.4.
Take $25.6 million and divide by 134.4 and you get $190,000 cost per site for the Superchargers in operation and under construction at the end of 2013 as it relates to book value.
Further, a number of these sites under construction are in Europe by that point in time and the costs are likely higher in Europe than in the U.S. This is before we get to odd number of plugs and other miscellaneous real world factors that need to be in the accounting. So in reference to the original $150,000 estimate in May, 2013, the average cost is higher, but not enough to all that significant.
