In previous posts, “Fisker’s Photovoltaic Cars,” and “Photovoltaic Powered Cars,” we have reported on the potential for commuters to power their vehicles with energy collected from rooftop photovoltaics.  But until now we haven’t been able to share some of our spreadsheet analysis with our readers.  While it’s still not possible to include these online interactive spreadsheets in WordPress, here are two on plain .html pages that hopefully can make more clear the costs and challenges.

Cross-section of series hybrid Chevy Volt, possibly in showrooms by 2010. (Photo: GM Volt)

In the online interactive spreadsheet “Gigawatts per E-Commuters” there are only a few assumptions - the quantity of commuters using electric cars, the average round-trip commute, and the average miles per kilowatt-hour. 

Based on the default assumptions on the spreadsheet - 15 million electric vehicle commuters, a 40 mile commute, and 4.0 miles per kilowatt-hour - it would take 150 gigawatt-hours of electricity to charge into such a fleet of battery-powered cars when they are plugged in every night.

Given these are off-peak hours, and given a 10 hour average recharge cycle, the electric power grid would have to deliver 15 gigawatts of additional power all night in order to recharge this quantity of cars.  Input your own assumptions! 

In California, for example, where during peak demand the power grid can deliver over 50 gigawatts, this is probably barely feasible.  But where will the additional electricity come from?  Even assuming massive grid-scale storage capacity, you only get about 1.5 gigawatt-hours per day from a one square mile solar thermal plant - you would need to build 100 of these.  A nuclear power station can easily output 1.0 gigawatts, and since they run continuously, that would add 24 gigawatt-hours per day - you would need to build about six of them.  But what if decentralized sources of electricity were used to power electric cars?

In another online interactive spreadsheet on this topic, “Photovoltaics per Electric Car,” we look at the cost of rooftop photovoltaics to power a car.  Our default assumptions are 12 watts per square foot of PV, 7 hours of sun per day, a 40 mile daily range requirement, and 3.5 miles per kilowatt-hour.  By further assuming $8.00 per watt (installed), $150 per kilowatt-hour of storage, the total system cost is under $15,000, and at a 25 year system life the cost per mile is only $.04.  Using these assumptions, it is already cost-effective for personal photovoltaic systems to power electric cars.  Input your own assumptions!

With series hybrid technology, you can have cars that run virtually all the time on electricity, since the normal duty cycle is 40 miles per day or less, but nonetheless are capable of driving 500+ miles on a tank of gasoline in the rare instances when that may be necessary.  With current prices and technologies, it is already arguable that photovoltaics can economically power series hybrid cars.