Powering Transportation with the Sun

By Bill Moore

Posted: 02 Mar 2010

Late last Friday, I had an interesting 45-minute meeting with three German gentlemen, plus their American colleague, at M's Pub in the Old Market section of Omaha. They represent SunCarrier, a division of A+F GmhB, which not only builds some of the world's largest single-axis solar trackers, but also builds utility-scale solar parks, some 1,500 in Spain alone.

They were in town for meetings with our Governor and university administration, among others. Given the state's abundant sunshine -- comparable to Gainesville, Florida and San Diego, California, surprisingly -- they are introducing influential people to their product (giant solar trackers) and their services (solar park construction and management). The previous day, they had been down in Kansas City for meetings with Black & Veach, which builds power plants. A B&V employee friend of mine, Bill Roush, suggested they talk to me about using solar energy to power electric cars. So, at 4 pm, I walked into M's Pub dressed in blue jeans, a worn leather bomber jacket and my German forester's cap; the Germans were wearing tailored suits and silk ties. Oops!

I apologized for being profoundly underdressed and they graciously accepted it and invited me to sit down and share their pizza and snacks, along with a bottle of Becks beer. With introductions done and business cards exchanged, we got down to the reason for the meeting: they wanted to meet me because of my knowledge of the electric vehicle industry. We talked shop about their technology; stuff like tracking systems, drive motors, wind loading, hail damage resistance.

At 4:45, they apologized that they had to run to catch their 6:30 flight, but promised they'd be back and have more time to talk. Leaving me with the rest of the pizza and an 80-page A+F GmbH corporate brochure, we parted company. As I drove back home in my E-85 burning Chevy S10 bearing the vanity license plate 'SUN POWR', I got to thinking about their interest in powering electric cars with solar energy. There are some good reasons to consider it, and some less attractive ones, starting with this basic fact of life: the sun only shines during the day.

That's pretty important when you think about, because if you plan to put solar panels on your house to charge your car -- as well as run your home -- the car needs to be parked in the vicinity of the collectors; and most working folks' cars aren't anywhere near those panels and inverter during the day. Sure, we can argue that putting electrons into the grid at home and taking them out at work is just as good as being plugged in at home, but I think that's sort of intellectually cheating. Most people don't plug their BEVs into the grid during the day. Instead they plug the car in at night, using the grid as a sort of "virtual" storage battery.

No, if you're going to do it right, the panels and the cars need to be on the same circuit, more or less. And in a few places like Google's Mountain View campus and others, that happens. The cars are parked under the panels and charged directly by solar photons. All this got me to thinking about the costs of using ancient sunlight versus modern sunlight: petroleum (and coal) vs PV. So, I started examining the numbers and here's what I came up with: numbers I shared with the German gentlemen, starting with my assumptions:

30 mpg ICE vehicle
30 mile commute (7,500 miles annually)
$2.80 gasoline
ICE will burn 250 gals of fuel = $700 annually

EV vehicle efficiency 250 watt hours/mile
EV will consume 7.5 kWh for 30 miles or 1,875 kWh annually to drive 7,500 miles.
1 gallon gasoline = 33kWh
$2.80 gal. gasoline equivalent to 8.4¢ kWh electricity.
EV consumes electric power equivalent of 56 gals of gasoline to drive 7,500 miles

Put another way, 1 gallon of gasoline will propel the ICE 30 miles. The same gallon equivalent in kWh of electricity will propel the EV 132 miles, 4.4 times the distance.

That makes a very strong case for the electric car over the internal combustion version burning gasoline. But let's compare their relative costs, starting with my assumptions about the PV system:

$3 watt in PV costs (not including BOS).
5 hours local solar radiation
7.5 kWh = 1,500watts x 5hrs.
$3 x 1500 = $4,500 PV system per vehicle (not including the balance of system costs)
$700 in gasoline costs = 6.42 years for PV pay-off at 2.80/gal gasoline.

In contrast, a PV system assumed to be 25¢ kWh is about 3 times more expensive than gasoline in this example, making "solar fuel" approximately equivalent to gasoline at $8.33 gallon. This also assumes 300+ days of sunshine. My PV system costs are only educated "guesstimates."

Based on this, a gallon of gasoline is going to have to sell for somewhere around $8.33 a gallon before "solar fuel" becomes competitive, at least at current PV system costs, which are coming down. That being said, though, if you consider the fact that an EV is 4.4 times more efficient than a ICE vehicle, than the EV would still come out ahead, assuming you don't have to do any battery replacement over the 6-7 year ROI period.

What this suggests to me are a couple possibilities. While a enlightened parking lot operator or employer might be induced to invest in a "solar fuel" installation, perhaps using A+F's SunCarrier system, allowing his employees to charge their Volts, Leafs, Codas, Thinks and a half dozen other EVs and PHEV's coming to market, I doubt many will do so. Instead, if you're going to use solar energy to power transportation, displacing gasoline and coal, I would think you'd want to use that energy to power public transit: electric light rail, ultra-capacitor-powered trolleys or BRTs, perhaps even personal rapid transit systems. You're moving more people, more efficiently than all those single-driver cars parked out there. Interestingly, the production and demand curves tend to more closely overlap with peak commuter transit ridership occurring in the morning and late afternoon, which a tracking PV system can more readily accommodate since it starts producing more power earlier and later in the day than the fixed system.

I could see PV installations being built along the track rights-away, feeding energy directly into the transit system, installed just far away enough to prevent being shaded by passing train cars.

This isn't to say, people shouldn't put PV panels on their homes -- or on or over company employee parking lots. I think all of these are commendable activities, but I think pairing electrified public transit and PV makes even better sense.

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