# Forums

## 12V Solar Panel Battery Charger on MS?

Just wondering if something like this good idea to use on model s so that during the day the sun is blight and you park at the same time vampire drain will be reduced or even charge? By the way I bought my from costco a while back but been using it oh my other car.

nickjhowe | April 27, 2013

Basic math: vampire load is about 10 miles per day = c. 3KWh. (307Wh/m * 10 miles)

12v solar charger, max 2W. Assume 12 hours sunlight = 12 * 12 *2 = 288Wh. = 9% of vampire load.

Joel N. Weber II | April 27, 2013

The more interesting question is, if you could cover every painted surface on the Model S with high efficiency solar panels, whether leaving the car parked in an outdoor parking lot at work would charge the car enough to cover anyone's commute.

nickjhowe | April 27, 2013

Check out the solar challenge across Australia - the only way you can do it is with meters and meters of panels in a vehicle weighing a few hundred pounds and ultra low Cd.

http://www.flickr.com/photos/globalgreenchallenge/6262489140/

nickjhowe | April 27, 2013

BTW - there are plenty of other threads discussing this on this forum.

Brian H | April 27, 2013

joel;
you'd be lucky to power the touchscreen.

rchiang | April 28, 2013

well maybe not possible to charge but reducing the vampire drain is a start. I wonder if they had a sun visor that cover the whole front windshield while you park you can just set it up to block the sun.

rchiang | April 28, 2013

It doesn't hurt to reduce the vampire drain. Tesla should of put these on the car as optional and see how many people want them.

http://www.solarelectricalvehicles.com/

Dr. Bob Reinke | April 28, 2013

2 Watts!! likely, the internal resistance of this device will produce a vampire load on your 12 Volt Model S instrument battery that will run it dead within 100 hours plugged in. Lucky for most, who are fascinated by this wizzardry, like nearly all other cars, Tesla shuts off the connection to the cig lighter receptical to prevent vampire loads like this. If this device were at least four times this size it may have a function. 8 Times larger, could provide the output you need to achieve your objective. But only for the 12 Volt instrument battery. Fisker covered the roof with quality Solar Cells and claimed that they could power the AC while parked--left owners with dead 12 volt batterys.

The 12 volt battery in your Model S has nothing to do with the drive battery.(400-600 volts) The juice flows from the main drive battery through voltage reduction converters to charge the 12 Volt instrument battery. To charge the main battery, you would need a solar cell serial output of over 400 VDC.

This junkis an "Old-wives-tale-that works no better than drinking a glass of air to cure a headache---sorry

jat | April 28, 2013

@Joel - not even close, you won't even get a couple of miles.

The LEAF has a small solar panel on it ostensibly to charge the accessories battery, but it makes zero difference. It is just extra cost and complexity for no value.

rscheirer | April 28, 2013

How about flexible solar woven or part of the car cover. The cars covered and some solar power to offset some loss d/t heat or even power some ventilation fan to keep interior cool. There are all kinds of flexible solar material for shingles and such why not make part of car cover?

Brian H | April 28, 2013

rc;
covered in detail elsewhere. Volkerize.com on panels. The area and solar angle are the main issues. Grossly inadequate.

dtesla | April 29, 2013

The earth receives about 1KW of energy from the sun per square meter. An very efficient solar panel converts 20% of the sun's energy to electricity. The MS has about a 4 square meter surface area (real, real rough estimate). So you could go 3 miles on one hour of charging. But that would be about enough to cover the daily SOC loss. That in itself would be enough power for me to pay \$4k for the option.

jat | April 29, 2013

@dtesla - the 1kW/m^2 number is the peak with the sun directly overhead, the panel perfectly angled toward it, etc. You aren't going to have that on a car, so you would be lucky to get 3kWh/m^2 for an entire day, assuming the car is in direct sunlight the whole time. If you are in more extreme latitudes, it gets worse than that.

You would really pay for the privilege of covering your entire car in solar panels (I wonder what rock chips will do sensitive solar panels), just to offsite vampire losses?

rchiang | April 29, 2013

If tesla had that option to put solar panel on the whole car including the hood I would buy it just to offset the reduction of vampire loss. Of course maybe they would have to have stronger coat on that hood to withstand chipping and so forth.

Brian H | April 29, 2013

There are much better ways to resolve vampire loss. Most of it occurs overnight, when (by definition) sunlight is scarce except at the poles in summer. ;)

Chuck Lusin | April 29, 2013

Would that mean two more color options, mono black and poly blue?

