USA Solar Journey

USA Solar Journey

Dear Tesla Enthusiasts,

A fellow Phd student and I are setting up a project to travel across the United States by using only solar energy ( We will be using flexible solar panels that can fit in a trailer. The idea is to make dialy stops every 200 miles at schools, universities and other high-profile destinations to educate the public about EV's and flexible solar panels. While we educate the people during the day, we will be charging our batteries so that we can drive off in the evening without having used any fossil fuels for charging.

Currently, we're looking for the appropriate (commercially available) vehicle to use for this trip and we came across the Tesla Roadster. There's a couple of important questions I need to answer before moving forward, and I thought you guys could help me out with some advice.

I know a fair share about charging methods for EV's, but I was wondering:
- Is it possible to charge the Roadster with a high-voltage DC connection (without making any alterations to the car)? That is, is one of the three charging methods DC? I'm asking this because we would prefer to not bring an additional inverter in the first step to go from DC (solar) to AC (input to car) back to DC (battery) to AC (drivetrain)!!!

I'm not sure if this is discussed in this forum, because the Roadster is not the first car you would want to connect a trailer to:
- Is it possible to connect a hitch to the Roadster? Have you heard of anyone who has towed anything? I know from Lotus Elise forums that people have attached a hitch to the frame under the car before:
So since the Roadster has the same frame, do you think this hitch component can be attached?

Thanks so much for your input.

I hope to own one myself one day.

Rob van Haaren

Vawlkus | 2011年1月4日

I do not believe the Roadster carries a hookup for a DC charge, I think it's only AC, although I do not know that for a fact.

I'm also fairly certain the Roadster does not have a provision fro a trailer hitch, since it would be a significant power drain.

ggr | 2011年1月4日

I think you need to do some more mathematics. 200 miles at, say, 250 Wh/mile is about 50KW (and that's not pulling a trailer). My house full of solar panels, in San Diego, on a good day, generates about 15-20 KWh (depending on the season). So you're looking at 2-3 days of charging for 200 miles of travel, if you don't use the grid, and the weather stays fine.


Rob360 | 2011年1月4日

Dear Greg,
You're right that we won't make 200 miles with a Tesla. The initial idea was to drive with electric motorcycles and for those it would be possible to get that range (they get ~10-15 miles/kWh).

So lets do the math for the Tesla:
With an average horizontal irradiation of 6.8 kWh/m2/day (from PVWatts) along the route (in summer) and 11% efficient panels, we get ~0.75kWh/m2/day. Take off 10% losses from charging and discharging the battery and you have 0.67kWh/m2/day sent to the motor. We can carry a total of 20 * 3m2 panels (each is actually 320Wp), so for the whole array we generate 0.67*60= 40 kWh/day.

So with 250 Wh/mile we would only get 160 miles. I just found this
and it appears the EPA [Wh/mile] number is 133 Wh/mile?
But I guess the true numbers are always a little disappointing with these kind of things. Is the 250Wh/mile what you get from your Roadster?

Thanks for the comments guys.

By the way, if you're interested in solar, those new CIGS panels of Ascent are very interesting. They're as thick as a creditcard and they only weigh 6kg for 320 Watts! You can check the website for more info.

Timo | 2011年1月4日

250Wh/mile is at 60mph, IIRC EPA "highway" testing is at 50mph which is about 220Wh/mile. That gives you about 260mile range (according to chart)

I don't know where you got that 133Wh/mile, that would be about 15-20mph speed. (same

(btw, that chart assumes 55kWh battery, but AFAIK Roadster battery is only 53kWh.)

ida-intl | 2011年1月5日

If you do make the solar trip, there are locations where you can charge up on power already generated by the sun. My manufacturing company generates all it's power needs from an on-site PV array, in fact we generate in excess of our consumption. We have a charge spot available outside (Derby, CT) for anyone who wants to use it. Free kwh sun-juice.

Rob360 | 2011年1月5日

@ Timo,

I got the 133 Wh/mile battery to wheel EPA number from a referenced source on the Tesla Roadster wikipedia page Not sure if it's in line with practical values, but I'm sure it must be much higher for towing a trailer.

The addition of the trailer would especially have an effect on acceleration, but I wonder how much the rolling resistance and air resistance contribute to a lower range at constant speeds. I've read things about motorcycles of 10-15% lowered range by adding a trailer.

Thanks for the tip! Even though we try to do this in a stand-alone idea, it is definitely worth considering. Where in Derby is it and what's the name of the company?

asblik | 2011年1月5日

Very interesting... So sounds like all your PV are inside the trailer which you'll unfold/setup during daytime while lecturing? And then collapse 'em into trailer for night time driving.

Have you considered Sun Power's E19/318 panels? I heard good things unless you already secured you're sponsorship?

Maybe speak to folks at TSLA explain plan and ask 'em for Roadster lease for a month :) Sounds epic... I don't think you really want to be out there at night on couple of electric bikes... much rather go w Roadster :D

Keep us posted,

asblik | 2011年1月5日

Also talk to Rob Wilder... he could give you more insights on his PV charging experience w the Roadster... check out his blog at,

Timo | 2011年1月5日

@h8tow8, Good video. That gives me some indication about overtaking acceleration: 50-80mph goes in about four seconds. You would be passing trucks in no time at all. That's about as fast as that same page "340 km/h en Ferrari F430 Scuderia Novitec Rosso !" makes from 80km/h to 130km/h (

@rob360, that EPA number is for kilometers, not miles. "133 W·h/km"

That translates to 212Wh/mile. If that is combined cycle I think it is quite accurate (EV:s in general have better mileage at city than in highways because they waste no energy idling).

Rob360 | 2011年1月6日

Thanks h8tow8, I will definitely ask him about his experiences.
the sunpower panels are very high efficiency, but since they're not as light and flexible as CIGS on plastic substrate, they won't be easy to tow and unfold. We've already acquired sponsoring from Ascent Solar, so we're all set in terms of panels.
I just uploaded the design of the trailer on

@ Timo,
I totally missed that! thanks for clearing this up. I'm gonna ask the guys like Rob Wilder and people from renew america roadtrip who did similar tours like us, but without towing the array.

Anyway thanks to all for posting your comments and ideas!


Brian H | 2011年1月7日

What speeds and roads? You can stretch mileage considerably if you're doing, say, 40 mph instead of 50 or 60.

Timo | 2011年5月20日

tesla446 post is spam. remove.

David70 | 2011年5月20日

More than a spam. I suspect a scam.

Timo | 2011年5月21日

I hope that some day near future we get rid of stupid wars so that US military could hunt down those spammer/scammer guys like they did to Osama. And with same results. No matter where they hide.