# A different idea of opurtunity charging.... and a little about re-charge systems.



## surgy (May 15, 2009)

Hello, I'm a little new to this idea but I am officially addicted to the whole concept of EV conversions. I am in the very early planning stages of my project and have a few questions that I haven't seen addressed as of yet.

My first question is; Why don't I see more EV conversions with solar panels on their roofs? I know it would ever be enough to do anything while you are driving. But what if you could get five 210 watt panels on the roof of your car. Wouldn't you get a few more miles every time you go to wal-mart on a sunny day? (it always takes me at least an hour to get in and out of there)

My second question is simply and extension of the first. Why not use a solar array (i know it would need to be in the 4KW range) to charge a battery bank and then use a direct charge controller to charge your cars batteries off of those? Would that not make your EV 100% clean?

Thank you for all of your comments and answers!


----------



## madderscience (Jun 28, 2008)

This is well trodden ground. (but I cannot resist repeating myself)
This is well trodden ground. (but I cannot resist repeating myself)

The reason you don't see EV conversion with solar panels is that the size and bulk of a solar panel that would be required to do anything useful would be such that it would be basically impossible to fit onto a normal car without ruining the aerodynamics or adding enough extra weight to cancel out any gain they may provide.

Last I checked, five 210 watt panels would be a much larger surface than the top of most vehicles.

The ONLY case where you might get a net positive using vehicle mounted panels would be a van roof or covered pickup bed that already provides a fairly large surface area without messing up the vehicle aerodynamics or adding a lot of extra weight.

As for charging at home, yes it makes a ton of sense to put a PV array up on the roof if your goal is to offset the energy used by the car. Typically what is done though is to use a grid tied system so that you don't need to fuss around with even more batteries. The solar panel feeds the grid if the car is not plugged in, and feeds the car if it is. During the night you can recharge the car off the grid and still be carbon neutral. (since you offset some coal burning or whatever during the day).

Depending on your latitude and how much you drive, a panel as little as 1 or 2 KW could offset an EV.

Good luck.


----------



## surgy (May 15, 2009)

i live in south central us with 4.5 peak sun hours. 2kw of pv panels eh? i figured it would take as much as 4kw... for a 144vdc car....


----------



## madderscience (Jun 28, 2008)

Well if I understand the concept of peak sun hours right:

4.5 peak sun hours would mean that over the course of a day, a properly oriented 1KW array could capture 4.5KWH of solar energy. So a 2KW array would double that, or create 9KWH of power. Lets be conservative and say that 2/3 of that, or 6KWH, actually makes it into your batteries, accounting for various energy transfer inefficiencies.

So if an electric car gets 250WH/mile (a decent battery-to-wheels efficiency for a compact car based EV conversion) then you are offsetting 24 miles of driving per day. The battery voltage of the car itself is basically irrelevant to the calculation.

On average I drive about 10 miles a day in my EV. so If I lived in your region I would only need about 1KW to offset my car.

That's my math. Bigger car, higher latitude, or more driving would of course require a bigger panel to offset.


----------



## surgy (May 15, 2009)

So what your saying is that if my car is settign in the wal-mart parking lot for say 1 hour.... You couldnt get enough energy from the roof top nto the batteries to make a difference what so ever?


----------



## vpoppv (Jul 27, 2009)

surgy said:


> So what your saying is that if my car is settign in the wal-mart parking lot for say 1 hour.... You couldnt get enough energy from the roof top nto the batteries to make a difference what so ever?


 Well, it may not be much help in charging the batteries, but it would probably help with their longevity. Batteries don't like to sit and do nothing, so that trickle charge at Wal-Mart might just add some life to them. At least that's what Dr. Larry believes, and his car has been on the road a while:

http://www.evconvert.com/article/larrys-ev

I've toyed with the idea myself, but solar is still relatively expensive, while batteries (at least the used ones I use) are cheap. I might start off with one on my accessory battery.....


----------



## ZEVUtah (Apr 10, 2008)

surgy said:


> Hello, I'm a little new to this idea but I am officially addicted to the whole concept of EV conversions. I am in the very early planning stages of my project and have a few questions that I haven't seen addressed as of yet.
> 
> My first question is; Why don't I see more EV conversions with solar panels on their roofs?


This has been done before and I was not the first to do it. 
http://www.evalbum.com/2058

The truth is I get just enough power from the solar panels to charge the 12 volt accessory battery and that is about all. 

The 1500 watt array on the workshop is enough to supply what little driving I do on most days. 

KJD
http://www.zevutah.com/


----------



## rmay635703 (Oct 23, 2008)

vpoppv said:


> Well, it may not be much help in charging the batteries, but it would probably help with their longevity. Batteries don't like to sit and do nothing, so that trickle charge at Wal-Mart might just add some life to them. At least that's what Dr. Larry believes, and his car has been on the road a while:


I have to strongly agree, having a small to moderate size solar trickle charger on the car can really help in the cases where you drive your batteries a bit further than they should be since batteries under charge, even a slow charge tend to not sulphate as rapidly. The speed batteries sulphate while sitting depends on temperature and DOD, so if you tend to run your batteries a tad low then let the car sit a solar charger will keep the batteries alive longer. Battery tenders and the like seem to work better when coupled with a trickle charger as well.

Food for thought.
Ryan


----------

