The Future Cost of Driving on Sunlight

By Bill Moore

Posted: 19 Jun 2010

I am giving a speech at the Electric Vehicles Summit in San Francisco this week. My topic is Projecting the Future of Transportation: Peak Oil, Energy and the Environment, maybe the most unenviable assignment of the conference, after the one on projecting battery costs reductions.

In preparing for the talk, I put together a colorful and probably controversial set of 47 slides, the next to last of which is maybe the most telling of all. I've reproduced it above. It is based on an article now a couple years old in Photon International that examined the energy production capacity of a hectare of ground, presumably in Europe, likely in southern Germany.

It concluded that whatever crop you planted on this field from rape seed (canola) to popular tree, the most you could produce was enough fuel to propel a single vehicle some 67,000 km (41,000 miles).

However, if you covered that same hectare (10,000 square meters or 2.47 acres) with photovoltaic panels, you could propel an electric-drive vehicle more than 3 million kilometers. I have used this particular comparison a number of time in the past, but I thought about what it would cost on a per mile basis to do this considering the relatively high cost of PV.

So, this morning between scraping the flaking paint off the south side of my house and drinking my morning cup of coffee, I decided to find out it might cost. As usual, I turned to Google and started looking for numbers I could crunch. Here's what I came up with. A 150 watt PV panel measures approximately 1 square meter; a hectare would require 10,000 of them. Note, I am simply assuming you lay the panels edge-to-edge up and down the field.

Under ideal conditions, the field would generate 1,500,000 watts or 1,500 kilowatts or 1.5 megawatts. One reference I came across stated that a 150 watt panel would generate one kilowatt hour per day, so the field would produce a theoretical 10,000 kWh a day. This would be enough electric power, again under near ideal conditions, to recharge 1,240 Chevy Volts, assuming 8 kWh of electrical energy per 40 miles.

That's great, of course, but what's the cost? We all know solar PV is expensive compared to other conventional 'fuels.' A couple Google sources indicated the most current installed cost for solar PV is between $7-9 per watt. I chose to multiply $8 by 1,500,000 watts and came up with an installed cost of $12 million, a fair chunk of change, to be sure. Now, a PV panel has an expected life time of 20 years, and there will be some degradation, but not a lot. I simply assumed the system would have the same power output at year 20 as in year one.

So, divide $12 million by 20 years and your annual cost is $600,000, again not including the cost of renting money; just simple, easy math. Assuming that all the EVs being charged by the solar hectare are as efficient as the Chevy Volt and it takes just 8kWh to drive 40 miles, the field can support 1240 Volts each driving 14,600 miles a year (40x365). This means the total energy bill per year for each car averages out to be $483 or the equivalent of 3.3¢ per mile. And this is without any pollution, other than the energy it took to manufacture the panels and support equipment in the first place.

Okay, so how many hectares of ground would it take to power, say, the U.S. automotive vehicle fleet based on these numbers? Just over 109,000 hectares if we're talking only about registered passenger cars, not light trucks, etc. That's equivalent to 420 square miles or roughly 1.5 percent of the area of the Mojave Desert in California.

Given what I've now learned, my presentation is going to get two more slides. Not only is it feasible to fuel our cars with the sun, but it is likely to be the most economic fuel of choice for the 21st century.

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