Solar Conestogas

Powering cars with solar cells installed on the car is an intriguing proposition, but unless we drive for very high efficiencies with resulting uncomfortable and impractical cars such as solar racers, it will probably not be possible to power cars with solar cells to the extent that we power cars with chemical fuels such as gasoline, diesel, LNG or hydrogen. We will probably stick with chemical fuels since hydrogen is an almost perfect fuel and can be generated with electricity generated by solar and then loaded aboard a car as a fuel with zero emissions and long vehicle range. As long as we develop a hydrogen infrastructure, from a technological point of view, we do not have to worry too much about outfitting cars with massive solar panels.

On the other hand, to be on the move completely under own power (slow but unlimited range) is a unique proposition. At sea to be under own power is easy by using sail. To be under own power on land is a little bit more difficult. Historically we sort of did it before, by using oxen to pull Conestoga wagons. The fuel for the oxen was the food that could be found along the way. In effect, a pioneer trip across the United States was driven by careful route management of forage and water opportunities.

This leads one to think if it would be possible to fit out a Maxi Taxi with solar panels and to be able to travel across the United States in relative comfort completely under own power. Hannah and I ran some numbers and, surprisingly, it is not at all that difficult.

Since it would be a design using today’s solar technology and electric car state of the art, it would not incorporate automated driving and convoying. Therefore the only real restriction is a five foot width.

Using today’s technology the rig would, sort of, look like this:

It is not fancy, but it is a quite reasonably comfortable set-up. What really charms me is that when there is no sun, it is nice and snug and when there is sun there will be plenty of shade.

As far as the numbers is concerned, the design relies on the Nissan Leaf drive train features.

This design uses an 80 kW motor to pull a 3300 pound car. That power is rarely used, but the Nissan Leaf is designed to run at highway speeds and therefore needs this punch.

The Nissan Leaf has a range of a little more than 100 miles and uses a 24 kWh battery pack (although this is a 360V DC set-up, and right now, I do not know if it is possible to efficiently charge this battery pack with DC solar).

If we were to keep the same weight (which looks possible using marine composite structures) and drive at lower than highway speeds, say 25 mph, the added drag from the taller rig would not be a problem and the overall result would be a similar range. (The five foot width would allow faster traffic to pass relatively easily, and, if needed, the rig should be able to make 60 mph, for shorter periods of time) Crossing the United States would be a leisurely process (at 100 miles per day, even in mid summer, it would take over 30 days) but it would be very interesting. It would allow a person to avoid interstates for most of the trip and result in very interesting planning decisions similar to those made by the pioneers.

This rig would probably charge in a nice sunny spot during top sun hours (a full charge on a good sunny day would take less than 8 hours) and then drive in the early morning or late afternoon. While driving on good sunny days (and roads with few trees) the four hour driving period could even add another 25 miles to the range from the undeployed panels resulting in 125 mile days.

At first I was concerned that the system could not pack enough punch to get across mountain passes, but that was one of those assumptions that results from bad thinking about physical numbers. The easiest way to look at this is to note that the Nissan Leaf has a third size fuel tank with the 24 kWh battery pack. I am almost certain that there are no US mountain passes that climb for an entire 1/3 tank without having a good pullout to get another 100 mile solar charge. (a recharging station is a little more difficult to find though, and therefore using a Nissan Leaf or even a Tesla would be a little scarier). Off course the most fun occurs on the downhill run where a very significant portion of the power is regenerated into the batteries. The trick is to keep the speed low and, since it is not a race, the technical solution is within reach.

Undoubtedly at some stage people would race across the US in rigs like this, but until that time I certainly would not mind volunteering for a Solar Conestoga trip.

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