Joel N. Weber II | April 29, 2013

That 20% is probably based upon the current best solar panels that are readily available and is probably not the best that could be done if serious research effort was invested in coming up with a solar panel design optimized to collect as much energy as possible from a small area, without worrying so much about the short term cost per watt. (Research into a design that's less sensitive to angle also might be possible.) I thought I saw something somewhere claiming that collecting at least 80% of the energy is theoretically possible.

If you could get half of 1 kw per square meter, and have four square meters available, that ought to be 2 kw; over the course of 8 hours, that would be 16 kwh. 12A at 120V is only about 1.5 kw.

jat | April 30, 2013

@Joel - the theoretical maximum efficiency of any solar panel is around 31% - I can dig up the scientific paper if you are interested. Basically, you can only use photons with energies in a narrow band, and modern PV panels actually use higher-energy photons after reflecting them off the back of the panel and losing some of their energy.

I think we are more likely to see a massive breakthrough in battery technology than PV.

Joel N. Weber II | April 30, 2013
Tesluthian | April 30, 2013

In my opinion, covering the whole car in solar cells is a bit much, and would not be aesthetically pleasing from a visual perspective. However, having solar panels on just the roof would have a sexy look and increase the visual appeal. Who cares how many watts it can put out? It''s the same difference with a whales tale or air foils, they're sexy, not super necessary.

If the solar roof doesn't put out a lot of watts, give the consumer the choice to have it charge a lower power system not connected to the main battery pack. For me that would be a portable battery pack that the solar roof would keep charged. Campers , beach goers, hikers etc could then take this portable battery pack charger with them to keep cell phones, computers etc charged while away from electrical outlets. This portable battery charger could also have a flashlight, night light, road safety blinker built in for times the car is stuck on the side of the road.

Other options for the solar roof power could be devised and given as choices.

DouglasR | April 30, 2013

Solar panels on the roof are kind of like the spoiler on the Performance model: they don't do anything, but some people think they look good.

dtesla | May 1, 2013

I go camping & pedal my bike off grid for multi-week adventures. I want the car to "start" and have enough juice to get me to a charger if it's not plugged in for a week or two.

\$4K is what I would pay. I would guess the actual cost would be more like \$20K, after someone invents and prefects the technology. Current paint on PV (that is some kind of ink based PV) are only about 10% efficient. And not suitable for the abuse a car takes. Lastly, I still want my current color... just have it generating electricity.

dtesla | May 1, 2013

jat's 31% is the theoretical limit for single junction PV (The most common PV used today). Multi junction PV is currently over 42% efficiency, but is very expensive. Joel is correct about the theoretical upper limit.

jat | May 1, 2013

@dtesla - in that case, why not just take a small portable generator with you, which will cost far less than \$4k and provide other benefits.

derek | May 1, 2013

rchiang The kind of solar charger you linked to is good for maintaining a charged 12v battery with no current drain.

That is to say, RVs, motorbikes, stored cars...their batteries all discharge when not in use - even if disconnected from the vehicle. To prevent this kind of discharge, these solar chargers can keep a full battery topped up. They do an abysmal job of actually charging anything, but can offset not "vampire drain" but just entropy.

I used one on my parked yard tractor for years, and it extended the useful life of the tractor battery, but wouldn't charge it measurably when depleted.

Tesluthian | May 1, 2013

Can't fit a small generator in your backpack.

DerekCrosby | May 1, 2013

Not only that but most of the posts assume access to the main battery. That is protected behind Charger Circuits, and other protection mechanisms.

The 12 V battery you're supposedly charging with the Costco or other "Consumer" solar panel only has access to the "Starter Type" battery, and has little to do with the actual vehicle battery, that propels the car forward and has a lot higher voltage than 12v.

rihhanarachel | May 2, 2013

I got the portable battery charger with desired cell lipos with the safety features. Take a look here: icharger stockist

olanmills | May 3, 2013

In ideal sunlight, there is about 100W per square foot. Even iwth a 100% efficient solar cell, solar panels that could fit on a car would not be useful for charging it.

DouglasR | May 3, 2013

A solar powered airplane -- now that's a different story.

http://news.yahoo.com/solar-plane-takes-off-historic-coast-coast-flight-...

thutruong4368 | March 22, 2015

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Our customers always ask us about the right size of solar panel to charge 12V leisure batteries in vehicles and boats. Unfortunately, based on our experience, there's no single right answer to this question. Solar panels for caravans, motorhomes and boats can all be very different.
http://12v-solarpanel.blogspot.com/2015/03/12v-solar-panel.html