Your Questions About Most Efficient Solar Panels In The World

Henry Dover answers:

Welcome to the wonderfull world of solar!
You probably have a 12Vdc 18 Watt solar panel, to figure out its charging amps capability we do this equation
Watts/Volts=Amps
18watts/12Vdc=1.5Amps

this is a conservative figure, since solar panel ratings are calculated using winter time sunlight, sunny locations and more daytime hours will give you higher amps.

A typical good condition car battery is rated at 40Ah (Amp hours).to find out the charge time, we use the following formula;
Amp Hours/Amps=T where T is time in hours
40Ah/1.5A=26hours

this is charge for a single battery, two batteries will double to over 52 hours.
Lets compare to charging a battery with your car, a car alternator puts out about 60 amps but usually run about half capacity.

40Ah/30amps=1.3Hours!
An alternator is far more efficient so charging with a small solar panel is best as an alternative or for low power applications.

As far as using an inverter to power a TV, we can calculate how long the battery will last by using the original formula.
A typical 19″tv will use 70 watts

70watts/12Vdc=5.8A
40Ah/5.8A=6.9hours

this figure is by drawing all the power from the battery, voltage inverters have a safety feature that will not let you discharge your battery all the way, so 40Ah battery will power a 19″ tv for about 4.5 to 5 hours.

Henry Dover answers:

First we need to examine the required parameters. “An electric car battery” is not a standard item. The Volt and I-Miev batteries are 16KW-hr. The Leaf battery is 24KW-hr and the Tesla Roadster battery holds 53KW-hr of energy. The larger the capacity the longer it will take to charge all else being equal.

The second issue is time. Even from the grid you can charge your electric vehicle with a Type I charger at low voltage and amperage or a Type II charger at a higher voltage and amperage. The Type II charger is likely to be 4 times as fast. The same will be true of the size of the solar panel array.

As long as a solar panel will add more to batteries than the losses it will charge the vehicle. So are we considering only standing losses of about 3% per month, daily driving up to the battery range of the vehicle, or do you want to consider the continuously running the vehicle? Lets use the Nissan Leaf as an example:

The leaf battery is 24KW-hr. In a month such a battery would lose about 3% of its charge just sitting around. This amounts to (24 x .03) .72KW-hr / month. On a daily basis this would be (.72 x 12/365) .02KW-hr Solar insolation varies by location and time of year. The daily average in Arizona at the peak time of the year is about 7KW-hr / sq meter / day. Solar panels vary in efficiency but 10% is not an unreasonable number with today’s technology. This would give us .7KW-hr of electricity / sq meter for our panels and a maintenance panel would only have to be (.2/.7) .286 sq meter in size. This would probably fit on your dashboard and such items are already sold: http://compare.ebay.com/like/320700323984?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

If however you anticipated using the full EPA range of the vehicle on a charge (73 miles) you would need 24 KW hr / day. Our best case solar panels would then have to be (24 / .7) about 34.29 sq meters (or 369 sq ft in size) This would approximately be equal to a surface area of 8 feet by 46 feet long. While this is hardly portable there have been some efforts to combine stationary and portable solar panels to drive electric cars: http://puregreencars.com/Green-Culture/Around-the-World-with-Solar-Taxi.html Here also is a portable solar panel trailer: http://www.grc.nasa.gov/WWW/Electrochemistry/doc/trailer_fc.html There are solar cars but these are not passenger vehicles. They are built ultra light and efficient: http://electric-vehicles-cars-bikes.blogspot.com/2009/10/solar-car-uses-less-power-than-toaster.html

Last if you were to try to power your Nissan Leaf continuously like a solar vehicle we might derive that the Leaf would require (24KW-hr/73 miles) about .329 KW-hr/mile. Traveling at 60 mph in one hour the vehicle would need 19.72 KW-hr / hour or about a 20 KW power supply. Commercial solar panels you might put on the roof of your house are rated from about 165 watts to just over 300 watts power output. You would need from about 66 to 121 of these panels to continuously power the vehicle. A genset trailer might be a better option: http://www.evnut.com/rav_longranger.htm