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  Topic Review (Newest First)
09-03-2015 02:06 PM
BobDiaz The issue I brought up was the fact that it would take a panel array of 4 feet by 8 feet above your electric Smart to only partly charge the battery. Worse yet, it would have to tip upward by your latitude AND face the sun in order to gather the maximum energy. That amount is not enough to fully charge the battery.

While a great deal of effort has been made in improving solar cell efficiency, currently 25% is about as good as it gets and most panels aren't that good; roughly 15%. An efficiency of 100% is considered impossible, but some research into this suggests that we might be able to go as high as 50%. Even with this high an efficiency, it's still not enough to fully charge the battery after one full day in the sun. The south western states get the most average sunlight in a day and the north as well as the eastern states fall short of this amount. (The area near Florida is the exception.)

If we hope to charge the car battery, a much larger set of panels on the roof of a house or office will be required. The problem is that the car must be plugged into these panels in order to charge the battery.

One thing I forgot to point out was the battery efficiency, which is roughly 70%. When I stated the following:

Now the Smart Electric battery capacity is 17.6 kWh, so a whole day of charging would charge the battery from 1/5 to 1/4 capacity. With a range of 76 miles, that's about 15 to 19 miles after a whole day of charging.
I forgot that it would take 25.1 kWh of energy to fully charge the battery. Thus the range would really be from around 10 to 13 miles from a full day's charge.

One could have a battery at the house that could charge during the day and be used to charge the Smart at night. The bad news is that each step loses 70% of the energy, resulting in 0.7 x 0.7 = 0.49, about half the energy is lost. This would require a 36kWh of energy to charge the battery using this approach.

Costs for installed solar have dropped; the price varies depending on the area, but it appears to be from $4 to $6 per installed watt. The solar panels are about $1 per watt, with the labor, permits, and mounting hardware taking up most of the instillation costs.

Bob Diaz
09-03-2015 06:33 AM
Pee-wee Germa
09-02-2015 09:41 PM
NCC1701 Better batteries and better PV cells are needed. It will happen. Eventually. Still, a solar powered charging station is likely to be more realistic for a good while.

Batteries aside, don't forget the other non-fossil energy sources. And research continues in the PV arena. I recently heard of the development of photo cells which use zero silver, replacing it with aluminum at 0.3% of the cost. Too bad the article doesn't say a thing about improving efficiency. But at least they're working on the cost.

Maybe a solar panel on the pano roof could trickle feed the battery while providing a cooling shade to the interior. :-)
09-02-2015 09:23 PM
BobDiaz The numbers won't be as much as you could hope for:

For example Southern California might get an average of 5 to 6 kWh per Square Meter each day, but that is only the amount of energy falling on the Square Meter of area. (A Square Meter is 3.28 feet by 3.28 feet, roughly 10.8 square feet.) Our best solar panels can convert up to 25% of this energy; however most are around 15% efficiency.

Take the area of a sheet of plywood 8' x 4' or 32 square feet. Now take 32 square feet / 10.8 square feet to a Square Meter = That gives us about 2.96 square meters of area, BUT at 25% efficiency it's 1/4 of that or 0.74 Square Meters. 5 to 6 kWh x 0.74 = 3.7 to 4.4 kWh per day.

Now the Smart Electric battery capacity is 17.6 kWh, so a whole day of charging would charge the battery from 1/5 to 1/4 capacity. With a range of 76 miles, that's about 15 to 19 miles after a whole day of charging.

Detailed data is found here:

Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors

Bob Diaz
08-30-2015 01:59 PM
SmartElectric Unfortunately, wouldn't do much.

How much money do you make? | Solar Powered in Toronto

According to figures from the government of Canada about average sunlight, a Toronto-based system can expect to produce an average of around 1,161 kilowatt hours of electricity each year, for every kilowatt of production capacity in your system.
Ok, let's say the car could support enough surface area for 333W panel (not a Smart ED, but the roof of a van could for example).

Then yearly that would be 1161kWh/3 = 387 kWh yearly production.

An average for electric car consumption is around 240 wh / km.

387,000/240 = 1612 km

To just charge overnight 387 kWh * 0.15 / kWh (overnight electricity rate with taxes) = $58

So, the panel could power the car for 1500 km or more, but for the same distance it's only $58 in electricity...

The whole point of electric cars here in Canada is to take advantage of low overnight electricity rates (low because supply > demand) to drive cheaply (like I do!).

Solar is excellent for reducing demand during peak electricity rates during the day, and pays for itself in 7 years without any tax incentives here in Ontario. But it doesn't make sense for electric cars yet.
08-30-2015 12:26 PM
Tiny solar cells could soon charge electric vehicles while on the road

Gizmag. I think this could be a boost to electric vehicles.

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