# Solar-based charging for EVs becoming a reality



## rbgrn (Jul 24, 2007)

My vision for the future of personal transportation involves an at-home solar-charging electric vehicle. The vehicle would be fully electric, running off of affordable lithium-based light-weight high-capacity high-discharge batteries. The vehicle charges overnight in a garage or near a parking facility. The charging facility (garage or otherwise) has a bank of much cheaper flooded lead-acid batteries in which it charges by means of a building exterior (roof and sides) made of high efficiency silicon solar and polymer solar skin. This allows for as free of energy as possible, only costing the driver vehicle maintenance.

This concept is nothing new. It isn't often seen because the current technology required is very cost prohibitive, however that is looking to change very soon.

It is assumed that flooded lead-acid batteries will always be cheaper than their higher tech counterparts, which is why they are used here. The trade off with those batteries is always size and weight. In a house or a garage, that isn't nearly the issue.

The two biggest technologies required here are efficient solar collectors and lighter, smaller batteries for the vehicle. Here are some promising new technologies that hope to solve these problems:

Here is a simple clip art diagram to illustrate the idea.









This concept is nothing new. It isn't often seen because the current technology required is very cost prohibitive, however that is looking to change very soon.

It is assumed that flooded lead-acid batteries will always be cheaper than their higher tech counterparts, which is why they are used here. The trade off with those batteries is always size and weight. In a house or a garage, that isn't nearly the issue.

The two biggest technologies required here are efficient solar collectors and lighter, smaller batteries for the vehicle. Here are some promising new technologies that hope to solve these problems:

For the in-home energy storage:
$1/Watt solar cells ready for mass production - This would enable a consumer to cover their roof in this type of solar cell which on a sunny day would provide most of the electricity required for a charge.
Plastic, paintable solar cells - Painting the walls and other exterior with this could supplement the power required.

For the vehicle's battery pack:
A123 Systems - This company makes a few different models of battery which boast incredible storage capacities and discharge rates, ideal for an EV. Unfortunately they don't sell to individuals but with any luck a deal will be worked out in the future. It's a matter of time before costs come down, availability goes up and we will be seeing these in EVs.
Lithium iron phosphate - This newer technology is much safer and lighter than previous generations of Lithium-based cells. The downside is a lower voltage and energy density, but It is still looking promising for use in EVs.

Imagine normally not having to pay for fuel! Believe it or not, it's a reality. The average person drives under 30 miles per day. With a very efficient solar collection system, you could collect that much energy on a sunny day for only the initial cost of materials, which is shrinking. With this system, you pull in to the garage at the end of the day, plug in over night and you're fully charged and ready to go again every morning.


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## Zap-n-Roll (Mar 3, 2011)

I love the idea, and if I could think of a way to implement it, I would be moving into an off-grid solar home.

The main obstacle, as far as I can see, is that the lead-acid batteries must be kept warm in the winter. How do you keep lead-acid batteries warm in the winter? You can't keep them in the sun-warmed living enclosure of a passive solar home because they release hydrogen gas which might cause a fire or an explosion. As far as I've gathered researching this very question on the internet, no one has a really good idea of how to keep them warm outdoors in supercold weather, either (it can, every few years or so, get down to -20F in these parts).

I've run across a couple of solutions. One is to use a product called Heatline (TM) to pass heat energy to the batteries.

www.heatline.com

I actually saw the Heatline idea on this forum.

http://www.diyelectriccar.com/forums/showthread.php/battery-box-insulation-61301.html

Another idea I've kind of cooked up is to use Dow Blue Foam to build an underground heat reservoir charged over the summer, and supplementally during the sunniest hours of the day in the cold months, using something like solar thermal parabolic troughs to concentrate solar rays. Since there is no limit to the amount of insulation one could use to contain the heat to be pumped into the thermal storage chamber, one could maintain a very high temperature for the cold months. Just run tubes through a heat storage medium in the chamber--dirt, for example--to charge it, and tubes to transfer heat to the batteries. You could leave the batteries under a roof with vents to keep them dry and allow hydrogen to escape, and insulate them all around with something really effective, like Aerogel insulation. The heat transfer fluid could be pumped around the batteries within the boundaries of the batteries' insulation, with a pump operating at the direction of a thermostat.

As far as I can tell, you can insulate batteries on all six sides as long as you leave a hole for the gas valve. I don't think it would affect the heating system's efficiency or performance much if you made the top readily removable to check terminals for corrosion every once in a while.

The idea would work doubly well if you could remove the batteries' winter insulation for the warm months to decrease the likelihood of high temperature damage. Something like a "coat" rather than a "box" of insulation.

If you added enough cheap lead-acid batteries to your system, you could warm your car's lithium batteries with any extra electrical energy you have available using the usual resistance heating, like you find in electric blankets. Obviously, you would want some insulation on your car's batteries, too. A "coat" of insulation might make more sense than a "box" of insulation for your car batteries, as well.

One advantage with this idea is that the underground thermal storage chamber and the battery shed above it can be built using concrete so that it will last hundreds of years (in areas not prone to earthquakes). Blue styrofoam would last forever, I think. This would reduce the need to replace the construction, as is the case with typical one-generation homes. We'd all probably be living in the Matrix by then, but apart from that, it might be more sustainable. No one is ever going to forget how to make lead-acid batteries, we can be sure of that.

I'd love to see this idea used widely. I've researched lead acid batteries and how to get them cheaply, and there seems to be a dozen or so ways you might get them for next to nothing. If anyone wants to tackle the design and engineering of my idea, give me a buzz on this website. I'd really like someone to analyze the ideas for feasibility and workability.


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