DIY Electric Car Forums > EV Conversions and Builds > Technical Discussion

rankhornjp · #1 12-13-2007, 08:01 PM

Im thinking of converting a truck to Electric, and was thinking i could build a bed cover out of solar panels to help maintain the battery packs. My truck bed is ~ 70in x 80in. Just have a couple of questions.

How effective are solars panels in recharging battery packs? Is it possible to use solar panels to help extend the range of an EV? Is it possible to run an EV exclusively off of solar panels at highway speed?

houseoffubar · #2 12-13-2007, 08:44 PM

No, Not even, and Not even close, But don't let that stop you.
Sorry, But as great as it sounds to use solar panels to power your truck, it just isn't even possible.
You can add the panels to the bed, and get a 5% or so increase in range, or top off charge for free if your truck sits all weekend in the sun. But there is not enough square feet in the bed of your truck to catch enough sun to do much good.

The good news is that you can buy a 1 kilowatt solar array, mount it on the house, garage, yard, and power your truck for free.
The good/bad news is that this will cost about $10,000, but will last as much as 50 years. I currently use $2,000 a year in gas just commuting 30mi. a day. That's $100,000 in the life of the panels, or a $90,000 savings. This would (for me) pay off the panels in 5 years, and provide me with free "gas" for the rest of my life, and then some.

Obviously this price hurts a bit at the beginning, but if you can spring for it, one way or another, it will pay big dividends.
Hope that this helps, Eric

david85 · #3 12-13-2007, 10:32 PM

Ak!! 40 KPH!!??

The freeway I run is POSTED at 110KPH and the flow is usually at least 120 (the odd driver will blow through at 140+).

Solar Power is a usefull addon, if you don't spend too much time driving and lots of time charging. If you live in a sunny climate and do a short commute to work where you can park in the sun, I think it could work.

But when you consider the cost of solar panels, I would rather have them on the house where they are less likely to be damaged, and you can have a larger collector bank.

rankhornjp · #4 12-14-2007, 06:00 AM

Ok, one says we can't, one has proof we can(taking your word, as i dont read japanese). Does anyone have the unbiased math, i.e. average draw of the motor, how much of that would the solar panels put back (i know it will vary by how big the panels are). Trying to figure out how feasible this may be, i only drive about 20 miles on a normal day, but i do make a regular 70 mile round trip every weekend, just trying to figure out my options, as I am new to this.

houseoffubar · #5 12-14-2007, 08:17 PM

Quote:

Originally Posted by rankhornjp

Ok, one says we can't, one has proof we can(taking your word, as i dont read japanese). Does anyone have the unbiased math, i.e. average draw of the motor, how much of that would the solar panels put back (i know it will vary by how big the panels are). Trying to figure out how feasible this may be, i only drive about 20 miles on a normal day, but i do make a regular 70 mile round trip every weekend, just trying to figure out my options, as I am new to this.

Sorry about that, I gave you an absolute answer of no, based on my interpretation of your desire to commute in a truck using solar only for maintaining cruising speed.
Perhaps a better answer to your question would be a collective of some of the others posted by MattW, and Lexus.
Yes it is possible to drive an EV using purely solar, but as others have said, this is pretty much only at very low speed, or using a vehicle like a solar challenge car (a few hundred pounds, and very aero) these can achieve speeds pushing above 80mph, under ideal conditions.
For pretty much any production vehicle it would be almost impossible to provide more than a few percentage of the required watts required.
To be honest, I am planning to cover some of the surfaces of my car with solar cells, but I have no illusions of getting much extra from them, and my car is very aerodynamic, and should come in about 900lbs. when completed.
I guess what I'm trying to say is Theoretical yes, practical no

Eric

rankhornjp · #6 12-17-2007, 10:43 PM

http://www.sciam.com/article.cfm?art...08C4CB8A197667

Found this article from Dec 06. Does anyone know anymore about this?

david85 · #7 12-18-2007, 12:19 PM

Quote:

Originally Posted by rankhornjp

http://www.sciam.com/article.cfm?art...08C4CB8A197667

Found this article from Dec 06. Does anyone know anymore about this?

Its very impressive, the highest efficiency I ever saw was 37%, (with concentration) but these guys are a 45%!? This is of course with concentration, (magnifier glass), but still, if they can make a plyable solar cell that is in the range of 50% efficient, well, I think solar cars would be possible....

But even if not, the amount of power that can be make economically on a fixed structure, such as a house, would also be much higher so you can still have a "solar car" just so long as you use a battery bank at home to recharge the car at night.

mattW · #8 12-14-2007, 07:06 AM

Just some quick trivia, It is possible to run at highway speeds on purely electric power, Check out the World Solar Challenge, but not in anything that looks like a normal car. Those solar cars can go 80+kph on sunlight alone with an 8m2 array but they are some of the most efficient vehicles on the planet. A solar car uses about 1.5hp to travel at highway speeds while a normal shaped/size car will use 10-15hp. So by extension with an 8m2 array (of quality solar panels) you are looking to get about a 10-15% increase in range while driving plus the ability to recharge at your destination. So in terms of a range extender it is a pretty expensive one, it would be better to go with better/more batteries. But if your car is parked for a reasonable amount of time in the sun in the car park at work (and you can't otherwise charge it) then it is a great idea and would give you a considerable boost to your batteries state of change, lower the final DOD and extend your battery life. So the choice will be dependant on your situation

rankhornjp · #9 12-14-2007, 08:14 AM

Lexus: Thanks for that. Let me/us know what you find out, if anything.

MattW: Thanks for the trivia. Knowing about solar cars is what prompted the line of thought. I know you need alot of power to accelerate, but as I understand it, that power requirement decreases as acceleration levels out and you maintain a constant speed. So the thought was; use the batteries to accelerate and then the solar panels would provide enough power to maintain speed. Not sure if this is possible, as Im just starting to gather info.

mattW · #10 12-14-2007, 08:40 AM

As I said in a standard car, 8 square meters (a lot) of solar panels on a sunny day will only give you 10-15% of the energy you need to travel at constant highway speeds. They will also increase your drag unless they fit flush with the roof. Solar cars have small battery packs but the reason they are effective is that they use 1/10th of the power of a standard car. If you had a low speed, high efficiency electric car it would possible be viable but i think it is best to invest your money in better batteries.